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Titolo:
SIMULTANEOUS P-31 MRS OF THE SOLEUS AND GASTROCNEMIUS IN SHERPAS DURING GRADED CALF MUSCLE EXERCISE
Autore:
ALLEN PS; MATHESON GO; ZHU G; GHEORGIU D; DUNLOP RS; FALCONER T; STANLEY C; HOCHACHKA PW;
Indirizzi:
STANFORD UNIV,SCH MED,DIV SPORTS MED,BURNHAM PAVIL STANFORD CA 94305 STANFORD UNIV,SCH MED,DEPT FUNCT RESTORAT STANFORD CA 94305 UNIV ALBERTA,DEPT BIOMED ENGN SCI MED EDMONTON AB T6G 2G3 CANADA UNIV CALGARY,CTR SPORTS MED CALGARY AB T2N 1N4 CANADA UNIV BRITISH COLUMBIA,DEPT ZOOL VANCOUVER BC V6T 1Z4 CANADA UNIV BRITISH COLUMBIA,SPORTS MED DIV VANCOUVER BC V6T 1Z4 CANADA
Titolo Testata:
American journal of physiology. Regulatory, integrative and comparative physiology
fascicolo: 3, volume: 42, anno: 1997,
pagine: 999 - 1007
SICI:
0363-6119(1997)42:3<999:SPMOTS>2.0.ZU;2-O
Fonte:
ISI
Lingua:
ENG
Soggetto:
HUMAN SKELETAL-MUSCLE; OXIDATIVE-PHOSPHORYLATION; METABOLIC-REGULATION; EXTREME ALTITUDE; NMR-SPECTROSCOPY; CREATINE-KINASE; ANDEAN NATIVES; ATP TURNOVER; CAPACITY; HETEROGENEITY;
Keywords:
METABOLIC REGULATION; MUSCLE METABOLISM; MUSCLE MAGNETIC RESONANCE SPECTROSCOPY; MAGNETIC RESONANCE SPECTROSCOPY; HIGH-ENERGY PHOSPHATES; ATP TURNOVER; HIGH-ALTITUDE ADAPTATION; LACTATE PARADOX;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
41
Recensione:
Indirizzi per estratti:
Citazione:
P.S. Allen et al., "SIMULTANEOUS P-31 MRS OF THE SOLEUS AND GASTROCNEMIUS IN SHERPAS DURING GRADED CALF MUSCLE EXERCISE", American journal of physiology. Regulatory, integrative and comparative physiology, 42(3), 1997, pp. 999-1007

Abstract

The observation that the amount of lactate formed during hypobaric hypoxia decreases with the severity of hypoxia has become known as the ''lactate paradox. '' We used noninvasive P-31 magnetic resonance spectroscopy (MRS) to further probe this problem and explore the nature of muscle metabolism during rest-exercise-recovery transitions in Sherpas indigenous to the high Himalayas of Nepal. MRS data were obtained using a whole body 1-m bore, 1.5-T Phillips Gyroscan spectrometer. Muscle-specific localization of MRS data acquisition was achieved by means ofa modified image-selected in vivo spectroscopy sequence (ISIS). The spectra acquired from the medial and lateral gastrocnemius muscle, richin fast-twitch fibers, were well constrained by selective excitation and by the boundary of the leg. The spectra from a third region contained signals predominantly from the soleus, a muscle formed mainly of slow-twitch fibers. We quantified relative concentration changes in phosphocreatine (PCr), P-i, and ATP during a series of calf muscle work bouts; free ADP concentrations were calculated on the assumption that the creatine phosphokinase reaction was always essentially at equilibrium. Hydrogen ion concentrations were calculated from the chemical shift of P-i, which represents the equilibrium between mono-and diprotonated phosphate. Plantar flexion was quantified using a calf muscle ergometer designed for operation within a 1-m whole body magnet. We found that the concentration of ATP was rigorously regulated and thus did notchange despite large changes in ATP turnover rates required through exercise. The relative concentrations of PCr and P-i were linear functions of the percent maximum work rate of the lateral and medial gastrocnemius, but on transition to exercise the fractional concentration changes in these metabolites were much less than the fractional change inmuscle ATP turnover rates. The relationship between muscle ATP turnover rate and free ADP concentration was complex; again, a kinetic orderof 1 was not observed. In contrast to the gastrocnemius, the soleus muscle sustained much smaller changes in the concentrations of these crucial metabolites during rest-work-recovery transitions. Unlike the situation in most other muscles rich in fast-twitch fibers characterizedby lactate-associated acidosis during muscle work, the intracellular pH in gastrocnemius of Sherpas was stable through these protocols, which is consistent with the low lactate production (i.e., with the lactate paradox) observed in indigenous highlanders.

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Documento generato il 22/09/20 alle ore 07:01:57