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Am J Physiol Cell Physiol 277: C1284-C1290, 1999;
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Vol. 277, Issue 6, C1284-C1290, December 1999

RAPID COMMUNICATION
Role of HERG-like K+ currents in opossum esophageal circular smooth muscle

Hamid I. Akbarali1, Hemant Thatte1, Xue Dao He1, Wayne R. Giles2, and Raj K. Goyal1

1 Center for Swallowing and Motility Disorders, Harvard Medical School, West Roxbury Veterans Affairs Medical Center, West Roxbury, Massachusetts 02132; and 2 Department of Physiology and Biophysics, University of Calgary, Calgary, Alberta, Canada T2N 4N1


    ABSTRACT
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

An inwardly rectifying K+ conductance closely resembling the human ether-a-go-go-related gene (HERG) current was identified in single smooth muscle cells of opossum esophageal circular muscle. When cells were voltage clamped at 0 mV, in isotonic K+ solution (140 mM), step hyperpolarizations to -120 mV in 10-mV increments resulted in large inward currents that activated rapidly and then declined slowly (inactivated) during the test pulse in a time- and voltage- dependent fashion. The HERG K+ channel blockers E-4031 (1 µM), cisapride (1 µM), and La3+ (100 µM) strongly inhibited these currents as did millimolar concentrations of Ba2+. Immunoflourescence staining with anti-HERG antibody in single cells resulted in punctate staining at the sarcolemma. At membrane potentials near the resting membrane potential (-50 to -70 mV), this K+ conductance did not inactivate completely. In conventional microelectrode recordings, both E-4031 and cisapride depolarized tissue strips by 10 mV and also induced phasic contractions. In combination, these results provide direct experimental evidence for expression of HERG-like K+ currents in gastrointestinal smooth muscle cells and suggest that HERG plays an important role in modulating the resting membrane potential.

human ether-a-go-go; resting membrane potential; cisapride; inward rectifier


    INTRODUCTION
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

IN MANY EXCITABLE TISSUES the K+ conductance that is responsible for the resting potential exhibits inward rectification (12). Inwardly rectifying K+ currents (Kir) exhibit high conductance at negative potentials but greatly reduced conductance at positive potentials, thus avoiding short circuiting of the action potential. In smooth muscle, Kir belonging to the Kir 2.1 family of K+ channels have been identified in small diameter resistance blood vessels (6) but not in visceral smooth muscle. Isolated visceral smooth muscle cells, in physiological solutions, express only very small background K+ currents (>20 pA). In most cases, this precludes detailed characterization of the K+ channels that are responsible for maintaining the resting potential. Partly for this reason, the question of whether a Kir contributes to the resting potential of these smooth muscle remains unresolved.

Recent findings have drawn attention to the possible role of a novel inwardly rectifying K+ channel, the human ether-a-go-go-related gene (HERG) K+ channel, in modulating the resting membrane potential (RMP) associated with cell cycle changes, and in the setting of RMP of microglia (3, 24). HERG K+ channels have six transmembrane-spanning regions and therefore are distinct from other inward rectifiers that have only two transmembrane-spanning regions (21, 23). In cardiac myocytes, the HERG channel encodes for a rapidly activating delayed rectifier K+ current (IKr) (17). Mutations of HERG, or use of HERG channel blockers have been shown to cause cardiac abnormalities such as the long Q-T syndrome (8, 17). Interestingly, the gastrointestinal prokinetic agent, cisapride, was recently reported to block heterologously expressed HERG channels (14, 15), consistent with its proarrhythmic cardiac effects.

In the present study, we provide evidence for the presence of HERG-like K+ current in esophageal circular smooth muscle, define its role in setting RMP, and demonstrate that effects of cisapride in the esophagus are due to inhibition of HERG-like K+ currents.


