title: Effects of the constitutively active proteolytic fragment of protein kinase C on the contractile properties of demembranated smooth muscle fibres.
abstract: The role of protein kinase C (PKC) in regulating the contractile state of smooth muscle was investigated using the constitutively active catalytic fragment of PKC (PKM) with skinned (demembranated) chicken gizzard fibres. PKM attenuated a submaximal contraction in gizzard smooth muscle skinned fibres, but not in rabbit cardiac skinned fibres. PKM-mediated relaxation of submaximal contractions of smooth muscle was accompanied by a reduction in the rate of ATP hydrolysis in the fibre and by phosphorylation of the 20 kDa light chain of gizzard myosin at the PKC sites (serine-1, serine-2 and threonine-9). In addition, several other endogenous proteins were phosphorylated by PKM. However, the inhibitory effects on tension and ATPase are consistent with the biochemical effects of PKC-catalysed phosphorylation of myosin, i.e. reduction of the actin-activated MgATPase activity of myosin prephosphorylated at serine-19 by myosin light chain kinase. Pretreatment of skinned fibres with PKM and ATP gamma S in the absence of Ca2+ had no inhibitory effect on the subsequent submaximal Ca(2+)-activation of force. Consistent with this observation, PKC was not able to utilize ATP gamma S as a substrate, confirming that the observed effects were the result of PKM-catalysed protein phosphorylation. We suggest that PKC may have two distinct effects on smooth muscle contraction: translocation of PKC to the sarcolemma on stimulation results in phosphorylation of a protein(s) other than myosin and a slow, sustained contraction; in some circumstances PKC may undergo proteolysis to PKM resulting in myosin phosphorylation at PKC-specific sites, a reduction in ATPase activity and relaxation of the muscle.
authors.affiliation: Department of Medical Biochemistry, University of Calgary, Alberta, Canada.
authors.forename: J E
authors.initials: JE
authors.lastname: Parente
authors.forename: M P
authors.initials: MP
authors.lastname: Walsh
authors.forename: W G
authors.initials: WG
authors.lastname: Kerrick
authors.forename: P E
authors.initials: PE
authors.lastname: Hoar
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D002462:Cell Membrane / Q000502:physiology; D002645:Chickens; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D009218:Myosins / Q000378:metabolism; D010446:Peptide Fragments / Q000494:pharmacology*; D010449:Peptide Mapping; D010766:Phosphorylation; D011493:Protein Kinase C / Q000494:pharmacology*
chemical_list: D010446:Peptide Fragments; D011493:Protein Kinase C; D000251:Adenosine Triphosphatases; D009218:Myosins