In eNOS knockout mice skeletal muscle arteriolar dilation to acetylcholine is mediated by EDHF.
The mechanisms that account for acetylcholine (ACh)-induced responses of skeletal muscle arterioles of mice lacking endothelial nitric oxide (NO) synthase (eNOS-KO) were investigated. Isolated, cannulated, and pressurized arterioles of gracilis muscle from male eNOS-KO (74.1 +/- 2.3 microm) and wild-type (WT, 87.2 +/- 2.1 microm) mice developed spontaneous tone accounting for 63 and 61% of their passive diameter (116.8 +/- 3.4 vs. 143.2 +/- 2.8 microm, respectively) and dilated dose-dependently to ACh (10(-9)-10(-7) M). These dilations were significantly smaller in vessels of eNOS-KO compared with WT mice (29.2 +/- 2.0 microm vs. 46.3 +/- 2.1 microm, at maximum concentration) but responses to the NO donor, sodium nitrite (NaNO(2), 10(-6)-3 x 10(-5) M), were comparable in the vessels of the two strains. N(G)-nitro-L-arginine (L-NNA, 10(-4) M), an inhibitor of eNOS, inhibited ACh-induced dilations by 60-90% in arterioles of WT mice but did not affect responses in those of eNOS-KO mice. In arterioles of eNOS-KO mice, dilations to ACh were not affected by indomethacin but were essentially abolished by inhibitors of cytochrome P-450, clotrimazole (CTZ, 2 x 10(-6) M) or miconazole (MCZ, 2 x 10(-6) M), as well as by either high K(+) (40 mM) or iberiotoxin [10(-7) M, a blocker of Ca(2+)-dependent K(+) channels (K(Ca) channels)]. On the other hand, in WT arterioles CTZ or MCZ inhibited ACh-induced dilations only by approximately 10% and only in the presence of L-NNA. These results indicate that in arterioles of eNOS-KO mice, endothelium-derived hyperpolarizing factor (EDHF), synthesized via cytochrome P-450, accounts entirely for the mediation of ACh-induced dilation via an increase in K(Ca)-channel activity. In contrast, in arterioles of WT mice, endothelium-derived NO predominantly mediates ACh-induced dilation in which participation of EDHF becomes apparent only after inhibition of NO synthesis.
Huang
A
A
Department of Physiology, New York Medical College, Valhalla, New York 10595, USA.
Sun
D
D
Smith
C J
CJ
Connetta
J A
JA
Shesely
E G
EG
Koller
A
A
Kaley
G
G
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D001160:Arterioles / Q000502:physiology*; D001685:Biological Factors / Q000494:pharmacology*; D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D018482:Muscle, Skeletal / Q000098:blood supply*; D019001:Nitric Oxide Synthase / Q000172:deficiency* / Q000502:physiology; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; D010455:Peptides / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D026902:Potassium Channel Blockers; D014664:Vasodilation / Q000187:drug effects*
D001685:Biological Factors; D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D010455:Peptides; D026902:Potassium Channel Blockers; C067410:endothelium-dependent hyperpolarization factor; C064719:iberiotoxin; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III; C496315:Nos3 protein, mouse; D000109:Acetylcholine; D011188:Potassium