    METHODS
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ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

Cell isolation and electrophysiology. Single smooth muscle cells from the distal part of the subdiaphragmatic esophagus of the opossum (Didelphis virgiana) were prepared by enzymatic dissociation as described previously (1). Patch-clamp experiments were done using the standard whole cell configuration, with a pipette solution containing (in mM) 100 potassium aspartate, 30 KCl, 5 HEPES, 5 ATP-Na2, 1 MgCl2, 0.1 GTP, and 5 EGTA. The pH was adjusted to 7.2 with KOH. The pipette resistance was 3-5 MOmega . The cells were initially perfused with a normal HEPES-buffered solution containing (in mM) 135 NaCl, 5.4 KCl, 0.33 NaH2PO4, 5 HEPES, 0.8 MgCl2, 2 CaCl2, and 5.5 glucose (pH 7.3 with NaOH). The isotonic K+ solution that was used for characterization of HERG K+ currents contained (in mM) 140 KCl, 0.1 CaCl2, 1 MgCl2, 5 HEPES, 5 tetraethylammonium, 3 4-aminopyridine, and 5.5 glucose. The pH was adjusted to 7.3 with KOH. Recordings were filtered at 1 kHz and sampled at 2.5 kHz. The voltage-clamp amplifier was an Axopatch 200 A (Axon Instruments). Capacitative transients were not electronically canceled. Data acquisition and analyses were preformed using pCLAMP 6 software. Figures 1-4 were prepared using Sigmaplot 4.0 and Origin 5.0.

In some experiments, intracellular membrane potentials were recorded, using microelectrodes filled with 3 M KCl (7), from smooth muscle cells of circular muscle strips obtained from distal esophagus. Atropine (1 µM), guanethidine (3 µM), and desensitizing concentrations of substance P (1 µM) were present in the perfusate. For tension recordings, circular smooth muscle strips were attached to a force transducer (Grass) in 3-ml organ baths. Tension was measured in the presence of atropine (1 µM) and tetrodotoxin (1 µM).

Immunostaining. Single smooth muscle cells from the opossum esophagus were fixed in 3.7% formaldehyde for 30 min at room temperature and permeabilized by adding 0.1% Triton X-100 in PBS. Nonspecific binding sites were blocked by incubating cells with 10% goat serum for 1 h at room temperature and were washed and then treated with rabbit anti-HERG antibody (1:100 dilution) for 90 min. The cells were washed twice in PBS and then incubated with polyclonal fluorescein isothiocyanate (FITC)-conjugated donkey anti-rabbit antibody (1:100 dilution) for 1 h. Cells were subsequently washed twice with PBS, mounted on slides, and imaged using an epifluorescence confocal microscope (MRC 1024; Bio-Rad), at ×80 magnification. To further investigate the specificity of the anti-HERG antibody, cells were treated with nonspecific IgG for 30 min at room temperature before incubation with the primary antibody. In another control, cells were labeled with FITC-conjugated donkey anti-rabbit antibody in the absence of primary antibody. In this experiment, epifluourescence was barely visible. Nonspecific binding was <10%, as ascertained by photon counting of these cells.

The anti-HERG antibody was a generous gift of Dr. Jeanne Nerbonne (Washington University, St. Louis, MO). Similar staining was also obtained using rabbit anti-HERG antibody from Alomone Labs (Jersualem, Israel). E-4031 was purchased from Wako Chemical Industries (Osaka, Japan). Cisapride was a generous gift from Jannsen Research Foundation (Beerse, Belgium). All other reagents were purchased from Sigma (St. Louis, MO).


    RESULTS
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

Kir in esophageal cells. Single smooth muscle cells isolated from the opossum esophageal circular muscle were perfused in high-K+ solution (140 mM K+) to enhance the size of the K+ currents and hence permit unambiguous identification and quantitative analysis. Ca2+-activated K+ currents, transient outward K+ currents, delayed rectifiers, and ATP-sensitive K+ currents were blocked by including tetraethylammonium (10 mM), 4-aminopyridine (3 mM), and low extracellular Ca2+ concentration (0.1 mM) to all superfusing solutions and by adding a high ATP concentration (5 mM) to the pipette solutions. Under these conditions, with the Nernst potential for K+ (EK) set at 0 mV, activation of K+ conductance produces inward currents. Hyperpolarization from 0 mV induced large transient inward currents (Fig. 1A). The kinetics of both activation and inactivation exhibited voltage dependence. The time constant for activation (when described by single exponential fits) decreased from 21 ± 2 ms at -60 mV to 8 ± 0.6 ms at -120 mV (n = 6). At potentials negative to approximately -60 mV, a substantial inactivation occurred, resulting in the crossover of the currents. These currents closely resemble those recorded from microglia and pituitary cells (5, 24) in which HERG has been shown to be the underlying K+ conductance. Families of transmembrane currents from the holding potential of 0 mV were recorded from eight cells and were normalized to peak currents at -120 mV. This current-voltage curve (Fig. 1B) demonstrates the presence of a Kir in these esophageal circular muscle cells.


