Inhibition of transmembrane calcium influx induces decrease in proteoglycan synthesis in immature rat Sertoli cells

Beyond increased cAMP synthesis,calcium influx has been involved in signal transduction triggered by the gonadotropin follicle-stimulating hormone (FS H), the main regulator of Sertoli cells functions. In order to delineate a possible involvement of calcium in the regulation of proteoglycan synthesis , we have examined the effect of low-voltage-activated calcium channel bloc ker verapamil on both [S-35]-sulfate and [H-3]-glucosamine incorporation in to proteoglycan molecules neosynthesized by cultured Sertoli cells from 20- day-old rats. Verapamil induced a dose- and time-dependent decrease in labe ling of both secreted and cell-associated proteoglycans, as determined by q uantitative solid-phase assay. This effect was mimicked by the addition of the calcium chelator EGTA, suggesting that verapamil[ effect resulted from the inhibition of transmembrane calcium influx. The decrease in apparent pr oteoglycan synthesis appeared to be attributable primarily to a lowering of the glycanation process, as shown by experiments using an exogenous accept or for glycosaminoglycan synthesis. Moreover, verapamil induced a decrease in relative proportion of heparan sulfate proteoglycans in the cell layer. Pulse-chase kinetics demonstrated that verapamil also altered proteoglycan catabolism, leading to glycosaminoglycan retention in the cell layer and in hibiting the proleoglycan desulfation step. We conclude that intracellular calcium is essential to maintain Sertoli cell proteoglycan expression and c ould thus be involved in the repression of Sertoli cell cAMP-dependent synt heses such as estradiol production. (C) 1999 Wiley-Liss, Inc.