TABLE 1

Comparison of apparent K_m values and IC₅₀ values of rOCT1 wild-type and two rOCT1 mutants determined under different experimental conditions

Apparent K_m values of TEA⁺ and MPP⁺ uptake and IC₅₀ values for the inhibition of uptake of 0.1 µM MPP⁺ by TEA⁺ or TBuA⁺ mediated by rOCT1, rOCT1(Y222F), and rOCT1(D475E) were determined. The measurements were performed with stably transfected HEK293 cells (I, II) or with oocytes in which the transporters were expressed (III). I, Tracer uptake was measured in dissociated HEK293 cells at 37°C after incubation for 1 second [MPP⁺ uptake in rOCT1 and rOCT1(Y222F)], 5 seconds [MPP⁺ uptake in rOCT1(D475E)], or 10 seconds (TEA⁺ uptake). In Figs. 3–5 and Supplemental Fig. 4, the compiled uptake measurements are shown. II, Tracer uptake was measured in monolayers of HEK293 cells at 37°C after incubation for 2 min. The uptake measurements are shown in Supplemental Figs. 2 and 3. III, Tracer uptake was measured in oocytes expressing rOCT1 or rOCT1 mutants after 30-min incubation at room temperature. These data are taken from our previous publications (Gorboulev et al., 1999, 2005; Popp et al., 2005). The apparent K_m values were calculated by fitting the Michaelis-Menten equation to the data, whereas IC₅₀ values were calculated by fitting the Hill equation to the data. Values are given as the mean ± S.D. values; the numbers of experiments are indicated in parenthesis.