Analysis of macroscopic ionic currents mediated by GABArho1 receptors during lanthanide modulation predicts novel states controlling channel gating.

GOUTMAN, JD; ESCOBAR, AL; DANIEL JUAN CALVO

British Journal of Pharmacology

Nature Publishing Group

Lugar: Londres; Año: 2005 vol. 146 p. 1000 - 1009

0007-1188

Analysis of macroscopic ionic currents mediated by GABAq1q1 receptors during lanthanide modulation predicts novel states controlling channel gating 1Juan D. Goutman, 2Ariel L. Escobar &* ,1Daniel J. CalvoJuan D. Goutman, 2Ariel L. Escobar &* ,1Daniel J. Calvo 1Laboratorio de Neurobiologı´ a Celular y Molecular, Instituto de Investigaciones en Ingenierı´ a Gene´ tica y Biologı´ a Molecular (INGEBI), Consejo Nacional de Investigaciones Cientı´ ficas y Te´ cnicas (CONICET), Departamento de Fisiologı´ a, Biologı´ a Molecular y Celular, Facultad de Ciencias Exactas y Naturales (FCEyN), Universidad de Buenos Aires (UBA), Vuelta de Obligado 2490, CP 1428 Ciudad Auto´ noma de Buenos Aires, Argentina and 2Department ofPhysiology, Texas Tech University Health Sciences Center, Lubbock, TX 79430-6551, U.S.A.Laboratorio de Neurobiologı´ a Celular y Molecular, Instituto de Investigaciones en Ingenierı´ a Gene´ tica y Biologı´ a Molecular (INGEBI), Consejo Nacional de Investigaciones Cientı´ ficas y Te´ cnicas (CONICET), Departamento de Fisiologı´ a, Biologı´ a Molecular y Celular, Facultad de Ciencias Exactas y Naturales (FCEyN), Universidad de Buenos Aires (UBA), Vuelta de Obligado 2490, CP 1428 Ciudad Auto´ noma de Buenos Aires, Argentina and 2Department ofPhysiology, Texas Tech University Health Sciences Center, Lubbock, TX 79430-6551, U.S.A.2Department ofPhysiology, Texas Tech University Health Sciences Center, Lubbock, TX 79430-6551, U.S.A. 1 Lanthanide-induced modulation ofGABA C receptors expressed in Xenopus oocytes was studied.Lanthanide-induced modulation ofGABA C receptors expressed in Xenopus oocytes was studied. 2 We obtained two-electrode voltage-clamp recordings ofionic currents mediated by recombinant homomeric GABAr1 receptors and performed numerical simulations ofkinetic models ofthe macroscopic ionic currents.We obtained two-electrode voltage-clamp recordings ofionic currents mediated by recombinant homomeric GABAr1 receptors and performed numerical simulations ofkinetic models ofthe macroscopic ionic currents.r1 receptors and performed numerical simulations ofkinetic models ofthe macroscopic ionic currents. 3 GABA-evoked chloride currents were potentiated by La3þ, Lu3þ and Gd3þ in the micromolar range.GABA-evoked chloride currents were potentiated by La3þ, Lu3þ and Gd3þ in the micromolar range. 4 Lanthanide effects were rapid, reversible and voltage independent.Lanthanide effects were rapid, reversible and voltage independent. 5 The degree ofpotentiation was reduced by increasing GABA concentration.The degree ofpotentiation was reduced by increasing GABA concentration. 6 Lu3þ also induced receptor desensitization and decreased the deactivation rate ofGABA r1Lu3þ also induced receptor desensitization and decreased the deactivation rate ofGABA r1 currents. 7 In the presence of300 mM Lu3þ, dose–response curves for GABA-evoked currents showed a significant enhancement of the maximum amplitude and an increase of the apparent affinity.In the presence of300 mM Lu3þ, dose–response curves for GABA-evoked currents showed a significant enhancement of the maximum amplitude and an increase of the apparent affinity. 8 The rate ofonset of TPMPA and picrotoxin antagonism ofGABA r1 receptors was modulated by Lu3þ.The rate ofonset of TPMPA and picrotoxin antagonism ofGABA r1 receptors was modulated by Lu3þ.3þ. 9 These results suggest that the potentiation ofthe anionic current was the result ofa direct lanthanide–receptor interaction at a site capable ofallosterically modulating channel properties.These results suggest that the potentiation ofthe anionic current was the result ofa direct lanthanide–receptor interaction at a site capable ofallosterically modulating channel properties. 10 Based on kinetic schemes, which included a second open state and a nonconducting desensitized state that closely reproduced the experimental results, two nonexclusive probable models ofGABA r1Based on kinetic schemes, which included a second open state and a nonconducting desensitized state that closely reproduced the experimental results, two nonexclusive probable models ofGABA r1r1 channels gating are proposed. British Journal of Pharmacology advance online publication, 10 October 2005; doi:10.1038/sj.bjp.0706411advance online publication, 10 October 2005; doi:10.1038/sj.bjp.0706411 Keywords: GABA; GABAC receptors; cationic modulation; chloride channels; lanthanides; kinetic modeling; human retina;GABA; GABAC receptors; cationic modulation; chloride channels; lanthanides; kinetic modeling; human retina; Xenopus oocytesoocytes Abbreviations: Cl, chloride; GABA, g-aminobutyric acid; I–V, current–voltage; HEPES, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acidCl, chloride; GABA, g-aminobutyric acid; I–V, current–voltage; HEPES, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid