L(+)-lactate transport in perfused rat skeletal muscle: kinetic characteristics and sensitivity to pH and transport inhibitors.
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.
Watt
P W
PW
Department of Physiology, University of Dundee, U.K.
MacLennan
P A
PA
Hundal
H S
HS
Kuret
C M
CM
Rennie
M J
MJ
D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D002731:4-Chloromercuribenzenesulfonate / Q000494:pharmacology; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002352:Carrier Proteins / Q000494:pharmacology; D002934:Cinnamates / Q000494:pharmacology; D003373:Coumaric Acids; D005260:Female; D006863:Hydrogen-Ion Concentration; D007773:Lactates / Q000493:pharmacokinetics*; D019344:Lactic Acid; D027501:Monocarboxylic Acid Transporters; D009132:Muscles / Q000378:metabolism*; D010477:Perfusion; D051381:Rats; D011919:Rats, Inbred Strains
D002352:Carrier Proteins; D002934:Cinnamates; D003373:Coumaric Acids; D007773:Lactates; D027501:Monocarboxylic Acid Transporters; C018253:alpha-cyanocinnamate; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; C007175:alpha-cyano-4-hydroxycinnamate; D019344:Lactic Acid; D002731:4-Chloromercuribenzenesulfonate; D000584:Amiloride