Stable CHO cell clones which selectively express all three rat tachykinin receptors were established by transfection. The binding of radiolabeled substance P and neurokinin A (substance K) to CHO clones expressing the NK1 and NK2 receptors, respectively, were saturatable and of high affinity (K d1=0.17 nM (NK1); 3.4 nM (NK2)). Scatchard analysis of the binding data indicated for both receptors binding to a single population of binding sites, and competition binding studies showed that the binding specificities of the receptors corresponded to those of classical NK1 and NK2 receptors. In contrast, the binding of eledoisin to the NK3 receptor expressed in the transfected CHO cells was of low affinity (IC50=240 nM) compared to the high affinity of the receptor found when it was transiently expressed in COS-7 cells (IC50=8 nM). However, in both cases the receptor exhibited the specificity of a classical NK3 receptor. The established cell clones may provide an important tool for further analysis of the molecular mechanisms involved in binding, activation, and coupling of receptors for tachykinin peptides.
