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      Effect of Sodium Gradient on the Rate of Relaxation of Rat Mesenteric Small Arteries from Potassium Contractures

      ,

      Journal of Vascular Research

      S. Karger AG

      Resistance vessels, Sodium, Na-Ca exchange, Relaxation, Potassium

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          Abstract

          We have measured the relaxation of rat mesenteric small arteries (internal diameter ca. 200 µm) from a potassium contracture under conditions where the transplasmalemmal sodium gradient was altered. Adjustment of the sodium gradient was made either by exposing vessels to ouabain (1 mM) for different periods to vary the intracellular sodium concentration (Na<sub>i</sub>), or by varying the sodium concentrations of the relaxation solutions (Na<sub>o</sub>). Under normal conditions (where we have previously shown Na<sub>i</sub> is about 19 m M), vessels relaxed completely within 1 min in low sodium solutions (Na<sub>o</sub> = 25 m M) using either sucrose, choline-Cl or MgCl<sub>2</sub> as substitutes. However, the relaxation (measured after 1 min) was reduced when sucrose substitution was used, and further experiments were made using this substitute. Here it was found that exposing vessels to ouabain, for example 90 min (thus increasing Nai to about 73 m M) and then performing the relaxation in a low sodium solution gave only about 50% relaxation after 1 min. Experiments with intermediate sodium concentrations in the relaxation medium showed that reduction to 100 m M had no significant effect on the relaxation, and that it was only below 50 mM that effects were most marked. The effects of altered sodium gradient were eliminated if the calcium concentration of the relaxation medium was zero. The results indicate that under normal physiological conditions, small changes in sodium gradient have little effect on calcium metabolism of rat mesenteric small arteries, but also that under extreme conditions net calcium extrusion does appear to be reduced by a reduced sodium gradient.

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          Author and article information

          Journal
          JVR
          J Vasc Res
          10.1159/issn.1018-1172
          Journal of Vascular Research
          S. Karger AG
          1018-1172
          1423-0135
          1984
          1984
          23 September 2008
          : 21
          : 6
          : 279-289
          Affiliations
          Biophysics Institute, Aarhus University, Denmark
          Article
          158530 Blood Vessels 1984;21:279–289
          10.1159/000158530
          © 1984 S. Karger AG, Basel

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          Page count
          Pages: 11
          Categories
          Research Paper

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