Analysis of macroscopic ionic currents mediated by GABArho1 receptors during lanthanide modulation predicts novel states controlling channel gating.
Lanthanide-induced modulation of GABA(C) receptors expressed in Xenopus oocytes was studied. We obtained two-electrode voltage-clamp recordings of ionic currents mediated by recombinant homomeric GABArho(1) receptors and performed numerical simulations of kinetic models of the macroscopic ionic currents.GABA-evoked chloride currents were potentiated by La(3+), Lu(3+) and Gd(3+) in the micromolar range. Lanthanide effects were rapid, reversible and voltage independent. The degree of potentiation was reduced by increasing GABA concentration.Lu(3+) also induced receptor desensitization and decreased the deactivation rate of GABArho(1) currents. In the presence of 300 microM Lu(3+), dose-response curves for GABA-evoked currents showed a significant enhancement of the maximum amplitude and an increase of the apparent affinity. The rate of onset of TPMPA and picrotoxin antagonism of GABArho(1) receptors was modulated by Lu(3+). These results suggest that the potentiation of the anionic current was the result of a direct lanthanide-receptor interaction at a site capable of allosterically modulating channel properties. 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 of GABArho(1) channels gating are proposed.
Goutman
Juan D
JD
Laboratorio de Neurobiología Celular y Molecular, INGEBI, CONICET, Departamento de Fisiología, Biología Molecular y Celular, FCEyN, Universidad de Buenos Aires, Vuelta de Obligado 2490, CP 1428 Ciudad Autónoma de Buenos Aires, Argentina.
Escobar
Ariel L
AL
Calvo
Daniel J
DJ
D018118:Chloride Channels / Q000187:drug effects* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects*; D028581:Lanthanoid Series Elements / Q000494:pharmacology*; D010721:Phosphinic Acids / Q000494:pharmacology; D010852:Picrotoxin / Q000494:pharmacology; D021122:Protein Subunits; D011725:Pyridines / Q000494:pharmacology; D018079:Receptors, GABA / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D018118:Chloride Channels; D028581:Lanthanoid Series Elements; D010721:Phosphinic Acids; D010852:Picrotoxin; D021122:Protein Subunits; D011725:Pyridines; D018079:Receptors, GABA; D005680:gamma-Aminobutyric Acid; C101879:(1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid; C087200:GABA-C receptor