Abstract
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 language | English (US) |
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Journal | American Journal of Physiology - Cell Physiology |
Volume | 270 |
Issue number | 1 39-1 |
State | Published - Jan 1996 |
Externally published | Yes |
Keywords
- Caffeine contracture
- Calcium current
- Cardiac myocytes
- Indo 1
- Sodium/calcium exchange current
ASJC Scopus subject areas
- Cell Biology
- Clinical Biochemistry
- Physiology
- Physiology (medical)