Transient currents in the glycine cotransporter GlyT1 reveal different steps in transport mechanism.
The relation between presteady-state (transient) currents elicited by voltage steps in the absence of organic substrate and transport-associated currents in the presence of glycine was investigated in Xenopus oocytes expressing the neuronal glycine transporter GlyT1b. Saturating amounts of glycine converted the transient currents in steady transport currents. Analysis of the transient currents abolished by the substrate confirmed the intramembrane nature of the underlying charge movement process. The sigmoidal Q/V relationship had a moderate slope consistent with the known GlyT1b stoichiometry. The transient currents were best fitted by the sum of two exponentials, with the slow time constant (tau (slow)) being in the order of tens of milliseconds. The apparent affinity for glycine was in the micromolar range and voltage-dependent, slightly decreasing at positive potentials. Numerical simulations show that a simplified, three-state model is sufficient to explain the main features of GlyT1b operation.
Cherubino
Francesca
F
Fondazione Maugeri IRCCS, Via Roncaccio 16, Tradate, VA, Italy.
Bossi
Elena
E
Miszner
Andreea
A
Ghezzi
Chiara
C
Peres
Antonio
A
D000818:Animals; D001692:Biological Transport / Q000502:physiology; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D005998:Glycine / Q000378:metabolism; D050487:Glycine Plasma Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D008564:Membrane Potentials / Q000502:physiology*; D009865:Oocytes / Q000166:cytology / Q000378:metabolism; D018408:Patch-Clamp Techniques; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D014982:Xenopus laevis
D050487:Glycine Plasma Membrane Transport Proteins; D011994:Recombinant Proteins; C493266:Slc6a9 protein, rat; D005998:Glycine