Residual inhibition in density of [3H]isradipine binding sites in rat brain membrane pretreated with amlodipine.

AIM

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.

CONCLUSION

Amlodipine and SM-6586 are Ca2+ antagonists which dissociate slowly from the Ca2+ channel in membranes.