Sodium-calcium exchange mechanism in vascular smooth muscle tissue as revealed by manipulating external magnesium.
Small reductions in external sodium ions [( Na+]o), which cause no contractile effects in normal Mg2(+)-containing medium, cause an immediate contraction when [Mg2+]o is simultaneously withdrawn from isolated rat aortic smooth muscle. These contractions are Ca2(+)-dependent and vary in magnitude with the extracellular Na concentration and the Na substitute used. In contrast to substitution with sucrose, mannitol, urea and choline, substitution with Tris or Li+ does not result in contractions, in the absence of [Mg2+]o with these comparatively low [Na+]o reductions. Choline, mannitol, sucrose and urea substitutions sometimes give rise to a fast contractile phase in the presence of [Mg2+]o, which relaxes within a short time (about 5 min). The rises in tension in response to lowering of [Na+]o in the absence of [Mg2+]o are inhibited by the Na+ influx blocker, amiloride. These data are compatible with the hypothesis that Mg2+ controls Na+/Ca2+ exchange in these low Na+ substitution experiments and also protects the cell from osmotically induced small changes in cell volume in rat aortic smooth muscle.
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Department of Physiology, State University of New York, Brooklyn.
Zhang
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D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001011:Aorta; D002118:Calcium / Q000378:metabolism*; D002122:Calcium Chloride / Q000494:pharmacology; D002794:Choline / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology*; D008353:Mannitol / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D009994:Osmolar Concentration; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology; D013395:Sucrose / Q000494:pharmacology; D014508:Urea / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
D008353:Mannitol; D013395:Sucrose; D011189:Potassium Chloride; D000584:Amiloride; D014508:Urea; D012964:Sodium; D014700:Verapamil; D008274:Magnesium; D002122:Calcium Chloride; D002794:Choline; D002118:Calcium