Effects of the Ca2(+)-antagonists nifedipine, verapamil, flunarizine and of the calmodulin antagonist trifluoperazine on muscarinic cholinergic receptors in rat cerebral cortex.

1. Studies were made of [3H]QNB binding to muscarinic receptors in a membrane fraction from the cerebral cortex of rats treated orally for 13 days with the Ca2(+)-antagonists nifedipine (20 mg/kg), verapamil (50 mg/kg), flunarizine (10 mg/kg) and with the calmodulin antagonist trifluoperazine (3 mg/kg). 2. The [3H]QNB binding capacity (Bmax) was decreased by three Ca2(+)-antagonists: nifedipine, verapamil and flunarizine, the decrease was most pronounced with nifedipine. 3. The decrease in the number of muscarinic receptors after nifedipine and flunarizine was accompanied by an increase in their affinity; verapamil decreased both the number and the affinity of muscarinic receptors. 4. The calmodulin antagonist trifluoperazine changed neither the number nor the affinity of muscarinic receptors. 5. It is suggested that continuous treatment with different Ca2+ or calmodulin antagonists leads to difference in character and degree of alterations in the basic characteristics of muscarinic receptors in rat cerebral cortex.