Am J Physiol Cell Physiol Email Content Delivery
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Am J Physiol Cell Physiol 274: C846-C852, 1998;
0363-6143/98 $5.00
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Chung, Y.
Right arrow Articles by Jue, T.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Chung, Y.
Right arrow Articles by Jue, T.
Vol. 274, Issue 3, C846-C852, March 1998

SPECIAL COMMUNICATION
Metabolic fluctuation during a muscle contraction cycle

Youngran Chung1, Robert Sharman2, Richard Carlsen3, Steven W. Unger1, Douglas Larson1, and Thomas Jue1

Departments of 1 Biological Chemistry, 2 Plastic Surgery, and 3 Human Physiology, University of California, Davis, California 95616-8635

    ABSTRACT
Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References

Gated 31P-nuclear magnetic resonance followed the metabolic fluctuation in rat gastrocnemius muscle during a contraction cycle. Within 16 ms after stimulation, the phosphocreatine (PCr) level drops 11.3% from its reference state. The PCr minimum corresponds closely to the time of maximum force contraction. Pi increases stoichiometrically, while ATP remains constant. During a twitch, PCr hydrolysis produces 3.1 µmol ATP/g tissue, which is substantially higher than the reported 0.3 µmol ATP · twitch-1 · g tissue-1 derived from steady-state experiments. The results reveal that a substantial energy fluctuation accompanies a muscle twitch.

nuclear magnetic resonance; metabolism; twitch; energetics

    INTRODUCTION
Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References

PHYSIOLOGISTS HAVE FOCUSED for many years on the bioenergetics of muscle contraction and the associated reaction steps. They have long attempted to relate chemical reaction kinetics to the time course of energy liberation. In the paradigm, ATP hydrolysis supplies all the energy demand and should equal the energy released into heat and work. Buffering the ATP loss is the creatine kinase reaction driving phosphocreatine (PCr) to ATP (19, 21-23, 32). In fact, the energy account does not always balance. The measured enthalpy production exceeds the available energy from ATP hydrolysis as reflected in the fall of the PCr level, and the initial rate of heat production is much faster than initial rate of PCr breakdown (6, 7, 11, 15). These observations have led researchers to question whether the change in PCr per twitch (Delta PCr/twitch) energy is sufficient to account for all the heat and work and to postulate reactions associated with an "unexplained" enthalpy (13, 14, 40).

At issue then is the Delta PCr/twitch. Even though the dynamic PCr change during a twitch underpins many postulated biochemical mechanisms, its quantified value is ambiguous. Many determinations apply a time-averaged technique, which divides the overall PCr utilization or rate of oxygen consumption (VO2) over a measurement period by the total number of twitches (2, 10). Such analysis assumes that the experimental observation over an averaged vs. a transient period does not introduce any significant errors. However, the time to peak force development is ~20 ms, or 2% of the total observation time under 1-Hz stimulation. Sampling the overall PCr change and then dividing by total number of twitches might mask a large but transient fluctuation, which would undermine the validity of the energy balance analysis.

Assessing the Delta PCr/twitch, however, has posed a formidable experimental hurdle. Although optical methods can rapidly track some cellular changes, so far they cannot follow the PCr reaction kinetics (36). Much of the current data on Delta PCr/twitch in muscle arise from the freeze-clamping or immersion method, which overcomes the limitations of the time-averaged measurements but depends critically on sample thickness. It has a time resolution of only 100 ms, much longer than the time to maximum force development (11, 17, 18, 38). Initial experiments on turtle and frog muscles at 0°C revealed a negligible change in ATP even during the isotonic contraction, which presumably should consume more energy than isometric contraction (32). Later, with the improved time resolution of the freeze-clamping technique, ATP changes, as reflected in the Delta PCr of 0.36 µmol/g muscle, became apparent and exhibited a linear relationship between the amount of work and the amount of breakdown (3, 18).

However, the well-resolved, dynamic profile of ATP utilization during a twitch is still uncertain, raising a residual question about whether the PCr breakdown occurs during contraction or relaxation or whether the energy is produced at the beginning or is available throughout the contraction cycle. Even with advanced freeze-clamping methods, energy production and PCr splitting typically are compared after a complete contraction-relaxation cycle or after many such cycles. Such measurements cannot reveal accurately the energy changes during the early stages of a twitch, in particular at time points below 100 ms (11, 17, 18, 38), yet these are exactly the critical time points that are essential in mapping the mechanical-chemical energy coupling process during muscle contraction.

With 31P-nuclear magnetic resonance (NMR), many studies have provided insights into the bioenergetics of normothermic muscle in vivo and have raised an opportunity to explore the metabolic fluctuation during a twitch (10, 24, 25). We have undertaken a study to develop a gated 31P-NMR technique with sufficient time resolution to observe the PCr hydrolysis during a contraction cycle in stimulated rat gastrocnemius muscle. Indeed, the PCr level falls rapidly within 16 ms after stimulation and exhibits a kinetics curve that mirrors the force development profile. Pi rises stoichiometrically, while the ATP level remains constant. The data indicate that PCr hydrolysis proceeds much more rapidly, as well as extensively, than previously observed in amphibian muscle at 0°C and may contribute significantly to the initial heat production. The NMR approach presents, then, a unique way to probe the coupling mechanism governing the transient interplay between chemical and mechanical energy in the fundamental unit of muscle contraction (21).

