Abstract
The effects of Ba++ on quiescent Purkinje fibers from sheep heart were examined using membrane potential recording and membrane current measurement by means of a voltage clamp. Depolarization was observed in either Na+ or Na+ -free solution containing 0.02 mM Ba++. The rate of depolarization was accelerated in the presence of Na+ and by repeated stimulation. Threshold potential was lowered and action potential duration was prolonged by Ba++. Changes caused by Ba++ were suppressed to some extent by Ca++. Inward currents found only in Na+-Tyrode's solution were increased and outward currents observed in Na+ -free Tyrode's solution were decreased by Ba++. The increased inward currents were more evident and lasted longer than the decreased outward current. The results suggest that the changes caused by Ba++ are mainly brought about by the increased Na+ current; a more detailed explanation of these changes is given by considering the competitive action between Ca++ and Ba++.
Footnotes
- Received April 13, 1972.
- Accepted September 4, 1972.
- © 1973 by The Williams & Wilkins Co.
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