Cellular Mg++ Accumulation is Altered by Extracellular Na+ and Directly Affects Agonist-Induced Mobilization of Ca++ in Vascular Smooth Muscle

  • Suraj S. Shetty
  • John V. Zawadzki
  • George B. Weiss
Part of the Advances in Experimental Medicine and Biology book series (AEMB, volume 311)


Effects of altered Na+, Ca++ and Mg++ concentrations on 45Ca and 28Mg distribution and binding as well as of changes in cellular Mg++ on mobilization of Ca++ by added norepinephrine (NE) were examined in the rabbit aortic media-intimal layer. Uptake of 45Ca at cellular high affinity sites was decreased by Mg++ much more than 28Mg uptake was altered by Ca++. Substitution of Na+ affects 45Ca uptake primarily at extracellular (La+++-accessible) binding sites. Muscles were pre-loaded with Mg++ by incubation in a low-Na+ solution (75% Na+ replaced isosmotically with sucrose) for 30 min followed by a 90 min exposure to a similar solution also containing 15 mM MgCl2. These tissues, upon examination in normal (154 mM) Na+-containing solution, indicated decreased retention of that cellular, high-affinity Ca++ fraction important for NE-induced contractile response. Accordingly, release of 45Ca from this site and associated tension responses to added NE were attenuated in these muscles. These results suggest that variations in extracellular Na+ concentration modulate binding and subsequent mobilization of activator Ca++ by agonists through alterations in cellular Mg++ content in vascular smooth muscle.


Vascular Smooth Muscle Contractile Response Muscle Strip 45Ca Uptake Incubation Solution 
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Copyright information

© Springer Science+Business Media New York 1992

Authors and Affiliations

  • Suraj S. Shetty
    • 1
  • John V. Zawadzki
    • 1
  • George B. Weiss
    • 1
  1. 1.Research DepartmentCIBA-GEIGY CorporationSummitUSA

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