ATP modulates Na+ channel gating and induces a non-selective cation current in a neuronal hippocampal cell line

Extracellular ATP evoked two excitatory responses in hippocampal neuroblast oma cells (HN2). The first, an opening of a receptor-operated non-selective cation channel and the second was a leftward shift in Na+ channel activati on. Both ATP (5-1000 muM) and 2 ' ,3 '-(4-benzoyl)-benzoyl-ATP (Bb-ATP, 50 muM) activated a non-selective cation current reversing near 0 mV and shift ed the Na+ activation and inactivation curves to the left. Based on a compa rison of a series of agonists and antagonists, the inward current appeared to be partially mediated by activation of a P2X(7) receptor, although hybri d channels cannot be ruled out. The shift in Na+ channel gating could be se parated from the opening of the cation channel, as application of the P2Y a ntagonist Reactive Blue-2 and GTP shifted the Na+ current activation to the left but failed to elicit the inward cation current. Both responses to ATP and Bb-ATP were insensitive to block by the P2X antagonist suramin (300 mu M) but were prevented by incubation in oxidized ATP (200 muM); a putative P 2X(7) receptor antagonist. Prior screening of the surface negative charge o f the membrane with a high concentration of divalent cations prevented both responses. We suggest that ATP(4-) activates a P2X receptor and becomes tr apped on a site, on or near the Na+ channel. Activation of the P2X receptor leads to the opening of a non-specific cation channel, while the binding o f ATP(4-) leads to a modified charge sensed by the Na+ channel, similar to what occurs in the presence of charged amphiphiles as well as a number of b eta -scorpion toxins. (C) 2001 Elsevier Science B.V. All rights reserved.