Abstract
Muscarinic receptor-linked G protein, Gi, can directely activate the specific K+ channel (I K(ach)) in the atrium and in pacemaker tissues in the heart. Coupling of Gi to the K+ channel in the ventricle has not been well defined. G protein regulation of K+ channels in isolated human ventricular myocytes was examined using the patch-clamp technique. Bath application of 1 μM acetylcholine (ACh) reversibly shortened the action potential duration to 74.4 ± 12.1% of control (at 90% repolarization, mean ± sd, n = 8) and increased the whole-cell membrane current conductance without prior β-adrenergic stimulation in human ventricular myocytes. The ACh effect was reversed by atropine (1 μm). In excised inside-out patch configurations, application of GTPγS (100 μm) to the bath solution (internal surface) caused activation of I K(ACh) and/or the background inwardlyrectifying K+ channel (I K1,) in ventricular cell membranes. I K(ACh) exhibited rapid gating behavior with a slope conductance of 44 ± 2 pS (n = 25) and a mean open lifetime of 1.8 ± 0.3 msec (n = 21). Single channel activity of GTPγS-activated I K1 demonstrated longlasting bursts with a slope conductance of 30 ± 2 pS (n = 16) and a mean open lifetime of 36.4 ± 4.1 msec (n = 12). Unlike I K(ACh)’ G protein-activated I K1 did not require GTP to maintain channel activity, suggesting that these two channels may be controlled by G proteins with different underlying mechanisms. The concentration of GTP at half-maximal channel activation was 0.22 μm in I K(ACh) and 1.2 μm in I K1. Myocytes pretreated with pertussis toxin (PTX) prevented GTP from activating these channels, indicating that muscarinic receptorlinked PTX-sensitive G protein, Gi, is essential for activation of both channels. G protein-activated channel characteristics from patients with terminal heart failure did not differ from those without heart failure or guinea pig. These results suggest that ACh can shorten the action potential by activating I K(ACh) and I K1 via muscarinic receptor-linked Gi, proteins in human ventricular myocytes.
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Allen, D.G., Morris, P.G., Orchard, C.H., Pirolo, J.S. 1985. A nuclear magnetic resonance study of metabolism in the ferret heart during hypoxia and inhibition of glycolysis. J. Physiol. 361:185–204
Baiser, J.R., Roden, D.M., Bennett, P.B. 1991. Single inward rectifier potassium channels in guinea pig ventricular myocytes: effects of quinidine. Biophys J. 59:150–161
Boyett, M.R., Kirby, M.S., Orchard, C.H., Roberts, A. 1988. The negative inotropic effect of acetylcholine on ferret ventricular myocardium. J. Physiol. 404:613–635
Breitwieser, G.E., Szabo, G. 1985. Uncoupling of cardiac muscarinic and β-adrenergic receptors from ion channels by a guanine nucleotide analogue. Nature 317:538–540
Colquhoun, D., Hawkes, A.G. 1981. On the stochastic properties of single ion channels. Proc. R. Soc. Lond. B. 211:205–235
Colquhoun, D., Hawkes, A.G. 1983. The principles of the stochastic interpretation of ion-channel mechanisms. In: Single-Channel Recording. B. Sakmann and E. Neher, editors. pp. 135–175, Plenum Publishing, New York
Colquhoun, D., Sigworth, F.J. (1983. Fitting and statistical analysis of single-channel records. In: Single-Channel Recording. B. Sakmann and E. Neher, editors. pp. 191–263, Plenum Publishing, New York
Elliott, A.C., Smith, G.L., Allen, D.G. 1989. Simultaneous measurements of action potential duration and intracellular ATP in isolated ferret hearts exposed to cyanide. Circ. Res. 64:583–591
Fleming, J.W., Wisler, P.L., Watanabe, A.M. 1992. Signal transduction by G proteins in cardiac tissues. Circulation 85:420–433
Fosset, M., Schmid-Antomarchi, H., De Wille, J.R., Lazduriski, M. 1988. Somatostatin activates glibenclamide-sensitive and ATP-regulated K+ channels in insulinoma cells via a G protein. FEBS Lett. 242:94–96
Hamill, O.P., Marty, A., Neher, E., Sakmann, B., Sigworth, F.J. 1981. Improved patch-clamp techniques for high-resolution current recording from cells and cell-free membrane patches. Pfluegers Arch. 391:85–100
Hartzell, H.C., Simmons, M.A. 1987. Comparison of effects of acetylcholine on calcium and potassium currents in frog atrium and ventricle. J. Physiol. 389:411–422
Heidbuchel, H., Callewaert, G., Vereecke, J., Carmeliet, E. 1993. Acetylcholine-medicated K+ channel activity in guinea-pig atrial cells is supported by nucleoside diphosphate kinase. Pfluegers Arch. 422:316–324
Heidbuchel, H., Vereecke, J., Carmeliet, E. 1990. Three differenct potassium channels in human atrium. Contribution to the basal potassium conductance. Circ. Res. 66:1277–1286
Hino, N., Ochi, R. 1980. Effect of acetylcholine on membrane currents in guinea-pig papillary muscle. J Physiol. 307:183–197
Isenberg, G., U. Klockner. 1982. Calcium tolerant ventricular myocytes prepared by preincubation in KB medium. Pfluegers ARch. 395:6–18
