Phosphorylation and desensitization of the neurokinin-1 receptor expressedin epithelial cells

A rat kidney epithelial cell line expressing the rat neurokinin-1 receptor( NK-1 R) was used to investigate the relationship between receptor phosphory lation and desensitization. Substance P (SP) maximally stimulated cellular inositol 1,4,5-trisphosphate (IP3) production 14-fold within 3 s, after whi ch cellular IP3 levels rapidly diminished to near basal levels in the conti nuing presence of SP. SP also caused concentration-dependent phosphorylatio n of the NK-1R, and this effect was blocked by a receptor antagonist. Stimu lation with 100 nM SP for as little as 2 s resulted in 90% desensitization of the receptor to restimulation by SP, and near-maximal receptor phosphory lation was observed at 5 s. Receptor desensitization was not affected by ag ents that affect protein kinase A. Phorbol 12-myristate 13-acetate (PMA) al so caused phosphorylation and desensitization of the receptor but with slow er kinetics and to a lesser extent than SP. PMA- but not SP-induced NK-1R d esensitization and phosphorylation were abolished by the protein kinase C i nhibitor bisindolylmaleimide 1. The concentration-response curves for SP-st imulated IP3, signaling and desensitization were similar, but the curve for NK-1R phosphorylation was shifted to the right and was steeper, suggesting that the relationship between desensitization and phosphorylation is compl ex. These results show that both rapid homologous and rapid heterologous NK -1R desensitizations may be mediated by receptor phosphorylation but occur via distinct mechanisms with different kinetics and efficacies.