Acetylcholine-induced relaxation in blood vessels from endothelial nitric oxide synthase knockout mice

1 Isometric tension was recorded in isolated rings of aorta, carotid, coron ary and mesenteric arteries taken from endothelial nitric oxide synthase kn ockout mice (eNOS(-/-) mice) and the corresponding wild-type strain (eNOS(/+) mice). The membrane potential of smooth muscle cells was measured in co ronary arteries with intracellular microelectrodes. 2 In the isolated aorta, carotid and coronary arteries from the eNOS(+/+) m ice, acetylcholine induced an endothelium-dependent relaxation which was in hibited by N-omega-L-nitro-arginine. In contrast, in the mesenteric arterie s, the inhibition of the cholinergic relaxation required the combination of N-omega-L-nitro-arginine and indomethacin. 3 The isolated aorta, carotid and coronary arteries from the eNOS(-/-) mice did not relax in response to acetylcholine. However, acetylcholine produce d an indomethacin-sensitive relaxation in the mesenteric artery from eNOS(- /-) mice. 4 The resting membrane potential of smooth muscle cells from isolated coron ary arteries was significantly less negative in the eNOS(-/-) mice (-64.8+/ -1.8 mV, n=20 and -58.4+/-1.9 mV, n=17, for eNOS(+/+) and eNOS(-/-) mice, r espectively). In both strains, acetylcholine, bradykinin and substance P di d not induce endothelium-dependent hyperpolarizations whereas cromakalim co nsistently produced hyperpolarizations (-7.9+/-1.1 mV, n=8 and -13.8+/-2.6 mV, n=4, for eNOS(+/+) and eNOS(-/-) mice, respectively). 5 These findings demonstrate that in the blood vessels studied: (1) in the eNOS(+/+) mice, the endothelium-dependent relaxations to acetylcholine invo lve either NO or the combination of NO plus a product of cyclo-oxygenase bu t not EDHF; (2) in the eNOS(-/-) mice, NO-dependent responses and EDHF-like responses were not observed. In the mesenteric arteries acetylcholine rele ases a cyclo-oxygenase derivative.