Abstract
The effect of temperature reduction on monkey ventricular action potentials has been studied. Under this condition the genesis of a notch separating the AP spike from the AP plateau has been related either to a conduction phenomenon or to a delay in the activation of the slow inward current. It is observed that the development of a notch at the beginning of the plateau depends both on the presence of a large outward, repolarising current, carried by chloride and/or potassium ions, and on the presence of a slow inward calcium current large enough to depolarise the membrane as the chloride current deactivates.