Increase of potassium flux by valinomycin in embryonic chick heart.

The effect of different concentrations of the antibiotic valinomycin, was determined on 42K efflux and Na, K content of embryonic chick hearts. Valinomycin produces an increase of K efflux which is progressive in time and markedly dependent on the concentration of external K (0-5 mM) and valinomycin (10(-8) to 10(-5) M). The changes in K efflux is not due to a reversal of the Na-K pump mechanism, secondary to ATP depletion: i) the increase of K efflux by valinomycin persists in the absence of external Na ions. ii) analysis of Na and K content and 42K influx measurements with and without valinomycin indicate that active K influx is not inhibited in a solution containing 0.5 mM K and only slightly decreased in a solution containing 5 mM K. Valinomycin, acting as a K carrier, presumably increases K conductance of the cell membrane resulting in a rise in K efflux.