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  		Fig. 1.   Inward rectifying K+ currents in opossum esophageal smooth muscle cells. Whole cell currents were measured in isotonic K+ solutions. A: family of currents recorded from holding potential of 0 mV. Voltage steps were applied in 10-mV increments from -120 to +30 mV. Note that hyperpolarization results in large inward currents that relax (inactivate) slowly. B: peak current-voltage relationship. Currents were normalized to peak amplitude at -120 mV and represent mean amplitude in 8 different cells.

Pharmacological properties of the HERG current. The pharmacological profile of the currents in isotonic K+ also provided evidence for the presence of HERG-like K+ currents in esophageal smooth muscle. To examine whether this inwardly rectifying current may result from the expression of HERG-like K+ current, known HERG blockers were applied. The methanesulfonanilide E-4031 strongly inhibits HERG K+ channels in the heart (20). Figure 2A shows that, in the esophageal cells, 1 µM E-4031 completely abolished the hyperpolarization-activated currents in isotonic K+ solution. The IC50 for this inhibition was 450 ± 53 nM (n = 5), which is within the range reported for inhibition of the HERG-like K+ channel (20, 24). Figure 2B shows that the prokinetic agent, cisapride, also strongly blocks the HERG-like K+ currents as it does in mammalian cells transfected with the HERG channel (14, 15). Families of current traces from one cell are shown in control and after 3 min of exposure to cisapride (1 µM). In the heart and in microglia cells, La3+ has been reported to block HERG currents (18). As shown in Fig. 2C, La3+ (100 µM) also markedly abolished the HERG currents in esophageal circular smooth muscle. In the final set of experiments in which inhibitors were used to characterize the K+ currents, BaCl2 was applied. It is known that conventional inwardly rectifying K+ currents (e.g., Kir 2.1) are blocked completely by very small concentrations (10-100 µM) of Ba2+ (12). As shown in Fig. 2D, 1 mM Ba2+ only partially abolished these currents, whereas 10 mM Ba2+ resulted in substantial block. These studies demonstrate that the inwardly rectifying currents in smooth muscle strongly resemble HERG-like K+ currents.


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  		Fig. 2.   Pharmacological profile of inwardly rectifying K+ currents and immunostaining in esophageal cells. A: effect of E-4031 (1 µM) on K+ currents. Cell was hyperpolarized to -120 mV from 0 mV. E-4031 (3-min perfusion) markedly inhibited inward currents. B: effect of cisapride (1 µM). Family of inward currents were elicited as shown in voltage protocol. Cisapride (1 µmM) significantly reduced human ether-a-go-go-related gene (HERG)-like K+ currents. C: effect of La3+. Cell was hyperpolarized to -100 mV. In presence of La3+, voltage step to -100 mV resulted in almost complete inhibition. D: effect of Ba2+. Inward currents were elicited by hyperpolarization to -90 mV from holding potential of 0 mV in absence and presence of 1 mM Ba2+ and then 10 mM Ba2+. Each concentration of Ba2+ was equilibrated for 3 min before voltage-clamp measurements. Note that, in 10 mM Ba2+, stepping back to 0 mV elicits inward Ba2+ currents through L-type Ca2+ channels. E: immunoflourescence due to anti-HERG antibody staining in single smooth muscle cell. Confocal image (×80 magnification) shows punctate staining distributed over entire cell surface.

The presence and localization of HERG channels in smooth muscle myocytes were confirmed with immunofluorescence staining. As shown in Fig. 2E, a punctate fluorescence pattern was observed on the sarcolemma of the single cells. This pattern of staining closely resembles that observed in cardiac tissue (4).

As a further test of the similarity of this K+ conductance to HERG-like K+ currents, the biophysical mechanism responsible for the observed inward rectification in esophageal cells was examined. In heterologously expressed HERG channels from mammalian heart, it has been shown that the mechanism of the inward rectification is voltage-gated fast inactivation (19). This possibility was evaluated by measuring the instantaneous current-voltage curve. Cells were briefly hyperpolarized to -120 mV to remove inactivation and then stepped back to test potentials of -120 to +30 mV (Fig. 3A). The instantaneous current-voltage relationship, which was measured by extrapolation of single exponential fits of the tail currents to the beginning of the test pulse, was approximately linear (Fig. 3B). A plausible explanation for this finding, based on previous work (19, 21), is that, in the absence of time-dependent inactivation, HERG K+ channels do not exhibit inward rectification. At depolarized potentials these K+ channels enter inactivated states very quickly, thus resulting in strong inward rectification.


