The vasodilator 17,18-epoxyeicosatetraenoic acid targets the pore-forming BK alpha channel subunit in rodents.
17,18-Epoxyeicosatetraenoic acid (17,18-EETeTr) stimulates vascular large-conductance K(+) (BK) channels. BK channels are composed of the pore-forming BK alpha and auxiliary BK beta1 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 beta1 gene-deficient (-/-), BK alpha (-/-), RyR3 (-/-) and wild-type mice. The 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 epoxyeicosatrienoic acid (EET) antagonist 14,15-epoxyeicosa-5(Z)-enoic acid (10 mum). BK channel currents were increased 3.5-fold in VSMC from BK beta1 (-/-) mice, whereas a 2.9-fold stimulation was observed in VSMC from RyR3 (-/-) mice (at membrane voltage 60 mV). The effects were similar compared with those observed in cells from wild-type mice. The BK current increase was neither influenced by strong internal calcium buffering (Ca(2)(+), 100 nm), nor by external calcium influx. The 17,18-EETeTr did not induce outward currents in VSMC BK alpha (-/-) cells. We next tested the vasodilator effects of 17,18-EETeTr on isolated arteries of BK alpha-deficient mice. Vasodilatation was largely inhibited in cerebral and mesenteric arteries isolated from BK alpha (-/-) mice compared with that observed in wild-type and BK beta1 (-/-) arteries. We conclude that 17,18-EETeTr represents an endogenous BK channel agonist and vasodilator. Since 17,18-EETeTr is active in small arteries lacking BK beta1, the data further suggest that BK alpha represents the molecular target for the principal action of 17,18-EETeTr. Finally, the action of 17,18-EETeTr is not mediated by changes of the internal global calcium concentration or local SR calcium release events.
Nephrology/Hypertension Division, Franz Volhard Clinic, HELIOS Klinikum-Berlin, Campus Buch, Berlin, Germany.
Hantz C
HC
Hercule
Birgit
B
Salanova
Kirill
K
Essin
Horst
H
Honeck
John R
JR
Falck
Matthias
M
Sausbier
Peter
P
Ruth
Wolf-Hagen
WH
Schunck
Friedrich C
FC
Luft
Maik
M
Gollasch
D000818:Animals; D001095:Arachidonic Acids / Q000494:pharmacology*; D002118:Calcium / Q000502:physiology; D020013:Calcium Signaling / Q000502:physiology; D002536:Cerebral Arteries / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D008638:Mesenteric Arteries / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008822:Mice, Transgenic; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D021122:Protein Subunits / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000502:physiology; D014665:Vasodilator Agents / Q000494:pharmacology*
D001095:Arachidonic Acids; D051036:Large-Conductance Calcium-Activated Potassium Channels; D021122:Protein Subunits; D019837:Ryanodine Receptor Calcium Release Channel; D014665:Vasodilator Agents; C070378:17,18-epoxy-5,8,11,14-eicosatetraenoic acid; D002118:Calcium