Extracellular magnesium and contractile responses to noradrenaline in the rat tail artery.
The effects of variations in extracellular magnesium concentration (Mg2+)0 on contractile responses to noradrenaline (NA) were studied in isolated rat tail arteries. Mg2+-free or high Mg2+ exposures caused (respectively) enhancement or inhibition of NA dose-response curves. Increases in (Mg2+)0 significantly increased NA-induced phasic contractions due to Ca release from a "membrane-bound" pool. Increases in (Mg2+)0 diminished the magnitude of Ca2+-induced relaxations due to a "membrane-stabilizing" effect. It is hypothesized that high (Mg2+)0 enhances NA-induced mobilization of stored calcium, as well as preventing the membrane-stabilizing effect of calcium ions through competition with Ca2+ at intracellular and membrane sequestrating sites, thus interfering with Ca2+ sequestration.
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D000818:Animals; D001158:Arteries / Q000502:physiology; D002118:Calcium / Q000502:physiology; D066298:In Vitro Techniques; D008274:Magnesium / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology*; D051381:Rats; D013623:Tail / Q000098:blood supply
D008274:Magnesium; D002118:Calcium; D009638:Norepinephrine