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  		Fig. 3.   Mechanism of inward rectification and steady-state availability of HERG currents. Biophysical mechanism of inward rectification was studied using a 2-step voltage protocol illustrated at top. A 30-ms prepulse was applied to -120 mV from the holding potential (0 mV), membrane potential was then stepped back to selected test potentials (from -120 to +30 mV in 10-mV increments). Instantaneous current amplitude was measured by fitting single exponentials to tail currents and extrapolating to beginning of test pulse. B: average instantaneous current-voltage relationship was normalized to amplitude of currents at -120 mV (n = 5). C: steady-state voltage dependence of availability. Two-step voltage protocol was applied as illustrated at top. A long prepulse (14 s) to selected membrane potentials (+20 to -120 mV) was applied followed by 100-ms test pulse to -120 mV. D: amplitude of test current was plotted against prepulse potential, resulting in steady-state availability curve that was fit with a Boltzman relationship of the form I/Imax = 1/{1 + [exp(V0.5 - V)/k]}, where I is curent and V is voltage. E: voltage dependence of noninactivating or window current. Currents were measured at end of prepulse from experiments as shown in C. Maximum window currents were observed between -50 and -70 mV (n = 5). open circle , Currents measured at end of prepulse in presence of cisapride (1 µM).

Removal of intracellular Mg2+ from the pipette solution did not prevent inward rectification in esophageal cells (data not shown), providing further evidence that the inward rectification due to expression of, e.g., the Kir 2.1 family of K+ channels was not responsible (13, 19).

To determine the steady-state voltage dependence of availability, cells were held at membrane potentials ranging from +20 to -120 mV for 14 s (Fig. 3C). At the end of this prepulse, a 100-ms test pulse of -120 mV was applied. Normalized peak inward test currents plotted against the prepulse potential demonstrate the steady-state voltage dependence of availability of the K+ conductance (Fig. 3D). The voltage at which one-half the channels are available for activation was -72 mV, and this Boltzmann relationship had a slope factor of 6.8.

Close inspection of Fig. 3C shows that a noninactivating current is present at the end of the prepulse. Current-voltage relationships of these "window currents" were measured by plotting the amplitude of the noninactivating current vs. the applied voltage. As shown in Fig. 3E, this relationship showed a U-shaped dependence on voltage, with the maximal steady-state currents being recorded near the resting membrane potential of smooth muscle cells (between -70 and -50 mV). The noninactivating currents were significantly blocked by 1 µM cisapride (Fig. 3E).

HERG currents in resting potential. The presence of a noninactivating K+ current at membrane potentials near the resting potential (Fig. 3E) suggest a role for the HERG-like K+ currents in the setting of RMP. To evaluate this possibility, we examined the effects of HERG blockers on the membrane potential and contractility in in vitro esophageal muscle strip preparations. E-4031 at concentrations of 100 nM produced a small tonic contraction. At higher concentrations (1-3 µM) spontaneous phasic contractions were elicited (Fig. 4A). Recordings of intracellular membrane potential showed that both E-4031(3 µM) and cisapride (5 µM) depolarized the membrane potential by ~10 mV (Fig. 4B). These observations provide further support for the essential role of the HERG channel in regulation of resting membrane potential and mechanical responses of the esophageal circular muscle.


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  		Fig. 4.   In vitro recordings from esophageal muscle strips. A: recording of developed tension from isolated esophageal muscle strip in organ bath. Application of E-4031 (0.1 µM) resulted in a small rise in tension. At higher concentrations (1 µM) phasic contractions were obtained. B: microelectrode recordings from esophageal muscle strips. Application of E-4031 (3 µM; top) depolarized by 7 mV. Bottom: cisapride (5 µM) depolarized muscle segments by ~11 mV.


