Gated /sup 31/P NMR study of tetanic contraction in rat muscle depleted of phosphocreatine
Rats were fed a diet containing 1% ..beta..-guanidino-propionic acid (GPA) for 6-12 wk to deplete their muscles of phosphocreatine (PCr). Gated /sup 31/P nuclear magnetic resonance (NMR) spectra were obtained from the gastrocnemius-plantaris muscle at various time points during either a 1- or 3-s isometric tetanic contraction using a surface coil. The energy cost of a 1-s tetanus in unfatigued control rat muscle was 48.4 ..mu..mol ATP x g dry wt/sup -1/ x s/sup -1/ and was largely supplied by PCr; anaerobic glycogenolysis was negligible. In GPA-fed rats PCr was undetectable after 400 ms. This had no effect on initial force generated per gram, which was not significantly different from controls. Developed tension in a 3-s tetanus in GPA-fed rats could be divided into a peak phase (duration 0.8-0.9 s) and a plateau phase (65% peak tension) in which PCr was undetectable and the (ATP) was < 20% of that in control muscle. Energy from glycogenolysis was sufficient to maintain force generation at this submaximal level. Mean net glycogen utilization per 3-s tetanus was 78% greater than in control muscle. However, the observed decrease in intracellular pH was less than that expected from energy budget calculations, suggesting either increased buffering capacity or modulation of ATP hydrolysis in the muscles of GPA-fed rats. The results demonstrate that the transport role of PCr is not essential in contracting muscle in GPA-fed rats. PCr is probably important in this regard in the larger fibers of control muscle. Although fast-twitch muscles depleted of PCr have nearly twice the glycogen reserves of control muscle, glycogenolysis is limited in its capacity to fill the role of PCr as an energy buffer under conditions of maximum ATP turnover.
- Research Organization:
- Univ. of Oxford, England
- OSTI ID:
- 5765469
- Journal Information:
- Am. J. Physiol.; (United States), Vol. 252:5
- Country of Publication:
- United States
- Language:
- English
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GLYCOGEN
ENZYMATIC HYDROLYSIS
MUSCLES
NUCLEAR MAGNETIC RESONANCE
PHYSIOLOGY
PHOSPHOCREATINE
BIOCHEMISTRY
ATP
CONTRACTION
DIET
PHOSPHORUS 31
PHOSPHOTRANSFERASES
RATS
AMINO ACIDS
ANIMALS
CARBOHYDRATES
CARBOXYLIC ACIDS
CHEMICAL REACTIONS
CHEMISTRY
DECOMPOSITION
ENZYMES
HYDROLYSIS
ISOTOPES
LIGHT NUCLEI
LYSIS
MAGNETIC RESONANCE
MAMMALS
NUCLEI
NUCLEOTIDES
ODD-EVEN NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC PHOSPHORUS COMPOUNDS
PHOSPHORUS ISOTOPES
PHOSPHORUS-GROUP TRANSFERASES
POLYSACCHARIDES
RESONANCE
RODENTS
SACCHARIDES
SOLVOLYSIS
STABLE ISOTOPES
TRANSFERASES
VERTEBRATES
551001* - Physiological Systems- Tracer Techniques