Regulation of hormone-responsive Sertoli cell adenylyl cyclase in a cell-free system.
Homologous desensitization of either FSH- or isoproterenol-responsive adenylyl cyclases in Sertoli cell membranes can be achieved in a cell-free system. Incubation of membrane particles from cultured immature Sertoli cells with either FSH or isoproterenol resulted in a time- and concentration-dependent loss of subsequent adenylyl cyclase response to the homologous hormone. Half-maximal refractoriness was achieved within 20-30 min of incubation. The concentration of FSH required to obtain half-maximal loss of adenylyl cyclase response (400 ng/ml) was in the same order of magnitude as the apparent Km for FSH-stimulated adenylyl cyclase activity (300 ng/ml). Hormone-induced homologous desensitization was dependent on the presence of both ATP and Mg2+. Increasing concentrations of ATP in the presence of FSH caused a concentration-dependent loss of subsequent response to the homologous hormone. Half-maximal desensitization was achieved at an ATP concentration of 0.2 mM. Increasing concentrations of Mg2+ in the presence of either FSH or isoproterenol caused desensitization for the homologous hormone. The concentration of Mg2+ giving half-maximal effect was approximately 5 mM in excess of ATP and EDTA. However, higher concentrations of free Mg2+, in the absence of hormone, caused desensitization of both FSH- and isoproterenol-sensitive adenylyl cyclase with half-maximal effect at approximately 30 mM. Hormone-specific desensitization was obtained in the presence of GTP. However, when GTP was substituted with the non-hydrolysable analogue GMPP(NH)P the hormonal activation remained constant throughout 90 min of incubation.(ABSTRACT TRUNCATED AT 250 WORDS)