Molecular and pharmacological characterization of the murine tachykinin NK(3) receptor

Starting with a partial sequence from Genbank, polymerase chain reaction (PCR) was utilized to isolate the full-length cDNA for NK(3) receptor from mouse brain. The murine NK(3) receptor has a predicted sequence of 452 amino acids, sharing 96% and 86% identity to the rat and human NK(3) receptors, respectively. Binding affinities and functional potencies of tachykinin receptor agonists were similar in HEK (human embryonic kidney) 293 cells expressing murine NK(3) receptor and human NK(3) receptor, although substance P and neurokinin A were more potent stimulators of Ca(2+) mobilization in murine NK(3) receptor cells. NK(3) receptor-selective antagonists from two structural classes, had 10- to 100-fold lower binding affinities for murine NK(3) receptor compared to human NK(3) receptor, and about 5- to 10-fold reduced potency in the murine NK(3) receptor functional assay. The results demonstrate species differences in the potencies of tachykinin receptor antagonists in murine and human NK(3) receptors, and the lower potencies in the former should be taken into consideration when using murine disease models.