ACTIVATION OF INOSITOL PHOSPHOLIPID TURNOVER AND CALCIUM SIGNALING INRAT SERTOLI CELLS BY P2-PURINERGIC RECEPTORS - MODULATION OF FOLLICLE-STIMULATING-HORMONE RESPONSES

To study the role of extracellular nucleotides in the regulation of Se rtoli cells, the effects of ATP and its analogs on the Ca2+-phospholip id- and cAMP-dependent pathways were tested. Cultured Sertoli cells fr om immature animals were incubated with ATP or structurally related co mpounds, and phosphoinositide (PI) turnover or cAMP accumulation was m easured. Among the several nucleotide phosphate analogs tested, adenos ine 5'-O-(3-thiotriphosphate) was the agonist most potent in stimulati ng inositol phosphate accumulation. The effects of purine nucleotides on PI turnover were time and concentration dependent. Because nonhydro lizable ATP analogs also stimulated PI turnover, ATP metabolites or me tabolic products are not responsible for the observed stimulation. The order of potency of the different ATP analogs [adenosine 5'-O-(3-thio triphosphate) > ATP congruent to UTP > beta,gamma-methyleneadenosine 5 '-triphosphate, 2-methylthio-ATP > adenosine] was consistent with the presence of P-2U receptors (nucleotide receptors) on the surface of th e Sertoli cell. Augmented PI turnover was accompanied by a transient i ncrease in Ca2+ concentration, measured in single Sertoli cells loaded with the intracellular Ca2+ indicator fura-2. When used alone, ATP an d its analogs did not have a direct effect on cAMP levels in the Serto li cell. However, ATP or its analogs inhibited FSH-dependent cAMP accu mulation by more than 70%. Purine nucleotides also efficiently blocked the effects of FSH distal to cAMP accumulation, because extracellular ATP completely reversed the changes in Sertoli cell shape induced by FSH. The nucleotide-dependent inhibition of cAMP accumulation was bloc ked by pertussis toxin to a different degree depending on the purine o r pirimidine nucleotide used. This indicated that more than one mechan ism contributes to the purine nucleotide-dependent inhibition of cAMP accumulation. These data provide evidence that purine nucleotide recep tors coupled to multiple pathways are present on the Sertoli cell in c ulture, and that extracellular ATP has profound biological effects on the FSH responsiveness of the Sertoli cell.