Demonstration and characterization of human cardiac porin: a voltage-dependent channel involved in adenine nucleotide movement across the outer mitochondrial membrane

Abstract

The porins are a class of voltage-dependent, anion-selective, channel-forming proteins located in the outer mitochondrial membrane (OMM). The porins are responsible for passage of adenine nucleotides across the OMM, as well as for specific binding of hexokinase and glycerol kinase. This porin-kinase complex has direct access to ATP generated by mitochondrial oxidative phosphorylation and may be important in the regulation of glycolysis. Porin had not been described previously in humans but, due to its importance in bioenergetics, would be expected to be present, especially in organs requiring a large and constant supply of energy. We therefore postulated that porin would occur in human myocardium where it would be important in cardiac function. Polyclonal antibodies to bovine myocardial and rat liver porins were utilized in transblotting experiments after polyacrylamide gel electrophoresis of human heart preparations from atria, ventricles, papillary muscles, and interventricular septum. These immunoblots demonstrated selective staining of a 34-kDa band. This was identical to the results obtained with purified porin and the antibodies. Also notable was the finding that the vast majority of this staining was found in the homogenate pellet after high speed centrifugation (20,000g), as would be expected for a mitochondrial protein. The demonstration of human cardiac porin by immunoblotting with rat liver and bovine myocardial porin antibodies is the first demonstration of cross-species identification of the porins. The success of this approach undoubtedly occurred because of strong homology between porins from a variety of species.