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Am J Physiol Cell Physiol 232: C59-C66, 1977;
0363-6143/77 $5.00
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AJP - Cell Physiology, Vol 232, Issue 1 59-C66, Copyright © 1977 by American Physiological Society

ARTICLES

Sodium in smooth muscle relaxation

T. S. Ma and D. Bose

The contraction of guinea-pig taenia coli due to high K+ could not be reversed by washing when Na+ was absent from the medium. Reintroduction of Na+ (7 mM or more) caused relaxation. Similar results were obtained with rat uterus. The effect of sodium replacement was not due to change in ionic strength because equal or higher osmoles of choline, Ca++, K+, Mn++, or Mg++ had little or no effect. Persistence of contraction in the Na+-free medium was not due to a "catch state" of the contractile apparatus. Impairment of Ca+ removal from the cytoplasm rather than persistent increase in Ca+ influx seemed to sustain the mechanical response. This was because D600 (a calcium influx blocker) failed to completely relax K+-induced contraction in the absence of Na+ and also because the ability of EGTA to produce relaxation was reduced in the absence of Na+. Measurement of tissue calcium content using the lanthanum method revealed coincident decrease in tissue calcium and tension to control level during Na+-mediated relaxation. The results suggest a role for transmembrane Na+-Ca++ exchange in causing the Na+-mediated relaxation of taenia undergoing Na+-free contracture.


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M. P. Blaustein and W. J. Lederer
Sodium/Calcium Exchange: Its Physiological Implications
Physiol Rev, July 1, 1999; 79(3): 763 - 854.
[Abstract] [Full Text] [PDF]


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