SODIUM-CALCIUM EXCHANGE DURING THE ACTION-POTENTIAL

Na-Ca exchange in atrial-type action potentials contributes most of it s current at a well-defined time during the late low plateau after the calcium current has deactivated. In ventricular cells with high plate au voltages, the situation is more complex, with the magnitude and dir ection of the exchange current changing continuously during the platea u. There is also very substantial overlap with the time course of the calcium current. We used rapid external solution switching to perturb the exchanger more directly during the plateau and have shown a very s ubstantial contribution throughout the action potential.