    MATERIALS AND METHODS
Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References

Animal preparation. Sprague-Dawley female rats (260-300 g) were anesthetized with 65 mg/kg body wt pentobarbital sodium and were prepared as described previously (4). A pentobarbital booster was administered in 4.5-mg doses every 45-60 min via an intraperitoneal catheter. The sciatic nerve was exposed, and its proximal ending was crushed so that only the distal limb muscle contracted. A stimulator (Grass S48) then initiated muscle contraction via a bipolar platinum electrode attached to the sciatic nerve. To prevent tissue drying and to insulate the electrode from the surrounding tissues, a thin layer of a mineral oil-petroleum jelly mixture was applied to the tissue incision. Through the Achilles tendon anchoring the gastrocnemius-plantaris-soleus muscle group to the ankle bone, a sewn 4-0 silk suture was connected to a transducer (Grass FT03C), whose signals were monitored by a Gould oscillographic recorder (Gould RS3200) or by a MacLab system, which first digitized the analog signal at 1 kHz. The contraction data were analyzed subsequently with Sigma Plot 5.0 (Jandel Scientific).

The muscle was subjected to an isolated electrical stimulation, and a recorder followed the developed force profile. After each stimulation, the suture was tightened until the developed force no longer increased. At that time, the suture length was tightened by an additional 10%. A series of tetanic stimulated contractions then followed to take up any slack. The muscle length adjustment procedure was then iterated. Typically a 12-V, 50-µs stimulation was sufficient to produce a supramaximal contraction of the entire gastrocnemius-plantaris-soleus muscle group. With this muscle preparation, the peak twitch force remained constant throughout 2-3 h of 1-Hz stimulation .

NMR. Spectra were recorded with a 7T horizontal bore GE Omega spectrometer. The animal was placed supine on a Lucite platform, below which a concentric 1.4/2.2 cm 31P/1H surface coil system was attached. The 1H coil detected the water signal for magnet shimming, while the 31P coil followed the high-energy phosphate signals. The gastrocnemius muscle was positioned directly over the surface coil, which was separated from the muscle by a thin Teflon sheet. The foot, knee, and ankle joint were securely clamped to Lucite plates to reduce motion. The typical stimulation protocol utilized a 12-V, 50-µs pulse at 1 Hz for a duration of ~2 min, followed by 7-8 min of rest. Twitch characteristics, including the peak twitch force, remained constant throughout the entire 2-3 h of the experiment. A thermistor probe monitored the muscle temperature, which was maintained between 35 and 36°C by a warm air bath.

The 31P signal acquisition utilized a 22-µs pulse, a 1-s repetition time, and 128 scans per block (2.3 min). The acquisition time (Acq) was set at 85 ms. At the center of the coil, the 31P 90° pulse was 22 µs, calibrated against a 0.1 M phosphate solution. Spectral width was set at 6,000 Hz; the data size was 512 words, zero filled to 2 kilowords. The free induction decay was apodized with an exponential function before Fourier transformation. All 31P signals were referenced to PCr as 0 parts per million (ppm). Comparison with fully relaxed, control 31P-NMR spectra yielded the appropriate saturation factors.

On muscle stimulation, a custom-built gating device sampled the 1-Hz output pulse and inserted a precise delay with <1 ± 0.1-ms resolution before sending a 4-V pulse to trigger NMR signal acquisition. The timing diagram is illustrated below
A B C
t1 Acq t2

With each data block, the spectrometer radio frequency pulse was triggered to the electrical stimulus at time point A. A delay, t1, after the stimulation elapsed before a signal gated the spectrometer to acquire a signal transient at time point B. The time interval between time points B and C corresponded to Acq, which was constant throughout all the experiments. A final time interval, t2, was inserted to maintain the relationship (t1 + Acq + t2) = 1 s. The spectrometer then acquired one data block, comprised of 128 transients and lasting for 2.3 min.

The first experiment started with a t1 of 5 ms. In each subsequent experiment, t1 was incremented stepwise, while t2 was decremented to maintain a constant recycle time (t1 + Acq + t2). Before the next data acquisition began, 7-8 min elapsed to allow the muscle PCr level to return to its resting state, as observed in the 31P spectra. All other experimental conditions were kept exactly the same to create an identical time course for the gradual PCr decline during the entire stimulation protocol. About 10-14 data blocks, corresponding to time points after the stimulation, were then collected. Each data block was analyzed, and the results were used to reconstruct the various metabolic profiles. The final t1 between stimulation and signal acquisition was incremented up to 400 s. This last point helped map precisely the steady-state level in the recovery phase.

In the experiments to determine the steady-state effect at 1-Hz stimulation, the number of scans per block was reduced to 64, and the total acquisition time was decreased to 30 s. Other signal acquisition and processing parameters, as well as the stimulation protocol, remained identical to the ones used in the transient experiments. A block of 31P data was then acquired at 30-s intervals. The total protocol yielded 10 blocks of data.

