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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)

Abstract

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.

Keywords

Vascular Smooth Muscle Contractile Response Muscle Strip 45Ca Uptake Incubation Solution 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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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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