ATP-INDUCED UNSPECIFIC CHANNEL IN YEAST MITOCHONDRIA

ATP induced swelling of isolated yeast mitochondria suspended in an is oosmotic solution of potassium gluconate. Valinomycin stimulated the s welling rate, indicating that K+ influx in the presence of ATP is rate -controlling. This swelling was inhibited by ADP, phosphate (probably acting on the external face of the inner membrane), and Mg2+, which fo rms a complex with ATP. ATP-induced swelling did not require working F -0-F-1-ATPase since it was not inhibited by oligomycin and uncoupler. CTP and GTP also induced a swelling. ATP also induced mitochondrial sw elling in potassium glutamate, chlo ride, and acetate but not in phosp hate solutions. Sodium, but not ammonium, can replace potassium ion. I t is probable that the ATP-channel opening also necessitates an electr ogenic cation influx. Respiration also induced swelling of mitochondri a suspended in isoosmotic potassium gluconate solution. ATP- or respir ation-induced swelling were inhibited equally by N,N'-dicyclohexylcarb odiimide, propanolol, and Zn2+ but not by quinine; all these drugs inh ibit the H+/K+ exchange. It was concluded that this unspecific channel is not open un der conditions used to measure oxidative phosphorylati on. Its physiological role remains unknown.