Effect of contractile duration on intracellular PO2 kinetics in Xenopus single skeletal myocytes.
Effect of contractile duration on intracellular PO2 kinetics in Xenopus single skeletal myocytes.
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收缩持续时间对非洲爪蟾单骨骼肌细胞内 PO2 动力学的影响。
DOI：
10.1152/japplphysiol.00874.2004
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
Hogan,MichaelC
中科院分区：
文献类型：
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作者：
Kindig,CaseyA;Howlett,RichardA;Hogan,MichaelC
有研究表明，骨骼肌o2摄取动力学遵循一阶控制模型。与此相一致的是，无论代谢扰动如何，在次最大工作强度下，V²应显示出1)相似的起始动力学和2)开关对称性。到目前为止，由于与o2可用性和纤维类型募集相关的许多混杂因素，在这个问题上尚未在全身研究中达成共识。为了测试单个肌细胞在不同的工作强度下是否表现出相似的细胞内Po2（PiO2）开启和关闭的瞬态动力学，我们研究了非洲爪蟾单个肌细胞（n= 8）在两轮电诱导的200（低）和400（高）毫秒收缩持续时间（每4秒收缩1次，试验之间15分钟，随机顺序）中通过磷光猝灭的PiO2。在高（24.1±3.2 Torr）与低（17.4±1.6 Torr）收缩时，PiO2的下降与V （o2）净增加成反比（P< 0.05）。然而，试验之间pio2从静止基线下降到结束收缩的平均反应时间（MRT；总变化的63%的时间）没有差异（高，77.8±11.5 vs低，76.1±13.6 s;P < 0.05）。收缩开始时的初始变化率，定义为ΔPiO2/MRT，高的明显大于低的（P< 0.05）。从收缩期结束到初始基线的PiO2off-transient MRT在高和低试验之间没有变化（高，83.3±18.3 vs低，80.4±21.6 s;P < 0.05）。这些数据表明，尽管青蛙分离的骨骼肌细胞的收缩持续时间和代谢需求不同，但pio2动力学是不变的。因此，这些发现表明，线粒体在受到增强的代谢刺激时，可以根据明显的一阶速率定律在收缩开始时做出更快的反应。
It has been suggested that skeletal muscle O2uptake (V̇o2) kinetics follow a first-order control model. Consistent with that, V̇o2should show both1) similar onset kinetics and2) an on-off symmetry across submaximal work intensities regardless of the metabolic perturbation. To date, consensus on this issue has not been reached in whole body studies due to numerous confounding factors associated with O2availability and fiber-type recruitment. To test whether single myocytes demonstrate similar intracellular Po2(PiO2) on- and off-transient kinetics at varying work intensities, we studiedXenopus laevissingle myocyte (n= 8) PiO2via phosphorescence quenching during two bouts of electrically induced isometric muscle contractions of 200 (low)- and 400 (high)-ms contraction duration (1 contraction every 4 s, 15 min between trials, order randomized). The fall in PiO2, which is inversely proportional to the net increase in V̇o2, was significantly greater (P< 0.05) during the high (24.1 ± 3.2 Torr) vs. low (17.4 ± 1.6 Torr) contraction bout. However, the mean response time (MRT; time to 63% of the overall change) for the fall in PiO2from resting baseline to end contractions was not different (high, 77.8 ± 11.5 vs. low, 76.1 ± 13.6 s;P> 0.05) between trials. The initial rate of change at contraction onset, defined as ΔPiO2/MRT, was significantly greater (P< 0.05) in high compared with low. PiO2off-transient MRT from the end of the contraction bout to initial baseline was unchanged (high, 83.3 ± 18.3 vs. low, 80.4 ± 21.6 s;P> 0.05) between high and low trials. These data revealed that PiO2dynamics in frog isolated skeletal myocytes were invariant despite differing contraction durations and, by inference, metabolic demands. Thus these findings demonstrate that mitochondria can respond more rapidly at the initial onset of contractions when challenged with an augmented metabolic stimulus in accordance with an apparent first-order rate law.