Peak area analysis utilized the Omega 6.2 curve-fitting algorithm to integrate the NMR signals. To account for motional artifacts during stimulation, the normalization procedure assumed that total 31P metabolite content should remain constant under the experimental conditions and set the total 31P signal as the normalizing factor in each spectrum, consistent with previous analysis procedures (24). Under no circumstances did the total peak area of the control or fully recovered spectra, before and after the stimulation episodes, differ by more than ±5%.

Intracellular pH was calculated from
pH = p<IT>K</IT> + log <FENCE><FR><NU>&dgr;<SUB>A</SUB> − &dgr;<SUB>o</SUB></NU><DE>&dgr;<SUB>o</SUB> − &dgr;<SUB>B</SUB></DE></FR></FENCE>
where pK = 6.9, delta A is the chemical shift (delta ppm) of [H2PO<SUP>−</SUP><SUB>4</SUB>] at 3.290 ppm, delta B is the delta ppm of [HPO <SUP>2−</SUP><SUB>4</SUB>] at 5.805 ppm, and delta o is the delta ppm of Pi referenced to PCr delta ppm as 0 ppm. Intracellular Mg concentration was calculated from the chemical shifts of alpha -ATP and beta -ATP (27). The ADP level was derived from 31P-NMR parameters and the creatine kinase equilibrium constant of 1.66 × 109 M-1 (26).

Curve fitting and statistical analysis. SigmaPlot 5.0 software (Jandel Scientific) was used to analyze the force development and NMR data to determine the kinetics time constants, SD, and SE. Statistical significance was assigned when Student's t-test indicated P < 0.05. For the steady-state kinetics analysis of PCr, the nonlinear fitting utilized the following equation for the stimulation and recovery phases, respectively
PCr(<IT>t</IT>) = PCr(ss) + [PCr(0) − PCr(ss)]<IT>e</IT><SUP>−<IT>t</IT>/&tgr;</SUP> (1)
where PCr(t) is PCr level at a given time after beginning of muscle stimulation, PCr(ss) is steady-state PCr level, PCr(0) is initial PCr level in the resting muscle, t is time after muscle stimulation, and tau  is the exponential time constant for PCr breakdown during muscle stimulation.

The extrapolated energy cost per twitch utilized the first order derivative of Eq. 1, evaluated at t = 0 (10)
dPCr(<IT>t</IT>)/d<IT>t</IT> = (−1/&tgr;)[PCr(0) − PCr(ss)]<IT>e</IT><SUP>−<IT>t</IT>/&tgr;</SUP>‖<SUB><IT>t</IT>=0</SUB> (2)

    RESULTS
Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References

Figure 1 shows a set of 31P spectra from rat gastrocnemius muscle. The control 31P spectrum from resting muscle is shown in Fig. 1A. Signal averaging with an NMR acquisition trigger set at 20 ms distal to the sciatic nerve stimulation pulse produced the spectrum in Fig. 1B. The PCr signal intensity declines, whereas the Pi signal increases. ATP level remains constant. Figure 1C shows clearly the 31P signal response at 20 ms after stimulation in a difference spectrum (Fig. 1B - Fig. 1A).

During a twitch, the PCr level declines initially and then recovers to 92.1 ± 3.0% of the resting level. With recovered PCr level as the reference state, under 1-Hz stimulation, the PCr falls during a twitch from 92.1 ± 3.0 to 80.8 ± 5.8% of the control level within 16 ms (Fig. 2A). A similar profile is observed at 0.2-Hz stimulation. The PCr profile is a slightly time-shifted mirror image of the force contraction response, which exhibits a maximum at 25 ms. The corresponding ATP levels remain constant, at 98.1 ± 5.9 and 95.2 ± 3.0% of control for 1- and 0.2-Hz stimulation, respectively. On the basis of the ATP chemical shift analysis, the Mg concentration does not show any detectable alteration (27).


View larger version (11K):
[in this window]
[in a new window]
  		Fig. 1.   31P-nuclear magnetic resonance (NMR) spectra at different time points during a muscle contraction cycle. A: control or resting state 31P-NMR spectrum before stimulation. Phosphocreatine (PCr), Pi, and beta -ATP signals resonate at 0, 4.83, and -15.6 parts per million (ppm), respectively. Averaged, steady-state 31P levels during 1-Hz stimulation are shown in Table 1. In particular, steady-state PCr level is 92.1 ± 3.0% of resting state value. Analysis of transient changes during a muscle contraction cycle utilizes steady-state value as reference. B: 20 ms after stimulation, PCr signal has decreased and Pi has increased. ATP remains constant. C: difference spectrum (A - B) confirms signal changes in PCr and Pi.


View larger version (21K):
[in this window]
[in a new window]
  		Fig. 2.   Dynamic physiological and metabolic response during a twitch. A: under 1-Hz stimulation, a single contraction profile (curve at bottom) shows a rapid rise in force development, which reaches a maximum at 25 ms. Force profile is representative (not the average) of 5 experiments. Average force parameters are described in Table 1. At same time, PCr level drops to a minimum at 16 ms. A similar PCr profile is observed under 0.2-Hz stimulation. B: corresponding Pi and pH profiles indicate a stoichiometric increase in Pi during contraction cycle. No statistically significant change in pH appears. ATP level remains constant.

