HORMONE-REGULATED K+ CHANNELS IN FOLLICLE-ENCLOSED OOCYTES ARE ACTIVATED BY VASORELAXING K+ CHANNEL OPENERS AND BLOCKED BY ANTIDIABETIC SULFONYLUREAS

Follicular oocytes from Xenopus laevis contain K+ channels activated by members of the recently recognized class of vasorelaxants that include cromakalim and pinacidil and blocked by antidiabetic sulfonylureas, such as glibenclamide. These channels are situated on the adherent follicular cells and are not present in denuded oocytes. Cromakalim-activated K+ channels are also activated by increases in intracellular cAMP, and cAMP-activated K+ channels are blocked bv glibenclamide. Although cromakalim and cAMP effects are synergistic, cromakalim activation of K+ channels is drastically reduced or abolished by treatments that stimulate protein kinase C (e.g., muscarinic effectors, phorbol esters). Gonadotropins, known to play an essential role in ovarian physiology, also activate cromakalim and sulfonylurea-sensitive K+ channels. Follicular oocytes constitute an excellent system for studying regulation of cromakalim-sensitive K+ channels that are important in relation to a variety of disease processes, such as cardiovascular dysfunction and asthma, as well as brain function.