title: Residual inhibition in density of [3H]isradipine binding sites in rat brain membrane pretreated with amlodipine.
abstract: OBJECTIVE
  To test changes in the density of [3H] isradipine binding sites in rat brain membrane pretreated with amlodipine and to compare with those of nifedipine and (+) SM-6586 (methyl 1, 4-dihydro-2, 6-dimethyl-3-(3-(N-benzyl-N-methylaminomethyl)-1,2,4- oxadiazolyl-5-yl)-4-(3-nitrophenyl) pyridine-5-carboxylate).
  
  
  METHODS
  The membrane-enriched fractions were prepared from rat brain. The brain membranes were preincubated with nifedipine (10 nmol L-1), amlodipine (1 mumol L-1) and SM-6586 (1 nmol L-1) or with no antagonists added for 45 min, and washing and centrifugation were performed 3 times. They were assayed with [3H]isradipine in incubation media. The Kd and Bmax values of the membrane fractions pretreated with the drugs were determined by Scatchard analysis.
  
  
  RESULTS
  The blockage of the [3H]isradipine binding sites induced by nifedipine was reversed by washing, enabling the low values of the specific binding sites to be observed. The blockages by amlodipine and SM-6586, on the other hand, were not readily reversed. No significant difference was found, however, between in the Kd walues of these drugs.
  
  
  CONCLUSIONS
  Amlodipine and SM-6586 are Ca2+ antagonists which dissociate slowly from the Ca2+ channel in membranes.
authors.affiliation: Department of Pharmacology, Niigata College of Pharmacy, Japan.
authors.forename: Y L
authors.initials: YL
authors.lastname: Qu
authors.forename: C
authors.initials: C
authors.lastname: Takamizawa
authors.forename: K
authors.initials: K
authors.lastname: Sugiyama
authors.forename: K
authors.initials: K
authors.lastname: Maruyama
authors.forename: K
authors.initials: K
authors.lastname: Hattori
authors.forename: K
authors.initials: K
authors.lastname: Watanabe
authors.forename: T
authors.initials: T
authors.lastname: Nagatomo
mesh_terms: D017311:Amlodipine / Q000737:chemistry / Q000494:pharmacology*; D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D001921:Brain / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D004095:Dihydropyridines / Q000737:chemistry / Q000494:pharmacology; D017275:Isradipine / Q000378:metabolism*; D008297:Male; D009543:Nifedipine / Q000737:chemistry / Q000494:pharmacology; D010069:Oxadiazoles / Q000737:chemistry / Q000494:pharmacology; D011869:Radioligand Assay; D051381:Rats; D017208:Rats, Wistar
chemical_list: D002121:Calcium Channel Blockers; D004095:Dihydropyridines; D010069:Oxadiazoles; C075861:SM 6586; D017311:Amlodipine; D009543:Nifedipine; D017275:Isradipine