Fig. 5.

Saturable transporter-associated currents in response to increasing concentrations of gramine.Xenopus oocytes were injected with either wild-type rSERT or D98E mutant cRNA, and two-electrode voltage-clamp experiments were performed as described in Materials and Methods. Oocytes were held at −80 mV and perfused with increasing concentrations of gramine in Ca²⁺-Ringer’s, pH 5.0. A, Data represent steady-state currents fit to Michaelis-Menten rectangular hyperbole by nonlinear regression (GraphPad Prism) from representative oocytes (n = 7). Mean apparentK_m values: wild-type rSERT (●), 2.2 ± 0.4 μm; D98E mutant (▪), 0.3 ± 0.04 μm. B, Comparison of currents induced by 5HT (5 μm) and gramine (5 μm) in Ca²⁺-Ringer’s, pH 7.6 or 5.0. 5HT- and gramine-activated currents in the D98E mutant at pH 7.6 were barely detectable above background. Data represent percentage of maximum 5HT-induced current observed for wild-type rSERT at pH 5.0.