title: Evidence for a lactate transport system in the sarcolemmal membrane of the perfused rabbit heart: kinetics of unidirectional influx, carrier specificity and effects of glucagon.
abstract: The kinetics and specificity of L-lactate transport into cardiac muscle were studied during a single transit through the isolated perfused rabbit heart using a rapid (15 s) paired-tracer dilution technique. Kinetic experiments revealed that lactate influx was highly stereospecific and saturable with an apparent Kt = 19 +/- 6 mM and a Vmax = 8.4 +/- 1.5 mumol/min per g (mean +/- S.E., n = 14 hearts). At high perfusate concentrations (10 mM), the inhibitors alpha-cyano-4-hydroxycinnamate (Ki = 7.3 mM), pyruvate (Ki = 6.5 mM), acetate (Ki = 19.4 mM) and chloroacetate (Ki = 28 mM) reduced L-lactate influx, and Ki values were estimated assuming a purely competitive interaction of the inhibitors with the monocarboxylate carrier. The monocarboxylic acids [14C]pyruvate and [3H]acetate were themselves transported, and sarcolemmal uptakes of respectively 38 +/- 1% and 70 +/- 8% were measured relative to D-mannitol. Perfusion of hearts for 10-30 min with 0.15 or 1.5 microM glucagon increased myocardial lactate production and simultaneously inhibited tracer uptake of lactate, pyruvate and acetate. It is concluded that a stereospecific lactate transporter exhibiting an affinity for other substituted monocarboxylic acids is operative in the sarcolemmal plasma membrane of the rabbit myocardium.
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism*; D005260:Female; D005934:Glucagon / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007700:Kinetics; D007773:Lactates / Q000378:metabolism*; D008297:Male; D027501:Monocarboxylic Acid Transporters; D009206:Myocardium / Q000378:metabolism*; D010477:Perfusion; D011817:Rabbits; D012508:Sarcolemma / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D007773:Lactates; D027501:Monocarboxylic Acid Transporters; D005934:Glucagon