The effect of the uncoupler carbonyl cyanide m-chlorophenylhydrazone on K+ transport, ATP level and intracellular pH of Chlorella fusca.

1. Low concentrations of the uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP) induced net K+ uptake by Chlorella fusca, optimal concentrations being 3 microM CCCP in the light and 1 microM CCCP in the dark. Higher concentrations increasingly stimulated K+ release. 2. Measurements of the unidirectional K+ fluxes showed that CCCP-induced net K+ uptake in the light was mainly a consequence of an inhibition of efflux. In the dark, influx was slightly stimulated in addition. 3. In conditions of CCCP-induced net K+ uptake, the ATP level was decreased by less than 10%. With higher CCCP concentrations it fell drastically. 4. By means of the 5,5-dimethyloxazolidine-2,4-dione distribution technique, an acidification of the cell interior on the addition of CCCP was found. 5. It is concluded that uncoupler-induced net K+ uptake is due to an enhanced proton leakage into the cell across the plasmalemma. Intracellular acidification by this process stimulates ATP-dependent K+/H+ exchange which, in itself, is not affected at low uncoupler concentrations.