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 electrophysiological properties. Voltage-clamp experiments on transfected oocytes reveal the presence of three types of membrane current which are absent in non-injected oocytes: (i) an organic substrate-independent current (uncoupled current); (ii) a transport-associated current, seen upon addition of betaine or GABA; (iii) presteady-state currents induced by voltage changes. The three kinds of current are analogous to those reported in structurally similar cotransporters. The transport-associated current is strictly dependent on the presence of Na(+). The good correlation between the amount of charge underlying the presteady-state currents and the transport-associated current indicates that both processes are due to the activity of the transporter.
Forlani
G
G
Laboratory of Cellular and Molecular Physiology, Department of Structural and Functional Biology, University of Insubria, Varese, Italy.
Bossi
E
E
Perego
C
C
Giovannardi
S
S
Peres
A
A
D000818:Animals; D001622:Betaine / Q000378:metabolism*; D002352:Carrier Proteins / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics; D002414:Cations, Monovalent; D004285:Dogs; D050485:GABA Plasma Membrane Transport Proteins; D008564:Membrane Potentials; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D014162:Transfection; D014982:Xenopus laevis; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D002352:Carrier Proteins; D002414:Cations, Monovalent; D050485:GABA Plasma Membrane Transport Proteins; C072207:betaine plasma membrane transport proteins; D001622:Betaine; D005680:gamma-Aminobutyric Acid