EFFECTS OF GDP AND CARBOXYATRACTYLATE ON CALCIUM-ION TRANSPORT IN BROWN FAT MITOCHONDRIA

Increasing the membrane potential in uncoupled brown fat mitochondria by adding 1 to 2 mM GDP in a potassium acetate-containing medium resul ts in biphasic swelling of the mitochondria. The first phase is due to electrogenic K+ transport; the second phase is activated by carboxyat ractylate and carnitine. Swelling is almost completely inhibited on fu rther increasing the GDP concentration, despite the high membrane pote ntial. In contrast to K+ transport, membrane-potential-dependent sodiu m transport is characterized, under the same conditions, by high rate, monophasic character, and insensitivity to carboxyatractylate and car nitine. We suggest that K+ transport regulation in brown fat mitochond ria depends on the effects of nucleotides and fatty-acid esters on the uncoupling protein and ADP/ATP antiporter.