As PCr level falls, Pi concentration increases (Fig. 2B). During a twitch, Pi rises ~1.8 times or 447.3 ± 138.3% of control before returning to 248.9 ± 54.5% of control. The dynamic Pi profile is inversely related to the PCr response. On the basis of the reported resting state values of PCr and Pi of 27.1 and 2.8 µmol/g wet tissue in rat gastrocnemius muscle, the calculated changes in PCr and Pi, after saturation factor correction, are 3.1 and 3.2 µmol/g wet tissue, respectively (24). The observed PCr-to-Pi reaction appears to be stoichiometric.

Concomitantly, pH appears to shift by 0.06 pH units, from 7.14 ± 0.02 to 7.08 ± 0.11. However, the limited accuracy of the measurement does not indicate that the change is statistically significant and precludes at this time any definitive interpretation. The experimental data are summarized in Table 1.

                              
View this table:
[in this window]
[in a new window]
  		Table 1.   Metabolic changes and contractile parameters during a muscle twitch

In contrast, the nongated, continuous acquisition of the 31P signals under 1-Hz stimulation reveals a different picture (Fig. 3, A and B). PCr gradually declines within 2.3 min to 79.8% and reaches a steady-state level of 74.8% of control. ATP still remains constant, but the Pi level rises and then falls inversely with respect to the PCr profile (Fig. 3B). The pH shows a gradual decline from 7.15 to 7.04, consistent with previous reports (10). The analysis of the PCr contraction and recovery phase kinetics indicates that the corresponding kinetics time constants (tau ) are 1.36 ± 0.07 and 0.89 ± 0.19 min. The average PCr value during a 2.3-min interval is then 89.9% of control, matching closely the observed 92.1% twitch recovery value observed in the transient, gated experiments (Table 1). The analysis of the data from the nongated, continuous signal acquisition experiments extrapolates to a Delta PCr/twitch of 0.3% or 0.08 µmol · twitch-1 · g tissue-1 (Eq. 2), consistent with previous reports (10, 29).


View larger version (20K):
[in this window]
[in a new window]
  		Fig. 3.   Steady-state metabolic response in rat gastrocnemius muscle during a 1-Hz stimulation. A: PCr level gradually declines to 74.8% of control during a continuous 1-Hz stimulation. Dotted line, linear regression through ATP points. B: Pi varies inversely with PCr, while pH appears to decline without statistical significance from 7.15 to 7.04. No. of scans per block was 64, and total acquisition time/block was reduced to 30 s. NMR acquisition continued for additional 400 s after stimulation ceased, to trace recovery curve. For steady-state kinetics analysis, nonlinear data fitting utilized Eq. 1 for stimulation and recovery phases, respectively.

    DISCUSSION
Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References

Detection of metabolic fluctuation. The experimental results indicate that the gated NMR technique can detect with ±1-ms time resolution the pronounced PCr fluctuation during a contraction cycle. Figure 1 clearly shows that high-energy phosphate signal intensities change sharply: PCr falls, Pi rises, and ATP remains constant. Such a distinct set of signal responses would argue strongly against a significant contribution from motional artifact as the muscle contracts. An overall sample movement away or toward the homogeneous detection volume should also produce a concerted change in the signal intensities as well as a substantial line broadening. Neither is observed. Moreover, the overall integrated signal areas in the 31P spectra are constant.

If the detection volume shifts between fast- and slowtwitch fibers, a contrasting set of 31P spectral changes can occur. The decrease in PCr during a twitch would imply a transition from detecting fast-twitch fibers to detecting slow-twitch fibers, which would produce changes in the NMR-observable 31P metabolite levels. In the transition from detecting fast- to detecting slow-twitch fibers, PCr will decrease from 35 to 17 mM, Pi will increase from 3 to 10 mM, but ATP will decrease from 9 to 5 mM (21, 25, 28, 31, 33). The magnitude and direction of the spectral changes, however, are not consistent with the observed experimental data: ATP level remains constant; PCr and Pi changes are inconsistent with predicted direction and values; the conversion of PCr to Pi is stoichiometric. Moreover, the constant overall integrated signals of the 31P-NMR spectra argue against any significant shift in the detection volume. The interpretation is consistent with the unlocalized NMR detection scheme that cannot discriminate fiber type differences with a 31P surface coil's sampling volume, which encompasses the entire muscle bed.

Because the NMR technique is not a one-shot detection scheme and depends on signal averaging over an acquisition time of 2.3 min, the research design must take into account the gradual PCr decline during the stimulation protocol. That indeed has occurred. The experimental condition for every acquisition data block matches identically the stimulation protocol and recycled time. Only the receiver acquisition trigger is stepped up incrementally. Sufficient time elapses to allow for full PCr recovery to its resting level, before the next block of data acquisition commences. Given such a protocol, the PCr decline during the course of stimulation should then be identical for each data block, even though the receiver acquisition trigger has advanced.

