Three kinds of currents in the canine betaine-GABA transporter BGT-1 expressed in Xenopus laevis oocytes

The cloned canine betaine-GABA cotransporter BGT-1 has been heterologously expressed in Xenopus laevis oocytes in order to characterize its electrophy siological properties. Voltage-clamp experiments on transfected oocytes rev eal the presence of three types of membrane current which are absent in non -injected oocytes: (i) an organic substrate-independent current (uncoupled current): iii) a transport-associated current, seen upon addition of betain e ol GABA; (iii! presteady-state currents induced by voltage changes. The t hree kinds of current are analogous to those reported in structurally simil ar cotransporters. The transport-associated current is strictly dependent o n the presence of Na+. The good correlation between the amount of charge un derlying the presteady-state currents and the transport-associated current indicates that both processes are due to the activity of the transporter. ( C) 2001 Elsevier Science B.V. All rights reserved.