Lactate transport in isolated mouse muscles studied with a tracer technique--kinetics, stereospecificity, pH dependency and maximal capacity.
Lactate transport across the sarcolemma of isolated mouse muscles was studied with a 14C tracer technique. The cellular tracer uptake could be inhibited by unlabelled L-lactate (and pyruvate) and to a lesser extent by D-lactase. The stereospecific fraction had a Km of 3.5 mM, and made up 50% of the total transport. The tracer uptake was unaffected by 0.05 mM DIDS and 0.2 mM amiloride, but was inhibited by cinnamate (Ki = 8 mM) and PCMBS (Ki = 0.8 mM). With high concentrations of the latter inhibitor compounds or with high concentrations of unlabelled L-lactate, the tracer uptake was inhibited 80%, which indicates that the main part of the transport involves facilitated diffusion. The remaining fraction (20%) was non-saturable, reduced at high pH, and could not be inhibited; it is probably mediated by diffusion of undissociated lactic acid. Lactate transport was pH-dependent, which is consistent with a lactate-H+ symport. The maximal transport capacity, as calculated from the pH changes measured with pH-sensitive micro-electrodes while the lactate gradient was 30 mM, was 11.8 mmol kg-1 min-1 (pH 6.2).
Juel
C
C
Zoophysiological Laboratory B, August Krogh Institute, Copenhagen, Denmark.
Wibrand
F
F
D002731:4-Chloromercuribenzenesulfonate / Q000494:pharmacology; D000818:Animals; D002934:Cinnamates / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007773:Lactates / Q000378:metabolism / Q000493:pharmacokinetics*; D051379:Mice; D009132:Muscles / Q000378:metabolism*; D011773:Pyruvates / Q000494:pharmacology
D002934:Cinnamates; D007773:Lactates; D011773:Pyruvates; D002731:4-Chloromercuribenzenesulfonate