Relations between the stage of cell maturation and lactate transporter activities in rat neonatal muscle cells in culture

Lactate transport was investigated in newborn rat muscle cells in culture. The aim was to study the lactate transport function at two stages of cell d ifferentiation in culture: (i) during the proliferative phase characterized by myoblasts and myotubes (MyB/MyT2) obtained after 2-3 seedings, (ii) whe n myotubes (MyT1) grow old in culture after 8-9 seedings. In both developme ntal stages MyB/MyT2, lactate was carried following a saturable and sigmoid al velocity curve: the Hill and the Scatchard plot analyses confirmed an al losteric or multisite mechanism of lactate transport with two classes of ca rriers: one of low and one of high affinity i.e., 8.6 and 0.95 mM, respecti vely, which are associated with high and low transport capacities (V-m) i.e ., 9.1 and 0.67 nM/ min/mg, respectively. With MyT1, the velocity curve of lactate transport presented a hyperbolic profile, and the Hill plot analysi s gave a Hill number near one suggesting that for cell aging in culture the decrease in cooperativity shows that lactate transport essentially occurs through the low affinity transport system. Inhibitor effects also contribut ed to evidence for at least two systems of transport. Results obtained from primary cells give evidence for the early activity of lactate transport sy stem at the Myb/MyT2 stage and its evolution during cell aging in culture ( MyT1). Sarcolemmal lactate transport in primary cultures of myocytes is acc omplished by multiple carriers, neither of which are MCT1 or MCT2 as confir med by immunoblots.