Acute action of choriogonadotropin on Leydig tumor cells: Changes in the topography of the mitochondrial peripheral-type benzodiazepine receptor

We examined the topography of the MA-10 Leydig tumor cell mitochondrial peripheral-type benzodiazepine receptor (PER). In previous studies, the 18 kDa PER was found to be functionally associated with the voltage-dependent anion channel, located in the junctions between outer and inner membranes. Transmission electron (TEM) and atomic force microscopy (AFM) of immunogold labeled PER on Leydig cell mitochondrial preparations showed that the 18 kDa PER protein is organized in clusters of 4-6 molecules. Addition of hCG to Leydig cells induces a rapid, within 30 sec, increase in PER ligand binding and morphological changes, namely redistribution of PER molecules in large clusters (>7 particles). These hCG-induced changes were inhibited by a cAMP-dependent protein kinase inhibitor and by the benzodiazepine flunitrazepam. AFM further demonstrated the rapid reorganization of the mitochondrial membrane, where the formation of contacts between the outer and the inner mitochondrial membrane may facilitate cholesterol transfer.