The vasodilator 17,18-Epoxyeicosatetraenoic acid targets the pore-forming BK channel subunit

Experimental Physiology (2007)DOI: 10.1113/expphysiol.2007.038166Hantz C Hercule 1, Birgit Salanova 1, Kirill Essin 2, Honeck Horst 3, John R Falck 4, Matthias Sausbier 5, Peter Rut 5, Wolf H Schunck 6, Friedrich C Luft 1, Maik Gollasch 2*To whom correspondence should be addressed. E-mail: maik.gollasch@charite.de
17,18-Epoxyeicosatetraenoic acid (17,18-EETeTr) stimulates vascular large-conductance K+ (BK) channels. BK channels are composed of the pore-forming BK and auxiliary BK ß1 subunits that confer an increased sensitivity for changes in membrane potential and calcium to BK channels. Ryanodine-sensitive, calcium-release channels (RyR3) in the sarcoplasmic reticulum (SR) control the process. To elucidate the mechanism of BK channel activation, we performed whole-cell and perforated-patch clamp experiments in freshly isolated cerebral and mesenteric artery vascular smooth muscle cells (VSMC) from Sprague-Dawley rats, BK 1-deficient (-/-) mice, BK (-/-), RyR3 (-/-) mice, and wild-type mice. 17,18-EETeTr (100 nM) increased tetraethylammonium (1 mM)-sensitive outward K+ currents in VSMC from wild-type rats and wild-type mice. The effects were not inhibited by the EET antagonist 14,15-epoxyeicosa-5(Z)-enoic acid (10 µM). BK channel currents were increased 3.5-fold in VSMC from BK 1 (-/-) mice whereas a 2.9-fold stimulation was observed in VSMC from RyR3 (-/-) mice (VM=60 mV). The effects were similar compared to those observed in cells from wild-type mice. The BK current increase was neither influenced by strong internal calcium buffering (Ca2+, 100 nM), nor by external calcium influx. 17,18-EETeTr did not induce outward currents in VSMC BK (-/-) cells. We next tested the vasodilator effects of 17,18-EETeTr on isolated arteries of BK -deficient mice. Vasodilation was largely inhibited in cerebral and mesenteric arteries isolated from BK (-/-) mice, compared to those observed in wild-type and BK 1 (-/-) arteries. We conclude that 17,18-EETeTr represents an endogenous BK channel agonist and vasodilator. Because 17,18-EETeTr is active in small arteries lacking BK 1, the data further suggest that BK represents the molecular target for 17,18-EETeTr's principal action. Finally, the action of 17,18-EETeTr is not mediated by changes of the internal global calcium concentration or local SR calcium release events.