Effects of manganese, glucose and isoprenaline on the action potential of anoxic ventricular muscle.

Abstract

Anoxia has previously been shown to depress the action potential of guinea pig ventricular muscle. It seemed possible that the anoxia-induced decreases in action potential duration and overshoot were related to a reduction in the slow inward current. The following indirect evidence was obtained in support of this view: 1. Anoxic muscle incubated in 50 mM glucose medium has a normal action potential duration and overshoot. In 5 mM glucose medium the action potential duration was severely reduced with only a small decline in overshoot. In the absence of glucose the action potential duration was further reduced and the amplitude was depressed by about 35 mV. Reincubation in 50 mM glucose medium quickly restored both duration and overshoot. 2. In 50 mM glucose medium, 20 mM manganese chloride (Mn++) reduced the action potential duration and overshoot. Both parameters were restored after washing with Mn++-free medium. 3. Changes in action potential duration at the 0 mV and +20 mV levels were correlated with changes in peak tension and rate of rise of tension. 4. Isoprenaline restored the reduced action potential duration of anoxic muscle incubated in 5 mM glucose medium: This effect was blocked by Mn++.