Many neurons receive a continuous, or 'tonic', synaptic input, which increa
ses their membrane conductance, and so modifies the spatial and temporal in
tegration of excitatory signals(1-3). In cerebellar granule cells, although
the frequency of inhibitory synaptic currents is relatively low, the spill
over of synaptically released GABA (gamma -aminobutyric acid)(4) gives rise
to a persistent conductance mediated by the GABA(A) receptor(5-7) that als
o modifies the excitability of granule cells(8). Here we show that this ton
ic conductance is absent in granule cells that lack the alpha6 and delta -s
ubunits of the GABAA receptor. The response of these granule cells to excit
atory synaptic input remains unaltered, owing to an increase in a 'leak' co
nductance, which is present at rest, with properties characteristic of the
two-pore-domain K+ channel TASK-1 (refs 9- 12). Our results highlight the i
mportance of tonic inhibition mediated by GABAA receptors, loss of which tr
iggers a form of homeostatic plasticity leading to a change in the magnitud
e of a voltage-independent K+ conductance that maintains normal neuronal be
haviour.