Indeed, both the continuous accumulation and 0.2-Hz gated experimental results confirm the above suppositions. Under nongated, continuous signal acquisition at 1-Hz stimulation, PCr declines within 2.3 min to a steady-state level corresponding to 74.8% of the resting control level. If overall PCr decline is divided by 2.3 min, the average PCr value during the course of the experiment is 89.9% of the resting control level. The value matches closely the observed 92.1% recovery level observed in the gated experiments and is in excellent agreement with literature studies of rat gastrocnemius muscle (10). At 0.2-Hz stimulation, the PCr declines less and reaches a higher steady-state level. However, the PCr kinetics profile during a twitch is still consistent with the one observed in experiments under 1-Hz stimulation (Fig. 2).

PCr fluctuation during a twitch. During a muscle twitch, the half times for the PCr kinetics are 8 and 14 ms, for the stimulation and recovery phases, respectively. The PCr formation and degradation rates are then 182 and 106 µmol · g tissue-1 · s-1. From the steady-state level, PCr falls by 11.3%, corresponding to a decrease of 3 µmol ATP · g tissue-1 · twitch-1. The PCr drop is equivalent to a 40% loss in the total ATP content (9, 24).

Such a Delta PCr/twitch value is in contrast to the 0.3% decrease derived from the nongated, continuous accumulation data: on the basis of analysis with Eq. 2, the ATP consumption during a twitch is only 0.08 µmol/g tissue, consistent with values reported in previous rat gastrocnemius muscle studies (7, 10, 14). In fact, the steady-state metabolism response, shown in Fig. 2, is in excellent agreement with previous findings and indicates consistency in the rat gastrocnemius muscle preparation. As a result, the Delta PCr/twitch derived from any steady-state PCr measurement divided by the number of twitches can underestimate the transient twitch response.

Similarly, freeze-clamping techniques would also underestimate the PCr changes. At the lowest time resolution of 100 ms after stimulation, the PCr level has recovered to its steady-state value and also reflects a 0.3% drop. It would still miss the transient PCr change that accompanies the contraction profile.

Energetics of a contraction. The metabolic energy cost per twitch appears to be quite large and raises questions about the prevailing paradigm of PCr mobilization and ATP utilization during a muscle contraction. For the PCr pool to buffer the ATP utilization at 106 µmol · g tissue-1 · s-1, the creatine kinase reaction must have the capacity to shift dramatically from its resting state flux of 7.4 µmol · g tissue-1 · s-1 from PCr to ATP (30), yet the enhanced forward flux from PCr to ATP is still below the estimated maximum rate (Vmax) of 145 µmol · g tissue-1 · s-1 (1). Given the forward flux rate of 7.4 µmol · g tissue-1 · s-1 in fast-twitch muscle, the ADP concentration must then increase from its calculated resting value of 0.016 mM by a factor of 14 during a contraction.

Such a large drop in PCr during contraction would require substantial energy restoration, arising from either glycolytic or oxidative phosphorylation sources. After a twitch contraction, PCr recovers much faster than after the end of stimulation, implicating distinct recovery mechanisms. On the basis of the in vitro Vmax for the phosphofructokinase, glycolysis does not appear to account for all the energy recovery after twitch (5). Either oxidative phosphorylation activity contributes to the twitch PCr recovery or the in vivo Vmax for phosphofructose kinase is much higher than the in vitro values. The glycolytic source is most likely not only glycogenolysis, since the glycogen content in muscle can directly support only a few contractions. After the end of stimulation, the PCr recovery kinetics is consistent with a predominant role of oxidative phosphorylation. These observations warrant further study.

Some support for an aerobic energy contribution emerges from the relative increase in oxygen consumption during muscle contraction as reported in the literature (6, 25). The basal VO2 for cat biceps and soleus (glycolytic vs. oxidative fibers) is between 0.07 and 0.08 µmol O2 · g tissue-1 · min-1. At 0.5-Hz stimulation, the VO2 increases six to seven times; at 1 Hz, it increases ~10 times. For glycolytic muscle, 0.5-Hz stimulation can raise the ADP level from 1.3 to 65 µmol/g tissue, a factor of 50, whereas for oxidative fiber the ADP level can rise from 4.1 to 30 µmol/g tissue, a factor of 7.3 (25). These relative changes would imply that ADP levels can shift dramatically. Such a change is within the adenine translocase Michaelis constant range of 6-66 µmol/g tissue (20, 25). The phosphorylation potential has also decreased, but assessing its impact is less clear, since the redox potential can also mediate respiratory control (8, 39).

