The interaction of the NK1 receptor antagonist CP-96,345 with L-type calcium channels and its functional consequences.

1. We investigated the effects of the non-peptide NK1 receptor antagonist, CP-96,345, its inactive enantiomer CP-96,344, and the racemic mixture (+/-)-CP-96,345, on the binding of [3H]-nimodipine and [3H]-diltiazem to L-type calcium channels in rat cerebral cortex membranes. In isolated peripheral tissues containing tachykinin receptors, the effects of (+/-)-CP-96,345 have been compared with those of diltiazem. 2. In guinea-pig trachea, (+/-)-CP-96,345 produced antagonism of responses to the selective NK1 agonists [Sar9, Met(O2)11]SP and substance P-methyl ester that was apparently competitive in nature (pKB 7.0-7.5), while in guinea-pig ileum the antagonism was not surmountable. 3. The reduction of maximum responses by (+/-)-CP-96,345 in the guinea-pig ileum was not selective; it was obtained with muscarinic agonists and other agents, and was also observed in the portal vein of the rat where NK1 receptors are not present. 4. The tissue-specific reduction of maximum responses by (+/-)-CP-96,345 in ileum was reproduced by diltiazem. 5. (+/-)-CP-96,345 produced a concentration-dependent enhancement of [3H]-nimodipine binding to rat cerebral cortex membranes with a maximal stimulation of 186 +/- 29% above control (EC50 83.2 nM). Scatchard analysis revealed that (+/-)-CP-96,345 increased the affinity of [3H]-nimodipine for its binding sites without affecting Bmax (control: KD = 0.32 nM; with 100 nM (+/-)-CP-96,345: KD = 0.074 nM).(ABSTRACT TRUNCATED AT 250 WORDS)