Bicuculline, pentobarbital and diazepam modulate spontaneous GABAA channels in rat hippocampal neurons

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Abstract
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 μM 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 μM 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 μM pentobarbital or 1 μM diazepam caused 2–4 fold increase in the maximum channel conductance of low conductance (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. British Journal of Pharmacology (2000) 131, 695–704; doi:10.1038/sj.bjp.0703621