Ozone Alteration of Membrane Permeability in Chlorella

Abstract

The addition of ozone to a suspension of C. sorokiniana causes a rapid loss of K+, as measured by efflux of 86Rb from prelabeled cells. The efflux of the tracer is stimulated some 15-20 times over that of the control. For about 100 .mu.l/l ozone, about 25 min (6 .times. 10-8 mol O3 delivered/min) of exposure are required for a 50% depletion of the intracellular K+. The stimulation of K+ efflux is nearly linearly dependent upon the amount of ozone delivered into the solution. Following short pulses of ozone (lasting 1-5 min), efflux rates return to the control level but only after about 15 min. While influx of K+ is ultimately inhibited by ozone, at low concentrations or for short exposure times the tracer influx is stimulated 100-200%. Ozone stimulation of an active pump mechanism is unlikely in view of a concomitant decrease in respiration. Thus, this influx may represent movement of K+ along its electrochemical gradient. Assuming that influx and efflux are in steady-state according to the Goldman equation, it was calculated that the membrane potential for K+ of -80 to -90 mV in control cells drops to -40 mV with ozone exposure and is accompanied by a calculated, increased permeability to K+ of 2- to 3-fold.