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Molecular mechanisms of benzodiazepine‐induced down‐regulation of GABA A receptor α 1 subunit protein in rat cerebellar granule cells
Author(s) -
Brown Maria J.,
Bristow David R.
Publication year - 1996
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 - 10.1111/j.1476-5381.1996.tb15512.x
Subject(s) - protein subunit , gabaa receptor , cerebellum , chemistry , neuroscience , microbiology and biotechnology , receptor , granule (geology) , biophysics , benzodiazepine , gabaa rho receptor , granule cell , biology , biochemistry , hippocampal formation , gene , paleontology , dentate gyrus
1 Chronic benzodiazepine treatment of rat cerebellar granule cells induced a transient down‐regulation of the γ‐aminobutyric acid A (GABA A ) receptor α 1 subunit protein, that was dose‐dependent (1 nM‐1 μ m ) and prevented by the benzodiazepine antagonist flumazenil (1 μ m ). After 2 days of treatment with 1 μ m flunitrazepam the α 1 subunit protein was reduced by 41% compared to untreated cells, which returned to, and remained at, control cell levels from 4–12 days of treatment. Chronic flunitrazepam treatment did not significantly alter the GABA A receptor α 6 subunit protein over the 2–12 day period. 2 GABA treatment for 2 days down‐regulates the α 1 subunit protein in a dose‐dependent (10 μ m ‐1 mM) manner that was prevented by the selective GABA A receptor antagonist bicuculline (10 μ m ). At 10 μ m and 1 mM GABA the reduction in α 1 subunit expression compared to controls was 31% and 66%, respectively. 3 The flunitrazepam‐induced decrease in α 1 subunit protein is independent of GABA, which suggests that it involves a mechanism distinct from the GABA‐dependent action of benzodiazepines on GABA A receptor channel activity. 4 Simultaneous treatment with flunitrazepam and GABA did not produce an additive down‐regulation of α 1 subunit protein, but produced an effect of the same magnitude as that of flunitrazepam alone. This down‐regulation induced by the combination of flunitrazepam and GABA was inhibited by flumazenil (78%), but unaffected by bicuculline. 5 The flunitrazepam‐induced down‐regulation of α 1 subunit protein at 2 days was completely reversed by the protein kinase inhibitor staurosporine (0.3 μ m ). 6 This study has shown that both flunitrazepam and GABA treatment, via their respective binding sites, caused a reduction in the expression of the GABA A receptor α 1 subunit protein; an effect mediated through the same neurochemical mechanism. The results also imply that the benzodiazepine effect is independent of GABA, and that the benzodiazepine and GABA sites may not be equally coupled to the down‐regulation process, with the benzodiazepine site being the more dominant. The biochemical mechanism underlying the benzodiazepine‐mediated down‐regulation of the α subunit protein seems to involve the activity of staurosporine‐sensitive protein kinases.