Characterization of high affinity neurotensin receptor NTR1 in HL‐60 cells and its down regulation during granulocytic differentiation

We investigated responses to neurotensin in human promyelocytic leukaemia HL‐60 cells. Neurotensin increased the cytosolic calcium concentration ([Ca 2+ ] i ) in a concentration‐dependent manner and also produced inositol 1,4,5‐trisphosphate (InsP 3 ). Among the tested neurotensin analogues, neurotensin 8–13, neuromedin‐N, and xenopsin also increased [Ca 2+ ] i , whereas neurotensin 1–11 and neurotensin 1–8 did not elicit detectable responses. SR48692, an antagonist of NTR1 neurotensin receptors, blocked the neurotensin‐induced [Ca 2+ ] i increase, whereas levocabastine, which is known as an NTR2 neurotensin receptor antagonist, did not attenuate the neurotensin‐evoked effect. The expression of NTR1 neurotensin receptors was confirmed by Northern blot analysis and reverse transcriptase‐polymerase chain reaction (RT–PCR). During 1.25% dimethylsulfoxide (DMSO)‐triggered granulocytic differentiation of HL‐60 cells, the neurotensin‐induced [Ca 2+ ] i rise became gradually smaller and completely disappeared 4 days after treatment with DMSO. The mRNA level for neurotensin receptors was also decreased after differentiation. The results show that HL‐60 cells express NTR1 neurotensin receptors and suggest that granulocytic differentiation involves transcriptional regulation of the receptors resulting in down‐regulation of the neurotensin‐induced signalling.British Journal of Pharmacology (1999) 126 , 1050–1056; doi: 10.1038/sj.bjp.0702378