A SINGLE-POINT MUTATION DECREASES PICROTOXININ SENSITIVITY OF THE HUMAN GABA RECEPTOR RHO-1 SUBUNIT

THE GABA receptor rho subunits are thought to form bicuculline-insensi tive and picrotoxinin-sensitive GABA(C) receptors. We have investigate d the role of the amino acid at position 309 in transmembrane segment M2 of the human rho 1 subunit as a determinant for picrotoxinin sensit ivity. The mutant rho 1P309S was constructed by exchanging proline 309 for serine, the corresponding amino acid of the human rho 2 subunit. Whole-cell recordings from HEK-293 cells transfected with rho 1P309S c DNA revealed that the sensitivity of the rho 1P309S channels for picro toxinin was four-fold lower than that of the wild type rho 1 subunit. The affinity of the mutant receptor for GABA was only slightly changed . These results provide direct evidence that the amino acid at positio n 309 is an important determinant for the picrotoxinin sensitivity of GABA receptors formed by the rho subunits.