title: Expression of CPI-17 and myosin phosphatase correlates with Ca(2+) sensitivity of protein kinase C-induced contraction in rabbit smooth muscle.
abstract: 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 alpha-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.
authors.affiliation: Department of Physiology and Biophysics, Georgetown University Medical Center, Washington, DC 20007, USA.
authors.forename: T P
authors.initials: TP
authors.lastname: Woodsome
authors.forename: M
authors.initials: M
authors.lastname: Eto
authors.forename: A
authors.initials: A
authors.lastname: Everett
authors.forename: D L
authors.initials: DL
authors.lastname: Brautigan
authors.forename: T
authors.initials: T
authors.lastname: Kitazawa
mesh_terms: D000199:Actins / Q000032:analysis / Q000096:biosynthesis; D000818:Animals; D001011:Aorta / Q000201:enzymology; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000032:analysis / Q000096:biosynthesis; D002273:Carcinogens / Q000494:pharmacology; D005263:Femoral Artery / Q000201:enzymology; D019204:GTP-Binding Proteins / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D007150:Immunohistochemistry; D008297:Male; D008840:Microfilament Proteins; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009124:Muscle Proteins / Q000032:analysis / Q000096:biosynthesis / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000201:enzymology*; D018994:Myosin Light Chains / Q000378:metabolism; D043263:Myosin-Light-Chain Phosphatase; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000032:analysis / Q000096:biosynthesis / Q000378:metabolism*; D010750:Phosphoproteins / Q000032:analysis / Q000096:biosynthesis / Q000378:metabolism*; D010766:Phosphorylation; D011169:Portal Vein / Q000201:enzymology; D011493:Protein Kinase C / Q000378:metabolism*; D011817:Rabbits; D014132:Trachea / Q000201:enzymology; D001743:Urinary Bladder / Q000201:enzymology; D014649:Vas Deferens / Q000201:enzymology; D000096985:Calponins
chemical_list: D000199:Actins; D002118:Calcium; D002135:Calcium-Binding Proteins; D002273:Carcinogens; D019204:GTP-Binding Proteins; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D008840:Microfilament Proteins; D009124:Muscle Proteins; D018994:Myosin Light Chains; D043263:Myosin-Light-Chain Phosphatase; D015240:Phorbol 12,13-Dibutyrate; D010749:Phosphoprotein Phosphatases; D010750:Phosphoproteins; D011493:Protein Kinase C; D000096985:Calponins; C491521:CPI-17 protein, Oryctolagus cuniculus