Influence of extracellular Na+ removal on cytosolic Ca2+ concentration in smooth muscle cells of rabbit cerebral artery

J. K. Kim, S. J. Kim, Y. C. Kim, I. So, K. W. Kim

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6 Scopus citations

Abstract

There are some controversies over the contribution of Na+/Ca2+ exchanger (NCX) to the regulation of cytosolic Ca2+ concentration ([Ca2+](c)) in smooth muscle. To prove the functional role of Na+/Ca2+ exchanger, we examined whether the removal of extracellular Na+ could affect [Ca2+](c) of rabbit cerebral arterial smooth muscle. The fluorescence ratio of fura-2 (R(340/380)) was measured in the single myocyte of rabbit middle cerebral artery and Na+ was substituted with the same concentration of NMDG+ or Li+. In 21 out of 230 cells tested, Na+-removal increased R(340/380) (ΔR(340/380)) by 115 ± 16.5% of the ΔR340/380 induced by 10 mM caffeine in the same cell. The Na+ removal-induced ΔR(340/380) was blocked by a selective inhibitor of cardiac type NCX exchanger (KB-R7943, (2-[2-[4- (4-nitrobenzyloxy) phenyl]ethyl]isothiourea, 10 μM). In those cells where the Na+-removal by itself did not increase R(340/380), the caffeine-induced ΔR(340/380) was increased by Na+-removal (130 ± 9.8% of control response, n=30). Under the whole-cell patch clamp condition, short application of caffeine induced transient increase of outward current (I(K,Ca)-transient) which reflect the change of subsarcolemmal [Ca2+]. The application of KB- R7943 increased the amplitude of I(K,Ca)-transient (n=4). These results suggest the functional existence of NCX in rabbit cerebral artery smooth muscle.

Original languageEnglish
Pages (from-to)135-145
Number of pages11
JournalJournal of Smooth Muscle Research
Volume35
Issue number5-6
DOIs
StatePublished - 1999

Keywords

  • Cytosolic Ca concentration
  • Na/Ca exchanger
  • Smooth muscle cell

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