MECHANISM OF POTENTIATION OF CONTRACTION BY DEPOLARIZATION DURING ACTION POTENTIALS IN GUINEA-PIG VENTRICULAR MUSCLE

¹ University Department of Pharmacology, South Parks Road, Oxford OX1 3QT

Action potentials were recorded from guinea-pig ventricular cells and contraction recorded by an optical technique. When the plateau of a single action potential was depolarized (by 70-120 pA applied 100 ms after the upstroke for 100 ms), contraction associated with the following normal action potential was potentiated. This potentiation was not seen in cells exposed to 10 mM-caffeine. The observations are consistent with potentiation of subsequent contraction by increased loading of caffeine-sensitive calcium stores, as a consequence of reduced Ca²⁺ extrusion or possibly Ca²⁺ entry via Na⁺-Ca²⁺ exchange during a depolarized plateau.

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