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Recently, ATP-sensitive potassium (KATP) channel has been described in rat liver mitochondria (Inoue et al., 1991). This channel is blocked not only by ATP but also by the antidiabetic sulfonylurea, glibenclamide, giving evidence that mitochondrial KATP channel may belong to the well known family of ATP-dependent potassium channels found in plasma membranes of cardiac, smooth and skeletal muscle cells (Quast & Cook, 1989), pancreatic B-cells (Petersen & Dunne, 1989) and in the nervous system (Mourre et al., 1990). In B-cells, KATP channels are specifically blocked by sulfonylureas which are the drugs capable to restore insulin secretion in patients affected by non-insulin-dependent diabetes mellitus (Petersen & Dunne, 1989). These channels are also blocked by some of non-sulfonylurea drugs like 8-methoxypsoralen (Szewczyk et al., 1992a) and 8-(N, N-dimethylamino) octyl-3, 4, 5-trimethoxybenzoate (Szewczyk et al., 1992b). KATP channels are activated by hormones such as somatostatin and galanin (De Weille et al., 1988, 1989), free fatty acids (Muller et al., 1992), as well as by K+ channel openers (Cook & Quast, 1990; Duty & Weston, 1990).

In order to understand the structure and function relationship of mitochondrial transporters, recent efforts have been focused on isolation of the individual carriers and their functional reconstitution into proteoliposomes (for review see Nalecz , 1986). In line with these studies we reported a successful purification by affinity chromatography of the dicarboxylate carrier from bovine heart mitochondria (Szewczyk et al., 1987). In general, heart mitochondria are considered optimal for studies on purification of the inner membrane proteins. This comes from the fact that the cristae/matrix ratio of these organelles is exceptionally high (more membranes per unit of weight of the mitochondrial preparation) and, in addition, from that the activity of proteolytic enzymes in heart homogenates is relatively low. On the other hand, however, it is known that the mitochondrial dicarboxylate carrier activity is much higher in liver than in heart (Sluse et al., 1971). Although it has not been clarified whether this is due to difference in total amount of the carrier protein in mitochondria, we found that only very little of the translocator protein could actually be isolated from heart (Szewczyk et al., 1987). Thus it seemed logical to try to isolate the dicarboxylate carrier from liver mitochondria.

It is now well established that the inner mitochondrial membrane contains at least twelve functionally different carriers (LaNoue & Schoolwerth, 1979). Some of the mitochondrial carriers have already been isolated in a pure form, some others have been extracted and partially purified and their activity has been measured after reconstitution into proteoliposomes (for review see Nalecz, 1986).