Modulatory role of magnesium on the contractile response of rat aorta to several agonists in normal and calcium-free medium.
Acute withdrawal of external Mg2+ increased basal tone of rat isolated aorta incubated in the presence of Ca2+. Above normal levels of Mg2+ (1-4 mM) inhibited basal tone while much higher levels of the divalent cation (64-256 nM) evoked contractile responses regardless of the presence of Ca2+. Contractile responses to noradrenaline (1 microM) and KCl (80 mM) were inhibited by addition of cumulative concentrations of Mg2+. Acetylcholine-induced contractions in the presence of physiological concentrations of Mg2+ (1 mM) decreased gradually to the basal tone, but a sustained contraction was observed in the absence of this ion. In Ca(2+)-free medium, acetylcholine-induced phasic responses indicate the existence of an acetylcholine-sensitive Ca2+ store. KCl induced contraction only in Krebs solution, although a small residual contraction could be observed in Ca(2+)-free medium in some experiments. Mg(2+)-depletion in the extracellular medium increased contractile responses induced by acetylcholine and KCl in Ca(2+)-free medium. These results suggest that extracellular Mg2+ modulates basal tone, Ca2+ channels and responsiveness to various agents in the absence of Ca2+.
Noguera
M A
MA
Departamento de Farmacologia, Facultad de Farmacia, Universidad de Valenica, Spain.
D'Ocon
M P
MP
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects* / Q000502:physiology*; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology* / Q000502:physiology; D003470:Culture Media; D005110:Extracellular Space / Q000378:metabolism; D066298:In Vitro Techniques; D007552:Isotonic Solutions; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology* / Q000502:physiology*; D008275:Magnesium Deficiency / Q000503:physiopathology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects* / Q000502:physiology*; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000502:physiology*; D009638:Norepinephrine / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar
D003470:Culture Media; D007552:Isotonic Solutions; C051865:Krebs-Ringer solution; D011189:Potassium Chloride; D008274:Magnesium; D000109:Acetylcholine; D002118:Calcium; D009638:Norepinephrine