Malmqvist U, Arner A, Makuch R, Dabrowska R
Department of Physiological Sciences, Lund University, Sölregatan 19, S-223 62 Lund, Sweden.
Pflugers Arch. 1996 Jun;432(2):241-7. doi: 10.1007/s004240050130.
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.
在豚鼠结肠带化学去表皮平滑肌纤维中研究了钙调蛋白在平滑肌收缩调节中的作用。钙调蛋白的一个19 kDa C末端片段使完全硫代磷酸化纤维中的力轻微降低（<5%），但在中等激活水平下使力降低约50%，且不影响轻链磷酸化水平。开发了一种在高镁离子浓度溶液中孵育的提取方法。蛋白质分析显示纤维中钙调蛋白量有选择性减少。每横截面积的最大主动力未受影响。主动力对钙离子的依赖性向较低钙离子浓度偏移且变得不那么陡峭。通过在含有纯化钙调蛋白的溶液中孵育，钙调蛋白提取的影响部分可以逆转。这些结果与以下假设一致：平滑肌细肌丝中的钙调蛋白抑制力的产生，并在调节平滑肌亚最大激活水平下横桥的协同附着中发挥作用。
