ACUTE ACTION OF CHORIOGONADOTROPIN ON LEYDIG TUMOR-CELLS - CHANGES INTHE TOPOGRAPHY OF THE MITOCHONDRIAL PERIPHERAL-TYPE BENZODIAZEPINE RECEPTOR

We examined the topography of the MA-10 Leydig tumor cell mitochondria l peripheral-type benzodiazepine receptor (PER). In previous studies, the 18 kDa PER was found to be functionally associated with the voltag e-dependent anion channel, located in the junctions between outer and inner membranes. Transmission electron (TEM) and atomic force microsco py (AFM) of immunogold labeled PER on Leydig cell mitochondrial prepar ations 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, nam ely redistribution of PER molecules in large clusters (>7 particles). These hCG-induced changes were inhibited by a cAMP-dependent protein k inase inhibitor and by the benzodiazepine flunitrazepam. AFM further d emonstrated the rapid reorganization of the mitochondrial membrane, wh ere the formation of contacts between the outer and the inner mitochon drial membrane may facilitate cholesterol transfer.