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Maitotoxin stimulates phosphoinositide breakdown in neuroblastoma hybrid NCB-20 cells
F Gusovsky1, T Yasumoto, J W Daly
1Laboratory of Bioorganic Chemistry, NIDDK, Bethesda, Maryland 20892.
Abstract:
1. Maitotoxin (MTX) was an extraordinarily potent stimulant of phosphoinositide breakdown in the neuroblastoma hybrid NCB-20 cells. 2. Maximal responses were obtained at 0.25-0.5 ng MTX/ml, and resulted in increased formation of [3H]inositol mono-, bis-, and trisphosphates. Increased formation of [3H]inositol bis- and trisphosphate was observed as early as 15 sec after the addition of MTX. 3. MTX-induced phosphoinositide breakdown in NCB-20 cells was not antagonized by organic (nifedipine, methoxyverapamil) or inorganic (Mn2+, Co2+, Cd2+) calcium channel blockers. However, the response on phosphoinositide breakdown was completely eliminated in the absence of extracellular calcium. 4. The results suggest that MTX either directly stimulates phosphoinositide breakdown in a calcium-dependent manner or acts indirectly through calcium channels insensitive to organic/inorganic calcium channel blockers.
Insights
Maitotoxin (MTX) potently stimulates phosphoinositide breakdown in neuroblastoma cells. This effect requires extracellular calcium but is independent of known calcium channel blockers, suggesting a novel mechanism.
Area of Science:
- Neuroscience
- Cell Biology
- Pharmacology
Background:
- Neuroblastoma hybrid NCB-20 cells are a model for studying cellular signaling pathways.
- Phosphoinositide breakdown is a critical process in cellular signal transduction.
- Maitotoxin (MTX) is a potent marine toxin with complex biological effects.
Purpose of the Study:
- To investigate the effect of Maitotoxin (MTX) on phosphoinositide breakdown in NCB-20 cells.
- To elucidate the role of extracellular calcium and calcium channels in MTX-induced signaling.
Main Methods:
- Treatment of NCB-20 cells with varying concentrations of MTX.
- Measurement of [3H]inositol phosphate formation (mono-, bis-, and trisphosphates).
- Assessment of MTX response in the presence and absence of extracellular calcium and calcium channel blockers.
Main Results:
- MTX strongly stimulated phosphoinositide breakdown, with maximal effects at 0.25-0.5 ng/ml.
- Increased inositol phosphate formation was observed rapidly, within 15 seconds of MTX addition.
- MTX-induced breakdown was calcium-dependent but unaffected by common calcium channel blockers.
Conclusions:
- MTX is a potent activator of phosphoinositide hydrolysis in neuroblastoma cells.
- The signaling pathway involves extracellular calcium but bypasses conventional calcium channels.
- MTX may act via novel calcium channels or directly stimulate the breakdown pathway.