Many muscle studies have shown a low absolute oxygen consumption rate, consistent with a slow oxidative phosphorylation component (21, 25). The observation supports the current paradigm that aerobic energy mobilization is associated primarily with the recovery phase. However, the VO2 values depend highly on the experimental model and conditions. In perfused rat hindlimb muscle, basal VO2 rises to 0.37 µmol O2 · g tissue-1 · min-1, a factor of five greater than the values observed in superfused cat muscle experiments, and increases to 1.73 µmol · g tissue-1 · min-1 during 1-Hz stimulation (16). Dividing the VO2 by the number of twitches per minute yields 0.03 µmol O2 · g tissue-1 · twitch-1 or 0.18 µmol ATP · g tissue-1 · twitch-1, given a P-to-O ratio of 3:1 (16, 35). Perfused rat hindlimb tetanus experiments, however, have led to an extrapolated oxygen consumption rate of 0.35 µmol O2 · g tissue-1 · contraction-1 or 2.1 µmol ATP · g tissue-1 · contraction-1 (34). Certainly the muscle aerobic respiratory capacity, mitochondrial content, temperature-dependent respiration rate, experimental model, and oxygen consumption measurement techniques can give rise to a range of VO2 values.

The gated NMR data have led to a calculated enthalpy from ATP hydrolysis (based on -34 kJ/mol) of -102 kJ · twitch-1 · g tissue-1 (7, 40). Although the enthalpy contribution from the high-energy phosphate splitting is much higher than previous observations, the experimental conditions, such as model, temperature, fiber type, and contraction duration, are sufficiently different to preclude a firm comparison and interpretation at this time (21). One perspective on the magnitude of the energy change in muscle contraction emerges from isometric tetanus study of rat soleus and extensor digitorum longus muscle. During isometric tetanus, PCr decreases by 2.13 µmol/g wet weight of muscle, while the heat production reaches 110 mJ/g at 17-18°C (12). In rat extensor digitorum longus muscle at 27°C, isometric tetanus produces 154 mJ/g (37). Additional experiments with matching NMR, VO2, and myothermic measurements on the identical normothermic rat muscle group in situ will be crucial in clarifying the mechanisms underlying the bioenergetics of a contraction.

In conclusion, this report outlines a gated NMR methodology to explore transient metabolic fluctuation during a twitch and shows a substantial PCr hydrolysis within 16 ms of stimulation. Pi increases stoichiometrically, while ATP remains constant. The rapid change in PCr raises questions about energy mobilization and balance within a muscle contraction cycle.

    ACKNOWLEDGEMENTS

This work was supported by National Institutes of Health Grants HL-09274 (to Y. Chung) and GM-44916 and by American Heart Association National Grant Award 94013850.

    FOOTNOTES

Address for reprint requests: T. Jue, Med: Biological Chemistry, University of California, Davis, CA 95616-8635.

Received 16 June 1997; accepted in final form 26 November 1997.

    REFERENCES
Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References

1.   Bittl, J. A., J. DeLayre, and J. S. Ingwall. Rate equation for creatine kinase predicts the in vivo reaction velocity: 31P NMR surface coil studies in brain, heart, and skeletal muscle of the living rat. Biochemistry 26: 6083-6090, 1987[Medline].

2.   Blei, M. L., K. E. Conley, and M. J. Kushmerick. Separate measures of ATP utilization and recovery in human skeletal muscle. J. Physiol. (Lond.) 465: 203-222, 1993[Abstract/Free Full Text].

3.   Cain, D. F., A. A. Infante, and R. E. Davies. Adenosine triphosphate and phosphorylcreatine and energy supplies for single contractions of working muscle. Nature 196: 214-217, 1962.

4.   Chung, Y., R. Sharman, R. Carlsen, S. Unger, D. Larson, and T. Jue. Metabolic fluctuation in skeletal muscle during a muscle contraction cycle (Abstract). Proc. Soc. Magn. Reson. Med. 1: 360, 1994.

5.   Connett, R. J., and K. Sahlin. Control of glycolysis and glycogen metabolism. In: Handbook of Physiology. Exercise: Regulation and Integration of Multiple Systems. Bethesda, MD: Am. Physiol. Soc., 1996, sect. 12, chapt. 19, p. 870-911.

6.   Curtin, N. A., C. Gilbert, K. M. Kretzschmar, and D. R. Wilkie. The effect of the performance of work on total energy output and metabolism during muscular contraction. J. Physiol. (Lond.) 238: 455-472, 1974[Abstract/Free Full Text].

7.   Curtin, N. A., and R. C. Woledge. Energy changes and muscular contraction. Physiol. Rev. 58: 690-716, 1978[Free Full Text].

8.   Erecinska, M., and D. F. Wilson. Regulation of cellular energy metabolism. J. Membr. Biol. 70: 1-14, 1982[Medline].

9.   Foley, J. M., S. J. Harkema, and R. A. Meyer. Decreased ATP cost of isometric contractions in ATP-depleted rat fast-twitch muscle. Am. J. Physiol. 261 (Cell Physiol. 30): C872-C881, 1991[Abstract/Free Full Text].

10.   Foley, J. M., and R. A. Meyer. Energy cost of twitch and tetanic contractions of rat muscle estimated in situ by gated 31P NMR. NMR Biomed. 6: 32-38, 1993[Medline].

11.   Gilbert, C., K. M. Kretzschmar, D. R. Wilkie, and R. C. Woledge. Chemical change and energy output during muscular contraction. J. Physiol. (Lond.) 218: 163-193, 1971[Abstract/Free Full Text].

12.   Gower, D., and K. M. Kretzschmar. Heat production and chemical change during isometric contraction of rat soleus muscle. J. Physiol. (Lond.) 258: 659-672, 1976[Abstract/Free Full Text].

