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PMID: 2463030 Published · ppublish English Journal Article

Kinetic and pharmacological properties of the GABA-induced chloride current in Aplysia neurones: a 'concentration clamp' study.

British journal of pharmacology ·Vol. 95 ·No. 3 ·1988-11-00 ·Pages 883-95

Ikemoto Y, Akaike N, Kijima H

Abstract

1. gamma-Aminobutyric acid (GABA) was applied by the 'concentration clamp' technique to isolated neurones of Aplysia. GABA induced a chloride current (ICl) due to activation of a single class of chloride-channel. 2. The concentration-response curve for the peak ICl gave an apparent dissociation constant of 6.4 X 10(-5) M and a Hill coefficient of 0.88. The current-voltage relationship was linear in the voltage range examined (-40 to +10 mV). 3. The activation phase of the ICl could be fitted to a single exponential function and desensitization followed the sum of two exponential functions. The time constants of activation and desensitization decreased with increasing concentrations of GABA but were voltage-independent. The recovery process from desensitization also followed the sum of two exponential functions. 4. As for the rate-limiting step of the channel activation, the hyperbolic relationship between the activation rate and GABA concentration showed that the rapid binding assumption holds, suggesting that the isomerization step is rate-limiting. The apparent channel closing rate constant was estimated to be 10 s-1 from the ordinate intercept of the linear part of the above relationship at lower concentrations. 5. Muscimol and beta-alanine induced a ICl, which cross-desensitized with that evoked by GABA. The GABA-ICl was not enhanced by diazepam (10(-6) M) or alpha-chloralose (10(-3) M), in fact depressant effects were evident. 6. Pentobarbitone decreased the GABA-ICl non-competitively without altering activation or desensitization kinetics. The concentration-inhibition curve gave a KD value of 8.9 x 10(-5) M and a Hill coefficient of 1.0. 7. These results suggest that GABA activates a single class of Cl channel in Aplysia neurones, which have one binding site for the agonist. The GABA receptor-Cl channel complex in Aplysia is pharmacologically and perhaps structurally different from that in vertebrates.

MeSH Terms
Animals Aplysia Chlorides/metabolism Diazepam/pharmacology Ion Channels/drug effects,metabolism Kinetics Muscimol/pharmacology Neurons/drug effects,metabolism Pentobarbital/pharmacology beta-Alanine/pharmacology gamma-Aminobutyric Acid/pharmacology
Chemicals
Chlorides Ion Channels beta-Alanine Muscimol gamma-Aminobutyric Acid Pentobarbital Diazepam
Authors & Affiliations
3 authors, click to expand affiliations / ORCID
Ikemoto Y
Department of Physiology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Akaike N
Kijima H
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Article Info
Journal
British journal of pharmacology
Abbr.
Br J Pharmacol
ISSN
0007-1188
DOI
10.1111/j.1476-5381.1988.tb11718.x
Published
1988-11-00
Pages
883-95
Language
English
Region
England
NLM ID
7502536
PMCID
PMC1854231
Subset
IM
External Links
PubMed source DOI: 10.1111/j.1476-5381.1988.tb11718.x PMC Full Text View journal details
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