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New insights into maitotoxin action
F Sladeczek1, B H Schmidt, R Alonso
1Centre National de la Recherche Scientifique/Institut National de la Santé et de la Recherche Médical, Centre de Pharmacologie-Endocrinologie, Montpellier, France.
Abstract:
Maitotoxin (3 ng/mol) induced a massive uptake of 45Ca2+ into BC3H1 cells. This effect exhibits a lag phase of 3 min. Inositol diphosphate formation occurred concomittantly with the 45Ca2+ uptake but inositol monophosphate formation was found only after a 5-min delay following toxin addition. Maitotoxin-induced 45Ca2+ influxes could not be blocked by either 1 microM verapamil, 1 microM nifedipine or 1 mM La3+ but was blocked by Zn2+ (IC50 = 41 microM). In addition to inositol phosphate formation and 45Ca2+ uptake, maitotoxin stimulated a large uptake of Na+ and a great loss of K+ in BC3H1 cells. In the absence of Ca2+ (1 mM EGTA) none of the four maitotoxin effects could be detected. After restoration of Ca2+, the maitotoxin effects reappeared even when the toxin itself was no longer present. The divalent cation, Co2+ (1 mM), inhibited ion movements induced by maitotoxin and also digitonin (8.1 microM). The toxin action showed a very pronounced pH dependence. At low pH, maitotoxin was inactive. The dose-response curves for H+ ion inhibition of maitotoxin-induced Ca2+ uptake showed a shift to the right when determined in the absence of HCO3- and HCO3-/Cl- ions. It was concluded that the primary action of maitotoxin in BC3H1 cells was a pore-forming or channel-forming activity of a non-classical type. Some properties of maitotoxin resemble those of alpha-latrotoxin, others those of pore-forming agents such as melittin or alpha-toxin of Staphylococcus aureus.
Insights
Maitotoxin triggers massive calcium (Ca2+) and sodium (Na+) uptake, along with potassium (K+) loss, in cells by forming non-classical pores. These effects require extracellular Ca2+ and are pH-dependent.
Area of Science:
- * Pharmacology
- * Cell Biology
- * Toxicology
Background:
- * Maitotoxin is a potent marine toxin known to affect cellular ion transport.
- * Its precise mechanism of action, particularly regarding ion channel modulation, remains incompletely understood.
Purpose of the Study:
- * To elucidate the cellular mechanisms underlying maitotoxin's effects on ion flux in BC3H1 cells.
- * To characterize the ion selectivity and environmental dependencies of maitotoxin-induced cellular responses.
Main Methods:
- * Measurement of 45Ca2+ uptake, inositol phosphate formation, Na+ uptake, and K+ loss in BC3H1 cells exposed to maitotoxin.
- * Investigation of the effects of various ion channel blockers (verapamil, nifedipine, La3+, Zn2+, Co2+), calcium chelation (EGTA), pH, and bicarbonate on maitotoxin activity.
Main Results:
- * Maitotoxin induced rapid 45Ca2+ uptake with a lag phase, accompanied by inositol diphosphate formation and delayed inositol monophosphate formation.
- * Maitotoxin stimulated Na+ influx and K+ efflux, which were dependent on extracellular Ca2+ and inhibited by Zn2+ and Co2+.
- * Toxin activity was pH-dependent, inactive at low pH, and modulated by bicarbonate and chloride ions.
Conclusions:
- * Maitotoxin likely acts by forming non-classical pores or channels, facilitating ion movement across the cell membrane.
- * The observed effects share similarities with other toxins like alpha-latrotoxin and pore-forming agents, suggesting a unique mechanism of action.