Endothelium-derived hyperpolarizing factor in human internal mammary artery is 11,12-epoxyeicosatrienoic acid and causes relaxation by activating smooth muscle BK(Ca) channels.
BACKGROUND
Left internal mammary arteries (LIMAs) synthesize endothelium-derived hyperpolarizing factor (EDHF), a short-lived K(+) channel activator that persists after inhibition of nitric oxide (NO) and prostaglandin synthesis. EDHF hyperpolarizes and relaxes smooth muscle cells (SMCs). The identity of EDHF in humans is unknown. We hypothesized that EDHF (1) is 11,12-epoxyeicosatrienoic acid (11,12-EET); (2) is generated by cytochrome P450-2C, CYP450-2C; and (3) causes relaxation by opening SMC large-conductance Ca(2+)-activated K(+) channels (BK(Ca)).


RESULTS
The identity of EDHF and its mechanism of action were assessed in 120 distal human LIMAs and 20 saphenous veins (SVs) obtained during CABG. The predominant EET synthesized by LIMAs is 11,12-EET. Relaxations to exogenous 11,12-EET and endogenous EDHF are of similar magnitudes. Inhibition of EET synthesis by chemically distinct CYP450 inhibitors (17-octadecynoic acid, N-methylsulfonyl-6-(2-propargyloxyphenyl)hexanamide), or a selective EET antagonist (4,15-epoxyeicosa-5(Z)-enoic acid) impairs EDHF relaxation. 11,12-EET activates a BK(Ca) current and hyperpolarizes LIMA SMCs. Inhibitors of BK(Ca) but not inward-rectifier or small-conductance K(Ca) channels abolish relaxation to endogenous EDHF and exogenous 11,12-EET. BK(Ca) and CYP450-2C mRNA and proteins are more abundant in LIMAs than in SVs, perhaps explaining the lack of EDHF activity of the SV. Laser capture microdissection and quantitative RT-PCR demonstrate that BK(Ca) channels are primarily in vascular SMCs, whereas the CYP450-2C enzyme is present in both the endothelium and SMCs.


CONCLUSIONS
In human LIMAs, EDHF is 11,12-EET produced by an EDHF synthase CYP450-2C and accounting for approximately 40% of net endothelial relaxation. 11,12-EET causes relaxation by activating SMC BK(Ca) channels.
Archer
Stephen L
SL
Vascular Biology Group, Cardiology Surgery, University of Alberta, Edmonton, Canada. sarcher@cha.ab.ca
Gragasin
Ferrante S
FS
Wu
Xichen
X
Wang
Shaohua
S
McMurtry
Sean
S
Kim
Daniel H
DH
Platonov
Michael
M
Koshal
Arvind
A
Hashimoto
Kyoko
K
Campbell
William B
WB
Falck
J R
JR
Michelakis
Evangelos D
ED
D015126:8,11,14-Eicosatrienoic Acid / Q000031:analogs & derivatives* / Q000378:metabolism* / Q000494:pharmacology; D000109:Acetylcholine / Q000494:pharmacology; D001685:Biological Factors / Q000378:metabolism*; D001920:Bradykinin / Q000494:pharmacology; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008323:Mammary Arteries / Q000187:drug effects / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000378:metabolism; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D024681:Potassium Channels, Calcium-Activated / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*; D014665:Vasodilator Agents / Q000494:pharmacology
D001685:Biological Factors; D051036:Large-Conductance Calcium-Activated Potassium Channels; D026902:Potassium Channel Blockers; D024681:Potassium Channels, Calcium-Activated; D014665:Vasodilator Agents; C400322:cytochrome P-450 CYP2C subfamily; C067410:endothelium-dependent hyperpolarization factor; C046783:11,12-epoxy-5,8,14-eicosatrienoic acid; D003577:Cytochrome P-450 Enzyme System; D019001:Nitric Oxide Synthase; D011451:Prostaglandin-Endoperoxide Synthases; D015126:8,11,14-Eicosatrienoic Acid; D000109:Acetylcholine; D001920:Bradykinin