A TRANSFORMED MURINE LEYDIG-CELL LINE EXPRESSES THE ET(A) RECEPTOR SUBTYPE

We recently demonstrated that transformed murine Leydig cells (MA-10) responded to endothelin-1 (ET-1) via increased steroidogenesis. This s tudy addresses the endothelin receptor subtype present on this cell li ne and whether or not the cells produce ET-1. The expression of the pr eproendothelin-1 (PPET-1) gene was investigated by Northern blot analy sis, and PPET-1 mRNA was found to be <0.2% of that present in pulmonar y endothelial cells. The medium from MA-10 cells, maintained under ser um-free conditions, was analyzed by radio-immunoassay to determine imm unoreactive-ET-1 production and ET-1 levels were found to be below the sensitivity of the assay (<10 pg/ml). The data from competitive bindi ng experiments with [I-125]ET-1 and unlabeled ET-1, ET-3 and receptor subtype selective ligands yielded a single class of high affinity bind ing sites with ET(A) receptor subtype characteristics. The results of this study demonstrate that MA-10 cells possess the ET(A) receptor sub type but do not produce significant quantities of ET-1 under basal con ditions.