Identification of subtype of K_ATP channel coupled with receptors for adenosine and FSH in the follicular cells of Xenopus oocyte

Abstract

Follicular cells surrounding Xenopus oocyte under voltage-clamp produce K⁺ current responses to follicle stimulating hormone (FSH), Adenosine (Ade) and intracellularly applied cAMP, presumably due to the opening of K_ATP channel. To identify the K_ATP channel subtype involved in the FSH-and Ade-induced responses, we investigated effects of various K⁺ channel openers (KCOs) and sulfonylurea receptor (SUR) blockers on the agonist-induced responses. Applications of PCO400, Cro, pinacidil but not diazoxide produced K⁺ current responses similar to the FSH- and Ade-induced responses in the order of PCO400 < Cro << pinacidil in favor of SUR2A. Application of glibenclamide, phentolamine and tolbutamide suppressed all the K⁺ current responses to FSH, Ade, cAMP, and KCOs. Furthermore, the both FSH- and Ade-induced responses were markedly augmented during the KCO-induced responses or vice versa. I-V curves for the K⁺ current responses induced by Cro, Ade and FSH showed outward rectification in normal [K⁺]o but weak inward rectification in 122 mM [K⁺]o. In addition, as observed previously with FSH- and Ade-induced responses, stimulations of P2Y receptor by UTP or PKC by PDBu markedly depressed the K⁺ current response to KCO in favor of Kir6.1. These results suggest that the K⁺ current responses to FSH and Ade may be produced by opening of a novel type of K_ATP channel comprising SUR2A and Kir6.1. [J Physiol Sci. 2008;58 Suppl:S77]