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This Article Full Text Full Text (PDF) All Versions of this Article: 562/2/333    most recent jphysiol.2004.076703v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Soragna, A. Articles by Peres, A. Search for Related Content PubMed PubMed Citation Articles by Soragna, A. Articles by Peres, A.

¹ Laboratory of Cellular and Molecular Physiology, Department of Structural and Functional Biology, and Center for Neurosciences, University of Insubria, Via Dunant 3, 21100 Varese, Italy

The relations between apparent affinity for substrates and operating rates have been investigated by two-electrode voltage clamp in the GABA transporter rGAT1 expressed in Xenopus oocytes. We have measured the transport current induced by the presence of GABA, as well as the charge equilibration rate in the absence of the neurotransmitter, in various experimental conditions known to affect the transporter characteristics. The apparent affinities for GABA and for Na⁺ were also determined in the same conditions. Two pharmacological actions and three mutated isoforms have been examined. In all cases significant correlations were found between the charge equilibration rates and apparent affinities for both substrates. In particular in the transport process, the apparent affinity for GABA appears to be inversely related to the sum of the unidirectional charge equilibration rates (+ß), while the Na⁺ apparent affinity is directly related to their ratio (ß/). Together these observations suggest a kinetic basis for GABA affinity with higher turnover rates resulting in lower affinity, and indicate that an efficient uptake requires a compromise between these two parameters.

(Received 3 October 2004; accepted after revision 27 October 2004; first published online 28 October 2004)
Corresponding author A. Peres: Department of Structural and Functional Biology, University of Insubria, Via Dunant 3, 21100 Varese, Italy. Email: antonio.peres{at}uninsubria.it

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