Tension transients initiated by photogeneration of MgADP in skinned skeletal muscle fibers.
Tension transients initiated by photogeneration of MgADP in skinned skeletal muscle fibers.
复制标题
由带皮骨骼肌纤维中 MgADP 的光生成引发的张力瞬变。
DOI：
10.1085/jgp.101.6.867
复制
发表时间：
1993
期刊：
影响因子：
--
通讯作者：
Walker,JW
中科院分区：
文献类型：
--
作者：
Lu,Z;Moss,RL;Walker,JW
在去皮骨骼肌纤维中加入MgADP可引起Ca（2+）激活的等长张力升高。这种张力增加的机制已被研究的快速光生成的ADP内皮肤的单纤维的兔腰肌。笼状ADP的光解（P2-1（2-硝基苯基）乙基腺苷5 '-二磷酸）导致等长收缩张力指数增加，表观速率常数kADP为9.6 +/- 0.3 s-1（平均值+/- SE，n = 28），标准条件下振幅PADP为4.9 +/- 0.3% Po（0.5 mM光释放MgADP，4 mM MgATP，pH 7.0，pCa 4.5，0.18 M离子强度，15 ℃）。PADP依赖于光释放MgADP的浓度以及MgATP的浓度。在三种MgATP浓度下的1/PADP与1/[MgADP]的图与MgADP和MgATP之间对横桥上相同位点的竞争一致。瞬时速率kADP也依赖于MgADP和MgATP的浓度。在4和1 mM MgATP下，kADP在0.1-0.5 mM MgADP的光释放后没有显著差异，但当在0.5 mM MgADP的光释放前加入3.5 mM MgADP时，kADP降低了28-40%。当MgATP从0.5到8 mM MgATP变化时，kADP加速约两倍。这些影响的MgATP和MgADP不容易占人口的高力产生的国家从逆转ADP解离过程。相反，结果表明，MgADP和MgATP之间的竞争在周期结束时的横桥减缓分离，导致力产生的横桥的积累。稳态Pi浓度从0.5 mM升高至30 mM导致kADP从10.2 +/- 0.5 s-1加速至27.8 +/- 1.8 s-1，表明张力升高涉及通过循环的Pi解离步骤的跨桥通量。
Addition of MgADP to skinned skeletal muscle fibers causes a rise in Ca(2+)-activated isometric tension. Mechanisms underlying this tension increase have been investigated by rapid photogeneration of ADP within skinned single fibers of rabbit psoas muscle. Photolysis of caged ADP (P2-1(2-nitrophenyl)ethyladenosine 5'-diphosphate) resulted in an exponential increase in isometric tension with an apparent rate constant, kADP, of 9.6 +/- 0.3 s-1 (mean +/- SE, n = 28) and an amplitude, PADP, of 4.9 +/- 0.3% Po under standard conditions (0.5 mM photoreleased MgADP, 4 mM MgATP, pH 7.0, pCa 4.5, 0.18 M ionic strength, 15 degrees C). PADP depended upon the concentration of photoreleased MgADP as well as the concentration of MgATP. A plot of 1/PADP vs. 1/[MgADP] at three MgATP concentrations was consistent with competition between MgADP and MgATP for the same site on the crossbridge. The rate of the transient, kADP, also depended upon the concentration of MgADP and MgATP. At both 4 and 1 mM MgATP, kADP was not significantly different after photorelease of 0.1-0.5 mM MgADP, but was reduced by 28-40% when 3.5 mM MgADP was added before photorelease of 0.5 mM MgADP. kADP was accelerated by about twofold when MgATP was varied from 0.5 to 8 mM MgATP. These effects of MgATP and MgADP were not readily accounted for by population of high force-producing states resulting from reversal of the ADP dissociation process. Rather, the results suggest that competition between MgADP and MgATP for crossbridges at the end of the cycle slows detachment leading to accumulation of force-generating crossbridges. Elevation of steady-state Pi concentration from 0.5 to 30 mM caused acceleration of kADP from 10.2 +/- 0.5 to 27.8 +/- 1.8 s-1, indicating that the tension rise involved crossbridge flux through the Pi dissociation step of the cycle.