ryanodine and Brain-Neoplasms

Neuropeptide Y (NPY) regulates neurotransmitter release through activation of the Y2 receptor subtype. We have recently characterized a human glioblastoma cell line, LN319, that expresses exclusively NPY Y2 receptors and have demonstrated that NPY triggers transient decreases in cAMP and increases in intracellular calcium responses. The present study was designed to further characterize calcium signalling by NPY and bradykinin (BK) in LN319 cells. Both agonists elevated free intracellular calcium ([Ca(2+)](i)) without soliciting calcium influx. NPY appeared to activate two distinct signalling cascades that liberate calcium from thapsigargin- and ryanodine-insensitive compartments. One pathway proceeded through phospholipase C (PLC)-dependent phosphatidylinositol turnover, while the other triggered calcium release through a so far unidentified mediator. Part of the response was sensitive to pertussis toxin (PTX) under conditions where the toxin totally abolished the NPY-mediated effects on cAMP. The calcium release induced by BK on the other hand was largely PTX-insensitive, PLC-dependent, and from both thapsigargin- and ryanodine-sensitive stores. Following stimulation with NPY, subsequent [Ca(2+)](i) responses to NPY were strongly depressed. Partial heterologous desensitization occurred, when BK was used as the first agonist, whereas NPY had no effect on a subsequent stimulation with BK. These data suggest that NPY-induced calcium mobilization in LN319 cells involves two different G proteins and signalling mediators, and a hitherto unidentified calcium compartment. Homologous desensitization of NPY signalling might be explained by receptor-G protein uncoupling, while heterologous desensitization by BK could be the result of either transient depletion or inhibition of a mediator in the calcium signalling cascades activated by NPY.

Topics: Animals; Bradykinin; Brain Neoplasms; Calcium; Cyclic AMP; Estrenes; Glioblastoma; GTP-Binding Proteins; Humans; Inositol Phosphates; Neuropeptide Y; Pertussis Toxin; Phosphodiesterase Inhibitors; Protein Binding; Pyrrolidinones; Receptors, Neuropeptide Y; Ryanodine; Signal Transduction; Swine; Thapsigargin; Tumor Cells, Cultured; Type C Phospholipases; Virulence Factors, Bordetella

PDGF-BB induces a rapid, sustained increase in intracellular calcium levels in U-1242 MG cells. We used several calcium channel blockers to identify the types of channels involved. L channel blockers (verapamil, nimodipine, nicardipine, nitrendipine and taicatoxin) had no effect on PDGF-BB induced alterations in intracellular calcium. Blockers of P, Q and N channels (omega-agatoxin-IVA, omega-conotoxin MVIIC and omega-conotoxin GVIA) also had no effect. This indicates that these channels play an insignificant role in supplying the Ca2+ necessary for PDGF stimulated events in U-1242 MG cells. However, a T channel blocker (NDGA) and the non-specific (NS) calcium channel blockers (FFA and SK&F 9365) abolished PDGF-induced increases in intracellular calcium. This indicates that PDGF causes calcium influx through both non-specific cationic channels and T channels. To study the participation of intracellular calcium stores in this process, we used thapsigargin, caffeine and ryanodine, all of which cause depletion of intracellular calcium stores. The PDGF effect was abolished using both thapsigargin and caffeine but not ryanodine. Collectively, these data indicate that in these human glioma cells PDGF-BB induces release of intracellular calcium from caffeine- and thapsigargin-sensitive calcium stores which in turn lead to further calcium influx through both NS and T channels.

Topics: Becaplermin; Brain Neoplasms; Caffeine; Calcium; Calcium Channel Blockers; Calcium Channels; Calcium Signaling; Calcium-Transporting ATPases; Elapid Venoms; Endoplasmic Reticulum; Enzyme Inhibitors; Flufenamic Acid; Glioma; Humans; Imidazoles; Ion Transport; Masoprocol; Neoplasm Proteins; Nicardipine; Nimodipine; Nitrendipine; omega-Agatoxin IVA; omega-Conotoxin GVIA; omega-Conotoxins; Peptides; Platelet-Derived Growth Factor; Proto-Oncogene Proteins c-sis; Ryanodine; Thapsigargin; Tumor Cells, Cultured; Verapamil