Department of Surgery, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
PLoS One. 2013 Apr 12;8(4):e60986. doi: 10.1371/journal.pone.0060986. Print 2013.
Initiation of force generation during vascular smooth muscle contraction involves a rise in intracellular calcium ([Ca(2+)]i) and phosphorylation of myosin light chains (MLC). However, reversal of these two processes alone does not account for the force inhibition that occurs during relaxation or inhibition of contraction, implicating that other mechanisms, such as actin cytoskeletal rearrangement, play a role in the suppression of force. In this study, we hypothesize that forskolin-induced force suppression is dependent upon changes in actin cytoskeletal dynamics. To focus on the actin cytoskeletal changes, a physiological model was developed in which forskolin treatment of intact porcine coronary arteries (PCA) prior to treatment with a contractile agonist resulted in complete suppression of force. Pretreatment of PCA with forskolin suppressed histamine-induced force generation but did not abolish [Ca(2+)]i rise or MLC phosphorylation. Additionally, forskolin pretreatment reduced filamentous actin in histamine-treated tissues, and prevented histamine-induced changes in the phosphorylation of the actin-regulatory proteins HSP20, VASP, cofilin, and paxillin. Taken together, these results suggest that forskolin-induced complete force suppression is dependent upon the actin cytoskeletal regulation initiated by the phosphorylation changes of the actin regulatory proteins and not on the MLC dephosphorylation. This model of complete force suppression can be employed to further elucidate the mechanisms responsible for smooth muscle tone, and may offer cues to pathological situations, such as hypertension and vasospasm.
在血管平滑肌收缩过程中，力的产生始于细胞内钙离子浓度的升高([Ca(2+)]i)和肌球蛋白轻链（MLC）的磷酸化。然而，仅逆转这两个过程并不能解释在舒张或收缩抑制期间发生的力抑制，这表明其他机制，如肌动蛋白细胞骨架重排，在力的抑制中发挥作用。在这项研究中，我们假设福司可林诱导的力抑制依赖于肌动蛋白细胞骨架动力学的变化。为了关注肌动蛋白细胞骨架的变化，开发了一种生理模型，其中在使用收缩激动剂处理完整的猪冠状动脉（PCA）之前用福司可林处理，导致力完全抑制。福司可林预处理 PCA 可抑制组胺诱导的力产生，但不消除 [Ca(2+)]i 升高或 MLC 磷酸化。此外，福司可林预处理减少了组胺处理组织中的丝状肌动蛋白，并防止了组胺诱导的肌动蛋白调节蛋白 HSP20、VASP、丝切蛋白和桩蛋白磷酸化的变化。总之，这些结果表明，福司可林诱导的完全力抑制依赖于肌动蛋白调节蛋白磷酸化变化引发的肌动蛋白细胞骨架调节，而不是 MLC 的去磷酸化。这种完全力抑制的模型可用于进一步阐明平滑肌张力的机制，并可能为高血压和血管痉挛等病理情况提供线索。
