Jacobs-El J, Ashley W, Russell B
Department of Physiology and Biophysics, University of Illinois College of Medicine, Chicago 60612-7342.
Am J Physiol. 1993 Jul;265(1 Pt 1):C79-84. doi: 10.1152/ajpcell.1993.265.1.C79.
Metabolic profile and contractile isoform expression commonly define classic fiber types in skeletal muscle. Little is known about how metabolic requirements determine expression of fast IIx and slow myosin isoforms in muscles undergoing fiber type conversion. Tibialis anterior muscles from female New Zealand White rabbits were stimulated continuously at 10 Hz for 4-21 days. Quantitative fiber analysis was made for oxidative potential by histochemistry and for fast IIx and slow myosin mRNA content by in situ hybridization. In control muscle we found 3 +/- 0.27% fibers coexpress both fast IIx and slow myosin mRNA and so were not assignable to a classic fiber type. After stimulation, increase in fiber oxidative potential was detectable by 4 days and preceded IIx mRNA increases on a fiber-by-fiber basis. Slow myosin transcripts were detected by 7 days in fibers with higher oxidative levels. Coexpression of IIx and slow transcripts peaked at 22 +/- 2.5% of fibers by 7 days. IIx then declined, leaving slow myosin expressed in 62 +/- 0.45% of fibers by 3 wk. We conclude that during fiber type transformation individual fibers can transcribe two myosin mRNAs synchronously. Metabolic demand precedes and may be linked to IIx and slow myosin isoform expression.
代谢特征和收缩性同工型表达通常可定义骨骼肌中的经典纤维类型。关于代谢需求如何决定正在进行纤维类型转换的肌肉中快肌IIx和慢肌球蛋白同工型的表达，目前所知甚少。对雌性新西兰白兔的胫骨前肌以10Hz的频率持续刺激4 - 21天。通过组织化学对氧化潜能进行定量纤维分析，并通过原位杂交对快肌IIx和慢肌球蛋白mRNA含量进行分析。在对照肌肉中，我们发现3±0.27%的纤维同时表达快肌IIx和慢肌球蛋白mRNA，因此无法归为经典纤维类型。刺激后，4天时可检测到纤维氧化潜能增加，且在逐个纤维的基础上早于IIx mRNA的增加。在氧化水平较高的纤维中，7天时可检测到慢肌球蛋白转录本。到7天时，IIx和慢肌转录本的共表达在22±2.5%的纤维中达到峰值。随后IIx下降，到3周时，慢肌球蛋白在62±0.45%的纤维中表达。我们得出结论，在纤维类型转变过程中，单个纤维可同步转录两种肌球蛋白mRNA。代谢需求先于并可能与IIx和慢肌球蛋白同工型表达相关。