    DISCUSSION
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

These results provide pharmacological, biophysical and immunohistochemical evidence for the expression of HERG-like K+ conductance in opossum esophageal smooth muscle cells and suggest a potential role for HERG in regulating resting membrane potential in these cells. The electrophysiological characteristics of this Kir in esophageal cells strongly resembles that of the HERG-like K+ currents previously described in GH3 cells, neuroblastoma cells, and microglia, as well as in heterologously expressed HERG channels in Xenopus oocytes (3, 5, 21, 24). Previous publications have established that this type of K+ conductance can be identified consistently when isotonic extracellular K+ concentrations ([K+]o) are used. HERG currents exhibit marked time- and voltage-dependent inactivation and are blocked by methanesulfonanilides such as E-4031 and by relatively high concentrations of Ba2+. Each of these properties was observed in our study of the inwardly rectifying HERG-like K+ current in the opossum esophageal cells.

The inward rectification of the HERG is thought to be due to a fast-inactivation mechanism at positive potentials (19). This type of K+ conductance underlies the "rapid" component of the delayed rectifier current in the heart, and it defines its biophysical properties as a repolarizing current. Thus, during an action potential, maximal currents through HERG channels occur soon after the membrane begins to repolarize, as these channels recover from the inactivated state (21). In esophageal smooth muscle cells, as is the case of microglia and neuroblastoma cells (3, 24), HERG-like K+ currents contribute to the resting potential. Our data (Fig. 3E) demonstrate that the noninactivating current is maximal near the resting potential of smooth muscle cells i.e., -70 to -50 mV. The conductance at -60 mV was ~25-30% of the maximal conductance at -120 mV. Because, in physiological solutions (5.4 mM K+), this K+ conductance will be scaled down by the square root of the changes in [K+]o, peak currents at -60 mV under physiological conditions will be approximately fivefold smaller than those shown in Fig. 1. Thus these currents will measure only ~20 pA near the resting potential. However, in the setting of a high input resistance (5-10 GOmega ), a 20-pA current can significantly modulate the resting potential.

HERG channel blockers depolarized muscle segments and induced contractions, further suggesting a role of HERG-like K+ currents in regulating resting potential. The gastrointestinal prokinetic agent cisapride (1 µM) completely blocks the HERG-like K+ currents in these smooth muscle cells (Fig. 2D). In cells transfected with the HERG channel, the IC50 for cisapride ranges from 6 to 45 nM (14, 15). In addition to its effects on the 5-hydroxytryptamine receptors, cisapride has been shown to have direct stimulating effects on gastrointestinal smooth muscle (20a). Cisapride also significantly blocked the noninactivating currents.

Several types of K+ channels are suggested to be involved in the control of the resting potential in gastrointestinal smooth muscle. These include intermediate-conductance Ca2+-activated K+ channels (22,), delayed rectifier K+ currents (10), transient outward K+ currents (2), and ATP-sensitive K+ channels (11). The results presented here strongly support an essential role of HERG-like K+ currents in regulating the electrophysiological and mechanical activity of gastrointestinal smooth muscle.


    ACKNOWLEDGEMENTS

This work was supported by National Institute of Diabetes and Digestive and Kidney Diseases Grants DK-46367 (H. I. Akbarali) and DK-31098 (R. K. Goyal), a Veterans Affairs Merit Award (R. K. Goyal), the Canadian Medical Research Council, the Heart and Stroke Foundation of Canada, and the Alberta Heritage Foundation for Medical Research (W. R. Giles).


    FOOTNOTES

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Address for reprint requests and other correspondence: H. I. Akbarali, Research 151, West Roxbury VA Medical Center, 1400 VFW Parkway, West Roxbury, MA 02132 (E-mail: hakbarali{at}hms.harvard.edu).

Received 22 July 1999; accepted in final form 3 September 1999.


    REFERENCES
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

1.   Akbarali, H. I., and R. K. Goyal. Effect of sodium nitroprusside on Ca2+ currents in opossum esophageal circular muscle cells. Am. J. Physiol. 266 (Gastrointest. Liver Physiol. 29): G1036-G1042, 1994[Abstract/Free Full Text].

2.   Akbarali, H. I., N. Hatakeyama, Q. Wang, and R. K. Goyal. Transient outward current in opossum esophageal circular muscle. Am. J. Physiol. 268 (Gastrointest. Liver Physiol. 31): G979-G987, 1995[Abstract/Free Full Text].

3.   Arcangeli, A., L. Bianchi, A. Becchetti, L. Faravelli, M. Coronnello, E. Mini, M. Olivotto, and E. Wanke. A novel inward-rectifying K+ current with a cell-cycle dependence governs the resting potential of mammalian neuroblastoma cells. J. Physiol. (Lond.) 489: 455-471, 1995[Medline].

