Figure 10. Accumulation of [³H]-MPP⁺ in rat SCG cultures by NAT-related and by NAT-unrelated mechanisms.

A, cultures incubated for 30 min with 64 nm [³H]-MPP⁺ in the absence (Ctr) or presence of 1 μM desipramine (Des). Ice and Des Ice indicate uptake measured for the two conditions on ice. Accumulation of [³H]-MPP⁺ is reduced to 5.4 % of the control value by the presence of 1 μM desipramine. B, effect of the OCT3 inhibitors cyanine 863 and oestradiol on the NAT-independent accumulation of 25 μM [³H]-MPP⁺. Cultures pretreated for 10 min with 0.3 μM reserpine and 5 μM desipramine were incubated with 5 μM desipramine and 25 μM MPP⁺ in the absence (Ctr) or presence of either 5 μM cyanine 863 (Cy 5.0) or 10 μM oestradiol (Estr 10). Ice indicates control uptake measured on ice. Data are shown as means ± s.e.m. (Ctr, Cy 5.0 and Estr 10, n = 6; Ice, n = 8). Cyanine (5 μM) and 10 μM oestradiol reduced accumulation to 64 and 80 %, respectively. ** P < 0.01 and * P < 0.05) denote significant differences from controls; Mann-Whitney U test). C, time-dependent accumulation of [³H]-MPP⁺. Cultures were incubated in the presence of 1 μM desipramine with 64 nm [³H]-MPP⁺ for indicated periods of time (○). ▵, same protocol, but with the accumulation of [³H]-MPP⁺ measured on ice. Data are shown as means ± s.e.m. (n = 5-6). D, concentration-dependent accumulation of [³H]-MPP⁺. Cultures were incubated for 30 min in the presence of desipramine with indicated concentrations of [³H]-MPP⁺ (○). ▵, same protocol, but with the accumulation of [³H]-MPP⁺ done on ice. Kinetic parameters deduced from the data yield a K_m of 115 ± 39 μM and a V_max of 34.1 ± 3.6 pmol per culture (means ± s.e.m., n = 4).