title: Lactate transport by rainbow trout white muscle: kinetic characteristics and sensitivity to inhibitors.
abstract: This study used an isolated-perfused tail-trunk preparation of rainbow trout to examine the uptake and release of lactate (Lac) and metabolic protons (delta H+M) in resting and exercised fish white muscle. In exercised muscle, L(+)-Lac efflux was inhibited (approximately 40%) by 5 mM alpha-cyano-4-hydroxycinnamate (CIN), but not by 0.5 mM 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) or 0.1 mM amiloride. These results suggest that Lac release occurs through a Lac(-)-H- symport and the free diffusion of lactic acid (HLac) or Lac-, but not via the Lac-/HCO3(-)-Cl- antiporter. Lac efflux was accompanied by delta H+m influx in all treatments, and increased delta H+m influx occurred after SITS treatment. In resting muscle, Lac uptake rates were greater than Lac efflux rates in the postexercise preparation. L-Lac influx exhibited partial saturation kinetics, whereas D(-)-Lac influx was linearly related to its extracellular concentration (0-32 mM). At 16 mM extracellular L-Lac, with a negligible transmembrane L-HLac gradient and an outwardly directed not driving force on L-Lac-, CIN, and SITS reduced net L-Lac uptake by 75 and 45%, respectively. At 16 mM extracellular concentration, D-Lac influx was 64% of the net L-Lac influx. These results suggest that in trout muscle at 16 mM extracellular L-Lac, the Lac -H+ symport accounts for 30-36%, the Lac-/HCO3(-)-Cl- antiport for 39-45%, and diffusion for 19-25% of uptake, although the latter is probably overestimated and the former underestimated for methodological reasons. Net L-Lac efflux was not affected by extracellular D-Lac concentration and/or D-Lac influx, implying the existence of a concurrent L-Lac efflux during L-Lac influx. The D-Lac influx kinetics data indicated that the Lac-/HCO3 antiport was not saturable in the extracellular D-Lac concentration range of 0-32 mM. This study clearly demonstrates the involvement of carrier-mediated transport in transmembrane Lac movement in fish muscle and supports the "active lactate retention" mechanism proposed by Turner and Wood (J. Exp. Biol. 105: 895-401, 1983).
authors.affiliation: Department of Biology, McMaster University, Hamilton, Ontario, Canada. ywang@rsmas.miami.edu
authors.forename: Y
authors.initials: Y
authors.lastname: Wang
authors.forename: P M
authors.initials: PM
authors.lastname: Wright
authors.forename: G J
authors.initials: GJ
authors.lastname: Heigenhauser
authors.forename: C M
authors.initials: CM
authors.lastname: Wood
mesh_terms: D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D001692:Biological Transport; D002245:Carbon Dioxide / Q000378:metabolism; D004058:Diffusion; D005260:Female; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007773:Lactates / Q000378:metabolism*; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D017686:Oncorhynchus mykiss / Q000378:metabolism*; D005082:Physical Exertion; D013237:Stereoisomerism
chemical_list: D001639:Bicarbonates; D007773:Lactates; D002245:Carbon Dioxide