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Relations between substrate affinities and charge equilibration rates in the rat GABA cotransporter GAT1
Author(s) -
Soragna Andrea,
Bossi Elena,
Giovannardi Stefano,
Pisani Rossana,
Peres Antonio
Publication year - 2005
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2004.076703
Subject(s) - affinities , xenopus , chemistry , biophysics , transporter , gaba transporter , neurotransmitter transporter , substrate (aquarium) , cotransporter , voltage clamp , conductance , reversal potential , receptor , stereochemistry , neurotransmitter , biochemistry , membrane potential , patch clamp , biology , sodium , organic chemistry , gene , mathematics , combinatorics , ecology
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 (α+β), while the Na + apparent affinity is directly related to their ratio (β/α). 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.