Homologous desensitization of bombesin-induced increases in intracellular Ca2+ in quiescent Swiss 3T3 cells involves a protein kinase C-independent mechanism.
Addition of bombesin to Swiss 3T3 cells causes a rapid and transient increase in the intracellular concentration of Ca2+ ([Ca2+]i), which is followed by desensitization to a subsequent addition of the peptide. The concentrations of bombesin used to study this acute cellular desensitization (0.1-0.5 nM) did not deplete the intracellular pool of Ca2+ released by inositol(1,4,5)trisphosphate, as shown by addition of vasopressin after consecutive additions of bombesin. Two lines of evidence support the conclusion that activation of protein kinase C (PKC) does not mediate the acute homologous desensitization of Ca2+ responses induced by bombesin. First, long-term treatment (48 h) of Swiss 3T3 cells with phorbol 12,13-dibutyrate (PDB) to deplete PKC did not prevent homologous desensitization. The responses to second additions of bombesin at 0.1, 0.25, and 0.5 nM were 42%, 26% and 11% of the initial responses, respectively. Second, the PKC inhibitor GF 109203X did not alter homologous desensitization at concentrations that completely prevented the inhibition of Ca2+ mobilization induced by PDB and blocked PDB-mediated phosphorylation of the prominent PKC substrate 80K/MARCKS. We conclude that acute homologous desensitization of Ca2+ responses induced by bombesin occurs through a PKC-independent mechanism.
Imperial Cancer Research Fund, London, United Kingdom.
J H
JH
Walsh
M
M
Bouzyk
E
E
Rozengurt
D016475:3T3 Cells / Q000187:drug effects*; D000818:Animals; D001839:Bombesin / Q000378:metabolism / Q000494:pharmacology*; D002118:Calcium / Q000032:analysis / Q000378:metabolism*; D002455:Cell Division; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000502:physiology; D005246:Feedback; D007211:Indoles / Q000494:pharmacology; D007457:Iodine Radioisotopes; D008301:Maleimides / Q000494:pharmacology; D051379:Mice; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D011233:Precipitin Tests; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000502:physiology*; D018004:Receptors, Bombesin; D017981:Receptors, Neurotransmitter / Q000032:analysis / Q000378:metabolism / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D014667:Vasopressins / Q000494:pharmacology
D007211:Indoles; D007457:Iodine Radioisotopes; D008301:Maleimides; D018004:Receptors, Bombesin; D017981:Receptors, Neurotransmitter; D014667:Vasopressins; D015240:Phorbol 12,13-Dibutyrate; D011493:Protein Kinase C; C070515:bisindolylmaleimide I; D001839:Bombesin; D002118:Calcium