NOVEL AND POTENT BK CHANNEL OPENERS - CGS-7181 AND ITS ANALOGS

This article discloses the identification of a novel series of the ope ner of the large-conductance Ca2+-activated K+ (BK) channel, CGS 7181, and its analogs, CGS 7184, CGS 7590, and CGS 7725. The stimulatory ef fects of these compounds on the channels were investigated at whole-ce ll and single channel levels using the patch-clamp technique in single smooth muscle cells from vascular (coronary artery) and non-vascular (bladder detrusor) tissues of several animal species. With a threshold of submicromolar concentration, extracellularly applied CGS 7181 and CGS 7184 (0.5-50 mu M) induced a concentration-dependent stimulation o f the whole-cell BK current (I-BK) and concomitant membrane hyperpolar ization in porcine coronary artery cells. The activation was prevented and reversed by TEA, but unaffected by nifedipine, suggesting that th e effect was not subsequent to Ca2+ entry. CGS 7184, CGS 7590, and CGS 7725 (0.1-50 mu M) produced augmentation of I-BK in a similar manner in cells From bladder detrusor of guinea pig, rat, and dog. The onset and offset of the drug actions were slow compared to the known BK chan nel opener NS004. The effects of compounds applied intracellularly wer e assessed on single BK channels in inside-out patches. With threshold concentrations ranging between 0.01 and 0.1 mu M, all compounds cause d a drastic and reversible increase in channel open-state probability. The onset and washout of drug actions were considerably faster in ins ide-out patches than in whole cells. It is concluded that CGS 7181 and its analogs directly open BK channels from either side of the membran e with a combination of potency and efficacy superior to any known BK channel openers, and an internal site of action best accounts for the results of our studies. (C) 1997 Wiley-Liss, Inc.