Maitotoxin and P2Z/P2X(7) purinergic receptor stimulation activate a common cytolytic pore

The effects of maitotoxin (MTX) on plasmalemma permeability are similar to these 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 bet ween these two possibilities, the effect of MTX was examined in 1) THP-1 mo nocytic cells before and after treatment with lipopolysaccharide and interf eron-gamma, a maneuver known to upregulate P2Z/P2X(7) receptor, 2) wild-typ e 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 monocyt es, addition of MTX produced a biphasic increase in the cytosolic free Ca2 concentration ([Ca2+](i)); the initial increase reflects MTX-induced Ca2influx, whereas the second phase correlates in time with the appearance of large pores and the uptake of ethidium. MTX produced comparable increases i n [Ca2+](i) and ethidium uptake in THP-1 monocytes overexpressing the P2Z/P 2X(7) receptor. In both wild-type HEK and HEK cells stably expressing the P 2Z/P2X(7) receptor, MTX-induced increases in [Ca2+](i) and ethidium uptake were virtually identical. The response of BW5147.3 cells to concentrations of MTX that produced large increases in [Ca2+](i) had no effect on ethidium uptake. In both THP-1 and HEK cells, MTX- and Bz-ATP-induced pores activat e with similar kinetics and exhibit similar size exclusion. Last, MTX-induc ed pore formation, but not channel activation, is greatly attenuated by red ucing the temperature to 22 degrees C, a characteristic shared by the P2Z/P 2X(7)-induced pore. Together, the results demonstrate that, although MTX ac tivates channels that are distinct from those activated by P2Z/P2X(7) recep tor stimulation, the cytolytic/oncotic pores activated by MTX- and Bz-ATP a re indistinguishable.