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-m ediated synaptic currents in cerebellar granule cells grown in a low ( 5 mM) potassium medium. In the presence of kynurenic acid (1 mM), to b lock the excitatory drive, bicuculline-sensitive synaptic events were recorded. Their amplitude distribution could be fitted by several Gaus sians having the same interpeak distance. In tetrodotoxin (TTX, 1 mu M ) spontaneous miniature events occurred at a lower frequency. Spontane ous currents reversed polarity at 8.17 +/- 0.63 mV, a potential close to E(Cl); the decay phase could be fitted with a single exponential ha ving at - 60 mV a time constant of 48.7 +/- 1.5 ms. In low noise recor dings, channel closing could be resolved during the decay phase of min iature events. It appeared that a single quantum of GABA opened few ch annels on the postsynaptic membrane.