AJP - Cell Physiology, Vol 246, Issue 3 288-C292, Copyright © 1984 by American Physiological Society
Heterogeneity in regard to enzymes and metabolites within individual muscle fibers
C. S. Hintz, M. M. Chi and O. H. Lowry
The possibility of variability along individual rat and human muscle fibers
was assessed for four enzymes and four substances responsive to
stimulation. Heterogeneity was determined by the differences between ends
of fiber segments several millimeters long and by fluctuations in
successive samples along the entire length of such segments. Among the
enzymes, a cytosolic enzyme, lactate dehydrogenase, varied the least:
average coefficient of variation (CV) of 5%. This is only a little greater
than the analytic error. On the other hand, the CV for a mitochondrial
enzyme, fumarase, was 13%. A mixed cytosolic-mitochondrial enzyme, malate
dehydrogenase, was intermediate (CV of 9%). The CV for glycogen
phosphorylase, which is normally bound to glycogen particles, was 34% along
one fiber segment. Among the nonenzyme components, average CVs in
stimulated fibers were 34, 20, 7, and 7%, respectively, for glucose
6-phosphate, phosphocreatine, ATP, and malate. Major differences were not
random but developed gradually over distances of 0.5-2 mm along the fibers,
and in some cases significant correlations between enzyme and metabolite
levels were demonstrable.
