| Abstract: | Characteristics of the interaction of verapamil with serotonin receptors were studied in rat brain membranes using a radioligand binding technique. While verapamil competed for the 3H]ketanserin binding sites at low concentrations with the Ki value of 0.41 microM, much higher concentrations were needed to inhibit the binding of 3H]serotonin to its binding sites, indicating higher affinity of verapamil binding for 5-HT2 than 5-HT1 receptors. The inhibitory action of verapamil on the 3H]ketanserin binding was stereoselective; the (-)isomer was about ten times more potent than the (+)isomer. The interaction of verapamil with 3H]-ketanserin was competitive and reversible. While D600, a verapamil derivative, also competed for the 3H]ketanserin binding sites, nifedipine and nicardipine had practically no ability to inhibit the ligand binding to 5-HT1 or 5-HT2 receptors. Although diltiazem competed for 5-HT2 receptors, the affinity was much less than verapamil and D600. |
