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 (GABA) 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 GABAA 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.
Frech
M J
MJ
Abteilung für Allgemeine Zoologie, FB Biologie, Universität Kaiserslautern, Postfach 3049, D-67653 Kaiserslautern, Germany.
Deitmer
J W
JW
Backus
K H
KH
D000818:Animals; D001306:Auditory Pathways / Q000187:drug effects; D001921:Brain / Q000187:drug effects; D002118:Calcium / Q000032:analysis / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects*; D016764:Cell Polarity / Q000187:drug effects; D002712:Chlorides / Q000032:analysis / Q000378:metabolism*; D005470:Fluorometry / Q000379:methods; D005998:Glycine / Q000494:pharmacology*; D007245:Inferior Colliculi / Q000166:cytology / Q000187:drug effects*; D007425:Intracellular Membranes / Q000737:chemistry* / Q000187:drug effects*; D008853:Microscopy / Q000379:methods; D009474:Neurons / Q000187:drug effects*; D018408:Patch-Clamp Techniques; D051381:Rats; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D015220:Calcium Channels; D002712:Chlorides; D005680:gamma-Aminobutyric Acid; D002118:Calcium; D005998:Glycine