AJP - Cell Physiology, Vol 248, Issue 3 357-C364, Copyright © 1985 by American Physiological Society
Effect of duration of stimulation and pH on energetics of rabbit rectococcygeus muscle
C. L. Gibbs, G. Kotsanas and I. McCance
The mechanical and energetic performance of the rabbit rectococcygeus
preparation have been studied at 27 degrees C. Energy flux has been
measured either myothermically (heat production) or by recording the O2
consumption and lactate production of the muscle. The maximal
active-to-basal O2 consumption ratio was 2.42. The peak oxidative energy
flux was 3.5 mW/g, and the peak initial rate was about 5.0 mW/g. We could
find no evidence for an increment in lactate production associated with
mechanical activity. The effects of increasing the stimulus duration on the
"economy" of force maintenance was assessed by plotting the heat-to-tension
ratio against duration. For stimulus periods up to 20 s there was no
evidence of a change in the economy: the slope of the relationship was
similar in myothermic and O2 consumption experiments with split muscles.
When total heat production was plotted against the stress-time integral for
stimulus periods up to 60 s at both pH 7.4 and 6.7, there was no change in
energy usage in the longer duration tetani (2-60 s). However, the reduction
in pH, which had minimal mechanical effects other than prolonging
relaxation, did slow the rate of evolution of recovery heat (time constant
doubled) and reduced the rate of O2 consumption. It is concluded that the
rectococcygeus preparation cannot make use of the energy-saving mechanisms
that operate in arterial and several invertebrate smooth muscles.
