AJP - Cell Physiology, Vol 261, Issue 2 C393-C397, Copyright © 1991 by American Physiological Society

ARTICLES

Ca2+ current and Ca2+ transients under action potential clamp in guinea pig ventricular myocytes

J. Arreola, R. T. Dirksen, R. C. Shieh, D. J. Williford and S. S. Sheu
Department of Pharmacology, School of Medicine and Dentistry, University of Rochester, New York 14642.

Precise characterization of the magnitude and kinetics of transsarcolemmal Ca2+ influx during an action potential (AP) is essential for a complete understanding of excitation-contraction coupling in heart. Using a voltage-clamp protocol that simulated a physiological AP (AP clamp), we characterized the properties of the Ca2+ current (ICa) in guinea pig ventricular myocytes. The AP-generated ICa showed a complex time course that was different from ICa generated by a square pulse. ICa activated rapidly during the upstroke of the AP and then partially inactivated during the plateau. The fast component of ICa reached a peak value of -7.6 +/- 1.0 pA/pF at 2.40 +/- 0.30 ms after depolarization, followed by a slow component with a peak value of -2.9 +/- 0.4 pA/pF during the plateau. ICa generated by an AP was composed of both L- and T-type Ca2+ channels. T-type Ca2+ current contributed to the fast component of ICa and L-type Ca2+ current contributed to both fast and slow components of ICa. Activation of beta-adrenoceptors enhanced ICa with a maximal effect lasting throughout the entire plateau of the AP. Measurements of cytosolic Ca2+ transients using fura-2 indicated that the ICa was responsible for triggering Ca2+ release from the sarcoplasmic reticulum. The AP clamp provides a new approach for investigation of the relationship between ICa and Ca2+ transients under more physiological conditions.

This article has been cited by other articles:

				H. A. Shiels, M. Vornanen, and A. P. Farrell Temperature dependence of cardiac sarcoplasmic reticulum function in rainbow trout myocytes J. Exp. Biol., December 1, 2002; 205(23): 3631 - 3639. [Abstract] [Full Text] [PDF]

				H. Dobrzynski, N. C. Janvier, R. Leach, J. B. C. Findlay, and M. R. Boyett Effects of ACh and adenosine mediated by Kir3.1 and Kir3.4 on ferret ventricular cells Am J Physiol Heart Circ Physiol, August 1, 2002; 283(2): H615 - H630. [Abstract] [Full Text] [PDF]

				J. L. Puglisi, W. Yuan, J. W. M. Bassani, and D. M. Bers Ca2+ Influx Through Ca2+ Channels in Rabbit Ventricular Myocytes During Action Potential Clamp : Influence of Temperature Circ. Res., September 17, 1999; 85 (6): e7 - e16. [Abstract] [Full Text] [PDF]

				L. Hove-Madsen and L. Tort L-type Ca2+ current and excitation-contraction coupling in single atrial myocytes from rainbow trout Am J Physiol Regulatory Integrative Comp Physiol, December 1, 1998; 275(6): R2061 - R2069. [Abstract] [Full Text] [PDF]

				V. K. Sharma, H. M. Colecraft, D. X. Wang, A. I. Levey, E. V. Grigorenko, H. H. Yeh, and S.-S. Sheu Molecular and Functional Identification of m1 Muscarinic Acetylcholine Receptors in Rat Ventricular Myocytes Circ. Res., July 1, 1996; 79(1): 86 - 93. [Abstract] [Full Text]

				R. A. Bouchard, R. B. Clark, and W. R. Giles Effects of Action Potential Duration on Excitation-Contraction Coupling in Rat Ventricular Myocytes : Action Potential Voltage-Clamp Measurements Circ. Res., May 1, 1995; 76(5): 790 - 801. [Abstract] [Full Text]