Effects of pH and anion substitution on magnesium accumulation in rabbit aortic smooth muscle.
The effects of anion substitution, pH and extracellular Mg2+ concentration on 28Mg accumulation were examined in rabbit aortic smooth muscle. Accumulation of 28Mg (expressed as a 28Mg/Mg2+ ratio) was not changed when the concentration of added, nonradioactive MgCl2 was increased from 1.5 to 15.0 mM. The 28Mg efflux rate was increased by added MgCl2 (0.15, 0.5 or 1.5 mM) in a dose-related manner after a similar delay of 5-10 min. Addition of 1.5 mM MgCl2, MgSO4 or magnesium aspartate hydrochloride enhanced 28Mg efflux and inhibited accumulation of 28Mg to the same extent. An increase or decrease in extracellular pH correspondingly increased or decreased 28Mg accumulation. However, the 28Mg efflux rate was not altered when extracellular pH was decreased. Efflux of 28Mg was increased by added 1.5 mM MgCl2 at pH 7.4 but not at pH 5.8. Thus, the net uptake of Mg2+ appears to be proportional to the concentration of extracellular Mg2+ in rabbit aorta. Low external pH decreases 28Mg retention in rabbit aorta by inhibiting the uptake of 28Mg rather than by increasing 28Mg efflux. Effects of added Mg2+ on transmembrane movements of 28Mg are not altered by changes in the associated anion. Extracellular Mg2+ appears to enter the cell and exchange with an intracellularly located pool of 28Mg in the same manner, regardless of whether the accompanying anion is sulfate, chloride or monoaspartate hydrochloride.
Research Department, Ciba-Geigy Corporation, Summit, N.J.
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Shetty
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Weiss
D000818:Animals; D000838:Anions / Q000494:pharmacology; D001011:Aorta / Q000378:metabolism*; D001224:Aspartic Acid / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008274:Magnesium / Q000378:metabolism* / Q000494:pharmacology; D015636:Magnesium Chloride; D008277:Magnesium Oxide / Q000494:pharmacology; D008278:Magnesium Sulfate / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D011817:Rabbits; D011868:Radioisotopes
D000838:Anions; D011868:Radioisotopes; D015636:Magnesium Chloride; D001224:Aspartic Acid; D008277:Magnesium Oxide; D008278:Magnesium Sulfate; D008274:Magnesium