AJP - Regulatory, Integrative and Comparative Physiology, Vol 267, Issue 2 408-R414, Copyright © 1994 by American Physiological Society
Exercise-induced 31P-NMR metabolic response of human wrist flexor muscles during partial neuromuscular blockade
M. Mizuno, A. Horn, N. H. Secher and B. Quistorff
Copenhagen Muscle Research Center, Denmark.
The effects of a depolarizing (decamethonium, DECA) and a nondepolarizing
neuromuscular blocking agent (vecuronium, VECU) on the phosphorus-31
nuclear magnetic resonance (31P-NMR)-detected metabolic response to muscle
contractions were studied separately in six healthy untrained males.
Subjects who showed splitting of the P(i) peak during graded rhythmic
forearm exercise without the drugs were selected. It was found that both
drugs abolished the P(i) peak splitting during exercise. Despite a similar
reduction in phosphocreatine (PCr) during exercise with each drug, a
smaller increase in P(i) was observed with DECA than with VECU (P <
0.05). End-exercise muscle pH was higher with DECA (6.93 +/- 0.07) than
with VECU (6.79 +/- 0.11) (P < 0.05). The PCr and P(i) recovery was two-
and threefold faster with DECA than with VECU, respectively (P < 0.05).
On the basis of the concept that depolarizing and nondepolarizing agents
have a preferential effect on fast- and slow-twitch muscle fibers,
respectively, the present results support the hypothesis that the
NMR-observed splitting of the P(i) peak reflects the metabolic differences
between the two major fiber types of human skeletal muscle.
