Characterization of antagonistic activity and binding properties of SR 95531, a pyridazinyl-GABA derivative, in rat brain and cultured cerebellar neuronal cells.
Experiments were performed to characterize the antagonistic activity and binding properties of SR 95531 [2-(3' carbethoxy-2'-propyl)-3-amino-6-paramethoxy-phenyl-piridazinium bromide] in rat brain. SR 95531 and bicuculline methiodide inhibited muscimol-stimulated 36Cl- uptake in cortical synaptoneurosomes in a concentration-dependent manner. The inhibitory potency of SR 95531 for the muscimol-stimulated 36Cl- uptake was 15 times higher than that of bicuculline methiodide. Scatchard plots of binding isotherms exhibited two apparent binding sites for [3H]SR 95531 in both the frontal cortex and cerebellum. The IC50 value of SR 95531 for muscimol-stimulated 36Cl- uptake into cortical synaptoneurosomes was in close agreement with the KD value of low-affinity binding sites of [3H]SR 95531 in the frontal cortex. Pretreatment of the membranes with phospholipase A2 invariably decreased [3H]SR 95531 binding in the frontal cortex and cerebellum. On the other hand, the treatment significantly increased [3H]gamma-aminobutyric acid (GABA) binding in a concentration-dependent manner in the frontal cortex. Although lower concentrations of phospholipase A2 did not affect [3H]GABA binding in the cerebellum, treatment with higher concentrations of phospholipase A2 increased the binding in this region. Specific binding of [3H]SR 95531 was also detected in cultures rich in cerebellar granule cells. Pretreatment with phospholipase A2 affected the binding of [3H]GABA and [3H]SR 95531 in these cells, as in the case of the cerebellum. These effects of phospholipase A2 on the binding of [3H]GABA and [3H]SR 95531 were partially prevented by the addition of delipidated bovine serum albumin.(ABSTRACT TRUNCATED AT 250 WORDS)
Ito
Y
Y
Department of Pharmacology, College of Pharmacy, Nihon University, Chiba, Japan.
Koshiba
T
T
Doi
M
M
Asami
S
S
Fukuda
H
H
Murakoshi
Y
Y
D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D002531:Cerebellum / Q000187:drug effects / Q000378:metabolism*; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism; D002713:Chlorine / Q000378:metabolism; D018756:GABA Antagonists; D007700:Kinetics; D008297:Male; D009118:Muscimol / Q000037:antagonists & inhibitors / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D011724:Pyridazines / Q000378:metabolism / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism
D018756:GABA Antagonists; D011724:Pyridazines; D009118:Muscimol; D002713:Chlorine; C049853:gabazine