title: The effects of caldesmon extraction on mechanical properties of skinned smooth muscle fibre preparations.
abstract: The role of caldesmon in the regulation of smooth muscle contraction was investigated in chemically skinned smooth muscle fibres from the guinea-pig taenia coli. A 19-kDa C-terminal fragment of caldesmon gave a minor (<5%) reduction of force in fully thiophosphorylated fibres, but reduced force by about 50% at intermediate activation levels without affecting the level of light chain phosphorylation. An extraction procedure was developed using incubation in solutions containing high Mg2+ concentrations. Protein analysis revealed a selective decrease in the amount of caldesmon in the fibres. Maximal active force per cross-sectional area was unaffected. The Ca2+ dependence of active force was shifted towards lower Ca2+ concentrations and became less steep. The effects of extraction of caldesmon could in part be reversed by incubation in a solution containing purified caldesmon. The results are consistent with the hypothesis that caldesmon in smooth muscle thin filaments inhibits force generation and plays a role in regulating cooperative attachment of cross-bridges at sub-maximal levels of activation in smooth muscle.
authors.affiliation: Department of Physiological Sciences, Lund University, Sölregatan 19, S-223 62 Lund, Sweden.
authors.forename: U
authors.initials: U
authors.lastname: Malmqvist
authors.forename: A
authors.initials: A
authors.lastname: Arner
authors.forename: R
authors.initials: R
authors.lastname: Makuch
authors.forename: R
authors.initials: R
authors.lastname: Dabrowska
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D002118:Calcium / Q000378:metabolism; D002148:Calmodulin-Binding Proteins / Q000494:pharmacology / Q000502:physiology*; D005260:Female; D006168:Guinea Pigs; D006652:Histological Techniques; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000502:physiology*; D009124:Muscle Proteins / Q000378:metabolism; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D018994:Myosin Light Chains / Q000378:metabolism; D010446:Peptide Fragments / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects
chemical_list: D002148:Calmodulin-Binding Proteins; D009124:Muscle Proteins; D018994:Myosin Light Chains; D010446:Peptide Fragments; D002118:Calcium