Influence of Na+ gradient on Ca2+ transients and contraction in vascular smooth muscle

S. Bova, W. F. Goldman, X. J. Yuan, M. P. Blaustein

Research output: Contribution to journalArticlepeer-review

81 Scopus citations


The effects of reducing external Na+ ([Na+](o)) and increasing internal Na+ ([Na+](i)) on evoked tension in arterial rings were correlated with intracellular Ca2+ transients evoked in cultured A7r5 cells. Contractions were elicited in rings of rat aorta and a small mesenteric artery branch by serotonin (5-HT), arginine vasopressin (AVP), or a high K+ concentration ([K+](o)). Contractions were augmented by reduction of [Na+](o) (replaced by Li+ or N-methylglucamine) or inhibition of the Na+ pump (to raise [Na+](i)). These effects were dependent on external Ca2+. Ca2+ transients were measured by digital imaging of fura-2/AM-loaded A7r5 cells. The apparent free Ca2+ concentration ([Ca2+](app)) in eight unstimulated cells was 110 ± 10 nM in the peripheral cytoplasm. Activation of A7r5 cells by 5-HT, AVP, or high [K+](o) evoked transient increases in [Ca2+](app). Lowering [Na+](o) or raising [Na+](i) elevated [Ca2+](app) significantly in unstimulated cells and increased the amplitude and duration of the Ca2+ transients. These effects required external Ca2+. Caffeine (5-10 mM) reduced [Ca2+](app) in resting cells and attenuated the vasoconstrictor-evoked Ca2+ transients in low [Na+](o). The data imply that Na+ gradient reduction promotes Ca2+ entry and slows Ca2+ extrusion via Na+-Ca2+ exchange. This increases cytosolic free Ca2+ and the intracellular Ca2+ stores so that more Ca2+ is delivered to the contractile apparatus during cell activation. Such augmented Ca2+ transients could induce the amplified vasoconstrictor-evoked contractions observed in arterial rings under reduced Na+ gradient conditions.

Original languageEnglish (US)
Pages (from-to)H409-H423
JournalAmerican Journal of Physiology - Heart and Circulatory Physiology
Issue number2 28-2
StatePublished - 1990
Externally publishedYes


  • A7r5 cells
  • arterial rings
  • digital imaging
  • sodium-calcium exchange

ASJC Scopus subject areas

  • Physiology
  • Cardiology and Cardiovascular Medicine
  • Physiology (medical)


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