THE INHIBITION OF RABBIT SKELETAL-MUSCLE CONTRACTION BY HYDROGEN-IONS AND PHOSPHATE
THE INHIBITION OF RABBIT SKELETAL-MUSCLE CONTRACTION BY HYDROGEN-IONS AND PHOSPHATE
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DOI：
10.1113/jphysiol.1988.sp016909
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发表时间：
1988-01-01
影响因子：
5.5
通讯作者：
PATE, E
中科院分区：
文献类型：
--
作者：
COOKE, R;FRANKS, K;PATE, E
1.用甘油化的兔腰肌研究了磷酸盐和质子对肌肉收缩力学和能量学的影响。2.通过在10 ℃加入Ca 2+（pCa 4-5）使纤维完全活化。C.在等渗负载夹具中测量收缩速度，并且通过施加纤维长度的一系列阶跃变化来测量未加载纤维的速度。使用酶系统将ADP产生与还原的烟酰胺腺嘌呤二核苷酸（NADH）偶联并通过光密度测量NADH的消耗来监测纤维ATP酶活性。3.在pH7.0和3 mM-磷酸盐时，等长张力（Po）为13.2 ± 1.5。0.9 N/cm 2（平均值±. S.E.M. n = 10个观察值），最大收缩速度（Vmax）为1.63 ± 0.05。0.05长度/s（n = 5），ATP酶活性为1.27 ± 0.001。0.12 s-1肌球蛋白头-1（n = 35）。在pH 7.0下，将磷酸盐从3 mM增加到20 mM不影响Vmax，导致ATP酶活性小幅降低（15-20%），并使Po降低约20%。在3 mM磷酸盐时，将pH从7改变为6，使Po降低45%，Vmax和ATP酶活性降低25- 30%。改变pH值和磷酸盐的影响是大约加性的所有参数测量。低pH和高浓度磷酸盐对这些参数的抑制是可逆的。4.力-速度关系采用非线性最小二乘法由Hill方程拟合。描述曲率的参数a/Po的值为0.20。力-速度关系的曲率不因加入磷酸盐或pH值的变化而改变。这些数据提供了关于肌动球蛋白相互作用的动力学和肌肉疲劳过程的信息。这些数据是一致的跨桥动力学模型，其中磷酸盐被释放在一个步骤中，涉及一个快速的平衡状态之间的动力冲程。质子的抑制作用更为复杂，可能涉及对蛋白质结构的特异性影响较小。6.在活骨骼肌的中度疲劳期间，已知MgATP浓度保持大约恒定在4 mM，磷酸盐从3增加到20 mM，质子从0.1增加到1 μ M。这些数据表明，在中度疲劳期间观察到的PO的抑制可以解释为磷酸盐和质子的水平增加，并且纤维Vmax和ATP酶活性的抑制可以解释为质子的增加。
1. The effects of phosphate and protons on the mechanics and energetics of muscle contraction have been investigated using glycerinated rabbit psoas muscle. 2. Fibres were fully activated by addition of Ca2+ (pCa 4-5) at 10.degree. C. The velocities of contraction were measured in isotonic load clamps, and the velocities of unloaded fibres were measured by applying a series of step changes in fibre length. Fibre ATPase activity was monitored using an enzyme system to couple ADP production to reduced nicotinamide-adenine dinucleotide (NADH) and measuring the depletion of NADH by optical density. 3. At pH 7.0 and 3 mM-phosphate, isometric tension (Po) was 13.2 .+-. 0.9 N/cm2 (mean .+-. S.E.M., n = 10 observations), the maximum contraction velocity (Vmax) was 1.63 .+-. 0.05 lengths/s (n = 5) and the ATPase activity was 1.27 .+-. 0.12 s-1 myosin head-1 (n = 35). Increasing phosphate from 3 to 20 mM at pH 7.0 does not affect Vmax, causes a small decrease in the ATPase activity (15-20%) and decreases Po by approximately 20%. Changing pH from 7 to 6 at 3 mM-phosphate decreases Po by 45% and both Vmax and ATPase activity by 25-30%. The effects of changing both pH and phosphate were approximately additive for all parameters measured. The inhibition of these parameters by low pH and high concentration of phosphate was reversible. 4. The force-velocity relation was fitted by the Hill equation using a non-linear least-squares method. The value of the parameter which describes the curvature, a/Po, was 0.20. The curvature of the force-velocity relation was not changed by addition of phosphate or by changes in pH. 5. These data provide information on both the kinetics of the actomyosin interaction and on the process of muscle fatigue. The data are consistent with models of cross-bridge kinetics in which phosphate is released within the powerstroke in a step involving a rapid equilibrium between states. The inhibition by protons is more complex, and may involve less specific effects on protein structure. 6. During moderate fatigue of living skeletal muscle, MgATP concentration is known to remain approximately constant at 4 mM, phosphate to increase from 3 to 20 mM, and protons from 0.1 to 1 .mu.M. The data suggest that much of the inhibition of Po observed during moderate fatigue can be explained by the increased levels of phosphate and protons, and that much of the inhibition of fibre Vmax and ATPase activity can be explained by the increase in protons.