title: Role of cell type in net lactate removal by skeletal muscle.
abstract: Net lactate uptake and subsequent pathways for removal were studied in three rabbit skeletal muscle preparations of distinct fiber type composition, i.e., glycolytic (99.1 +/- 0.2% type IIb fibers), oxidative (97.5 +/- 0.6% type I fibers), and mixed (type I, IIa, and IIb fibers). Single-pass perfusions were carried out for 3 h in the presence of glucose, lactate, and [U-14C]lactate. Lactate levels, initially set at either 1 mM (n = 4/prep) or 2 mM (n = 4/prep), were elevated twice during the perfusion at 60 and 120 min. Net lactate uptake (mumol.100 g-1.min-1) was first observed in the oxidative preparation, 1.4 +/- 0.2, at an arterial lactate concentration of approximately 2.5 mM, whereas net lactate uptake in the glycolytic, 0.7 +/- 0.2, and mixed preparations, 7.0 +/- 0.5, was first observed at 4 mM. Net lactate balance, [14C]lactate removal, and 14CO2 release demonstrated strong linear correlations (r = 0.94-0.98) with arterial lactate concentration. To quantify the fate of [14C]lactate, preparations were perfused at a single elevated lactate concentration (approximately 8 mM) for 2 h. Oxidation was the primary means of disposal in the oxidative and mixed preparations, whereas glyconeogenesis dominated removal in the glycolytic preparation. The arterial lactate concentration at which a given muscle switches from net production to net removal, the rate of removal, and subsequent pathway(s) for disposal are a function of that muscle's fiber type composition.
authors.affiliation: Department of Exercise Science, University of Southern California, Los Angeles 90089-0652.
authors.forename: M J
authors.initials: MJ
authors.lastname: Pagliassotti
authors.forename: C M
authors.initials: CM
authors.lastname: Donovan
mesh_terms: D000818:Animals; D002245:Carbon Dioxide / Q000032:analysis; D002250:Carbon Radioisotopes; D002417:Cattle; D004912:Erythrocytes / Q000378:metabolism; D006019:Glycolysis; D066298:In Vitro Techniques; D007700:Kinetics; D007773:Lactates / Q000378:metabolism*; D008297:Male; D009132:Muscles / Q000098:blood supply / Q000378:metabolism* / Q000502:physiology; D009928:Organ Specificity; D010101:Oxygen Consumption; D010477:Perfusion; D011817:Rabbits; D011865:Radioisotope Dilution Technique
chemical_list: D002250:Carbon Radioisotopes; D007773:Lactates; D002245:Carbon Dioxide