Effects of pH on the uncoupled, coupled and pre-steady-state currents at the amino acid transporter KAAT1 expressed in Xenopus oocytes

1. The effects of pH on the different kinds of currents occurring at the le pidopteran amino acid cotransporter KAAT1 have been examined using heterolo gous expression in Xenopus oocytes and voltage clamp. 2. Acidic pH (5.5-4.5) caused a slight depression of the uncoupled current and a complete inhibition of the coupled and transient currents, in the pre sence of either Na+ or K+, the two ions physiologically relevant to the tra nsport process. 3. Conversely, at alkaline pH (9) no statistically: significant effects cou ld be observed on uncoupled, coupled and transient currents compared to the effects at pH 7.6. 4. These effects of pH indicate that operation of the transporter is maxima l in the physiologically alkaline native environment. 5. The dose-response curves for the inhibition of coupled and transient cur rents were similar, with respective pK(a) values of 6.29 +/- 0.05 and 6.40 +/- 0.03 and respective Hill coefficient values (n(H)) of 0.93 +/- 0.07 and 1.08 +/- 0.08, suggesting that the two effects carl be explained by a sing le proton binding to the same site in the transporter.