Characteristics of lactate transfer in isolated cardiac myocytes.

L-lactate uptake of isolated cardiac myocytes was investigated, since due to different lactate concentrations in the interstitial fluid and vascular space, lactate uptake cannot be studied satisfactorily in whole hearts. Lactate uptake exhibits sigmoidal saturation kinetics. Pyruvate (2.3 mM) inhibits L-lactate uptake at lower lactate concentrations (less than 15 mM) and enhances L-lactate uptake at higher (greater than 25 mM) lactate concentration. L-lactate uptake is increased at lowered pH (7.1) to an extent not explainable by non-ionic diffusion. The results are discussed in terms of a complex L-lactate carrier system which might involve cooperative mechanisms and H+-co- or OH- -countertransport.