An understanding of the mechanisms that regulate signaling by the substance
P (SP) or neurokinin 1 receptor (NK1-R) is of interest because of their ro
le in inflammation and pain. By using activators and inhibitors of protein
kinase C (PKC) and NK1-R mutations of potential PKC phosphorylation sites,
we determined the role of PKC in desensitization of responses to SP. Activa
tion of PKC abolished SP-induced Ca2+ mobilization in cells that express wi
ld-type NK1-R. This did not occur in cells expressing a COOH-terminally tru
ncated NK1-R (NK1-R delta 324), which may correspond to a naturally occurri
ng variant, or a point mutant lacking eight potential PKC phosphorylation s
ites within the COOH tail (NK1-R Ser-338, Thr-339, Ser-352, Ser-387, Ser-38
8, Ser-390, Ser-392, Ser-394/Ala, NK1-RKC4). Compared with wild-type NK1-R,
the t1/2 of SP-induced Ca2+ mobilization was seven- and twofold greater in
cells expressing NK1-R delta 324 and NK1-RKC4, respectively. In cells expr
essing wild-type NK1-R, inhibition of PKC caused a 35% increase in the t1/2
of SP-induced Ca2+ mobilization. Neither inhibition of PKC nor receptor mu
tation affected desensitization of Ca2+ mobilization to repeated challenge
with SP or SP-induced endocytosis of the NK1-R. Thus PKC regulates SP-induc
ed Ca2+ mobilization by full-length NK1-R and does not regulate a naturally
occurring truncated variant. PKC does not mediate desensitization to repea
ted stimulation or endocytosis of the NK1-R.