Two kinds of calcium channels in canine atrial cells: Differences in kinetics, selectivity, and pharmacology

Abstract

Currents through Ca channels were recorded in single canine atrial cells using whole-cell recording with patch pipettes. Two components of Ca channel current could be distinguished. One ("Ifast") was present only if cells were held at negative potentials, was most prominent for relatively small depolarizations, and inactivated within tens of milliseconds. The other ("Islow")corresponding to the Ca current previously reported in single cardiac cells, persisted even at relatively positive holding potentials, required stronger depolarizations for maximal current, and inactivated much more slowly. Both currents were unaffected by tetrodotoxin and both were reduced by Co. Ifast had the same size and kinetics when Ca was exchanged for Ba, while I, 10, was bigger and slower with Ba as the charge carrier. In isotonic BaC12, fluctuation analysis showed that Ifa. had a smaller single channel current than II Islow. Islow was much more sensitive to block by nitrendipine than was Ifast"also, but not Islow was increased by the dihydropyridine drug BAY K8644. Isoproterenol produced large increases in Islow but had no effect on Ifast. © 1985, Rockefeller University Press., All rights reserved.