4.   Babij, P., G. R. Askew, B. Nieuwenhuijsen, C. Su, T. R. Bridal, B. Jow, T. M. Argentieri, J. Kulik, L. J. DeGennaro, W. Spinelli, and T. J. Colatsky. Inhibition of cardiac delayed rectifier K+ current by overexpression of the long-QT syndrome HERG G628S mutation in transgenic mice. Circ. Res. 83: 668-678, 1998[Abstract/Free Full Text].

5.   Bauer, C. K. The erg inwardly rectifying K+ current and its modulation by thyrotrophin-releasing hormone in giant clonal rat anterior pituitary cells. J. Physiol. (Lond.) 510: 63-70, 1998[Abstract/Free Full Text].

6.   Bradley, K. K., J. H. Jaggar, A. D. Bonev, T. J. Heppner, E. R. Flynn, M. T. Nelson, and B. Horowitz. Kir2.1 encodes the inward rectifier potassium channel in rat arterial smooth muscle cells. J. Physiol. (Lond.) 515: 639-651, 1999[Abstract/Free Full Text].

7.   Crist, J. R., X. D. He, and R. K. Goyal. Chloride-mediated junction potentials in circular muscle of the guinea pig ileum. Am. J. Physiol. 261 (Gastrointest. Liver Physiol. 24): G742-G751, 1991[Abstract/Free Full Text].

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10.   Farrugia, G., J. L. Rae, and J. H. Szurszewski. Characterization of an outward potassium current in canine jejunal circular smooth muscle and its activation by fenamates. J. Physiol. (Lond.) 468: 297-310, 1993[Abstract/Free Full Text].

11.   Hatakeyama, N., Q. Wang, R. K. Goyal, and H. I. Akbarali. Muscarinic suppression of ATP-sensitive K+ channel in rabbit esophageal smooth muscle. Am. J. Physiol. 268 (Cell Physiol. 37): C877-C885, 1995[Abstract/Free Full Text].

12.   Hille, B. Ionic Channel of Excitable Membrane. Sunderland, MA: Sinauer, 1992.

13.   Matsuda, H., A. Saigusa, and H. Irisawa. Ohmic conductance through inwardly rectifying K+ channel and blocking by internal Mg2+. Nature 325: 156-159, 1987[Medline].

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15.   Rampe, D., M. L. Roy, A. Dennis, and A. M. Brown. A mechanism for the proarrhythmic effects of cisapride (Propulsid): high affinity blockade of the human cardiac potassium channel HERG. FEBS Lett. 417: 28-32, 1997[Medline].

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17.   Sanguinetti, M. C., C. Jiang, M. E. Curran, and M. T. Keating. A mechanistic link between an inherited and an acquired cardiac arrhythmia: HERG encodes the IKr potassium channel. Cell 81: 299-307, 1995[Medline].

18.   Sanguinetti, M. C., and N. K. Jurkiewicz. Lanthanum blocks a specific component of IK and screens membrane surface change in cardiac cells. Am. J. Physiol. 259 (Heart Circ. Physiol. 28): H1881-H1889, 1990[Abstract/Free Full Text].

19.   Smith, P. L., T. Baukrowitz, and G. Yellen. The inward rectification mechanism of the HERG cardiac potassium channel. Nature 379: 833-836, 1996[Medline].

20.   Spector, P. S., M. E. Curran, M. T. Keating, and M. C. Sanguinetti. Class III antiarrhythmic drugs block HERG, a human cardiac delayed rectifier K+ channel. Open-channel block by methanesulfonanilides. Circ. Res. 78: 499-503, 1996[Abstract/Free Full Text].

20a.   Syed, M., H. Tokuno, and T. Tomita. Effects of cisapride on isolated guinea-pig colon. Jpn. J. Pharmacol. 51: 47-56, 1989[Medline].

21.   Trudeau, M. C., J. W. Warmke, B. Ganetzky, and G. A. Robertson. HERG, a human inward rectifier in the voltage-gated potassium channel family. Science 269: 92-95, 1995[Abstract/Free Full Text].

22.   Vogalis, F., and R. K. Goyal. Activation of small conductance Ca2+-dependent K+ channels by purinergic agonists in smooth muscle cells of the mouse ileum. J. Physiol. (Lond.) 502: 497-508, 1997[Medline].

