Cardiac staircase and NMR-determined intracellular sodium in beating rat hearts

C. S. Lotan, S. K. Miller, T. Simor, G. A. Elgavish

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8 Citations (Scopus)


Isolated, perfused rat hearts (30°C, n = 13) were paced from 218 ± 4 beats/min to 433 ± 4 beats/min while systolic and diastolic pressure were recorded and intracellular Na+ concentration ([Na+](i)) was monitored by 23Na nuclear magnetic resonance (NMR) spectroscopy. [Na+](i) increased progressively with increasing stimulation frequency. In seven hearts (group I) an initial, progressive increase in systolic pressure was observed followed by a decrease in pressure with further increase in frequency. From the onset, a progressive decrease in systolic pressure was observed in group H (n = 6) in response to increased frequency. In group I an [Na+](i) increase of up to 134 ± 7% of control (P < 0.001) was observed, whereas in group H the gain in [Na+](i) with increasing pacing rate was attenuated, reaching a maximum of 120 ± 3% of control (P < 0.02). The differential pressure response between group I and group H hearts may reflect an enhanced sensitivity of rat hearts to the shortening of the restitution period of the sarcoplasmic reticulum, outweighing the positive inotropic effect induced by an increased [Na+](i). Only in rat hearts whose [Na+](i)-induced increase in pressure outweighs the restitution deficit would a complete positive inotropic effect be anticipated.

Original languageEnglish
Pages (from-to)H332-H340
JournalAmerican Journal of Physiology - Heart and Circulatory Physiology
Issue number1 38-1
Publication statusPublished - 1995


  • cardiac pacing
  • isolated perfused rat heart
  • sodium pump lag
  • sodium-23 nuclear magnetic resonance

ASJC Scopus subject areas

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

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