The modulation of pacing-induced changes in intracellular sodium levels by extracellular Ca2+ in isolated perfused rat hearts

Tamás Simor, Tamás Lóránd, Balázs Gaszner, Gabriel A. Elgavish

Research output: Contribution to journalArticle

7 Citations (Scopus)


This study demonstrates the inverse relationship between extracellular free calcium ([Ca(o)](f)) and intracellular sodium ([Na(i)]) in isolated perfused rat hearts and thus supports the role of [Na(i)] in the 'calcium paradox'. It also shows that the extent of the increase in [Na(i)] (Δ[Na(i)]), and the extent of the decrease in left ventricular developed pressure (ΔLVDP) in isolated perfused rat hearts, induced by pacing, is modulated by [Ca(o)](f). At low (0.24 mM) as well as normal (1.15 mM) [Ca(o)](f), [Na(i)] increased with pacing, progressively and significantly (P<0.01 and P<0.05, respectively), reaching a maximum of 12.56 ± 0.46 and 9.22 ± 0.16 mM at 500 beats/min, respectively. At high [Ca(o)](f) (2.2 mM), however, no pacing-induced increase in [Na(i)] was observed. Simultaneously, within the pacing range of 250-500 beats/min, the interval-force relationship was negative for all [Ca(o)](f). With decreasing [Ca(o)](f), a gradually increasing Δ[Na(i)] was induced. We hypothesise that a [Ca(o)](f) dependent Na-Ca exchanger activity modulates Na+ uptake, and thus baseline [Na(i)]. During incremental pacing, the increase in pacing rate induces a [Ca(o)](f)-dependant Δ[Na(i)], which may interact further with the sarcolemmal Na-Ca exchanger activity. As a result, both baseline [Na(i)] and the pacing-induced, [Ca(o)](f)- dependant Δ[Na(i)] modulate the net Ca2+ uptake, and thus SR Ca, in a manner that results in a modulated left ventricular force development.

Original languageEnglish
Pages (from-to)1225-1235
Number of pages11
JournalJournal of Molecular and Cellular Cardiology
Issue number4
Publication statusPublished - Apr 1997


  • Cardiac staircase
  • Extracellular calcium
  • Intracellular sodium
  • Na NMR
  • Pacing
  • Perfused rat heart

ASJC Scopus subject areas

  • Molecular Biology
  • Cardiology and Cardiovascular Medicine

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