Pharmacological differentiation of the P2X7 receptor and the maitotoxin-activated cationic channel

The ATP-P2X(7) receptor subtype and a maitotoxin-activated ion channel were studied to determine factors which identify them as separate entities in the control of a cytotolytic pore. Activation of ATP-P2X(7) receptors with 2'-3'-O-(benzylbenzyl) ATP (BzATP) or maitotoxin ion channels resulted in influx of ethidium bromide and cell death. Maitotoxin (25-250 pM)-induced ethidium bromide uptake and cell death was sensitive to extracellular Ca2+, the ionic composition of the buffer, reduced by the calmodulin inhibitor W7, (N-(s-aminohexyl)-5-chloro-1-naphthalenesulfonamide) (10-100 muM) but unaffected by the ATP-P2X(7) receptor antagonist oxidized ATP, (adenosine 5'-triphosphate periodate oxidized sodium salt) (oATP). BzATP (10-200 muM)-induced ethidium bromide uptake and cell death were inhibited by oATP, unaffected by W7, inhibited by high ionic concentrations but only slightly dependant on external Ca2+. These results are consistent with the existence of a pharmacological mechanism for controlling cell death consisting of an ATP-P2X(7) receptor, a maitotoxin-activated ion channel and a cytolytic pore. (C) 2004 Elsevier B.V. All rights reserved.