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Abstract
31Phosphorus nuclear magnetic resonance spectroscopy was used to examine skeletal
muscle in 29 patients with mitochondrial myopathy, 9 male and 20 female. Gastrocnemius
was investigated in 15 patients and 30 normal subjects and finger flexor muscle (flexor
digitorum superficialis, fds) in 24 patients and 35 normal controls. Both muscles
were studied in 10 of the patients. Results were abnormal (outside the full range
of normal values) in all but 2 patients. In 86% of patients (25/29) abnormalities
were detected in resting muscle. In most cases there was a low phosphocreatine/ATP
ratio, high calculated free [ADP] and low phosphorylation potential. At rest, abnormality
was detected with equal ease in fds and gastrocnemius. Exercise and recovery increased
the sensitivity of MRS in detecting abnormal metabolism. Finger flexion was better
tolerated by patients than plantar flexion and gave bigger changes in metabolite concentrations
and intracellular pH. Thus, results from fds were more easily differentiated from
normal. Exercise duration was significantly shorter than in controls while phosphocreatine
depletion was more rapid than normal, consistent with a shortfall in mitochondrial
ATP synthesis. Nearly all patients (25/27, 93%) showed abnormalities during recovery
from exercise. [ADP] was high during exercise and its recovery was delayed, providing
increased drive for oxidative phosphorylation. Phosphocreatine resynthesis during
recovery (which reflects oxidative ATP synthesis) was slow both in absolute terms
and in relation to [ADP]. Recovery of intracellular pH after exercise was significantly
more rapid than normal, consistent with an upregulation of proton efflux.(ABSTRACT
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