L-type calcium current in rod- and spindle-shaped myocytes isolated from rabbit atrioventricular node.
The atrioventricular node (AVN) is vital to normal cardiac function. The present report describes the properties of L-type calcium current (ICa) in rod- and spindle-shaped myocytes isolated from the rabbit AVN. With depolarizing voltage clamps from a holding potential of -40 mV, a rapidly activating ICa was observed, which peaked at +10 mV in most cells and exhibited a "bell-shaped" current-voltage relation. ICa was abolished by nifedipine (2-20 microM) and cadmium (100-200 microM) and was greatly reduced by manganese (1 mM). At +10 mV, time to peak ICa was 3.3 +/- 0.15 (SE) ms (n = 12) and ICa current density was 9.3 +/- 1.2 pA/pF (n = 9). Steady-state activation and inactivation curves for ICa showed half-maximal activation at -3.6 mV [slope factor (k) = 6.6 mV] and half-maximal inactivation at -25.8 mV (k = 6.5 mV). The time course of decay of ICa during a depolarizing pulse was voltage dependent and biexponential. The time course of recovery of ICa from inactivation was also biexponential (with two time constants tau 1 = 194.7 and tau 2 = 907.4 ms). Under current clamp, spontaneous action potentials from AVN cells were blocked by nifedipine as well as by cadmium, suggesting that L-type ICa was largely responsible for the action potential upstroke.
Department of Physiology, School of Medical Sciences, University of Bristol, United Kingdom.
J C
JC
Hancox
A J
AJ
Levi
D000818:Animals; D001283:Atrioventricular Node / Q000166:cytology / Q000502:physiology*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002478:Cells, Cultured; D002586:Cesium / Q000494:pharmacology; D002712:Chlorides / Q000494:pharmacology; D004553:Electric Conductivity; D006321:Heart / Q000502:physiology*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009543:Nifedipine / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D011817:Rabbits; D013997:Time Factors
D015220:Calcium Channels; D002712:Chlorides; D002586:Cesium; D011189:Potassium Chloride; C028019:cesium chloride; D009543:Nifedipine