Stable expression of high affinity NK1 (substance P) and NK2(neurokinin A) receptors but low affinity NK3 (neurokinin B) receptors in transfected CHO cells

Abstract

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.