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Hormone-evoked calcium release from intracellular stores is a quantal process
S Muallem1, S J Pandol, T G Beeker
1Laboratory of Membrane Biology, Cedars-Sinai Medical Center, Los Angeles, California 90048.
The Journal of Biological Chemistry
|January 5, 1989
Summary
Hormone-evoked calcium (Ca2+) release from intracellular stores is a quantal process, not continuous. This quantal release mechanism is linked to inositol 1,4,5-trisphosphate (Ins-1,4,5-P3) mediated calcium release.
Area of Science:
- Cellular Biology
- Biochemistry
- Physiology
Background:
- Calcium ions (Ca2+) act as crucial intracellular second messengers.
- Hormonal stimulation triggers Ca2+ release from intracellular stores, but the nature of this release (continuous vs. quantal) is debated.
Purpose of the Study:
- To investigate whether hormone-mediated Ca2+ release is a continuous or quantal process.
- To compare hormone-evoked Ca2+ release with that induced by ionomycin and inositol 1,4,5-trisphosphate (Ins-1,4,5-P3).
Main Methods:
- Studied Ca2+ mobilization using hormones, ionomycin, and Ins-1,4,5-P3 in acini.
- Measured changes in free cytosolic Ca2+ concentration ([Ca2+]i) and 45Ca efflux.
- Investigated Ca2+ release from intracellular stores in permeabilized cells.
Main Results:
- Hormone-mediated Ca2+ release occurred only during the initial 2-4 seconds of stimulation.
- Submaximal hormone concentrations released only a fraction of intracellular Ca2+, with stores remaining depleted until stimulation ceased.
- Ionomycin induced increasing rates of Ca2+ release with increasing concentrations, releasing all intracellular Ca2+.
- Increasing Ins-1,4,5-P3 concentrations released increasing fractions of Ca2+, but never all mobilizable Ca2+.
Conclusions:
- Hormone-evoked Ca2+ release is a quantal process, characterized by discrete release events.
- The quantal nature of hormone-evoked Ca2+ release appears to reflect the quantal properties of Ins-1,4,5-P3-mediated Ca2+ release from intracellular stores.