Molecular cloning, mutations and effects of NK1 receptor antagonists reveal the human-like pharmacology of gerbil NK1 receptors

Abstract The present study investigates the pharmacology of the cloned neurokinin 1 receptor from the gerbil (gNK 1 R), a species claimed to have human-like NK 1 R (hNK 1 R) pharmacology. The amino acid sequence of NK 1 R was cloned. The hNK 1 R, rat NK 1 R (rNK 1 R), gNK 1 R and mutants of the gNK 1 R were expressed in CHO cells. The affinity and potency of NKR agonists and the NK 1 R antagonists CP99994 and RP67580 (NK 1 R-selective) and ZD6021 (NK1/2R) were assessed in vitro by monitoring [ 3 H]-SarMet SP binding and substance P-evoked mobilization of intracellular Ca 2+ . The gerbil foot tap (GFT) method was used to assess the potency of the antagonists in vivo . The gNK 1 R coding sequence displayed an overall 95% and 97% homology with hNK 1 R and rNK 1 R, respectively. The affinity of the NK 1 R-selective agonist 3 H-SarMet SP for human and gerbil NK 1 R was similar (2.0 and 3.1 nM) but lower for rNK 1 R (12.4 nM). The rank order potency of the agonists for NK 1 R was SP ≥ ASMSP ≥ NKA ⋙ pro7NKB in all species. The NK 1 R antagonists, ZD6021 and CP99994, had comparable affinity and potency for gerbil and human NK 1 R, but were 1000-fold less potent for rNK 1 R. In contrast, RP67580 had comparable affinity and potency for all three species. Mutations in positions 116 and 290 did not affect agonist potency at the gNK 1 R while the potency of the antagonists ZD6021 and CP99994 were markedly decreased (10–20-fold). It is concluded that gNK 1 R has similar antagonist pharmacology as the human-like orthologue and that species differences in antagonist function depend on key residues in the coding sequence and antagonist structure.