title: Regulation of hormone-responsive Sertoli cell adenylyl cyclase in a cell-free system.
abstract: 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)
mesh_terms: D000255:Adenosine Triphosphate / Q000502:physiology; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D002474:Cell-Free System; D002478:Cells, Cultured; D005640:Follicle Stimulating Hormone / Q000494:pharmacology*; D006160:Guanosine Triphosphate / Q000502:physiology; D007545:Isoproterenol / Q000494:pharmacology*; D007700:Kinetics; D008274:Magnesium / Q000502:physiology; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D012708:Sertoli Cells / Q000187:drug effects / Q000201:enzymology*; D013997:Time Factors
chemical_list: D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D005640:Follicle Stimulating Hormone; D000262:Adenylyl Cyclases; D008274:Magnesium; D007545:Isoproterenol