Intracellular Na+ regulation in cardiac myocytes

Donald M Bers, William H. Barry, Sanda Despa

Research output: Contribution to journalArticle

229 Scopus citations

Abstract

Intracellular [Na+] ([Na+]i) is regulated in cardiac myocytes by a balance of Na+ influx and efflux mechanisms. In the normal cell there is a large steady state electrochemical gradient favoring Na+ influx. This potential energy is used by numerous transport mechanisms, including Na+ channels and transporters which couple Na+ influx to either co- or counter-transport of other ions and solutes. Six sarcolemmal Na+ influx pathways are discussed in relatively quantitative terms: Na+ channels, Na+/Ca2+ exchange, Na+/H+ exchange, Na+/Mg2+ exchange, Na+/HCO3 - cotransport and Na+/K+/2Cl- cotransport. Under normal conditions Na+/Ca2+ exchange and Na+ channels are the dominant Na+ influx pathways, but other transporters may become increasingly important during altered conditions (e.g. acidosis or cell volume stress). Mitochondria also exhibit Na+/Ca2+ antiporter and Na+/H+ exchange activity that are important in mitochondrial function. These coupled fluxes of Na+ with Ca2+, H+ and HCO3 - make the detailed understanding of [Na+]i regulation pivotal to the understanding of both cardiac excitation-contraction coupling and pH regulation. The Na+/K+-ATPase is the main route for Na+ extrusion from cells and [Na+]i is a primary regulator under physiological conditions. [Na+]i is higher in rat than rabbit ventricular myocytes and the reason appears to be higher Na+ influx in rat with a consequent rise in Na+/K+-ATPase activity (rather than lower Na+/K+-ATPase function in rat). This has direct functional consequences. There may also be subcellular [Na+]i gradients locally in ventricular myocytes and this may also have important functional implications. Thus, the balance of Na+ fluxes in heart cells may be complex, but myocyte Na+ regulation is functionally important and merits focused attention as in this issue.

Original languageEnglish (US)
Pages (from-to)897-912
Number of pages16
JournalCardiovascular Research
Volume57
Issue number4
DOIs
StatePublished - Apr 1 2003
Externally publishedYes

Keywords

  • Myocytes
  • Na-channel
  • Na/Ca-exchanger
  • Na/H-exchanger
  • Na/K-pump

ASJC Scopus subject areas

  • Cardiology and Cardiovascular Medicine

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