Anion translocators in rat-heart mitochondria

Abstract

At least seven different anion translocators have been demonstrated in rat liver mitochondria [ 1,2] . These translocators may be distinguished from each other by their specificity for substrates and their differential sensitivity to inhibitors [3] . Most anions enter the mitochondria in exchange for internal anions [4] (for a review, see [2]). A one to one stoichiometry has been found for the exchanges catalysed by the phosphate [5], the dicarboxylate [6], the oxoglutarate [6] and the tricarboxylate [6] translocators. Tricarboxylate anions penetrate through the liver mitochondrial membrane in exchange either for intramitochondrial malate or for other intramitochondrial tricarboxylate anions [7,8]. In liver mitochondria the dicarboxylate translocator catalyses not only a dicarboxylate/phosphate exchange, but also a dicarboxylate/dicarboxylate exchange [9]. The latter exchange may be effected by different translocators as proposed by Meijer and Tager [lo] and Robinson et al. [3] . The phosphate moves across the mitochondrial membrane either via the phosphate translocator in exchange for hydroxyl ions, or via the dicarboxylate translocator in exchange for dicarboxylate ions. Sulphydryl-binding reagents such as the mercurials [ 11, 121 and N-ethylmaleimide [ 131 inhibit the movement of phosphate. N-ethylmaleimide blocks the movement of phosphate via the phosphate translocator [ 141 and mersalyl via both the phosphate and dicarboxylate translocators [ 151. The movement of dicarboxylates is also sensitive to mersalyl but the dicarboxylate/phosphate exchange may be completely blocked at concentrations that inhibit the dicarboxylate/dicarboxylate exchange partially [3, lo] . 2-Oxoglutarate crosses the rat-liver mitochondrial membrane in exchange for dicarboxylate ions such as L-malate or malonate [ 161. The purpose of this paper is to describe some of the properties of the anion translocators of heartmuscle mitochondria and to show that it is possible to dissociate the activity of the oxoglutarate translocator from those of the other translocators. The properties of the oxoglutarate translocator will be described in detail elsewhere. In addition, the present paper confirms the observation made by England and Robinson that the tricarboxylate translocator has little activity, if any, in heart mitochondria [ 171 .