Steady-state twitch Ca2+ fluxes and cytosolic Ca2+ buffering in rabbit ventricular myocytes

Leanne M D Delbridge, Jose W M Bassani, Donald M Bers

Research output: Contribution to journalArticlepeer-review

65 Scopus citations


Intracellular Ca2+ ([Ca2+]i) transients and transsarcolemmal Ca2+ currents were measured in indo 1-loaded isolated rabbit ventricular myocytes during whole cell voltage clamp to quantitate the components of cytosolic Ca2+ influx and to describe the dynamic aspects of cytosolic Ca2+ buffering during steady-state contraction (0.5 Hz, 22°C). Sarcolemmal Ca2+ influx was directly measured from the integrated Ca2+ current (ICa) recorded during the clamp (158 ± 10 attomoles; amol). Sarcoplasmic reticulum (SR) Ca2+ content was determined from the integrated electrogenic Na+/Ca2+ exchange current (IX) induced during rapid application and sustained exposure of cells to caffeine to elicit the release of the SR Ca2+ load (1,208 ± 170 amol). The mean steady-state SR Ca2+ load was calculated to be 87 ± 13 μM (μmol/l nonmitochondrial cytosolic volume). Ca2+ influx via ICa represented ∼ 14% of the stored SR Ca2+ and 23% of the total cytosolic Ca2+ flux during a twitch (47 ±6 μM). Comparison of electrophysiologically measured Ca2+ fluxes with Ca2+ transients yields apparent buffering values of 60 for caffeine contractures and 110 for twitches (ΔCa2+ total/ΔCa2+ free). This is consistent with the occurrence of "active" buffering of cytosolic Ca2+ by SR Ca2+ uptake during the twitch.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Cell Physiology
Issue number1 39-1
StatePublished - Jan 1996
Externally publishedYes


  • Caffeine contracture
  • Calcium current
  • Cardiac myocytes
  • Indo 1
  • Sodium/calcium exchange current

ASJC Scopus subject areas

  • Cell Biology
  • Clinical Biochemistry
  • Physiology
  • Physiology (medical)


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