13.   Homsher, E. Muscle enthalpy production and its relationship to actomyosin ATPase. Annu. Rev. Physiol. 49: 673-690, 1987[Medline].

14.   Homsher, E., and J. C. Kean. Unexplained enthalpy production in contracting skeletal muscles. Federation Proc. 41: 149-154, 1982[Medline].

15.   Homsher, E., J. A. Rall, A. Wallner, and N. V. Ricchiuti. Energy liberation and chemical change in frog skeletal muscle during single isometric tetanic contractions. J. Gen. Physiol. 65: 1-21, 1975[Abstract/Free Full Text].

16.   Hood, D. A., J. Gorski, and R. L. Terjung. Oxygen cost of twitch and tetanic isometric contractions of rat skeletal muscle. Am. J. Physiol. 250 (Endocrinol. Metab. 13): E449-E456, 1986[Abstract/Free Full Text].

17.   Infante, A. A., and R. E. Davies. Adenosine triphosphate breakdown during a single isotonic twitch of frog sartorius muscle. Biochem. Biophys. Res. Commun. 9: 410-415, 1962.

18.   Infante, A. A., D. Klaupiks, and R. E. Davies. Phosphorylcreatine consumption during single-working contractions of isolated muscle. Biochim. Biophys. Acta 94: 504-515, 1965[Medline].

19.   Jacobus, W. E. Respiratory control and the integration of the heart high energy phosphate metabolism by mitochondrial creatine kinase. Annu. Rev. Physiol. 47: 707-725, 1985[Medline].

20.   Jacobus, W. E., R. W. Moreadith, and K. M. Vandegaer. Mitochondrial respiratory control. J. Biol. Chem. 257: 2397-2402, 1982[Abstract/Free Full Text].

21.   Kushmerick, M. J. Energetics of muscle contraction. In: Handbook of Physiology. Skeletal Muscle. Bethesda, MD: Am. Physiol. Soc., 1983, sect. 10, chapt. 7, p. 189-236.

22.   Kushmerick, M. J., and R. E. Davies. The chemical energetics of muscle contraction. II. The chemistry, efficiency and power of maximally working sartorius muscles. Proc. R. Soc. Lond. B Biol. Sci. 174: 315-353, 1969[Medline].

23.   Kushmerick, M. J., R. E. Larson, and R. E. Davies. The chemical energetics of muscle contraction. I. Activation heat, heat of shortening and ATP utilization for activation-relaxation processes. Proc. R. Soc. Lond. B Biol. Sci. 174: 293-313, 1969[Medline].

24.   Kushmerick, M. J., and R. A. Meyer. Chemical changes in rat leg muscle by phosphorus nuclear magnetic resonance. Am. J. Physiol. 248 (Cell Physiol. 17): C542-C549, 1985[Abstract/Free Full Text].

25.   Kushmerick, M. J., R. A. Meyer, and T. R. Brown. Regulation of oxygen consumption in fast- and slow-twitch muscle. Am. J. Physiol. 263 (Cell Physiol. 32): C598-C606, 1992[Abstract/Free Full Text].

26.   Lawson, J. W. R., and R. L. Veech. Effects of pH and free Mg2+ on the Keq of the creatine kinase reaction and other phosphate hydrolyses and phosphate transfer reactions. J. Biol. Chem. 254: 6528-6537, 1979[Abstract/Free Full Text].

27.   London, R. E. Methods for measurement of intracellular magnesium: NMR and fluorescence. Annu. Rev. Physiol. 53: 241-258, 1991[Medline].

28.   Madapillimattam, A. G., A. Cross, M. L. Nishio, and K. N. Jeejeehoy. Stability of high-energy substrates in fast- and slow-twitch muscle: comparison of enzymatic assay of biopsy with in vivo 31P nuclear magnetic resonance. Anal. Biochem. 217: 103-109, 1994[Medline].

29.   Meyer, R. A. A linear model of muscle respiration explains monoexponential phosphocreatine changes. Am. J. Physiol. 254 (Cell Physiol. 23): C548-C553, 1988[Abstract/Free Full Text].

30.   Meyer, R. A., T. R. Brown, B. L. Krilowicz, and M. J. Kushmerick. Phosphagen and intracellular pH changes during contraction of creatine-depleted rat muscle. Am. J. Physiol. 250 (Cell Physiol. 19): C264-C274, 1986[Abstract/Free Full Text].

31.   Meyer, R. A., T. R. Brown, and M. J. Kushmerick. Phosphorus nuclear magnetic resonance of fast- and slow-twitch muscle. Am. J. Physiol. 248 (Cell Physiol. 17): C279-C287, 1985[Abstract/Free Full Text].

32.   Mommaerts, W. F. H. M. Is adenosine triphosphate broken down during a single muscle twitch? Nature 174: 1083-1084, 1954.

33.   Phillips, S. K., M. Takei, and K. Yamada. The time course of phosphate metabolites and intracellular pH compared to recovery in rat soleus muscle. J. Physiol. (Lond.) 460: 693-704, 1993[Abstract/Free Full Text].

