Abstract
Objective:To characterize the role of K+channels, the cytochrome P-450 (CYP) metabolite 5,6-EET, and gap junctions in modulation of arteriolar myogenic tone by a non-nitric oxide nonprostaglandin mediator, termed “endothelium-dependent hyperpolarizing factor” (EDHF), released to acetylcholine (ACh) in skeletal muscle arterioles. Methods:In isolated rat gracilis arterioles, simultaneous changes in smooth muscle (aSM) [Ca2+]i(assessed by changes in fura-2 ratiometric signal, RCa) and diameter were measured in response to ACh in the presence of indomethacin and L-NAME. Results:ACh, the KATPchannel opener pinacidil, and the Ca2+channel inhibitor verapamil elicited comparable decreases in aSM [Ca2+]i(max.: −32 ± 3%, 29 ± 3%, and −30 ± 3%, respectively) and arteriolar dilations (max.: 90 ± 4%, 96 ± 2%, and 95 ± 2%, respectively). ACh-induced responses were inhibited by KCl-depolarization, KCachannel blockers (TEA, charybdotoxin), or gap junction inhibitors (18α-glycyrrhetinic acid, hyperosmolar sucrose). The KATPchannel inhibitor glibenclamide, the KIRchannel inhibitor barium chloride, or the CYP inhibitor 17-octadecynoic acid (ODYA) were without effect. The putative EDHF analogue 5,6-EET elicited constrictions in the presence of the endothelium that could be prevented by indomethacin or a TxA2receptor antagonist, whereas in the absence of the endothelium, EDHF elicited only small, charybdotoxin-insensitive decreases in aSM RCaand dilations (max.: −8 ± 2% and 27 ± 4%, respectively). Conclusions:In skeletal muscle arterioles, EDHF 1) substantially and rapidly reduces myogenic tone by decreasing aSM [Ca2+]ivia opening KCachannels, 2) it is unlikely to be 5,6-EET or other CYP metabolites, but 3) requires functional gap junctions. Microcirculation (2001) 8, 265–274.