Residues within transmembrane segment M2 determine chloride conductance of glycine receptor homo- and hetero-oligomers.
We have expressed glycine receptor (GlyR) alpha and beta subunit cDNAs in HEK-293 cells to study the functional properties of homo- versus hetero-oligomeric GlyR channels. Dose-response curves of whole-cell currents in cells expressing alpha 1 subunits revealed an average Hill coefficient of h = 4.2. Co-expression with the beta subunit markedly increased glycine-gated whole-cell currents, which now exhibited a mean Hill coefficient of only h = 2.5. For alpha 1, alpha 2 and alpha 3 homo-oligomers, the main-state single-channel conductances were 86, 111 and 105 pS, respectively, recorded at symmetrical Cl- concentrations of 145 mM. The mutant alpha 1 G221A gave rise to a main-state of 107 pS. This indicates that the main-state of alpha homo-oligomers depends on residue 221 which is located within transmembrane segment M2. Importantly, the main-state conductances of alpha 1/beta, alpha 2/beta and alpha 3/beta hetero-oligomers were only 44, 54 and 48 pS, respectively. The latter values are similar to those found in spinal neurons, suggesting that native GlyRs are predominantly alpha/beta hetero-oligomers. Co-expression of alpha 1 with mutant beta subunits revealed that residues within and close to segment M2 of the beta subunit determine the conductance differences between homo- and hetero-oligomers.
Bormann
J
J
Max-Planck-Institut für Hirnforschung, Frankfurt, Germany.
Rundström
N
N
Betz
H
H
Langosch
D
D
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D002712:Chlorides / Q000378:metabolism*; D003001:Cloning, Molecular; D004247:DNA; D004553:Electric Conductivity; D005998:Glycine; D006801:Humans; D008969:Molecular Sequence Data; D051381:Rats; D018009:Receptors, Glycine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
D002712:Chlorides; D018009:Receptors, Glycine; D004247:DNA; D005998:Glycine