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      Influence of Magnesium on Calcium- and Potassium-Related Responses in Vascular Smooth Muscle

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          The influence of Mg on Ca- and K-related responses of rabbit aortic strips was studied. Aortic strips bathed in either a K-free or 60.0 mM K solution were less sensitive to Ca in the presence of 1.2 mM Mg. Ca induced greater maximum tension in the aortic strips in the presence of Mg when bathed in 60.0 mM K. Addition of K to a K-free medium induced a slight relaxation at low concentrations (<1.0 mM) which was Ca dependent. The relaxation was less in the presence of Mg. With Mg in the medium throughout the experiment (90 min), the threshold concentration of K, inducing a contractile response, was increased as was the maximum tension. Acute addition of Mg decreased the maximum response to K. When K was lowered from 5.4 to 0.0 mM a contractile response, absent in the presence of Mg, occurred. When the K was increased, the tension returned to baseline. At 25–30 mM K, the tension again increased, reaching a maximum at 40–50 mM K. <sup>45</sup>Ca uptake was stimulated at all K concentrations producing a contraction. Mg depressed this increase in uptake. <sup>45</sup>Ca efflux was more rapid into a 50.0 mM than into 0.0 mM K solution. Mg delayed <sup>45</sup>Ca efflux. It is concluded from these data that Mg has two components in its effect on the Ca associated with K responses. One is a competition with Ca at extracellular sites probably at the membrane, and the other is intracellular, probably a competition with Ca at sequestration sites.

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          Author and article information

          J Vasc Res
          Journal of Vascular Research
          S. Karger AG
          18 September 2008
          : 13
          : 6
          : 321-337
          Department of Pharmacology, The University of Texas Health Science Center at San Antonio, San Antonio, Tex.
          158103 Blood Vessels 1976;13:321–337
          © 1976 S. Karger AG, Basel

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          Pages: 17
          Research Paper


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