EXISTENCE OF P-2-PURINOCEPTORS ON HUMAN AND PORCINE GRANULOSA-CELLS

This study examines the possible roles of extracellular purine nucleot ides in regulating ovarian granulosa cell function. Using luteinized h uman (L-hGC) and porcine granulosa cells (PGC), we examined the effect s of purine nucleotides on intracellular free Ca2+ concentrations ([Ca -2+], and whether they have any effect on steroidogenesis and cell pro liferation. L-hGC and PGC were responsive to ATP and ADP at concentrat ions ranging from 0.1-100 mu mol/L in a dose-dependent manner. There w as a difference between L-hGC and PGC in the rank orders of agonist po tencies for stimulating [Ca2+](i): for L-hGC, UTP > ATP > ATP gamma s > ADP > AMPPNP >> AMP and adenosine; for PGC, 2-methylthio ADP (2-meS ADP) > ADP > ATP = ATP gamma s = UTP > AMPPNP >> AMP and adenosine. No apparent additivity between the responses elicited by UTP and the pur ine nucleotides (ATP and ADP) was shown in L-hGC. On the other hand, a n apparent additive effect between the responses to ADP and UTP was sh own on PGC. Furthermore, ATP was a competitive antagonist of the actio n of ADP on [Ca2+](i) levels in PGC. ATP, ADP, and AMP as well as aden osine stimulated basal progesterone and estradiol secretion from L-hGC , however, UTP had no effect on steroidogenesis in L-hGC. On the other hand, purine nucleotides and UTP as well as adenosine inhibited proge sterone and estradiol secretion on PGC. However, 2-meS ADP, the most p otent agonist for P-2T-purinoceptors, did not affect steroidogenesis i n PGC. Purine nucleotides had no influence on cell proliferation of L- hGC and PGC. These results indicate the existence of P-2U-purinoceptor s on L-hGC and P-2U- plus P-2T-purinoceptors on PGC, and that the inhi bitory effect of purine nucleotides on steroidogenesis in PGC is most likely due to Ai-adenosine receptors and also P-2U-purinoceptors.