Josephson, I., Sperelakis, N. 1982. On the ionic mechanism underlying adrenergic-cholinergic antagonism in ventricular muscle. J. Gen. Physiol 79:69–86
Kitakaze, M., Hori, M., Kamada, T. 1993. Role of adenosine and its interaction with alpha adrenoceptor activity in ischaemic and reperfusion injury of the myocardium. Cardiovasc. Res. 27:18–27
Koumi, S-i., Arentzen, C.E., Backer, C.L., Wasserstrom, J.A. 1994. Alterations in muscarinic K+ channel response to acetylcholine and to G protein-mediated activation in atrial myocytes isolated from failing human hearts. Circulation 90:2213–2224
Koumi, S-i., Backer, C.L., Arentzen, C.E. 1995a. Characterization of the inwardly-rectifying K+ channel in human cardiac myocytes: Alterations in channel behavior in myocytes isolated from patients with idiopathic dilated cardiomyopathy. Circulation 92:164–174
Koumi, S-i., Backer, C.L., Arentzen, C.E., Sato, R. 1995b. β-Adrenergic modulation of the inwardly-rectifying potassium channel in isolated human ventricular myocytes: Alteration in channel response to β-adrenergic stimulation in failing human hearts. J. Clin. Invest. 96:2870–2881
Kurachi, Y. 1995. G protein regulation of cardiac muscarinic potassium channel. Am. J. Physiol. 269:C821-C830
Kurachi, Y., Nakajima, T., Sugimoto, T. 1986. On the mechanism of activation of muscarinic K+ channels by adenosine in isolated atrial cells: involvement of GTP-binding proteins. Pfluegers Arch. 407:264–274
Loffelholz, K., Pappano, A.J. 1985. The parasympathetic neuroeffector junction of the heart. Pharmacol Rev. 37:1–24
Martin, J.M., Subers, E.M., Halvorsen, S.W., Nathanson, N.M. 1987. Functional and physical properties of chick atrial and ventricular GTP-binding proteins: Relationship to muscarinic acetylcholine receptor-mediated responses. J. Pharmacol. Exp. Ther. 240:683–688
McMorn, S.O., Harrison, S.M., Zang, W.J., Yu, X.J., Boyett, M.R. 1993. A direct negative inotropic effect f acetylcholine on rat ventricular myocytes. Am. J. Physiol. 265:H1393-H1400
Mitra R., Morad M. 1985. A uniform enzymatic method for dissociation of myocytes from hearts and stomachs of vertebrates. Am. J. Physiol. 249:H1056-H1060
Narahashi, T., Tsunoo, A., Yoshii, M. 1987. Characterization of two types of calcium channels in moust neuroblastoma cells. J. Physiol 383:231–249
Nichols, C.G., Lederer, W.J. 1991. Adenosine triphosphate-sensitive potassium channels in the cardiovascular system. Am. J. Physiol. 261:H1675-H1686
Noma, A., Shibasaki, T. 1985. Membrane current through adenosine-triphosphate-regulated potassium channels in guinea-pig ventricular cells. J. Physiol. 363:463–480
Pfaffinger, P.J., Martin, J.M., Hunter, D.D., Nathanson, N.M., Hille, B. 1985. GTP-binding proteins couple cardiac muscarinic receptors to a K channel. Nature 317:536–538
Prystowsky, E.N., Jackman, W.M., Rinkenberger, R.L., Heger, J.J., Zipes, D.P. 1981. Effect of autonomie blockade on ventricular refractoriness and atrioventricular nodal conduction in man: Evidence supporting a direct cholinergic action on ventricular muscle refractoriness. Circ. Res. 49:511–518
Robishaw, J.D., Foster, K.A. 1989. Role of G proteins in the regulation of the cardiovascular system. Annu. Rev. Physiol. 51:229–244
Sakmann, B., Trube, G. 1984a. Voltage-dependent inactivation of inward-rectifying single-channel currents in the guinea-pig heart cell membrane. J. Physiol. 347:659–683
Sakmann, B., Trube, G. 1984b. Conductance properties of single inwardly rectifying potassium channels in ventricular cells from guinea-pig heart. J. Physiol. 347:641–657
Sato, R., Hisatome, I., Wasserstrom, J.A., Arentzen, C.E., Singer, D.H. 1990. Acetylcholine-sensitive potassium channels in human atrial myocytes. Am. J. Physiol. 259:H1730-H1735
Soejima, M., Noma, A. 1984. Mode of regulation of the ACh-sensitive K channel by the muscarinic receptor in rabbit atrial cells. Pfluegers Arch. 400:424–431
Trube, G., Hescheler, J. 1984. Inward-rectifying channels in isolated patches of the heart cell membrane: ATP-dependent and comparison with cell-attached patches. Pfluegers Arch. 401:178–184
Wess, J. 1993. Mutational analysis of muscarinic acetylcholine receptors: structural basis of ligand/receptor/G protein interactions. Life Sciences 53:1447–1463
Zang, W.J., Yu, X.J., Honjo, H., Kirby, M.S., Boyett, M.R. 1993. On the role of G protein activation and phosphorylation in desensitization to acetylcholine in guinea-pig atrial cells. J. Physiol. 464:649–679
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Koumi, S.i., Sato, R., Nagasawa, K. et al. Activation of inwardly rectifying potassium channels by muscarinic receptor-linked G protein in isolated human ventricular myocytes. J. Membrane Biol. 157, 71–81 (1997). https://doi.org/10.1007/s002329900217
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DOI: https://doi.org/10.1007/s002329900217