P2RX7 and posterior cortical atrophy: Indeed, a previous estimate of P2X7 relative Ca2+ permeability from reversal potentials reported a PCa/PNa of 35 (Bretschneider et al., 1995), which is far in excess of what is predicted for a channel with a Pf% reading of ~5% (Egan and Khakh, 2004) (Table 1).