title: Magnesium withdrawal and contraction of arterial smooth muscle: effects of EDTA, EGTA, and divalent cations.
abstract: The divalent cation chelators, CaEDTA and EGTA, were demonstrated to exert opposite effects on contractions of rat aortic smooth muscle induced by withdrawal of external magnesium ([Mg2+]0). Addition of CaEDTA potentiated such contractions more than 100%, while EGTA promoted rapid relaxation. Rapid relaxation of contractions induced by withdrawal of [Mg2+]0 could also be induced by Mn, Ni, and Cd but not Sr. Using EC50's, a relative descending order of contractile inhibition was noted for the divalent cations: Mn greater than Cd greater than Mg greater than Ni. The ability of CaEDTA to potentiate contractions produced by withdrawal of [Mg2+]0, as well as the ability of divalent cations to relax contractions of aortic smooth muscle, appears to be related to actions on the transmembrane flux of Ca2+. These findings thus lend support to the view that Mg ions either play an important role in regulating membrane permeability to [Ca2+]0 or occupy membrane sites which are exchangeable with membrane-bound Ca in certain types of aterial smooth muscle.
mesh_terms: D000818:Animals; D001011:Aorta; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D002413:Cations, Divalent / Q000494:pharmacology; D004347:Drug Interactions; D004492:Edetic Acid / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000378:metabolism / Q000502:physiology*; D051381:Rats
chemical_list: D002413:Cations, Divalent; D004533:Egtazic Acid; D004492:Edetic Acid; D008274:Magnesium; D002118:Calcium