Intracellular chloride and calcium transients evoked by gamma-aminobutyric acid and glycine in neurons of the rat inferior colliculus

Microfluorometric recordings showed that the inhibitory neurotransmitters gamma-aminobutyric acid (GilBA) and glycine activated transient increases in the intracellular Cl- concentration in neurons of the inferior colliculus (IC) from acutely isolated slices of the rat auditory midbrain. Current recordings in gramicidin-perforated patch mode disclosed that GABA and glycine mainly evoked inward or biphasic currents. These currents were dependent on HCO3- and characterized by a continuous shift of their reversal potential (E-GABA/gly) in the positive direction. In HCO3--buffered saline, GABA and glycine could also evoke an increase in the intracellular Ca2+ concentration. Ca2+ transients occurred only with large depolarizations and were blocked by Cd2+, suggesting an activation of voltage-gated Ca2+ channels. However, in the absence of HCO3-, only a small rise, if any, in the intracellular Ca2+ concentration could be evoked by GABA or glycine, We suggest that the activation of GABA, or glycine receptors results in an acute accumulation of Cl- that is enhanced by the depolarization owing to HCO3- efflux, thus shifting E-GABA/gly to more positive values. A subsequent activation of these receptors would result in a strenghtened depolarization and an enlarged Ca2+ Influx that might play a role in the stabilization of inhibitory synapses In the auditory pathway, (C) 1999 John Wiley Sr Sons, Inc. I Neurobiol 40: 386-396. 1999.