Acta Physiologica 78. (1991)

1. szám - C. Szabó, Mária Faragó, E. Dóra, Ildikó Horváth, A. G. B. Kovách: Influence of extracellular magnesium on the contractile and endothelium-dependent dilatory responses of feline mesenteric arteries

Acta Physiologien Hungarica, Volume 78 (l),pp. 19—26 (1991) INFLUENCE OF EXTRACELLULAR MAGNESIUM ON THE CONTRACTILE AND ENDOTHELIUM­­DEPENDENT DILATORY RESPONSES OF FELINE MESENTERIC ARTERIES Cs. Szabó, Mária Faragó, Б. Dóra, Ildikó Horváth, A. G. B. Kovách EXPERIMENTAL RESEARCH DEPARTMENT AND SECOND INSTITUTE OF PHYSIOLOGY, SEMMELWEIS UNIVERSITY MEDICAL SCHOOL, BUDAPEST, HUNGARY Received: June 6, 1990 Accepted: October 3, 1990 To clarify the effect of extracellular magnesium on the vascular reactivity of feline isolated mesenteric arteries, the effects of slight alterations in the extracellular magnesium concentration on the contractile and endothelium-dependent dilatory responses were investigated in vitro. The contractions, induced by noradrenaline 10-8-10-5 M, were not affected in the mesenteric artery at low extracellular magnesium (0.8 mM versus to the normal, 1.2 mM). High (1.6 and 2.0 mM) magnesium exerted a modest inhibitory effect on the contractile responses. This depression of the contraction was accompanied with a significant shift to the right in the EC50 value for noradrenaline. The endothelium-dependent relaxations induced by acetylcholine 10_8-10-5 M, were inhibited by high (1.6 and 2.0 mM) magnesium. Lowering of the extracellular magne­sium concentration to 0.8 mM, however, failed to alter the dilatory potency of acetyl­choline. The depression of the dilatory responses was also accompanied with a shift to the right in the ECS0 values for acetylcholine. The present results show , that contractions and endothelium-dependent relaxations of the mesenteric artery are modulated by the extracellular magnesium asymmetrically: slight magnesium deficiency does not affect these responses, whereas elevation of the concentration of this ion inhibits both pro­cesses. Extracellular magnesium probably affects rather the binding of these contractile and endothelium-dependent dilatory agonists to their receptors than the calcium influx into the endothelial- and smooth muscle cells in this vessel. Keywords: feline mesenteric artery, extracellular magnesium, contraction, endo­thelium-dependent relaxation, noradrenaline, acetylcholine During the past decade considerable amount of data has been generated concerning the effect of extracellular magnesium ions on the vascular smooth muscle tone and reactivity. It has been shown, that acute withdrawal of magnesium elevates the basal tone of the arteries. Contractile responses to various agonists are also enhanced at lowered extracellular magnesium. Eleva­tion of magnesium concentration in the medium, however, relaxes the smooth muscle and attenuates vasoconstriction [see 2, 3, 4, 5, 6, 18]. In these effects of magnesium, several underlying mechanisms have been proposed. Magnesium is able to compete with calcium for the membrane Correspondence should be addressed to Csaba Szabó Experimental Research Department and Second Institute of Physiology, Semmelweis University Medical School, 1082 Budapest, Üllői u. 78/a, Hungary

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