Russ David W
Department of Physical Therapy and Rehabilitation Science, University of Maryland-Baltimore School of Medicine, Baltimore, MD, USA.
Med Sci Sports Exerc. 2008 Jan;40(1):88-95. doi: 10.1249/MSS.0b013e318158e450.
The extent to which factors associated with muscle contraction activate Akt remains unclear. This study examined the influences of mechanical (active and passive tension), neural (activation frequency), and metabolic (glycogen depletion) factors on Akt activation during in situ contractions.
Muscle length was modified to produce comparable active contractile forces in three protocols, despite a twofold difference in stimulation frequency (15 vs 30 Hz); a fourth protocol used 30-Hz stimulation at optimal length to produce greater active forces. Two protocols were performed at optimal length, using 15- or 30-Hz stimulation (15 Hz opt and 30 H zopt, respectively). Two other protocols used 30-Hz stimulation at shortened or lengthened positions (30 Hz sub and 30 Hz supra, respectively).
The principal finding was that the 30-Hz opt protocol induced significantly greater Akt phosphorylation (approximately threefold relative to control) than did the other protocols, suggesting that activation of this signaling pathway is most sensitive to active tension. This result could not be attributed to differences in glycogen depletion, stimulation frequency, or fatigue. Despite producing the lowest force-time integral, the 30-Hz supra protocol, which had the greatest passive tension, exhibited a greater degree of Akt phosphorylation than did the 15-Hz opt and 30-Hz sub protocols. Although these differences were not significant, they suggest a possible secondary role for passive tension, which may interact with active tension in activating the Akt signaling pathway.
Akt activation seems more sensitive to active contractile tension than to passive tension. Activation frequency seems to play no role in the phosphorylation of Akt.
与肌肉收缩相关的因素激活Akt的程度尚不清楚。本研究考察了机械因素（主动和被动张力）、神经因素（激活频率）和代谢因素（糖原耗竭）对原位收缩过程中Akt激活的影响。
在三种实验方案中改变肌肉长度以产生相当的主动收缩力，尽管刺激频率相差两倍（15对30Hz）；第四个实验方案在最佳长度下使用30Hz刺激以产生更大的主动力。在最佳长度下进行两种实验方案，分别使用15Hz或30Hz刺激（分别为15Hz opt和30Hz opt）。另外两种实验方案在缩短或延长位置使用30Hz刺激（分别为30Hz sub和30Hz supra）。
主要发现是，30Hz opt实验方案诱导的Akt磷酸化显著高于其他实验方案（相对于对照组约为三倍），表明该信号通路的激活对主动张力最敏感。该结果不能归因于糖原耗竭、刺激频率或疲劳的差异。尽管产生的力-时间积分最低，但具有最大被动张力的30Hz supra实验方案显示出比15Hz opt和30Hz sub实验方案更高程度的Akt磷酸化。虽然这些差异不显著，但它们表明被动张力可能具有次要作用，其可能在激活Akt信号通路中与主动张力相互作用。
Akt激活似乎对主动收缩张力比对被动张力更敏感。激活频率似乎在Akt的磷酸化中不起作用。
