Inhibition of anion transport across the mitochondrial membrane by amytal

It has been found that amytal competitively inhibits succinate (+ rotenone) oxidation by intact uncoupled mitochondria. Similar results were obtained in metabolic state 3, the K_i value being 0.45 mM. Amytal did not effect succinate oxidation by broken mitochondria and submitochondrial particles (at a concentration which inhibited succinate oxidation by intact mitochondria). Amytal inhibited the swelling of mitochondria suspended in ammonium succinate or ammonium malate but was without effect on the swelling of mitochondria in ammonium phosphate and potassium phosphate in the presence of valinomycin+carbonylcyanide p-trifluoromethoxyphenylhydrazone.Using [¹⁴C] succinate and [¹⁴C] citrate it has been shown that amytal inhibited the succinate/succinate, succinate/P_i, succinate/malate, and citrate/citrate and citrate/malate exchanges. Amytal inhibited P_i transport across mitochondrial membrane only if preincubated with mitochondria. Other barbiturates: phenobarbital, dial, veronal were found to inhibit [¹⁴C]succinate/anion (P_i, succinate, malonate, malate) exchange reactions in a manner similar to amytal. It is concluded that barbiturates non-specifically inhibit the dicarboxylate carrier system, tricarboxylate carrier and P_i translocator. It is postulated that the inhibition of succinate oxidation by barbiturates is caused mainly by the inhibition of succinate and P_i translocation across the mitochondrial membrane.