Differences in calmodulin and calmodulin-binding proteins in phasic and tonic smooth muscles

Abstract

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 (∼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, Ca2+/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.

Phosphorylated HSP27 essential for acetylcholine-induced association of RhoA with PKCα

“…The different patterns of contractions have been attributed to regional differences in the gene transcription and synthesis of nitric oxide synthetase in the colonic myenteric plexus (33). On the basis of their functional behavior, visceral smooth muscles have been classified into sphincteric and nonsphincteric smooth muscles that represent tonic and phasic muscles (11,16,31). Phasic muscle shows a very wide range of contractile activity that varies from a fully relaxed basal state to a large-amplitude rapid contraction and rapid relaxation response.…”

Effect of O-4-ethoxyl-butyl-berbamine in combination with pegylated liposomal doxorubicin on advanced hepatoma in mice

“…CaM is a ubiquitous calcium-binding protein that is responsible for many intracellular actions of calcium [21][22][23][24][25][26][27][28][29][30] . Lot of evidences suggest that CaM not only plays an important role in the proliferation of normal cells, but also is related to hepatoma growth [2,31] .…”

Mechanisms involved in carbachol‐induced Ca2+ sensitization of contractile elements in rat proximal and distal colon

“…However, the GTP-induced Ca 2 þ sensitization was more potent in the proximal than in the distal colon (Figure 2). It was reported that the amount of contractile proteins, the composition of their isoforms and the extent of their phosphorylation are different between phasic and tonic smooth muscle tissues (Lorenz et al, 2002;Szymanski et al, 2002). Ca 2 þ -induced contractions in the proximal colon were smaller than those in the distal colon.…”