The Journal of General Physiology
Keystone Symposia
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Published online December 13, 2007
doi:10.1085/jgp.200609701
The Journal of General Physiology, Vol. 131, No. 1, 87-97
The Rockefeller University Press, 0022-1295 $30.00
© 2007 Wotring et al.
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ARTICLE

 Charge Scan Reveals an Extended Region at the Intracellular End of the GABA Receptor Pore that Can Influence Ion Selectivity



Virginia E. Wotring1 and David S. Weiss2

1 Department of Neurobiology, University of Alabama at Birmingham, Birmingham, AL 35294
2 Department of Physiology, University of Texas Health Science Center at San Antonio, San Antonio, TX 78229

Correspondence to David S. Weiss: weissd{at}uthscsa.edu

Selective permeability is a fundamental property of ion channels. The Cys-loop receptor superfamily is composed of both excitatory (ACh, 5-HT) and inhibitory (GABA, glycine) neurotransmitter-operated ion channels. In the GABA receptor, it has been previously shown that the charge selectivity of the integral pore can be altered by a single mutation near the intracellular end of the second transmembrane-spanning domain (TM2). We have extended these findings and now show that charge selectivity of the anionic {rho}1 GABA receptor can be influenced by the introduction of glutamates, one at a time, over an 8–amino acid stretch (–2' to 5') in the proposed intracellular end of TM2 and the TM1–TM2 intracellular linker. Depending on the position, glutamate substitutions in this region produced sodium to chloride permeability ratios (PNa+/Cl–) varying from 0.64 to 3.4 (wild type PNa+/Cl– = 0). In addition to providing insight into the mechanism of ion selectivity, this functional evidence supports a model proposed for the homologous nicotinic acetylcholine receptor in which regions of the protein, in addition to TM2, form the ion pathway.

Abbreviations used in this paper: nACh, nicotinic acetylcholine; SCAM, substituted cysteine accessibility method; TM2, second transmembrane domain.


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