Depressing effect of insulin on the K⁺-current response induced by adenosine in the follicular cells of Xenopus oocyte

Abstract

Application of adenosine (Ade) induces K⁺-current response in the follicular cells surrounding a Xenopus oocyte under voltage clamp. This Ade-induced response is produced by activation of Gs, subsequent adenylate cyclase, cAMP-dependent protein kinase, and by opening of the ATP-sensitive K⁺ channels. Application of 20 nM insulin initially augmented the Ade-induced response, and subsequently depressed. The depressing effect of insulin on the K⁺-current response was irreversible. Application of 100 μM cromakalim (Cro) induces a K⁺-current response similar to the Ade-induced response. The Cro-induced response was not depressed significantly by prior application of 20 nM insulin for the same period as the case of Ade-induced response. Prior application of 30 nM Lavendustin A (Lav.A), an inhibitor of protein tyrosine kinase, markedly blocked the effect of insulin on the Ade-induced response. Application of Lav. A alone to the cells did not affect the Ade-induced response significantly. Application of 1 μM PAO, an inhibitor of protein tyrosine phosphatase, alone depressed the Ade-induced response but did not depress the Cro-induced response significantly. These results suggested that the depressing effect of insulin on the Ade-induced response might be regulated by activation of protein tyrosine kinase through the stimulation of insulin receptor. [Jpn J Physiol 55 Suppl:S138 (2005)]