Mediation of EDHF-induced reduction of smooth muscle [Ca(2+)](i) and arteriolar dilation by K(+) channels, 5,6-EET, and gap junctions.
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) [Ca(2+)](i) (assessed by changes in fura-2 ratiometric signal, R(Ca)) and diameter were measured in response to ACh in the presence of indomethacin and L-NAME.


RESULTS
ACh, the K(ATP) channel opener pinacidil, and the Ca(2+) channel inhibitor verapamil elicited comparable decreases in aSM [Ca(2+)](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, K(Ca) channel blockers (TEA, charybdotoxin), or gap junction inhibitors (18alpha-glycyrrhetinic acid, hyperosmolar sucrose). The K(ATP) channel inhibitor glibenclamide, the K(IR) channel 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 TxA(2) receptor antagonist, whereas in the absence of the endothelium, EDHF elicited only small, charybdotoxin-insensitive decreases in aSM R(Ca) and dilations (max.: -8 +/- 2% and 27 +/- 4%, respectively).


CONCLUSIONS
In skeletal muscle arterioles, EDHF 1) substantially and rapidly reduces myogenic tone by decreasing aSM [Ca(2+)](i) via opening K(Ca) channels, 2) it is unlikely to be 5,6-EET or other CYP metabolites, but 3) requires functional gap junctions.
Ungvari
Z
Z
Department of Pathophysiology, Semmelweis University of Medicine, Budapest, Hungary.
Koller
A
A
D015126:8,11,14-Eicosatrienoic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology*; D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001160:Arterioles / Q000187:drug effects / Q000502:physiology*; D001685:Biological Factors / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000737:chemistry; D017629:Gap Junctions / Q000502:physiology*; D066298:In Vitro Techniques; D007700:Kinetics; D008856:Microscopy, Fluorescence; D018482:Muscle, Skeletal / Q000098:blood supply; D009131:Muscle, Smooth, Vascular / Q000737:chemistry* / Q000166:cytology / Q000502:physiology; D015221:Potassium Channels / Q000494:pharmacology* / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D014664:Vasodilation / Q000187:drug effects*
D001685:Biological Factors; D015221:Potassium Channels; C067410:endothelium-dependent hyperpolarization factor; C040776:5,6-epoxy-8,11,14-eicosatrienoic acid; D015126:8,11,14-Eicosatrienoic Acid; D000109:Acetylcholine; D002118:Calcium