Cholinergic modulation of the Ca2+ response to bradykinin in neuroblastoma cells.
Fura 2 imaging was used to measure intracellular Ca2+ signals in N1E-115 mouse neuroblastoma cells during combined activation of bradykinin (BK) and cholinergic receptors. BK and carbachol (CCh) both activate phospholipase C (PLC) and cause Ca2+ release from inositol 1,4,5-trisphosphate (IP3)-sensitive Ca2+ stores. The Ca2+ signal in response to CCh is prolonged by the activation of Ca2+ influx, but BK does not appear to activate the influx pathway. When BK and CCh are applied together (BK+CCh), the Ca2+ response is composed of both Ca2+ release and Ca2+ influx. Ca2+ influx is also activated by BK+CCh in a subset of cells that does not respond with a intracellular Ca2+ concentration increase when CCh is presented by itself. This suggests that CCh stimulates a Ca(2+)-silent cholinergic receptor that is not coupled to Ca2+ release but acts synergistically with BK receptors to activate Ca2+ influx. Pertussis toxin reduces influx without affecting release, indicating that the G protein that modulates the influx pathway is different from the G protein responsible for activating PLC. Cholinergic stimulation also causes progressive heterologous desensitization of BK-evoked Ca2+ release. Desensitization has the unique property of continuing to develop after the cholinergic agonist is removed and the cholinergic Ca2+ response has fully recovered. Heterologous desensitization is not the result of Ca2+ store depletion or a long-lasting inhibition of PLC or IP3-dependent Ca2+ release. Instead, it appears to involve an early step in the BK-signaling cascade, possibly at the level of the B2 receptor or associated G proteins.
Coggan
J S
JS
Department of Biological Sciences, Stanford University, Pacific Grove, California 93950, USA.
Thompson
S H
SH
D000818:Animals; D001920:Bradykinin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D018679:Cholinergic Agonists / Q000494:pharmacology*; D051379:Mice; D018721:Muscarinic Agonists / Q000494:pharmacology; D009447:Neuroblastoma / Q000378:metabolism* / Q000473:pathology; D037342:Pertussis Toxin; D011950:Receptors, Cholinergic / Q000378:metabolism; D015398:Signal Transduction; D014407:Tumor Cells, Cultured; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D018679:Cholinergic Agonists; D018721:Muscarinic Agonists; D011950:Receptors, Cholinergic; D010566:Virulence Factors, Bordetella; D002217:Carbachol; D037342:Pertussis Toxin; D001920:Bradykinin; D002118:Calcium