The Journal of Neurophysiology Vol. 82 No. 1 July 1999, pp. 1-9
Copyright ©1999 by the American Physiological Society

GABA-Induced Cl Current in Cultured Embryonic Human Dorsal Root Ganglion Neurons

 ¹Neurophysiology and Spinal Cord Pharmacology Laboratories, Veterans Affairs Medical Center; and  ²Department of Neurology and  ³The Miami Project to Cure Paralysis, University of Miami School of Medicine, Miami, Florida 33101

Valeyev, Alexander Y., John C. Hackman, Alice M. Holohean, Patrick M. Wood, Jennifer L. Katz, and Robert A. Davidoff. GABA-Induced Cl Current in Cultured Embryonic Human Dorsal Root Ganglion Neurons. J. Neurophysiol. 82: 1-9, 1999.-Aminobutyric acid (GABA)-activated channels in embryonic (5-8 wk old) human dorsal root ganglion (DRG) neurons in dissociated culture were characterized by whole cell and single-channel techniques. All DRG neurons when held at negative holding membrane potentials displayed inward current to micromolar concentrations of GABA applied by pressure pulses from closely positioned micropipettes. The current was directly proportional to the concentration of GABA (EC₅₀, 111 µM; Hill coefficient, 1.7). DRG neurons also responded to micromolar concentrations of pentobarbital and alphaxalone but not to cis-4-aminocrotonic acid (CACA), glycine, or taurine. Baclofen (100 µM) affected neither the holding currents nor K⁺ conductance (when patch pipettes were filled with 130 mM KCl) caused by depolarizing pulses. Whole cell GABA-currents were blocked by bicuculline, picrotoxin, and t-butylbicyclophosphorothionate (TBPS; all at 100 µM). The reversal potential of whole cell GABA-currents was close to the theoretical Cl equilibrium potential, shifting with changes in intracellular Cl concentration in a manner expected for Cl-selective channels. The whole cell I-V curve for GABA-induced currents demonstrated slight outward rectification with nearly symmetrical outside and inside Cl concentrations. Spectral analysis of GABA-induced membrane current fluctuations showed that the kinetic components were best fitted by a triple Lorentzian function. The apparent elementary conductance for GABA-activated Cl channels determined from the power spectra was 22.6 pS. Single-channel recordings from cell-attached patches with pipettes containing 10 µM GABA indicated that GABA-activated channels have a main and a subconductance level with values of 30 and 19 pS, respectively. Mean open and closed times of the channel were characterized by two or three exponential decay functions, suggesting two or three open channel states and two closed states. Single channels showed a lack of rectification. The actions of GABA on cultured human embryonic DRG neurons are mediated through the activation of GABA_A receptors with properties corresponding to those found in the CNS of human and other mammalian species but differing from those of cultured human adult DRG neurons.