CAN THE BINDING OF CA2+ TO 2 REGULATORY SITES ON TROPONIN-C DETERMINE THE STEEP PCA-TENSION RELATIONSHIP OF SKELETAL-MUSCLE
CAN THE BINDING OF CA2+ TO 2 REGULATORY SITES ON TROPONIN-C DETERMINE THE STEEP PCA-TENSION RELATIONSHIP OF SKELETAL-MUSCLE
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DOI：
10.1073/pnas.77.8.4717
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发表时间：
1980-01-01
期刊：
影响因子：
--
通讯作者：
KAWAI, M
中科院分区：
文献类型：
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作者：
BRANDT, PW;COX, RN;KAWAI, M
采用高密度的实验点，采用最小二乘法对Hill方程进行拟合，确定了单皮肌纤维张力与Ca2+浓度的关系。张力/Ca2+关系斜率的平均Hill系数在5-6之间，pKd为。5.9. 由于肌钙蛋白C上有4个Ca2+结合位点，只有2个位点调节MgATP的水解，Ca2+结合对张力的调节可能受到其他因素的极大影响。一个重要的因素是完成一个周期所需的时间，一旦启动，相对于时间钙离子仍然结合到肌钙蛋白c。pCa/张力关系将转移到更高的pCa值，作为跨桥循环时间的比例，以Ca2+结合时间的增加。pCa/张力曲线可能随着张力的增加而逐渐向左移动，这是因为肌丝晶格中的应变逐渐增加了循环时间。这种左移将产生比实际Ca2+结合曲线更陡峭的pCa/张力关系。预估的pCa/张力曲线随周期时间的变化与早期实验对活性状态和Ca2+对最大缩短速度的影响的解释有关。
The relationship between tension and Ca2+ concentration in single skinned muscle fibers was determined with a high density of experimental points and the data fitted by a least squares method to the Hill equation. The mean Hill coefficient for the slope of the tension/Ca2+ relationship is between 5-6 and the pKd is .apprx. 5.9. Because there are 4 Ca2+ binding sites on troponin C and only 2 regulate hydrolysis of MgATP, the regulation of tension by Ca2+ binding is probably greatly modified by other factors. One important factor is the time required for a cross-bridge to complete a cycle once initiated, relative to the time Ca2+ remains bound to troponin C. The pCa/tension relationship will shift to higher pCa values as the ratio of cross-bridge cycle time to the Ca2+ bound time increases. The pCa/tension curve may progressively shift to the left with increase in tension because strain in the myofilament lattice progressively increases the cycle time. This left shift will produce a pCa/tension relationship that is steeper than the actual Ca2+ binding curve. The anticipated shift of the pCa/tension curve with cycle time bears on interpretations of earlier experiments on the active state and effects of Ca2+ on the maximal velocity of shortening.