Abstract
SR 48968, a non-peptide tachykinin NK 2 receptor antagonist, has been shown to possess sub-micromolar affinity for NK 3 receptors present in the guinea pig. In the present study, we have compared the binding affinities of SR 48968 to the cloned human and rat NK 3 receptors expressed in CHO cells. Using [ 125I]-[MePhe 7]-neurokinin B as the radioligand, SR48968 displayed an IC 50 value of 350 nM for the human NK 3 receptor as compared with a value of greater than 10 μM for the rat NK 3 receptor. Exposure of cells transfected with human NK 3 receptor cDNA to [Pro 7]-neurokinin B increased inositol phospholipid turnover in a concentration-dependent manner and this response was blocked competitively by SR 48968. Our results demonstrate that SR 48968 is an antagonist at the human NK 3 receptor and may be a useful tool for elucidating the species-dependent variations in the non-peptide antagonist binding site(s) on the NK 3 receptor.
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