Characteristics of GABAA channels in rat dentate gyrus

Abstract

Single channel currents were activated by GABA (0.5 to 5 microM) in cell-attached and inside-out patches from cells in the dentate gyrus of rat hippocampal slices. The currents reversed at the chloride equilibrium potential and were blocked by bicuculline (100 microM). Several different kinds of channel were seen: high conductance and low conductance, rectifying and "nonrectifying." Channels had multiple conductance states. The open probability (Po) of channels was greater at depolarized than at hyperpolarized potentials and the relationship between Po and potential could be fitted with a Boltzmann equation with equivalent valency (z) of 1. The combination of outward rectification and potential-dependent open probability gave very little chloride current at hyperpolarized potentials but steeply increasing current with depolarization, useful properties for a tonic inhibitory mechanism.

Outwardly Rectifying Tonically Active GABAAReceptors in Pyramidal Cells Modulate Neuronal Offset, Not Gain

“…Lesser rectification of GABA A Rs at higher GABA concentrations has been suggested to be secondary to a lesser effect of increased GABA binding with saturating GABA concentrations and consequently an increased role of voltage-dependent desensitization . We cannot, however, exclude the possibility that higher GABA concentrations recruit receptors with less marked rectification or no rectification at all (Birnir et al, 1994;Burgard et al, 1996).…”

“…GABA A receptor rectification GABA A Rs can exhibit both outward and inward rectification (Weiss, 1988;Birnir et al, 1994;Gage and Chung, 1994;Yoon, 1994;Burgard et al, 1996;Eghbali et al, 1997;Mennerick et al, 2001;. Studies of recombinant receptors in different expression systems indicate that the degree of rectification depends upon the subunit composition of the GABA A Rs, with many receptor subtypes showing no or minimal rectification (Verdoorn et al, 1990;Burgard et al, 1996).…”

“…Studies of recombinant receptors in different expression systems indicate that the degree of rectification depends upon the subunit composition of the GABA A Rs, with many receptor subtypes showing no or minimal rectification (Verdoorn et al, 1990;Burgard et al, 1996). Using modeling and experimental data, rectification has been attributed to voltagedependent deactivation of GABA A Rs (Mellor and Randall, 1998) though other mechanisms, such as voltage dependence of desensitization, conductance and opening time may also play a role (Birnir et al, 1994;Yoon, 1994). More recently, the outward rectification of GABA A Rs at low GABA concentrations has been suggested to be secondary to an increased GABA binding rate and a larger opening rate at depolarized potentials .…”

“…There is growing evidence from single channel recordings from neurons that GABA A receptors can under certain circumstances show outward rectification (Birnir et al, 1994), which is dependent upon the presence of low GABA concentrations . How does this affect the I-V relationship of phasic and tonic GABA A R-mediated signals?…”

GLP-1 and Exendin-4 Transiently Enhance GABAA Receptor–Mediated Synaptic and Tonic Currents in Rat Hippocampal CA3 Pyramidal Neurons

“…All animal procedures were conducted in accordance with the local ethics guidelines and approved animal care protocols by the Uppsala djurförsöksetiska nämnd, Uppsala, Sweden (Uppsala Animal Ethical Board). Hippocampal slices were prepared as previously described (37). Briefly, the animal was decapitated and the brain rapidly removed and immersed into the ice-cold artificial cerebrospinal fluid (ACSF) containing (in millimoles per liter): 124 NaCl, 3 KCl, 2.5 CaCl 2 , 1.3 MgSO 4 , 26 NaHCO 3 , 2.5 Na 2 HPO 4 , and 10 glucose with pH 7.3-7.4 when bubbled with 95% O 2 and 5% CO 2 .…”