Outward current and electrogenic sodium pump in Purkinje fibers.

The effects of metabolic inhibitors (ouabain, dihydroouabain, and 2,4-dinitrophenol (2,4-DNP) and of cooling on the membrane current of Purkinje fibers were studied by means of a voltage clamp. Within seconds after cooling or application of the drugs the outward current was found to be reduced. On longer cooling or poisoning, the potassium equilibrium potential was shifted in positive direction, the time-dependent membrane currents were depressed, and possibly the potassium conductance was altered. It is suggested that the early reduction in outward current is caused by inhibition of an electrogenic sodium pump.