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Smoothly graded Ca2+ release from inositol 1,4,5-trisphosphate-sensitive Ca2+ stores
M D Bootman1, T R Cheek, R B Moreton
1Babraham Institute Laboratory of Molecular Signalling, Department of Zoology, University of Cambridge, United Kingdom.
The Journal of Biological Chemistry
|October 7, 1994
Summary
Histamine releases intracellular calcium (Ca2+) in a dose-dependent manner, suggesting discrete calcium pools are recruited by hormones. This quantal release mechanism is not due to cell desensitization.
Area of Science:
- Cell biology
- Biochemistry
- Physiology
Background:
- Hormone stimulation causes complex intracellular calcium ion concentration ([Ca2+]i) changes.
- Understanding calcium release from intracellular stores is crucial.
Purpose of the Study:
- Investigate histamine's ability to release intracellular Ca2+ stores.
- Clarify mechanisms regulating Ca2+ release under varying conditions.
Main Methods:
- Used video imaging of single Fura-2-loaded HeLa cells.
- Applied histamine in stepwise and pulsatile manners.
- Conducted experiments in Ca(2+)-free and Ca(2+)-containing media at 20°C and 37°C.
Main Results:
- Stepwise histamine increases released proportional amounts of intracellular Ca2+ in Ca(2+)-free medium, resembling quantal release.
- Quantal release occurred at both temperatures and was not due to desensitization.
- In Ca(2+)-containing medium, histamine evoked smoothly graded [Ca2+]i responses proportional to concentration.
Conclusions:
- Hormone-evoked Ca2+ release from intracellular stores is limited by hormone concentration.
- Complex [Ca2+]i signals do not result from all-or-none release of the entire Ca2+ pool.
- The hormone-sensitive intracellular Ca2+ pool likely consists of discrete units recruited concentration-dependently.