23.   Warmke, J. W., and B. Ganetzky. A family of potassium channel genes related to eag in Drosophila and mammals. Proc. Natl. Acad. Sci. USA 91: 3438-3442, 1994[Abstract/Free Full Text].

24.   Zhou, W., F. S. Cayabyab, P. S. Pennefather, L. C. Schlichter, and T. E. DeCoursey. HERG-like K+ channels in microglia. J. Gen. Physiol. 111: 781-794, 1998[Abstract/Free Full Text].

Am J Physiol Cell Physiol 277(6):C1284-C1290
0002-9513/99 $5.00 Copyright © 1999 the American Physiological Society


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Y. Zhu, C. M. Golden, J. Ye, X.-Y. Wang, H. I. Akbarali, and J. D. Huizinga
ERG K+ currents regulate pacemaker activity in ICC
Am J Physiol Gastrointest Liver Physiol, December 1, 2003; 285(6): G1249 - G1258.
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 J. Neurophysiol.Home page
T. Sacco, A. Bruno, E. Wanke, and F. Tempia
Functional Roles of an ERG Current Isolated in Cerebellar Purkinje Neurons
J Neurophysiol, September 1, 2003; 90(3): 1817 - 1828.
[Abstract] [Full Text] [PDF]

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 Am. J. Physiol. Gastrointest. Liver Physiol.Home page
A. M. Farrelly, S. Ro, B. P. Callaghan, M. A. Khoyi, N. Fleming, B. Horowitz, K. M. Sanders, and K. D. Keef
Expression and function of KCNH2 (HERG) in the human jejunum
Am J Physiol Gastrointest Liver Physiol, June 1, 2003; 284(6): G883 - G895.
[Abstract] [Full Text] [PDF]

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 Am. J. Physiol. Gastrointest. Liver Physiol.Home page
E. Parr, M. J. Pozo, B. Horowitz, M. T. Nelson, and G. M. Mawe
ERG K+ channels modulate the electrical and contractile activities of gallbladder smooth muscle
Am J Physiol Gastrointest Liver Physiol, March 1, 2003; 284(3): G392 - G398.
[Abstract] [Full Text] [PDF]

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 J. Biol. Chem.Home page
F. Shoeb, A. P. Malykhina, and H. I. Akbarali
Cloning and Functional Characterization of the Smooth Muscle Ether-a-go-go-related Gene K+ Channel. POTENTIAL ROLE OF A CONSERVED AMINO ACID SUBSTITUTION IN THE S4 REGION
J. Biol. Chem., January 17, 2003; 278(4): 2503 - 2514.
[Abstract] [Full Text] [PDF]

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 Am. J. Physiol. Cell Physiol.Home page
S. Ohya, B. Horowitz, and I. A. Greenwood
Functional and molecular identification of ERG channels in murine portal vein myocytes
Am J Physiol Cell Physiol, September 1, 2002; 283(3): C866 - C877.
[Abstract] [Full Text] [PDF]

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 J. Neurosci.Home page
M. Lecchi, E. Redaelli, B. Rosati, G. Gurrola, T. Florio, O. Crociani, G. Curia, R. R. Cassulini, A. Masi, A. Arcangeli, et al.
Isolation of a Long-Lasting eag-Related Gene-Type K+ Current in MMQ Lactotrophs and Its Accommodating Role during Slow Firing and Prolactin Release
J. Neurosci., May 1, 2002; 22(9): 3414 - 3425.
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 Am. J. Physiol. Regul. Integr. Comp. Physiol.Home page
M. Vornanen, A. Ryokkynen, and A. Nurmi
Temperature-dependent expression of sarcolemmal K+ currents in rainbow trout atrial and ventricular myocytes
Am J Physiol Regulatory Integrative Comp Physiol, April 1, 2002; 282(4): R1191 - R1199.
[Abstract] [Full Text] [PDF]

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 Am. J. Physiol. Gastrointest. Liver Physiol.Home page
S. Ohya, K. Asakura, K. Muraki, M. Watanabe, and Y. Imaizumi
Molecular and functional characterization of ERG, KCNQ, and KCNE subtypes in rat stomach smooth muscle
Am J Physiol Gastrointest Liver Physiol, February 1, 2002; 282(2): G277 - G287.
[Abstract] [Full Text] [PDF]

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