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). 6. CP-96,345, CP-96,344, and the racemate all inhibited [3H]-diltiazem binding in rat cerebral cortex membranes with Ki values of 22.5 nM, 34.5 nM and 29.9 nM respectively; a similar value was obtained for diltiazem itself (33.6 nM). In comparison, CP-96,345 and ( +/- )-CP-96,345 inhibited the binding of[125I]-Bolton-Hunter-conjugated substance P in this tissue with Ki values of 59.6 nM and 82.0 nM respectively, while CP-96,344 had no measurable affinity (IC50> 10 microM).7. Substance P and a range of ligands selective for NK1, NK2, or NK3 receptors had no significant effect at 10 microM on either [3H]-diltiazem or [3H]-nimodipine binding.8. The results indicate that in addition to possessing affinity for the NK1 receptor, the non-peptide antagonist, CP-96,345, displays high affinity for [3H]-diltiazem binding sites on L-type calcium channels.The functional effect that may be observed in integrated models will be a consequence of either property, or be a composite effect of NK1 receptor antagonism and L-channel blockade.
Guard
S
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Parke-Davis Neuroscience Research Centre, Addenbrookes Hospital Site, Cambridge.
Boyle
S J
SJ
Tang
K W
KW
Watling
K J
KJ
McKnight
A T
AT
Woodruff
G N
GN
D000818:Animals; D001713:Biphenyl Compounds / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects* / Q000378:metabolism; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism; D004110:Diltiazem / Q000493:pharmacokinetics / Q000494:pharmacology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism; D064729:Neurokinin-1 Receptor Antagonists; D009553:Nimodipine / Q000493:pharmacokinetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D013237:Stereoisomerism; D013373:Substance P / Q000378:metabolism; D013388:Succinimides / Q000378:metabolism; D014132:Trachea / Q000187:drug effects / Q000378:metabolism
D001713:Biphenyl Compounds; C043194:Bolton Hunter reagent-substance P conjugate; D015220:Calcium Channels; D064729:Neurokinin-1 Receptor Antagonists; D013388:Succinimides; D013373:Substance P; D009553:Nimodipine; D004110:Diltiazem; C066892:CP 96345