Alternative splicing of a Drosophila GABA receptor subunit gene identifies determinants of agonist potency

Alternative splicing of the Drosophila melanogaster Rdl gene yields four ionotropic GABA receptor subunits. The two Rdl splice variants cloned to date, RDLac and RDLbd (DRC17-1-2), differ in their apparent agonist affinity. Here, we report the cloning of a third splice variant of RdL(ac), RDLad. Two-electrode voltage clamp electrophysiology was used to investigate agonist pharmacology of this expressed subunit following cRNA injection into Xenopus laevis oocytes. The EC50 values for GABA and its analogues isoguvacine, muscimol, isonipecotic acid and 3-amino sulphonic acid on the RDLad homomcric receptor differed from those previously described fur RDLac and DRC17-1-2 receptors. In addition to providing a possible physiological role for the alternative splicing of Rdl, these data delineate a hitherto functionally unassigned region of the N-terminal domain of GABA receptor subunits, which affects agonist potency and aligns closely with known determinants of potency in nicotinic acetylcholine receptors. Thus, using expression in Xenopus oocytes, we have demonstrated differences in agonist potency for the neurotransmitter GABA (and four analogues) between splice variant products of the Drosophila melanogaster Rdl gene encoding homomer-forming GABA receptor subunits. (C) 2001 IBRO. Published by Elsevier Science Ltd. All rights reserved.