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 guineapig taenia coli. A 19-kDa C-terminal fragment of caldesmon gave a minor (2+ 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.