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1 Department of Pharmacology, The University of Texas Medical School at San Antonio, San Antonio, Texas
The effect of magnesium on calcium-induced responses of rabbit vascular smooth muscle, i.e., aorta, femoral artery, carotid artery, portal vein and atrial musele of rabbit, rat and guinea pig was studied. In the presence of magnesium (0.6-4.8 mM), the ED50 for calcium was significantly increased over that observed in magnesium-free medium in the aorta and femoral and carotid arteries and significantly decreased in portal veins of rabbit. Also, in the presence of magnesium (0.6-4.8 mM), the ED50 for calcium was signifieantly increased in rabbit atria. However, no change in ED50 was observed with magnesium in rat and guinea-pig atria. Magnesium in all concentrations significantly increased the maximum tension responses in rabbit aorta, but not in atria, femoral artery and portal vein of rabbit. In aorta tension decline studies, multiple components of calcium movenment in the absence of magnesium, and three kinetically defined components in the presence of magnesium were observed. In atrial tension decline studies, two kinetically defined phases for calcium movement in the presence of high concentrations of magnmesium (2.4-4.8 mM) and three kinetically defined phases for calcium in the presence of low concentrations (0.6-1.2 mM) and in the absence of magnesium were observed, It is concluded from these results that magnesium competes with calcium at the membrane and at inntracellular calcium-binding sites.
Submitted on February 8, 1973
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