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Mechanisms responsible for quantal Ca2+ release from inositol trisphosphate-sensitive calcium stores
J B Parys1, L Missiaen, H D Smedt
1Laboratorium voor Fysiologie, Campus Gasthuisberg O/N-K.U.Leuven, B-3000 Leuven, Belgium.
Pflugers Archiv : European Journal of Physiology
|July 1, 1996
Summary
Cellular activation triggers inositol trisphosphate (InsP3) production, leading to quantal calcium (Ca2+) release via InsP3 receptors (InsP3Rs). This partial Ca2+ release mechanism, crucial for cell signaling, remains incompletely understood.
Area of Science:
- Cellular Biology
- Molecular Physiology
- Biochemistry
Background:
- Hormones, growth factors, and neurotransmitters activate cells, increasing inositol trisphosphate (InsP3) levels.
- Activated InsP3 receptors (InsP3Rs) mediate calcium (Ca2+) release from intracellular stores.
- Submaximal agonist doses induce a graded, partial Ca2+ release, termed 'quantal Ca2+ release'.
Purpose of the Study:
- To critically review and evaluate proposed mechanisms for quantal Ca2+ release.
- To assess the functional importance of different InsP3R regulation pathways.
- To elucidate the underlying molecular mechanisms of InsP3-induced Ca2+ release.
Main Methods:
- Literature review of experimental evidence.
- Critical analysis of proposed mechanistic models.
- Evaluation of functional data from cellular studies.
Main Results:
- Quantal Ca2+ release is characterized by an initial rapid phase followed by a slower phase.
- Proposed mechanisms include InsP3R heterogeneity, inactivation, and Ca2+-dependent regulation.
- A Ca2+-mediated conformational change in InsP3Rs is the most probable key feature.
Conclusions:
- Quantal Ca2+ release allows Ca2+ stores to act as increment detectors for cellular responses.
- While Ca2+-mediated conformational changes are likely involved, the precise mechanism remains unclear.
- Multiple mechanisms may operate concurrently in intact cells to regulate InsP3-induced Ca2+ release.