Tachykinin NK(2) 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
NK(2) receptor gene (TACR2). In addition, the potency of the endogenous
peptide agonist
neurokinin A (NKA), and the small molecule antagonists
saredutant (NK(2)-selective) and
ZD6021 (pan-NK antagonist) at the various
NK(2) receptor protein variants were determined. The TACR2 gene was sequenced from 37 individuals. Two
amino acid changing SNPs encoding the
NK(2) 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 Ca(2+) were monitored by FLIPR. The potency of
saredutant and
ZD6021 was evaluated by their ability to inhibit NKA-induced increases in intracellular Ca(2+). NKA evoked increases in intracellular Ca(2+) with a potency ranging between 1 and 5nM in CHO cells expressing the different constructs.
Saredutant and
ZD6021 blocked NKA-evoked increases in intracellular Ca(2+) with pK(b) 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 Ca(2+) signalling.