Ca channel gating during cardiac action potentials

• Published in: Biophysical journal Vol. 58; no. 4; pp. 1059 - 1065
• Main Authors: Mazzanti, M., DeFelice, L.J.
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Elsevier Inc 01-10-1990; Biophysical Society; The Biophysical Society
• Subjects: Action Potentials - physiology; Animals; Barium - metabolism; Biological and medical sciences; Biophysical Phenomena; Biophysics; Calcium Channels - physiology; Cell physiology; Chick Embryo; Fundamental and applied biological sciences. Psychology; gating; heart; Heart - physiology; In Vitro Techniques; Kinetics; Membrane and intracellular transports; membrane potential; Molecular and cellular biology; Heart; Barium; Calcium; Electrical conductance; Patch clamp method; Action potential; Ionic channel; Kinetics
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/S0006-3495(90)82448-6

How do Ca channels conduct Ca ions during the cardiac action potential? We attempt to answer this question by applying a two-microelectrode technique, previously used for Na and K currents, in which we record the patch current and the action potential at the same time (Mazzanti, M., and L. J. DeFelice. 1987. Biophys. J. 12:95–100, and 1988. Biophys. J. 54:1139–1148; Wellis, D., L. J. DeFelice, and M. Mazzanti. 1990. Biophys. J. 57:41–48). In this paper, we also compare the action currents obtained by the technique with the step-protocol currents obtained during standard voltage-clamp experiments. Individual Ca channels were measured in 10 mM Ca/1 Ba and 10 mM Ba. To describe part of our results, we use the nomenclature introduced by Hess, P., J. B. Lansman, and R. W. Tsien (1984. Nature (Lond.). 311:538–544). With Ba as the charge carrier, Ca channel kinetics convert rapidly from long to short open times as the patch voltage changes from 20 to -20 mV. This voltage-dependent conversion occurs during action potentials and in step-protocol experiments. With Ca as the charge carrier, the currents are brief at all voltages, and it is difficult to define either the number of channels in the patch or the conductance of the individual channels. Occasionally, however, Ca-conducting channels spontaneously convert to long-open-time kinetics (in Hess et al., 1984, notation, mode 2).