Cardiac Ca channel currents at the level of single cells and single channels.

Ca channels in excitable membranes are of great importance for many cellular functions. Modulation of these channels by voltage, neurotransmitters and drugs regulates Ca influx into the cell and thereby alters the functional state of the cell (7). For many years, quantitative analysis has been seriously complicated by experimental problems (see 2, 8, 10). There has been no preparation as suitable and no drug as specific for Ca channels, as the squid axon and TTX are for Na channels (10). The advent of the isolated adult heart cell and the development of powerful new electrophysiological methods, however, have opened up the possibility to record Ca channel activity at the level of single cells and single channels and to obtain evidence on molecular mechanisms of Ca channel gating and modulation.