The kinetics of transport of lactate and pyruvate into isolated cardiac myocytes from guinea pig. Kinetic evidence for the presence of a carrier distinct from that in erythrocytes and hepatocytes.
1. Time courses for the uptake of L-lactate, D-lactate and pyruvate into isolated cardiac ventricular myocytes from guinea pig were determined at 11 degrees C or 0 degrees C (for pyruvate) in a citrate-based buffer by using a silicone-oil-filtration technique. These conditions enabled initial rates of transport to be measured without interference from metabolism of the substrates. 2. At a concentration of 0.5 mM, transport of all these substrates was inhibited by approx. 90% by 5 mM-alpha-cyano-4-hydroxycinnamate; at 10 mM-L-lactate a considerable portion of transport could not be inhibited. 3. Initial rates of L-lactate and pyruvate uptake in the presence of 5 mM-alpha-cyano-4-hydroxycinnamate were linearly related to the concentration of the monocarboxylate and probably represented diffusion of the free acid. The inhibitor-sensitive component of uptake obeyed Michaelis-Menten kinetics, with Km values for L-lactate and pyruvate of 2.3 and 0.066 mM respectively. 4. Pyruvate and D-lactate inhibited the transport of L-lactate, with Ki values (competitive) of 0.077 and 6.6 mM respectively; the Ki for pyruvate was very similar to its Km for transport. The Ki for alpha-cyano-4-hydroxycinnamate as a non-competitive inhibitor was 0.042 mM. 5. These results indicate that L-lactate, D-lactate and pyruvate share a common carrier in guinea-pig cardiac myocytes; the low stereoselectivity for L-lactate over D-lactate and the high affinity for pyruvate distinguish it from the carrier in erythrocytes and hepatocytes. The metabolic roles for this novel carrier in heart are discussed.
Poole
R C
RC
Department of Biochemistry, School of Medical Sciences, University of Bristol, U.K.
Halestrap
A P
AP
Price
S J
SJ
Levi
A J
AJ
D000818:Animals; D001667:Binding, Competitive; D001693:Biological Transport, Active / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D003373:Coumaric Acids / Q000494:pharmacology; D004912:Erythrocytes / Q000378:metabolism*; D006168:Guinea Pigs; D006352:Heart Ventricles / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D007773:Lactates / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D027501:Monocarboxylic Acid Transporters; D009206:Myocardium / Q000378:metabolism*; D011773:Pyruvates / Q000378:metabolism*; D051381:Rats
D002352:Carrier Proteins; D003373:Coumaric Acids; D007773:Lactates; D027501:Monocarboxylic Acid Transporters; D011773:Pyruvates; C007175:alpha-cyano-4-hydroxycinnamate