Bicuculline, pentobarbital and diazepam modulate spontaneous GABA(A) channels in rat hippocampal neurons.
Spontaneously opening, chloride-selective channels that showed outward rectification were recorded in ripped-off patches from rat cultured hippocampal neurons and in cell-attached patches from rat hippocampal CA1 pyramidal neurons in slices. In both preparations, channels had multiple conductance states and the most common single-channel conductance varied. In the outside-out patches it ranged from 12 to 70 pS (Vp=40 mV) whereas in the cell-attached patches it ranged from 56 to 85 pS (-Vp=80 mV). Application of GABA to a patch showing spontaneous channel activity evoked a rapid, synchronous activation of channels. During prolonged exposure to either 5 or 100 microM GABA, the open probability of channels decreased. Application of GABA appeared to have no immediate effect on single-channel conductance. Exposure of the patches to 100 microM bicuculline caused a gradual decrease on the single-channel conductance of the spontaneous channels. The time for complete inhibition to take place was slower in the outside-out than in the cell-attached patches. Application of 100 microM pentobarbital or 1 microM diazepam caused 2 - 4 fold increase in the maximum channel conductance of low conductance (<40 pS) spontaneously active channels. The observation of spontaneously opening GABA(A) channels in cell-attached patches on neurons in slices suggests that they may have a role in neurons in vivo and could be an important site of action for some drugs such as benzodiazepines, barbiturates and general anaesthetics.
Birnir
B
B
Membrane Biology Program, John Curtin School of Medical Research, Australian National University, Canberra ACT, 0200 Australia. bryndis.birnir@mphy.lu.se
Eghbali
M
M
Everitt
A B
AB
Gage
P W
PW
D000818:Animals; D001640:Bicuculline / Q000494:pharmacology*; D002478:Cells, Cultured; D003975:Diazepam / Q000494:pharmacology*; D018757:GABA Modulators / Q000494:pharmacology*; D006624:Hippocampus / Q000187:drug effects* / Q000502:physiology; D007473:Ion Channels / Q000187:drug effects*; D010424:Pentobarbital / Q000494:pharmacology*; D051381:Rats; D011963:Receptors, GABA-A / Q000187:drug effects*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D018757:GABA Modulators; D007473:Ion Channels; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid; D010424:Pentobarbital; D003975:Diazepam; D001640:Bicuculline