Watchko J F, Sieck G C
Department of Pediatrics, Magee-Womens Hospital, University of Pittsburgh School of Medicine, Pennsylvania 15213.
J Appl Physiol (1985). 1993 Sep;75(3):1341-7. doi: 10.1152/jappl.1993.75.3.1341.
We correlated the fatigue resistance (FR) of the costal diaphragm (DIA) and external abdominal oblique (EAO) of the rat during postnatal development with their respective 1) myosin heavy chain (MHC) phenotypes and 2) oxidative capacities [indexed by quantitative measurements of succinic dehydrogenase (SDH) enzyme activity]. FR was measured in vitro during isometric contractions with the use of the Burke fatigue test. FR of the DIA and EAO was high in newborns and declined during postnatal development. SDH activity was uniformly low in neonatal DIA and EAO and increased during early postnatal development before declining to adult levels. FR did not significantly correlate with SDH activity (r2 = 0.01) but did relate to the MHC phenotype as indexed by the ratio of adult MHC isoform content (slow + IIa + IIx + IIb) to developmental MHC isoform content (slow + neonatal; r2 = 0.88, P < 0.01). Stepwise regression revealed that neonatal MHC expression alone accounted for 60% of the developmental variance in FR. The correlation between FR and MHC phenotype was improved if SDH was also considered, i.e., the ratio of SDH to MHC phenotype (r2 = 0.99, P < 0.01). We conclude that FR of respiratory muscle during development relates to a balance between the energetic demands of the muscle contractile proteins as reflected by MHC isoform composition and its oxidative capacity with MHC phenotype alone exerting a strong predictive effect on FR.
我们将出生后发育过程中大鼠肋膈膜（DIA）和腹外斜肌（EAO）的抗疲劳能力（FR）与其各自的1）肌球蛋白重链（MHC）表型和2）氧化能力[通过琥珀酸脱氢酶（SDH）酶活性的定量测量来衡量]进行了关联。使用伯克疲劳试验在体外等长收缩过程中测量FR。DIA和EAO的FR在新生儿中较高，并在出生后发育过程中下降。新生儿DIA和EAO中的SDH活性均较低，并在出生后早期发育过程中增加，然后降至成年水平。FR与SDH活性无显著相关性（r2 = 0.01），但与以成年MHC亚型含量（慢 + IIa + IIx + IIb）与发育MHC亚型含量（慢 + 新生儿）之比为指标的MHC表型相关（r2 = 0.88，P < 0.01）。逐步回归显示，仅新生儿MHC表达就占FR发育变异的60%。如果同时考虑SDH，即SDH与MHC表型之比，则FR与MHC表型之间的相关性会得到改善（r2 = 0.99，P < 0.01）。我们得出结论，发育过程中呼吸肌的FR与肌肉收缩蛋白的能量需求之间的平衡有关，这通过MHC亚型组成反映，并且其氧化能力与MHC表型单独对FR具有很强的预测作用。
