Occurrence and pharmacological characterization of four human tachykinin NK2 receptor variants.

Tachykinin NK2 receptor antagonists are potentially beneficial in treating various disorders including irritable bowel syndrome, urinary incontinence, depression and anxiety. The current study evaluates the frequency of single nucleotide polymorphisms (SNPs) in the human NK2 receptor gene (TACR2). In addition, the potency of the endogenous peptide agonist neurokinin A (NKA), and the small molecule antagonists saredutant (NK2-selective) and ZD6021 (pan-NK antagonist) at the various NK2 receptor protein variants were determined. The TACR2 gene was sequenced from 37 individuals. Two amino acid changing SNPs encoding the NK2 receptor variants Ile23Thr and Arg375His were found. The frequency of the four possible protein variants differed between populations. Site-directed mutagenesis was performed introducing either SNP or both SNPs into the TACR2 gene and the constructs were transfected into CHO cells. NKA-evoked increases in intracellular Ca2+ were monitored by FLIPR. The potency of saredutant and ZD6021 was evaluated by their ability to inhibit NKA-induced increases in intracellular Ca2+. NKA evoked increases in intracellular Ca2+ with a potency ranging between 1 and 5nM in CHO cells expressing the different constructs. Saredutant and ZD6021 blocked NKA-evoked increases in intracellular Ca2+ with pKb values ranging between 8.8–9.3 and 7.9–8.7, respectively. The current study demonstrates that polymorphisms leading to the Ile23Thr and Arg375His amino acid exchanges are highly prevalent in the human TACR2 gene. These polymorphisms however do not appear to affect the potency of the endogenous agonist NKA or the small molecule antagonists saredutant and ZD6021 with respect to intracellular Ca2+ signalling.