Figure 2. Concentration dependence and the kinetic characteristics of L-carnitine uptake.   A: Concentration dependence of carnitine uptake by HCLE or HCjE cells; B and C:  the kinetic characteristics of L-[³H]carnitine uptake with the Eadie–Hofstee plot indicating dependence of the uptake rate (v) on uptake rate/carnitine concentration (v/s) for HCLE (B) and HCjE (C) cells, respectively. HCLE or HCjE cells were pre-incubated for 60 min with uptake buffer, then different concentrations of L-carnitine were added to the incubation medium and the uptake was measured for 30 min at pH 7.4 and 37 °C in the presence of Na⁺. The concentration of L-[³H]carnitine was kept constant at 24 nM and the concentration of L-carnitine was varied (range 1- 480 µM) by addition of unlabeled L-carnitine. Values are the mean±SD (n=4).