Clark B J, Acker M A, McCully K, Subramanian H V, Hammond R L, Salmons S, Chance B, Stephenson L W
Department of Pediatrics, Children's Hospital, Philadelphia 19105.
Am J Physiol. 1988 Feb;254(2 Pt 1):C258-66. doi: 10.1152/ajpcell.1988.254.2.C258.
Chronic stimulation converts skeletal muscle of mixed fiber type to a uniform muscle made up of type I, fatigue-resistant fibers. Here, the bioenergetic correlates of fatigue resistance in conditioned canine latissimus dorsi are assessed with in vivo phosphorus-31 nuclear magnetic resonance (31P-NMR) spectroscopy. After chronic electrical stimulation, five dogs underwent 31P-NMR spectroscopic and isometric tension measurements on conditioned and contralateral control muscle during stimulation for 200, 300, 500, and 800 ms of an 1,100-ms duty cycle. With stimulation, phosphocreatine (PCr) fell proportional to the degree of stimulation in both conditioned and control muscle but fell significantly less in conditioned muscle at all but the least intense stimulation period (200 ms). Isometric tension, expressed as a tension time index per gram muscle, was significantly greater in the conditioned muscle at the two longest stimulation periods. The overall small change in PCr and the lack of a plateau in tension observed in the conditioned muscle are similar to that seen in cardiac muscle during increased energy demand. This study indicates that the conditioned muscle's markedly enhanced resistance to fatigue is in part the result of its increased capacity for oxidative phosphorylation.
慢性刺激可将混合型纤维的骨骼肌转变为由I型抗疲劳纤维组成的均匀肌肉。在此，通过体内磷-31核磁共振（31P-NMR）光谱法评估了条件化犬背阔肌抗疲劳的生物能量相关性。在慢性电刺激后，五只犬在1100毫秒占空比的200、300、500和800毫秒刺激期间，对条件化肌肉和对侧对照肌肉进行了31P-NMR光谱和等长张力测量。随着刺激，磷酸肌酸（PCr）在条件化肌肉和对照肌肉中均与刺激程度成比例下降，但在除最轻微刺激期（200毫秒）外的所有刺激期，条件化肌肉中的下降明显较少。在两个最长刺激期，以每克肌肉的张力时间指数表示的等长张力在条件化肌肉中显著更大。条件化肌肉中PCr的总体微小变化以及未观察到张力平台期，与心肌在能量需求增加时的情况相似。这项研究表明，条件化肌肉对疲劳的显著增强抵抗力部分是其氧化磷酸化能力增加的结果。
