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Expression of CPI‐17 and myosin phosphatase correlates with Ca 2+ sensitivity of protein kinase C‐induced contraction in rabbit smooth muscle
Author(s) -
Woodsome Terence P.,
Eto Masumi,
Everett Allen,
Brautigan David L.,
Kitazawa Toshio
Publication year - 2001
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2001.t01-1-00553.x
Subject(s) - phosphatase , myosin , contraction (grammar) , chemistry , rabbit (cipher) , biophysics , phosphorylation , kinase , muscle contraction , protein kinase a , microbiology and biotechnology , medicine , endocrinology , biochemistry , biology , statistics , mathematics
1 Various smooth muscles have unique contractile characteristics, such as the degree of Ca 2+ sensitivity induced by physiological and pharmacological agents. Here we evaluated six different rabbit smooth muscle tissues for protein kinase C (PKC)‐induced Ca 2+ sensitization. We also examined the expression levels of myosin light chain phosphatase (MLCP), the MLCP inhibitor phosphoprotein CPI‐17, and the thin filament regulator h‐calponin. 2 Immunohistochemical and Western blot analyses indicated that CPI‐17 was found primarily in smooth muscle, although expression varied among different tissues. Vascular muscles contained more CPI‐17 than visceral muscles, with further distinction existing between tonic and phasic subtypes. For example, the tonic femoral artery possessed approximately 8 times the cellular CPI‐17 concentration of the phasic vas deferens. 3 In contrast to CPI‐17 expression patterns, phasic muscles contained more MLCP myosin‐targeting subunit than tonic tissues. Calponin expression was not statistically different. 4 Addition of phorbol ester to α‐toxin‐permeabilized smooth muscle caused an increase in contraction and phosphorylation of both CPI‐17 and myosin light chain (MLC) at submaximal [Ca 2+ ] i . These responses were several‐fold greater in femoral artery as compared to vas deferens. 5 We conclude that the expression ratio of CPI‐17 to MLCP correlates with the Ca 2+ sensitivities of contraction induced by a PKC activator. PKC stimulation of arterial smooth muscle with a high CPI‐17 and low MLCP expression generated greater force and MLC phosphorylation than stimulation of visceral muscle with a relatively low CPI‐17 and high MLCP content. This implicates CPI‐17 inhibition of MLCP as an important component in modulating vascular muscle tone.