Pflügers Archiv

, Volume 398, Issue 1, pp 27–32 | Cite as

Effects of magnesium on45Ca uptake and release at different sites in rabbit aortic smooth muscle

  • H. Karaki
  • K. Hatano
  • G. B. Weiss
Article

Abstract

Effects of 1.5 mM Mg2+ on muscle tension and on45Ca uptake and release at different sites in the rabbit aortic media-intimal layer were investigated. The sustained contraction induced by either 10−6 M norepinephrine (NE) or 60 mM K+ was not affected by 1.5 mM Mg2+ in the presence of 1.5 mM Ca2+. However, the contractions elicited with NE or K+ in 0.03 mM Ca2+-containing solution were inhibited by 1.5 mM Mg2+ by 67% and 27%, respectively. Total45Ca uptake measured in the presence of either 1.5 mM or 0.03 mM Ca2+ was not affected by 1.5 mM Mg2+. The rate of residual45Ca uptake (45Ca uptake followed by a wash in La3+-containing solution at low temperature) measured in the presence of 1.5 mM Ca2+ was slightly lower in the presence of 1.5 mM Mg2+. However, the increase in rate of residual45Ca uptake induced by NE or the net increase in the residual45Ca uptake induced by K+ was not decreased by 1.5 mM Mg2+. The residual45Ca uptake measured in the presence of 0.03 mM Ca2+ was reduced to 64% and 24% of controls by addition of 1.5 mM Mg2+ or Sr2+, respectively. A part of the residual45Ca was released by NE. Uptake of45Ca at this NE-affected Ca2+ site did not take place in the presence of 1.5 mM Mg2+ when the Ca2+ concentration of the medium was 0.03 mM. However, this45Ca uptake component was only partially inhibited when the Ca2+ concentration of the medium was 1.5 mM. The NE-induced increase in45Ca efflux was not inhibited by 1.5 mM Mg2+. From these results, Mg2+ appears to be a weak antagonist for both Ca2+ entry into the vascular smooth muscle cell and Ca2+ binding at a high affinity intracellular site.

Key words

Vascular smooth muscle Rabbit aorta Calcium uptake Calcium efflux Calcium binding Magnesium Norepinephrine High potassium 

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Copyright information

© Springer-Verlag 1983

Authors and Affiliations

  • H. Karaki
    • 1
  • K. Hatano
    • 1
  • G. B. Weiss
    • 1
  1. 1.Department of PharmacologyUniversity of Texas Health Science Center at DallasDallasUSA

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