Heterogeneity of muscarinic receptors in lamb isolated coronary resistance arteries

Abstract

1 In vitro experiments in a microvascular myograph were designed to characterize postjunctional muscarinic receptors producing contraction both in the presence and absence of the endothelium in coronary resistance arteries (normalized diameter of 150-450 jm), isolated from the left ventricle of hearts from 3-6 month old lambs. Preferential muscarinic receptor antagonists were used to determine the receptor subtype: pirenzepine (MI receptor), AFDX 116 (M2 receptor), 4-DAMP and pFHHSiD (M3 receptor). 2 The rank order of potency for muscarinic agonist-induced increases in tension in endothelium-intact preparations was oxotremorine-M = methacholine = acetylcholine (ACh) > carbachol. Removal of the endothelium increased the potency of ACh, but this procedure did not change either the sensitivity or maximal response to carbachol. 3 The contractile response to ACh was reproducible. Incubation with 3 x 10-7-3 x 10-6 M pirenzepine induced non-parallel rightward shifts and depressed the maximum of the concentration-response curve to ACh in endothelium-intact arteries. The slope by Schild analysis was 2.9 ± 0.8 (P <0.05, n = 7). Atropine, AFDX 116, 4-DAMP and pFHHSiD produced parallel rightward shifts of the curves to ACh and the slopes of the Schild plots were not significantly different from unity. The pKB values for the antagonists from plots constrained to unity in endothelium-intact segments were: atropine (9.4), 4-DAMP (9.0), pFHHSiD (7.9) and AFDX 116 (6.2). 4 In endothelium-denuded arteries, pirenzepine, AFDX 116 and pFHHSiD caused concentrationdependent, parallel rightward displacements of the concentration-response curves to ACh and the slopes of the Schild plots were not significantly different from unity. The plots constrained to a slope of unity gave the following pKB values: pFHHSiD (8.7), pirenzepine (7.5) and AFDX 116 (6.2). 5 In the presence of the endothelium, low concentrations of pirenzepine (10-9-1-' M) produced leftward shifts of the ACh concentration-response curves. This potentiating effect of pirenzepine was reversed by endothelial cell removal. In preparations precontracted with the thromboxane-mimetic, U46619, the putative MI-selective agonist, McN-A-343, induced a biphasic relaxation with log IC50 of 8.53 ± 0.14 and 5.02 ± 0.08 for the first and second phase of the relaxation, respectively, and maximal relaxations of 22.8 ± 4.3% and 41.1 ± 5.4% (n = 16). McN-A-343 relaxed the vessels in the presence of 10-' M pFHHSiD and 3 x 10-7 M AFDX 116, but not after incubation with 10-9 M pirenzepine.6 It is concluded from the pKB values for the antagonists used, that contraction induced by ACh in lamb coronary resistance arteries, in either the presence or the absence of the endothelium, is mediated via the M3 subtype of muscarinic receptors, while muscarinic receptors of another subtype at the endothelium seem to modulate the contractile response to ACh.

M1 and M3 muscarinic receptors in human pulmonary arteries

“…In addition, there was a reverse order of magnitude (Table 3) These data derived from human pulmonary vessels are in contrast to results obtained in other vascular tissues where only M3 receptors have been shown to be involved in the AChinduced relaxation (Duckles & Garcia-Villalon, 1990;Jaiswal et al, 1991). However, involvement of an endothelial Ml receptor in the ACh-induced relaxation has also been suggested by Simonsen et al (1993) in lamb isolated coronary arteries. Rubanyi and coworkers (1987) found in dog femoral artery preparations, that pirenzepine was a more potent antagonist against McN-A-343-induced relaxation than against that produced by ACh.…”

Mismatched pre- and postnatal nutrition leads to cardiovascular dysfunction and altered renal function in adulthood

“…A number of potential cellular signaling changes could be hypothesized to underlie the altered vascular reactivity. To investigate this possibility, we focused on myosin light chain kinase (MLCK), a key component of smooth muscle signaling pathways, and acetylcholine receptors (M3) on smooth muscle cells (35). We found that MLCK mRNA levels in the coronary artery were increased in UC, but not UU, compared with CC ( Fig.…”

Cholinergic modulation of non-adrenergic, non-cholinergic relaxation in isolated, small coronary arteries from lambs

“…The hearts were excised immediately after death and placed in ice-cold physiological salt solution (PSS) to reduce cardiac metabolism. Throughout the subsequent dissection, the hearts were bathed in cold PSS (4 °C) of the following composition (mM): NaCl 119, NaHCO 3 Proximal segments of LAD and small, third-to fourth-order, subepicardial branches of the LAD were dissected as previously described for lamb small coronary arteries [36]. Pial arteries from lamb brains were also dissected and the ChAT activity therein determined as a positive control [13,18].…”

“…In isolated segments of both proximal and distal coronary arteries, exogenous acetylcholine may induce either relaxation or contraction by activation of receptors present on the endothelium or smooth muscle, respectively [19,36,37,38]. Electrical field stimulation (EFS) of bovine and porcine large coronary arteries has been reported to produce atropine-sensitive contractions [16,22,23].…”