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Differences in calmodulin and calmodulin-binding proteins in phasic and tonic smooth muscles
Pawel T Szymanski1, Grazyna Szymanska, Raj K Goyal
1Center for Swallowing and Motility Disorders, Harvard Medical School, West Roxbury, Massachusetts 02132, USA.
American Journal of Physiology. Cell Physiology
|December 18, 2001
Summary
Smooth muscle calmodulin (CaM) and myosin light chain kinase (MLCK) levels differ between phasic esophageal body and tonic lower esophageal sphincter muscles. Higher CaM and MLCK in the esophageal body support varied contractions, while lower levels in the sphincter enable sustained tone.
Area of Science:
- Physiology
- Molecular Biology
- Gastroenterology
Background:
- Smooth muscle function varies between phasic and tonic behaviors.
- Calmodulin (CaM) and its binding proteins are crucial for smooth muscle contraction.
- Differences in protein densities may underlie distinct muscle contractile properties.
Purpose of the Study:
- To investigate the relationship between calmodulin (CaM) and CaM-binding protein densities and the phasic/tonic behavior of smooth muscles.
- To quantify CaM and related proteins in the opossum esophageal body (EB) and lower esophageal sphincter (LES).
Main Methods:
- Quantitative analysis using gel electrophoresis, immunoprecipitation, and Western blot.
- Hemagglutinin epitope-tagged CaM (HA-CaM) overlay assay with densitometry.
- Measurement of protein phosphorylation and content, including CaM, myosin light chain kinase (MLCK), and caldesmon (CaD).
Main Results:
- Total CaM concentration was significantly higher (25%) in the phasic EB compared to the tonic LES.
- Myosin light chain kinase (MLCK) and caldesmon (CaD) content and activity were 3-4 fold higher in EB than LES.
- Key CaM-binding proteins like myosin, Ca(2+)/CaM kinase II, and calponin were similar in both muscles.
Conclusions:
- Higher CaM and MLCK in the EB may facilitate a wider range of contractile forces characteristic of phasic muscle.
- Increased CaD in the EB might contribute to phasic contractile regulation.
- Lower levels of CaM, MLCK, and CaD in the LES may explain its tonic contractile behavior and limited force range.