Cav1.4 Encodes a Calcium Channel with Low Open Probability and Unitary Conductance

AbstractWhen transiently expressed in tsA-201 cells, Cav1.4 calcium channels support only modest whole-cell currents with unusually slow voltage-dependent inactivation kinetics. To examine the basis for this unique behavior we used cell-attached patch single-channel recordings using 100mM external barium as the charge carrier to determine the single-channel properties of Cav1.4 and to compare them to those of the Cav1.2. Cav1.4 channel openings occurred infrequently and were of brief duration. Moreover, openings occurred throughout the duration of the test depolarization, indicating that the slow inactivation kinetics observed at the whole-cell level are caused by sustained channel activity. Cav1.4 and Cav1.2 channels displayed similar latencies to first opening. Because of the rare occurrence of events, the probability of opening could not be precisely determined but was estimated to be