Spontaneously opening GABA(A) channels in CA1 pyramidal neurones of rat hippocampus

Spontaneous, single channel, chloride currents were recorded in 48% of cell -attached patches on neurones in the CAl region of rat hippocampal slices. In some patches, there was more than 1 channel active. They showed outward rectification: both channel conductance and open probability were greater a t depolarized than at hyperpolarized potentials. Channels activated by gamm a-aminobutyric acid (GABA) in silent patches on the same neurones had simil ar conductance and outward rectification, The spontaneous currents were inh ibited by bicuculline and potentiated by diazepam. It was concluded that th e spontaneously opening channels were constitutively active, nonsynaptic GA BA(A) channels. Such spontaneously opening GABA(A) channels may provide a t onic inhibitory mechanism in these cells and perhaps in other cells that ha ve GABA(A) receptors although not having a GABA(A) synaptic input. They may also be a target for clinically useful drugs such as the benzodiazepines.