Exposure to ouabain, dinitrophenol, or lithium decreased the pacemaker current (IK2) amplitude, and prolonged ouabain exposure replaced IK2 with an oscillatory inward current in sheep fibers.
Inhibition of the Na-K pump by ouabain in sheep Purkinje fibers decreases the pacemaker current IK2 and induces an arrhythmogenic oscillatory inward current (IOS).
We studied the effect of ouabain and other inhibitors of the Na-K pump on the pacemaker current (IK2) in sheep cardiac Purkinje fibers. We found that exposure to ouabain (2 X 10(7) M) caused an apparent decrease in the amplitude of the IK2 activation curve. We also found that a similar effect was caused by exposure to dinitrophenol (DNP) or lithium-substituted Tyrode's solution. Our studies showed that after prolonged (more than 60 minutes) exposure to ouabain a characteristic current noise appeared and IK2 was replaced by an oscillatory inward current (IOS). The apparent threshold for IOS was -50 to -60 mV and the peak amplitude of this current increased with increasing levels of depolarization positive to threshold. These results suggest that (1) the apparent decrease in IK2 may be a consequence of ionic redistribution due to Na-K pump inhibition; (2) cardiac glycosides cause abnormal impulse generation by an ionic mechanism separate from IK2 and involving IOS.
Aronson et al. (Sun,) reported a other. Ouabain, dinitrophenol (DNP), and lithium-substituted Tyrode's solution was evaluated on Pacemaker current (IK2) and oscillatory inward current (IOS). Exposure to ouabain, dinitrophenol, or lithium decreased the pacemaker current (IK2) amplitude, and prolonged ouabain exposure replaced IK2 with an oscillatory inward current in sheep fibers.
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