Chloride diffusion from liposomes

Abstract

1. 1. Cl − efflux from egg phosphatidylcholine liposomes is faster than that of K +, both against exchangeable anions such as Cl − itself, and against impermeable external anions such as SO 4 2− . 2. 2. At 27 °C, Cl − is released from such liposomes at a rate of 30–40% per h against Cl −, Br − and SCN −, 20% per h against I −, NO 3 − and acetate, and 10% per h or less against SO 4 2− . 3. 3. Valinomycin increases both Cl − and K + efflux rates against external Na 2-SO 4, but both valinomycin and uncoupler are required to produce a movement of Cl − and K + equal in rate to the Cl −-Cl − exchange. 4. 4. Liposomes composed of dimyristoyllecithin and dipalmitoyllecithin are more permeable to both K + and Cl −, above their transition temperatures, than are egg lecithin liposomes. Valinomycin promotes both Cl − and K + efflux from dipalmitoyllecithin liposomes, but uncoupler has almost no additional effect. 5. 5. It is concluded, in agreement with McGivan (Ph. D. dissertation, University of Bristol (1968) and Singer (Can. J. Physiol. Pharmacol. (1973) 51, 523–531), that the overall process of Cl − movement is by a compulsory anion (e.g. Cl −-OH −) exchange. But it is suggested that this may be a result of the formation of HCl by reaction of Cl − with membrane water, followed by the diffusion of that HCl molecule across the membrane and the release of Cl − on the other side, thus creating a localised pH gradient in the membrane.