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Twitch-dependent SR Ca accumulation and release in rabbit ventricular myocytes
J W Bassani1, R A Bassani, D M Bers
1Department of Physiology, Loyola University School of Medicine, Maywood, Illinois 63304.
The American Journal of Physiology
|August 1, 1993
Summary
Researchers used caffeine-induced contractures and thapsigargin to measure sarcoplasmic reticulum (SR) calcium release per twitch and SR calcium reuptake. It takes 4-5 twitches to fully reload the SR after depletion.
Area of Science:
- Muscle Physiology
- Cellular Biology
- Biochemistry
Background:
- The sarcoplasmic reticulum (SR) is crucial for regulating intracellular calcium (Ca) levels in muscle cells.
- Understanding SR Ca handling is vital for muscle function and dysfunction.
Purpose of the Study:
- To quantify the fraction of SR Ca released during a single muscle twitch.
- To determine the number of twitches required for SR Ca reuptake after depletion.
- To investigate the role of SR Ca-adenosinetriphosphatase (ATPase) in Ca handling.
Main Methods:
- Utilized caffeine-induced contractures (Ccaf) to assess SR Ca content.
- Employed thapsigargin (TG) to inhibit the SR Ca-ATPase and block Ca reuptake.
- Measured intracellular Ca (Cai) transients using the fluorescent indicator indo 1.
Main Results:
- Sustained caffeine exposure completely depletes SR Ca in under 5 seconds.
- Four to five twitches are needed to restore SR Ca to steady-state levels after depletion (tau = 1.6 twitches).
- 90 seconds of TG exposure fully inhibits SR Ca-ATPase, preventing Ca reuptake after reloading twitches.
Conclusions:
- The SR Ca-ATPase can limit Ca influx-activated contraction when the SR is Ca-depleted.
- This study provides quantitative insights into SR Ca release and reuptake dynamics in muscle cells.