Chitano Pasquale, Wang Lu, Tin Gabrielle Y Y, Ikebe Mitsuo, Paré Peter D, Seow Chun Y
Centre for Heart Lung Innovation - St Paul's Hospital, University of British Columbia, Vancouver, BC, Canada, V6Z 1Y6.
Respiratory Division, Department of Medicine, University of British Columbia, Vancouver, BC, Canada, V6Z 1Y6.
J Cell Sci. 2017 Aug 1;130(15):2468-2480. doi: 10.1242/jcs.202812. Epub 2017 Jun 8.
Smooth muscle is able to function over a much broader length range than striated muscle. The ability to maintain contractility after a large length change is thought to be due to an adaptive process involving restructuring of the contractile apparatus to maximize overlap between the contractile filaments. The molecular mechanism for the length-adaptive behavior is largely unknown. In smooth muscle adapted to different lengths we quantified myosin monomers, basal and activation-induced myosin light chain (MLC) phosphorylation, shortening velocity, power output and active force. The muscle was able to generate a constant maximal force over a two fold length range when it was allowed to go through isometric contraction/relaxation cycles after each length change (length adaptation). In the relaxed state, myosin monomer concentration and basal MLC phosphorylation decreased linearly, while in the activated state activation-induced MLC phosphorylation and shortening velocity/power output increased linearly with muscle length. The results suggest that recruitment of myosin monomers and oligomers into the actin filament lattice (where they form force-generating filaments) occurs during muscle adaptation to longer length, with the opposite occurring during adaptation to shorter length.
与横纹肌相比，平滑肌能够在更广泛的长度范围内发挥功能。在长度发生较大变化后仍能保持收缩能力，这被认为是由于一个适应性过程，该过程涉及收缩装置的重组，以使收缩细丝之间的重叠最大化。长度适应性行为的分子机制在很大程度上尚不清楚。在适应不同长度的平滑肌中，我们对肌球蛋白单体、基础和激活诱导的肌球蛋白轻链（MLC）磷酸化、缩短速度、功率输出和主动力进行了量化。当肌肉在每次长度变化后进行等长收缩/舒张循环（长度适应）时，它能够在两倍的长度范围内产生恒定的最大力。在松弛状态下，肌球蛋白单体浓度和基础MLC磷酸化呈线性下降，而在激活状态下，激活诱导的MLC磷酸化以及缩短速度/功率输出随肌肉长度呈线性增加。结果表明，在肌肉适应更长长度的过程中，肌球蛋白单体和寡聚体被募集到肌动蛋白丝晶格中（在那里它们形成产生力的细丝），而在适应更短长度的过程中则发生相反的情况。