34.   Robinson, D. M., R. W. Ogilvie, P. C. Tullson, and R. I. Terjung. Increased peak oxygen consumption of trained muscle requires increased electron flux capacity. J. Appl. Physiol. 77: 1941-1952, 1994[Abstract/Free Full Text].

35.   Ruderman, N. B., F. W. Kemmer, M. N. Goodman, and M. Berger. Oxygen consumption in perfused skeletal muscle. Biochem. J. 190: 57-64, 1980[Medline].

36.   Tamura, M., N. Oshino, B. Chance, and I. A. Silver. Optical measurements of intracellular concentration of rat heart in vitro. Arch. Biochem. Biophys. 191: 8-22, 1978[Medline].

37.   Wendt, I. R., and C. L. Gibbs. Energy production of rat extensor digitorum longus muscle. Am. J. Physiol. 224: 1081-1086, 1973.

38.   Wilkie, D. R. Heat work and phosphorylcreatine break-down in muscle. J. Physiol. (Lond.) 195: 157-183, 1968[Abstract/Free Full Text].

39.  Wilson, D. F., K. Nishiki, and M. Erecinska. Energy metabolism in muscle and its regulation during individual contraction-relaxation cycles. Trends Biochem. Sci. 16-19, 1981.

40.   Woledge, R. C., N. A. Curtin, and E. Homsher. Energetic Aspects of Muscle Contraction. New York: Academic, 1985.

AJP Cell Physiol 274(3):C846-C852
0363-6143/98 $5.00 Copyright © 1998 the American Physiological Society


This article has been cited by other articles:


Home page
 J. Physiol.Home page
S. A. Jubrias, N. K. Vollestad, R. K. Gronka, and M. J. Kushmerick
Contraction coupling efficiency of human first dorsal interosseous muscle
J. Physiol., April 1, 2008; 586(7): 1993 - 2002.
[Abstract] [Full Text] [PDF]

Home page
 J. Appl. Physiol.Home page
R. A. Howlett, C. A. Kindig, and M. C. Hogan
Intracellular PO2 kinetics at different contraction frequencies in Xenopus single skeletal muscle fibers
J Appl Physiol, April 1, 2007; 102(4): 1456 - 1461.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Physiol. Cell Physiol.Home page
Y. Chung, S.-J. Huang, A. Glabe, and T. Jue
Implication of CO inactivation on myoglobin function
Am J Physiol Cell Physiol, June 1, 2006; 290(6): C1616 - C1624.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Physiol. Regul. Integr. Comp. Physiol.Home page
C. L. Murrant
Stimulation characteristics that determine arteriolar dilation in skeletal muscle
Am J Physiol Regulatory Integrative Comp Physiol, August 1, 2005; 289(2): R505 - R513.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Physiol. Cell Physiol.Home page
Y. Chung, P. A. Mole, N. Sailasuta, T. K. Tran, R. Hurd, and T. Jue
Control of respiration and bioenergetics during muscle contraction
Am J Physiol Cell Physiol, March 1, 2005; 288(3): C730 - C738.
[Abstract] [Full Text] [PDF]

Home page
 J. Appl. Physiol.Home page
D. Bendahan, G. J. Kemp, M. Roussel, Y. L. Fur, and P. J. Cozzone
ATP synthesis and proton handling in muscle during short periods of exercise and subsequent recovery
J Appl Physiol, June 1, 2003; 94(6): 2391 - 2397.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Physiol. Endocrinol. Metab.Home page
D. W. Russ, M. A. Elliott, K. Vandenborne, G. A. Walter, and S. A. Binder-Macleod
Metabolic costs of isometric force generation and maintenance of human skeletal muscle
Am J Physiol Endocrinol Metab, February 1, 2002; 282(2): E448 - E457.
[Abstract] [Full Text] [PDF]

Home page
 Proc. Natl. Acad. Sci. USAHome page
R. G. Shulman and D. L. Rothman
The "glycogen shunt" in exercising muscle: A role for glycogen in muscle energetics and fatigue
PNAS, January 16, 2001; 98(2): 457 - 461.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Physiol. Cell Physiol.Home page
J. A. L. Jeneson, H. V. Westerhoff, and M. J. Kushmerick
A metabolic control analysis of kinetic controls in ATP free energy metabolism in contracting skeletal muscle
Am J Physiol Cell Physiol, September 1, 2000; 279(3): C813 - C832.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Physiol. Heart Circ. Physiol.Home page
Y. Chung and T. Jue
Regulation of respiration in myocardium in the transient and steady state
Am J Physiol Heart Circ Physiol, October 1, 1999; 277(4): H1410 - H1417.
[Abstract] [Full Text] [PDF]

Home page
 Proc. Natl. Acad. Sci. USAHome page
R. G. Shulman, F. Hyder, and D. L. Rothman
Cerebral energetics and the glycogen shunt: Neurochemical basis of functional imaging
PNAS, May 22, 2001; 98(11): 6417 - 6422.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Chung, Y.
Right arrow Articles by Jue, T.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Chung, Y.
Right arrow Articles by Jue, T.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Visit Other APS Journals Online