title: Lactate uptake by skeletal muscle sarcolemmal vesicles decreases after 4 wk of hindlimb unweighting in rats.
abstract: We investigated the effects of 4 wk of hypodynamia on the rate of lactate transport in skeletal muscle sarcolemmal vesicles from control and hindlimb-suspended rats. Characterization of the sarcolemmal preparations was achieved with a marker enzyme (K+-p-nitrophenylphosphatase) and measurement of 1 mM [U-14C]lactate transport activity under zero-trans conditions with or without a pH gradient or the transport inhibitor alpha-hydroxycinnamate. Preparations from the two groups were not significantly different concerning yield and purification. Based on these results, we used this model to analyze the lactate transport activity after hypodynamia by tail suspension. Hindlimb suspension caused a shift from slow to fast myosin heavy chain isoforms in soleus muscles with a 40% decrease in the citrate synthase activity (from 35.3 +/- 3.7 to 21.4 +/- 2.1 mu mol x g-1 x min-1; P < 0.05). Lactate (1 mM) uptake in vesicles from the two groups was a function of time, and the rate after hindlimb suspension was significantly decreased in the suspended compared with the control group (2.25 +/- 0.44 and 3.50 +/- 0.26 nmol x min-1 x mg protein-1, respectively; P < 0.05). These differences were not observed for a higher lactate concentration (50 mM). These results suggest that the level of physical activity plays a role in the regulation of sarcolemmal lactate transport activity implicated in the exchanges of lactate between producing and utilizing cells, organs, and tissues, which are major ways of carbohydrate energy distribution in humans and others species.
authors.affiliation: Laboratoire de Physiologie des Interactions, Service d'Exploration de la Fonction Respiratoire, Hopital Arnaud de Villeneuve, Montpellier, France.
authors.forename: H
authors.initials: H
authors.lastname: Dubouchaud
authors.forename: P
authors.initials: P
authors.lastname: Granier
authors.forename: J
authors.initials: J
authors.lastname: Mercier
authors.forename: C
authors.initials: C
authors.lastname: Le Peuch
authors.forename: C
authors.initials: C
authors.lastname: Prefaut
mesh_terms: D009597:4-Nitrophenylphosphatase / Q000378:metabolism; D000818:Animals; D001835:Body Weight / Q000502:physiology; D002950:Citrate (si)-Synthase / Q000378:metabolism; D006614:Hindlimb / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D019344:Lactic Acid / Q000378:metabolism*; D008297:Male; D018482:Muscle, Skeletal / Q000201:enzymology / Q000378:metabolism*; D009210:Myofibrils / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000378:metabolism; D009929:Organ Size / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D012508:Sarcolemma / Q000201:enzymology / Q000378:metabolism*; D014893:Weightlessness / Q000009:adverse effects*; D018474:Weightlessness Simulation
chemical_list: D019344:Lactic Acid; D002950:Citrate (si)-Synthase; D009597:4-Nitrophenylphosphatase; D018995:Myosin Heavy Chains