Electrostatic potential in the lateral fenestrations may contribute to selecting cations over anions. Sagittal sections of the electrostatic potential surface calculated using the APBS tools (Baker et al., 2001). (A) zfP2X4 with supplemented side chains. Homology models of rP2X2 (B) and hP2X5 (C). Surface is colored based on the potential, contoured from −6 kcal mol⁻¹ (red) to +6 kcal mol⁻¹ (blue). White denotes 0 kcal mol⁻¹.