Author(s): Watt PW, MacLennan PA, Hundal HS, Kuret CM, Rennie MJ
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Abstract We have examined lactate uptake (as the rate of net muscle lactate accumulation) and unidirectional inward transport (measured by a paired-tracer dilution method) in muscle of the perfused skinned rat hindlimb. Inhibition of tracer influx (fractional uptake at 1 mM L(+)-lactate, 43.3 +/- 3.1\% but only 32.9 +/- 1.8\% at 50 mM lactate) suggested some competition between tracer and native forms of the carboxylate for transport. D(-)-lactate (50 mM) did not inhibit uptake of tracer L(+)-lactate. Pyruvate (25 mM), but none of five other monocarboxylates, inhibited uptake of tracer lactate, by 22\% (P less than 0.01). Altering perfusate pH from 7.4 to 6.8 caused a 36\% increase (P less than 0.001) in the unidirectional L(+)-lactate transport at 1 mM L(+)-lactate, whereas increasing pH to 7.7 reduced transport by 18\% (P less than 0.01). Tracer lactate influx was inhibited by 500 microM 4-acetamido-4'-isothiocyanostilbene (SITS) (19\%), 5 mM alpha-cyano-4-hydroxycinnamic acid (CIN) (20-30\%), 1 mM amiloride (27\%) and by a thiol group reagent p-chloromercuribenzenesulphonic acid (pCMBS) (26\%). Overall the results indicate that at least two processes are involved in the transfer of lactate: one, saturable, with a Vmax of 0.84 mumol.min-1.g-1 and an apparent Km of 21 mM was sensitive to SITS, CIN, and a thiol group reagent; the other was non-saturable and insensitive to SITS and CIN with an apparent rate constant of 0.1 min-1.
This article was published in Biochim Biophys Acta
and referenced in Journal of Cancer Science & Therapy