慢肌纤维和快肌纤维中三磷酸腺苷光解后磷酸盐释放速率
Rate of phosphate release after photoliberation of adenosine 5'-triphosphate in slow and fast skeletal muscle fibers.
作者信息
He Z, Stienen G J, Barends J P, Ferenczi M A
机构信息
National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, United Kingdom.
出版信息
Biophys J. 1998 Nov;75(5):2389-401. doi: 10.1016/s0006-3495(98)77683-0.
Inorganic phosphate (Pi) release was determined by means of a fluorescent Pi-probe in single permeabilized rabbit soleus and psoas muscle fibers. Measurements of Pi release followed photoliberation of approximately 1.5 mM ATP by flash photolysis of NPE-caged ATP in the absence and presence of Ca2+ at 15 degrees C. In the absence of Ca2+, Pi release occurred with a slow rate of 11 +/- 3 microM . s-1 (n = 3) in soleus fibers and 23 +/- 1 microM . s-1 (n = 10) in psoas fibers. At saturating Ca2+ concentrations (pCa 4.5), photoliberation of ATP was followed by rapid force development. The initial rate of Pi release was 0.57 +/- 0.05 mM . s-1 in soleus (n = 13) and 4.7 +/- 0.2 mM . s-1 in psoas (n = 23), corresponding to a rate of Pi release per myosin head of 3.8 s-1 in soleus and 31.5 s-1 in psoas. Pi release declined at a rate of 0.48 s-1 in soleus and of 5.2 s-1 in psoas. Pi release in soleus was slightly faster in the presence of an ATP regenerating system but slower when 0.5 mM ADP was added. The reduction in the rate of Pi release results from an initial redistribution of cross-bridges over different states and a subsequent ADP-sensitive slowing of cross-bridge detachment.
通过荧光磷酸根探针测定了单个透化兔比目鱼肌和腰大肌纤维中的无机磷酸根（Pi）释放。在15℃下，在不存在和存在Ca2+的情况下，通过NPE-笼化ATP的闪光光解对约1.5 mM ATP进行光释放后，测量Pi释放。在不存在Ca2+的情况下，比目鱼肌纤维中Pi释放的速率较慢，为11±3 μM·s-1（n = 3），腰大肌纤维中为23±1 μM·s-1（n = 10）。在饱和Ca2+浓度（pCa 4.5）下，ATP的光释放后会迅速产生力。比目鱼肌中Pi释放的初始速率为0.57±0.05 mM·s-1（n = 13），腰大肌中为4.7±0.2 mM·s-1（n = 23），对应于比目鱼肌中每个肌球蛋白头部的Pi释放速率为3.8 s-1，腰大肌中为31.5 s-1。比目鱼肌中Pi释放以0.48 s-1的速率下降，腰大肌中以5.2 s-1的速率下降。在存在ATP再生系统的情况下，比目鱼肌中的Pi释放略快，但添加0.5 mM ADP时则较慢。Pi释放速率的降低是由于不同状态下横桥的初始重新分布以及随后ADP敏感的横桥分离减慢所致。
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