REGULATION OF THE NEUROTENSIN RECEPTOR AND INTRACELLULAR CALCIUM MOBILIZATION IN HT29 CELLS

  • 1 June 1990
    • journal article
    • research article
    • Vol. 253  (3) , 1049-1056
Abstract
Regulation of the neurotensin receptor-inositol phosphate-intracellular Ca2+ ([Ca2+]i) pathway was studied in HT29 cells. Preincubation with neurotensin or phorbol 12-myristate, 13-acetate decreased the number of cell surface neurotensin receptors and neurotensin-induced increased of inositol trisphosphates and [Ca2+]i. The phorbol 12-myristate, 13-acetate-(43 .+-. 1% at 1 .mu.M) but not the neurotensin (65 .+-. 9% at 10nM)-induced decrease in receptors was blocked by staurosporine. The decrease in cell surface receptors was accompanied by a 55 .+-. 7% shift of specifically bound 125I-neurotensin from the plasma membrane fraction to the light vesicle fraction of sucrose density gradients if a 37.degree. C incubation step was included. The time course for desensitization of [Ca2+]i mobilization was more rapid (maximal at .apprxeq. 1 min) that for loss of receptors (maximal at 45 min). After a 5-min exposure to neurotensin, the cell surface receptor number rapidly returned to control levels in the absence of agonist, but [Ca2+]i sensitivity to neurotensin recovered only partially. Incubation with carbachol, ATP or phorbol 12-myristate, 13-acetate desensitized the subsequent [Ca2+]i response to neurotensin. These results demonstrate a polyphosphoinositide-[Ca2+]i pathway in HT29 cells stimulable by neurotensin and other agents. The results from pre-incubation studies indicate that the neurotensin receptor-signaling pathway is homologously and heterologously regulated. Finally, differences in time courses for loss and recovery of cell surface receptors and desensitization of the [Ca2+]i response, as well as the lack of effect on 125I-neurotensin binding of other agonists that desensitize the neurotensin [Ca2+]i response, suggest that receptor internalization alone does not account for desensitization of the system.