Existence of a low-threshold and sustained inward current in rabbit atrio-ventricular node cells.
Single myocytes were dissociated from the atrio-ventricular (AV) node of rabbit hearts. Spontaneous action potentials of the N or NH type were recorded from the fusiform AV node cells. Under whole-cell voltage clamp, these cells were characterized by the presence of hyperpolarization-activated cation current (I(f)), delayed rectifier K+ current (IK), and L-type Ca2+ current (ICa,L). After blocking I(f) and IK, depolarizing pulses from -80 mV revealed a sustained inward current, which was suppressed by 1 microM nicardipine. The activation threshold of the sustained inward current was around -60 mV and the maximum amplitude was 25.4 +/- 20.1 pA at -40 mV (n = 15). The current was also blocked by 1 microM verapamil. The sustained inward current was not decreased (125 +/- 32% of control, N = 5) by reducing [Ca2+]o from 1.8 to 0.1 mM, while it was nearly suppressed by depleting [Na+]o, differently from ICa,L. We concluded that the nicardipine-sensitive sustained inward current is largely attributable to Ist described in the rabbit sino-atrial node pacemaker cells. I(f) and Ist were not found in rod-shape AV node cells.
Guo
J
J
Department of Physiology, Faculty of Medicine, Kyoto University, Japan.
Noma
A
A
D000200:Action Potentials; D000818:Animals; D001283:Atrioventricular Node / Q000166:cytology / Q000502:physiology*; D066298:In Vitro Techniques; D009206:Myocardium / Q000166:cytology*; D009529:Nicardipine / Q000008:administration & dosage / Q000494:pharmacology; D011817:Rabbits; D014700:Verapamil / Q000008:administration & dosage / Q000494:pharmacology
D014700:Verapamil; D009529:Nicardipine