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Calcium-induced calcium release from sarcoplasmic reticulum vesicles
Journal of Biochemistry
|September 1, 1981
Summary
Calcium (Ca2+) passively permeates sarcoplasmic reticulum vesicles, especially at low magnesium. This Ca2+ release mechanism resembles Ca2+-induced Ca2+ release in muscle fibers, with two vesicle types identified.
Area of Science:
- Biochemistry
- Cell Biology
- Muscle Physiology
Background:
- Sarcoplasmic reticulum (SR) is crucial for calcium ion (Ca2+) regulation in muscle cells.
- Understanding passive Ca2+ permeability is key to muscle function and dysfunction.
Purpose of the Study:
- To investigate the passive permeability of sarcoplasmic reticulum vesicles for Ca2+.
- To characterize the factors influencing Ca2+ efflux from these vesicles.
Main Methods:
- Utilized the Millipore filtration technique with radioactive 45Ca isotope.
- Measured Ca2+ efflux rates under varying Ca2+ and Mg2+ concentrations.
Main Results:
- Ca2+ efflux rate increased with micromolar extravesicular Ca2+ at low Mg2+ concentrations.
- Ca2+ release was enhanced by caffeine and inhibited by procaine and Mg2+.
- Kinetic analysis indicated two populations of vesicles, with approximately two-thirds exhibiting Ca2+ release.
Conclusions:
- The observed Ca2+ release mechanism shares properties with Ca2+-induced Ca2+ release in skinned muscle fibers.
- Two distinct populations of sarcoplasmic reticulum vesicles exist regarding passive Ca2+ permeability.