Toepfer Christopher N, West Timothy G, Ferenczi Michael A
Molecular Medicine Section, National Heart and Lung Institute, Imperial College London, London, UK.
Laboratory of Molecular Physiology, NHLBI, National Institutes of Health, Bethesda, MD, USA.
J Physiol. 2016 Sep 15;594(18):5237-54. doi: 10.1113/JP272441. Epub 2016 Jul 24.
Regulatory light chain (RLC) phosphorylation has been shown to alter the ability of muscle to produce force and power during shortening and to alter the rate of force redevelopment (ktr ) at submaximal [Ca(2+) ]. Increasing RLC phosphorylation ∼50% from the in vivo level in maximally [Ca(2+) ]-activated cardiac trabecula accelerates ktr . Decreasing RLC phosphorylation to ∼70% of the in vivo control level slows ktr and reduces force generation. ktr is dependent on sarcomere length in the physiological range 1.85-1.94 μm and RLC phosphorylation modulates this response. We demonstrate that Frank-Starling is evident at maximal [Ca(2+) ] activation and therefore does not necessarily require length-dependent change in [Ca(2+) ]-sensitivity of thin filament activation. The stretch response is modulated by changes in RLC phosphorylation, pinpointing RLC phosphorylation as a modulator of the Frank-Starling law in the heart. These data provide an explanation for slowed systolic function in the intact heart in response to RLC phosphorylation reduction.
Force and power in cardiac muscle have a known dependence on phosphorylation of the myosin-associated regulatory light chain (RLC). We explore the effect of RLC phosphorylation on the ability of cardiac preparations to redevelop force (ktr ) in maximally activating [Ca(2+) ]. Activation was achieved by rapidly increasing the temperature (temperature-jump of 0.5-20ºC) of permeabilized trabeculae over a physiological range of sarcomere lengths (1.85-1.94 μm). The trabeculae were subjected to shortening ramps over a range of velocities and the extent of RLC phosphorylation was varied. The latter was achieved using an RLC-exchange technique, which avoids changes in the phosphorylation level of other proteins. The results show that increasing RLC phosphorylation by 50% accelerates ktr by ∼50%, irrespective of the sarcomere length, whereas decreasing phosphorylation by 30% slows ktr by ∼50%, relative to the ktr obtained for in vivo phosphorylation. Clearly, phosphorylation affects the magnitude of ktr following step shortening or ramp shortening. Using a two-state model, we explore the effect of RLC phosphorylation on the kinetics of force development, which proposes that phosphorylation affects the kinetics of both attachment and detachment of cross-bridges. In summary, RLC phosphorylation affects the rate and extent of force redevelopment. These findings were obtained in maximally activated muscle at saturating [Ca(2+) ] and are not explained by changes in the Ca(2+) -sensitivity of acto-myosin interactions. The length-dependence of the rate of force redevelopment, together with the modulation by the state of RLC phosphorylation, suggests that these effects play a role in the Frank-Starling law of the heart.
调节性轻链（RLC）磷酸化已被证明可改变肌肉在缩短过程中产生力量和功率的能力，并改变次最大[Ca(2+)]浓度下的力量重新发展速率（ktr）。在最大[Ca(2+)]激活的心脏小梁中，将RLC磷酸化水平从体内水平提高约50%可加速ktr。将RLC磷酸化水平降低至体内对照水平的约70%会减慢ktr并减少力量产生。ktr在1.85 - 1.94μm的生理肌节长度范围内依赖于肌节长度，并且RLC磷酸化可调节这种反应。我们证明，在最大[Ca(2+)]激活时，Frank-Starling机制是明显的，因此不一定需要细肌丝激活的[Ca(2+)]敏感性发生长度依赖性变化。伸展反应受RLC磷酸化变化的调节，这表明RLC磷酸化是心脏Frank-Starling定律的调节因子。这些数据为完整心脏中因RLC磷酸化减少而导致的收缩功能减慢提供了解释。
心肌中的力量和功率已知依赖于肌球蛋白相关调节性轻链（RLC）的磷酸化。我们探讨了RLC磷酸化对心脏制剂在最大激活[Ca(2+)]时重新发展力量（ktr）能力的影响。通过在生理肌节长度范围（1.85 - 1.94μm）内快速升高通透小梁的温度（温度跃升0.5 - 20ºC）来实现激活。使小梁在一系列速度下进行缩短斜坡运动，并改变RLC磷酸化程度。后者通过RLC交换技术实现，该技术可避免其他蛋白质磷酸化水平的变化。结果表明，将RLC磷酸化增加50%可使ktr加速约50%，与肌节长度无关，而将磷酸化降低30%相对于体内磷酸化获得的ktr会使ktr减慢约50%。显然，磷酸化会影响阶跃缩短或斜坡缩短后ktr的大小。使用双态模型，我们探讨了RLC磷酸化对力量发展动力学的影响，该模型提出磷酸化会影响横桥附着和脱离的动力学。总之，RLC磷酸化会影响力量重新发展的速率和程度。这些发现是在饱和[Ca(2+)]浓度下最大激活的肌肉中获得的，并且不能用肌动球蛋白相互作用的Ca(2+)敏感性变化来解释。力量重新发展速率的长度依赖性以及RLC磷酸化状态的调节表明，这些效应在心脏的Frank-Starling定律中起作用。
Zotero 插件
