Residual inhibition in density of [3H]isradipine binding sites in rat brain membrane pretreated with amlodipine
Qu, Y.L.; Takamizawa, C.; Sugiyama, K.; Maruyama, K.; Hattori, K.; Watanabe, K.; Nagatomo, T.
Zhongguo Yao Li Xue Bao 16(4): 289-293
1995
ISSN/ISBN: 0253-9756 PMID: 7668088 Document Number: 441731
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). 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. 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. Amlodipine and SM-6586 are Ca2+ antagonists which dissociate slowly from the Ca2+ channel in membranes.