Maitotoxin and P2Z/P2X(7) purinergic receptor stimulation activate a common cytolytic pore.
The effects of maitotoxin (MTX) on plasmalemma permeability are similar to those caused by stimulation of P2Z/P2X(7) ionotropic receptors, suggesting that 1) MTX directly activates P2Z/P2X(7) receptors or 2) MTX and P2Z/P2X(7) receptor stimulation activate a common cytolytic pore. To distinguish between these two possibilities, the effect of MTX was examined in 1) THP-1 monocytic cells before and after treatment with lipopolysaccharide and interferon-gamma, a maneuver known to upregulate P2Z/P2X(7) receptor, 2) wild-type HEK cells and HEK cells stably expressing the P2Z/P2X(7) receptor, and 3) BW5147.3 lymphoma cells, a cell line that expresses functional P2Z/P2X(7) channels that are poorly linked to pore formation. In control THP-1 monocytes, addition of MTX produced a biphasic increase in the cytosolic free Ca(2+) concentration ([Ca(2+)](i)); the initial increase reflects MTX-induced Ca(2+) influx, whereas the second phase correlates in time with the appearance of large pores and the uptake of ethidium. MTX produced comparable increases in [Ca(2+)](i) and ethidium uptake in THP-1 monocytes overexpressing the P2Z/P2X(7) receptor. In both wild-type HEK and HEK cells stably expressing the P2Z/P2X(7) receptor, MTX-induced increases in [Ca(2+)](i) and ethidium uptake were virtually identical. The response of BW5147.3 cells to concentrations of MTX that produced large increases in [Ca(2+)](i) had no effect on ethidium uptake. In both THP-1 and HEK cells, MTX- and Bz-ATP-induced pores activate with similar kinetics and exhibit similar size exclusion. Last, MTX-induced pore formation, but not channel activation, is greatly attenuated by reducing the temperature to 22 degrees C, a characteristic shared by the P2Z/P2X(7)-induced pore. Together, the results demonstrate that, although MTX activates channels that are distinct from those activated by P2Z/P2X(7) receptor stimulation, the cytolytic/oncotic pores activated by MTX- and Bz-ATP are indistinguishable.
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Rammelkamp Center for Education and Research, Department of Physiology, Case Western Reserve University School of Medicine, Cleveland, Ohio 44109, USA. wschilling@metrohealth.org
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D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D004996:Ethidium / Q000493:pharmacokinetics; D007425:Intracellular Membranes / Q000378:metabolism; D008223:Lymphoma / Q000378:metabolism / Q000473:pathology; D008387:Marine Toxins / Q000494:pharmacology*; D051379:Mice; D009000:Monocytes / Q000187:drug effects / Q000378:metabolism; D009994:Osmolar Concentration; D035964:Oxocins; D018048:Receptors, Purinergic P2 / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D058486:Receptors, Purinergic P2X7; D013696:Temperature; D014407:Tumor Cells, Cultured; D015854:Up-Regulation / Q000502:physiology; D000095702:Polyether Toxins
D000255:Adenosine Triphosphate; D002118:Calcium; D004996:Ethidium; D008387:Marine Toxins; D035964:Oxocins; D018048:Receptors, Purinergic P2; D058486:Receptors, Purinergic P2X7; C546469:P2rx7 protein, mouse; C033901:3'-O-(4-benzoyl)benzoyladenosine 5'-triphosphate; C020394:maitotoxin; D000095702:Polyether Toxins