Functionally distinct chloride-mediated GABA responses in rat cerebellar
granule cells cultured in a low potassium medium.
Martina, Marco, Caterina Virginio and Enrico Cherubini.
Biophysics Sector, International School for Advanced Studies (SISSA), Via
Beirut 2-4, 34014 Trieste, Italy.
APStracts 3:0231N, 1996.
The patch clamp technique was used to study whole cell currents evoked by (-
aminobutyric acid (GABA) in rat cerebellar granule cells cultured in 5 mM
potassium, a condition that favours the development of functional GABAergic
synapses. GABA activated both high and low sensitivity receptors. The high
sensitivity receptor had an EC50 of 13 (M whereas the low sensitivity one had
an EC50 of 255 (M. The GABAA receptor agonist isoguvacine activated only the
high sensitivity receptor with an EC50 of 16 (M. When GABA was applied during
the desensitized phase of the response elicited by a saturating concentration
of isoguvacine, it was still able to induce a small response whereas when
isoguvacine was applied during the desensitizing phase of GABA-evoked current
no response was detected. GABA responses were highly heterogeneous regarding
their sensitivity to bicuculline. In a small number of cells (3/25),
bicuculline (10 (M) completely abolished GABA-evoked currents. In the majority
of the neurons (22/25) the blocking effect of bicuculline (100 (M) was 64 ( 4
%.The bicuculline-resistant component was abolished by picrotoxin (100 (M). In
bicuculline, the dose/response curve for GABA was fitted with a sigmoidal
curve with an EC50 value of 209 (M. These data indicate that functional new
GABA receptor types with unusual pharmacology could be swithched on by
conditions that maintain cells in their undifferentiated state.
Received 19 June 1996; accepted in final form 30 September 1996.
APS Manuscript Number J491-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996