ATP suppresses the K+ current responses to FSH and adenosine in the follicular cells of Xenopus oocyte

The application of either follicle-stimulating hormone (FSH) or adenosine (Ade) induces a K+-current response in the follicular cells surrounding a Xenopus oocyte under a voltage clamp. These K+-current responses are reported to be produced by an increase in intracellular cAMP. A previous application of ATP to the same cells markedly depressed the K+-current responses to FSH and Ade. Furthermore, a 2 min application of phorbol 12,13-dibutyrate (PDBu), an activator of protein kinase C (PKC), significantly depressed the K+-current responses to FSH and Ade, but it had no significant effect on the Cl--current response to ATP. An application of either ATP or PDBu also depressed the K+-current response induced by intracellularly applied cAMP. In contrast to the effect of PDBu, the application of I-octanol, an inhibitor of gap junction channel, significantly depressed both the Ade- and ATP-induced responses, indicating that the acting site of 1-octanol is different from that of PKC. The results suggest that the depressing effect of ATP on the FSH- and Ade-induced K+-current responses might be mediated by PKC activation and that the site of PKC action might be downstream of the cAMP production involved in the K+ channel opening.