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Calcium release mechanisms in smooth muscle
1Department of Pharmacology, Faculty of Medicine, University of Tokyo, Japan.
Japanese Journal of Pharmacology
|December 1, 1990
Summary
Smooth muscle intracellular calcium stores have two release mechanisms: calcium-induced calcium release (CICR) and inositol 1,4,5-trisphosphate (IP3)-induced calcium release (IICR). Ryanodine selectively removes CICR, revealing IICR
Area of Science:
- Physiology
- Cell Biology
- Biochemistry
Background:
- Intracellular calcium (Ca2+) signaling is crucial for smooth muscle contraction.
- Smooth muscle Ca2+ stores possess distinct release mechanisms, including Ca-induced Ca release (CICR) and IP3-induced Ca release (IICR).
Purpose of the Study:
- To investigate the properties of intracellular Ca2+ stores in guinea pig smooth muscles.
- To differentiate the roles of CICR and IICR in agonist-induced contractions.
Main Methods:
- Saponin-skinned smooth muscle fiber bundles were utilized.
- Fluorescent Ca2+ indicators were employed to monitor Ca2+ dynamics.
- Ryanodine was used for 'functional removal' of the S alpha compartment.
Main Results:
- Smooth muscle Ca2+ stores comprise two compartments: S alpha (CICR and IICR) and S beta (IICR only).
- CICR is activated by >1 microM Ca2+ and is ryanodine-sensitive.
- IICR exhibits Ca2+-dependent regulation, with a positive feedback effect at low Ca2+ concentrations.
- Ryanodine treatment selectively removes S alpha's Ca2+ uptake capacity.
- Ca2+ release from S alpha is vital for the initial phase of agonist-induced contractions, particularly in pulmonary arteries.
Conclusions:
- The S alpha compartment plays a significant role in initiating smooth muscle contractions via Ca2+ release.
- Understanding these Ca2+ release mechanisms is key to comprehending smooth muscle physiology and pathophysiology.