Mediation by M₃‐muscarinic receptors of both endothelium‐dependent contraction and relaxation to acetylcholine in the aorta of the spontaneously hypertensive rat

Abstract

1 Experiments were designed to characterize the subtype(s) of endothelial muscarinic receptor that mediate(s) endothelium-dependent relaxation and contraction in the aorta of spontaneously hypertensive rats (SHR). 2 Rings of SHR aorta with endothelium were suspended in organ baths for the measurement of isometric force. Ecothiopate (an inhibitor of acetylcholinesterase) was present throughout the experiments. Endothelium-dependent contraction to acetylcholine was studied in quiescent aortic rings in the presence of N0-nitro-L-arginine (to prevent the formation of nitric oxide). Endothelium-dependent relaxation to acetylcholine was obtained during contraction to phenylephrine and in the presence of indomethacin (to inhibit cyclo-oxygenase activity). Responses to acetylcholine were assessed against the non-preferential muscarinic receptor antagonist, atropine, and the preferential antagonists pirenzepine (M,), methoctramine (M2) and 4-diphenylacetoxy-N-methylpiperidine methobromide (4-DAMP; M3).3 The potency of acetylcholine in inducing endothelium-dependent contraction was 6.54 ± 0.07 (EC5,,). Atropine, pirenzepine, methoctramine and 4-DAMP displayed competitive antagonism towards the endothelium-dependent contraction to acetylcholine. The pA2 values for these muscarinic receptor antagonists were estimated from Arunlakshana-Schild plots to be (-logM) 9.48 ± 0.07, 6.74 ± 0.22, 6.30 ± 0.20 and 9.39 ± 0.22 respectively. The potency of acetylcholine in inducing endotheliumdependent relaxation was 7.82 ± 0.09 (ICW). Atropine, pirenzepine and 4-DAMP displayed competitive antagonism towards the endothelium-dependent relaxation to acetylcholine but methoctramine had no effect. The pA2 values for atropine and 4-DAMP for the relaxation to acetylcholine were estimated from Arunlakshana-Schild plots to be (-log M) 9.15 ± 0.23 and 9.63 ± 0.28, respectively. These results suggest that the muscarinic M3 receptor subtype mediates both endothelium-dependent relaxation and contraction to acetylcholine in SHR aorta.

Exercise restores endothelial function independently of weight loss or hyperglycaemic status in db/db mice

“…Acetylcholine interacts with endothelial muscarinic M 3 receptors and causes NO release and vasodilatation [32]. It is possible that vascular dysfunction in diabetes is a result of impaired muscarinic receptor activity [33].…”

Release of C-type natriuretic peptide accounts for the biological activity of endothelium-derived hyperpolarizing factor

“…The observation that responses to EDHF and CNP are inhibited by PTx, which selectively inhibits G i [endothelial M 3 receptors activated by ACh to release EDHF remain active because they are coupled to G q (36,37)], intimates that EDHFand CNP-mediated relaxations are brought about by NPR-C activation and G i coupling to a smooth muscle K ϩ channel. The phenomenon of GIRKs, which are regulated by the ␤␥ subunits of G i , is well established in neuronal cells (38) and cardiomyocytes (39); such channels have similar characteristics to those mediating vascular smooth muscle hyperpolarization in response to EDHF and are inhibited by Ba 2ϩ .…”

A role for muscarinic receptors in neutrophil extracellular trap formation and levamisole-induced autoimmunity

“…Potential toxic intermediates generated in the interaction between levamisole and NET proteins may explain this observation. Activation of M3 receptors on vascular endothelial cells by acetylcholine promotes arterial vasodilation via nitric oxide synthesis (46). However, direct stimulation of M3 receptors on vascular smooth muscle cells promotes vasoconstriction in pathologies in which the vascular endothelium is disrupted (47).…”