Spontaneous gaba-mediated synaptic currents in cerebellar granule cells in culture

The whole-cell configuration of the patch clamp technique was used to characterize the electrophysiological properties of spontaneous GABA-mediated synaptic currents in cerebellar granule cells grown in a low (5 mM) potassium medium. In the presence of kynurenic acid (1 mM), to block the excitatory drive, bicuculline-sensitive synaptic events were recorded. Their amplitude distribution could be fitted by several Gaussians having the same interpeak distance. In tetrodotoxin (TTX, 1 μM) spontaneous miniature events occurred at a lower frequency. Spontaneous currents reversed polarity at 8.17 ± 0.63 mV, a potential close to E_ci; the decay phase could be fitted with a single exponential having at - 60 mV a time constant of 48.7 ± 1.5 ms. In low noise recordings, channel closing could be resolved during the decay phase of miniature events. It appeared that a single quantum of GABA opened few channels on the postsynaptic membrane.