Effects of chlorotrifluoroethylene oligomer fatty acids on recombinant GABA receptors expressed in Xenopus oocytes

GABA-activated Cl- current was expressed in Xenopus oocytes after injecting cRNA that had been transcribed in vitro from complementary DNA (cDNA) coding for a single GABA rho(i)-subunit cloned from human retina. The expressed current was insensitive to 100 mu M bicuculline, but was activated by the GABA analogue trans-4-aminocrontonic acid (TACA). Anion-selective permeability of the expressed rho(1)-subunit was determined by isotonically replacing the extracellular Cl- with different anions. The anion permeability was very similar to the native GABA, receptor/channel following a sequence of SCN- > I- > NO3- > Br- greater than or equal to Cl-. Halogenated fatty acids, such as chlorotrifluoroethylene (CTFE) and perfluorinated oligomer acids inhibited the GABA-induced current in oocytes expressing the human retinal GABA rho(1)-subunit or rat brain GABA(A) receptor alpha(1),beta(2),gamma(2) subunits. The inhibitory effect of halogenated fatty acids demonstrated a carbon chain length-dependent manner of: C-10 > C-8 > C-6 > C-4. Perfluorinated C-8-oligomer acid (PFOA) was less effective at blocking this channel than the C-8-CTFE oligomer acid. Radiolabeled GABA binding assay indicated that CTFE oligomer acids do not interfere at the GABA binding site of the receptor. Furthermore, the C-8-CTFE oligomer fatty acid did not compete with picrotoxin for binding sites within the pore of the channel. These studies demonstrated that the heterologous expression system is useful for studying the molecular interaction between potential neurotoxic agents and neuroreceptors. Our results provide detailed information that should contribute to our understanding of the structure and function of retinal GABA receptors.