Failure of opiates to increase the hydrolysis of GTP in neuroblastoma-glioma 108-15 cells

• Published in: Life sciences (1973) Vol. 33; no. 9; p. 879
• Main Authors: Musacchio, J M, Schen, C
• Format: Journal Article
• Language: English
• Published: Netherlands 29.08.1983
• Subjects: Alprostadil; Animals; Cell Line; Cyclic AMP - metabolism; Etorphine - pharmacology; Glioma - metabolism; Guanine Nucleotides - metabolism; Guanosine Triphosphate - metabolism; Mice; Naloxone - pharmacology; Neuroblastoma - metabolism; Prostaglandins E - pharmacology; Tritium
• ISSN: 0024-3205
• DOI: 10.1016/0024-3205(83)90627-6

It has been repeatedly demonstrated that the neuroblastoma-glioma (NG 108-15) cell line has opiate receptors that inhibit adenylate cyclase and it has been proposed that this inhibition is mediated by a naloxone reversible stimulation of a low Km GTPase (Koski and Klee, Proc. Natl. Acad. Sci. 78:4185, 1981). The guanine nucleotides of NG cells were labeled with [3H]guanine followed by incubation with 10(-6)M guanine. Etorphine (10(-6)M) or vehicle were added and the incubations continued for 1-4 min. The reaction was stopped with 5 percent TCA containing nucleotides as carriers and markers for the HPLC. Marker nucleotides were detected at 254 nm and the labeled nucleotides by liquid scintillation spectrometry. In several experiments, etorphine failed to produce any measurable change in the labeled nucleotides or in the GTP/GDP ratios. To verify that the opiate receptors were functional we measured its capacity to inhibit the formation of cAMP induced by PGE1. We also studied the effects of naloxone and PGE1 on the formation of cAMP in opiate tolerant cells. Tolerant cells responded to naloxone with a 50 percent increase in cAMP, indicating again that the opiate receptors were functional. Our results are consistent with the idea that in intact NG108-15 cells the opiate-mediated hydrolysis of GTP observed in cell membrane preparations is of very small magnitude.