Differences in calmodulin and calmodulin-binding proteins in phasic and tonic smooth muscles.
To determine whether densities of calmodulin (CaM) and CaM-binding proteins are related to phasic and tonic behavior of smooth muscles, we quantified these proteins in the opossum esophageal body (EB) and lower esophageal sphincter (LES), which represent phasic and tonic smooth muscles, respectively. Gel electrophoresis, immunoprecipitation, Western blot, and hemagglutinin epitope-tagged CaM (HA-CaM) overlay assay with quantitative scanning densitometry and phosphorylation measurements were used. Total protein content in the two smooth muscles was similar (approximately 30 mg protein/g frozen tissue). Total tissue concentration of CaM was significantly (25%) higher in EB than in LES (P < 0.05). HA-CaM-binding proteins were qualitatively similar in LES and EB extracts. Myosin, myristoylated alanine-rich C kinase substrate protein, Ca(2+)/CaM kinase II, and calponin contents were also similar in the two muscles. However, content and total activity of myosin light chain kinase (MLCK) and content of caldesmon (CaD) were three- to fourfold higher in EB than in LES. Increased CaM and MLCK content may allow for a wide range of contractile force varying from complete relaxation in the basal state to a large-amplitude, high-velocity contraction in EB phasic muscle. Increased content of CaD, which provides a braking mechanism on contraction, may further contribute to the phasic contractile behavior. In contrast, low CaM, MLCK, and CaD content may be responsible for a small range of contractile force seen in tonic muscle of LES.
Szymanski
Pawel T
PT
Center for Swallowing and Motility Disorders, Harvard Medical School, West Roxbury, Massachusetts 02132, USA.
Szymanska
Grazyna
G
Goyal
Raj K
RK
D000818:Animals; D015153:Blotting, Western; D002135:Calcium-Binding Proteins / Q000032:analysis*; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000032:analysis / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism*; D002148:Calmodulin-Binding Proteins / Q000032:analysis; D004943:Esophagogastric Junction / Q000378:metabolism; D004947:Esophagus; D006388:Hemagglutinins; D008840:Microfilament Proteins; D009119:Muscle Contraction / Q000502:physiology*; D009130:Muscle, Smooth / Q000737:chemistry* / Q000201:enzymology*; D009219:Myosin-Light-Chain Kinase / Q000032:analysis / Q000378:metabolism; D019814:Myristic Acid / Q000378:metabolism; D009893:Opossums; D010766:Phosphorylation; D011493:Protein Kinase C / Q000032:analysis / Q000378:metabolism; D011994:Recombinant Proteins; D000096985:Calponins
D002135:Calcium-Binding Proteins; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D006388:Hemagglutinins; D008840:Microfilament Proteins; D009219:Myosin-Light-Chain Kinase; D019814:Myristic Acid; D011493:Protein Kinase C; D011994:Recombinant Proteins; D000096985:Calponins