INVESTIGATIONS OF THE INHIBITORY EFFECT OF PROPRANOLOL, CHLORPROMAZINE, QUININE, AND DICYCLOHEXYLCARBODIIMIDE ON THE SWELLING OF YEAST MITOCHONDRIA IN POTASSIUM ACETATE - EVIDENCES FOR INDIRECT EFFECTS MEDIATED BY THE LIPID PHASE

The mode of action of propranolol, chlorpromazine, and quinine, three cationic drugs inhibiting swelling of yeast mitochondria in potassium acetate, was investigated by looking at their effect on fluorescent pr obes of the polar heads and of the nonpolar moiety of the membranes, u nder inhibitory conditions of swelling. As expected, propranolol and c hlorpromazine exhibited specificity for anionic phospholipids since th ey increased the binding of the anionic probe 1-anilino 8-naphthalenes ulfonate (ANS). Although propranolol did not release 1,6-diphenyl-1,3, 5-hexatriene (DPH) from the hydrophobic moiety of the membrane, it inc reased the excimer/monomer fluorescence ratio of 10-(l-pyrene)decanoat e, suggesting that it induced a limitation in the movements of the ali phatic chains of phospholipids. Opposite to propranolol, chlorpromazin e removed DPH from the membrane, suggesting that it bound essentially to the hydrophobic moiety. However, chloramphenicol, which was also ab le to remove DPH but did not increase the binding of ANS, did not inhi bit swelling. Inhibition by chlorpromazine therefore appeared to be re lated to its binding to the hydrophobic moiety of anionic phospholipid s. Quinine had no effect on membrane properties: at inhibitory concent rations of swelling in potassium acetate, it did not inhibit swelling in ammonium phosphate (mediated by the phosphate/H+ cotransporter), wh ereas propranolol and chlorpromazine did, suggesting a more specific e ffect of quinine on (a) protein(s) involved in the K+/H+ exchange. Dic yclohexylcarbodiimide (DCCD), which irreversibly inhibits the swelling in potassium acetate, bound to ethanolamine heads; despite this effec t, DCCD had no major consequences on the binding of the probes. Conseq uently, propranolol and chlorpromazine are of no help for characterizi ng protein(s) catalyzing the K+/H+ exchange, although their effect on lipids seems to involve limited zones of the inner mitochondrial membr ane. Quinine and DCCD, although they also bind to lipids, may inhibit the activity by acting on a limited number of proteins.