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Analysis of GABA A ‐ and GABA B ‐receptor mediated effects on intracellular Ca 2+ in DRG hybrid neurones
Author(s) -
Yokogawa Tomonori,
Kim Seung U,
Krieger Charles,
Puil Ernest
Publication year - 2001
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1038/sj.bjp.0704244
Subject(s) - chemistry , bicuculline , biophysics , extracellular , receptor , agonist , gabaa receptor , biochemistry , biology
Using pharmacological analysis and fura‐2 spectrofluorimetry, we examined the effects of γ‐aminobutyric acid (GABA) and related substances on intracellular Ca 2+ concentration ([Ca 2+ ] i ) of hybrid neurones, called MD3 cells. The cell line was produced by fusion between a mouse neuroblastoma cell and a mouse dorsal root ganglion (DRG) neurone. MD3 cells exhibited DRG neurone‐like properties, such as immunoreactivity to microtubule‐associated protein‐2 and neurofilament proteins. Bath applications of capsaicin and α, β‐methylene adenosine triphosphate reversibly increased [Ca 2+ ] i . However, repeated applications of capsaicin were much less effective. Pressure applications of GABA (100 μ M ), (Z)‐3‐[(aminoiminomethyl) thio] prop‐2‐enoic acid sulphate (ZAPA; 100 μ M ), an agonist at low affinity GABA A ‐receptors, or KCl (25 m M ), transiently increased [Ca 2+ ] i . Bath application of bicuculline (100 n M – 100 μ M ), but not picrotoxinin (10 – 25 μ M ), antagonized GABA‐induced increases in [Ca 2+ ] i in a concentration‐dependent manner (IC 50 =9.3 μ M ). Ca 2+ ‐free perfusion reversibly abolished GABA‐evoked increases in [Ca 2+ ] i . Nifedipine and nimodipine eliminated GABA‐evoked increases in [Ca 2+ ] i . These results imply GABA response dependence on extracellular Ca 2+ . Baclofen (500 n M – 100 μ M ) activation of GABA B ‐receptors reversibly attenuated KCl‐induced increases in [Ca 2+ ] i in a concentration‐dependent manner (EC 50 =1.8 μ M ). 2‐hydroxy‐saclofen (1 – 20 μ M ) antagonized the baclofen‐depression of the KCl‐induced increase in [Ca 2+ ] i . In conclusion, GABA A ‐receptor activation had effects similar to depolarization by high external K + , initiating Ca 2+ influx through high voltage‐activated channels, thereby transiently elevating [Ca 2+ ] i . GABA B ‐receptor activation reduced Ca 2+ influx evoked by depolarization, possibly at Ca 2+ ‐channel sites in MD3 cells.British Journal of Pharmacology (2001) 134 , 98–107; doi: 10.1038/sj.bjp.0704244