Figure 6.

P2X2/5 receptor stimulation evokes sustained NMDG conductance in Xenopus oocytes. Permeability dynamics of P2X2 (A) and P2X2/5 (B). Representative currents evoked by ATP (100 μm) in Xenopus oocytes expressing P2X2 or P2X2/5 receptors recorded in NMDG external solution at a holding potential of −60 mV. I₁ and I₂ correspond to channels permeant to small cations or NMDG⁺, respectively. Note the faster I₁ to I₂ transition for P2X2 receptors compared with P2X2/5, and the lack of reversibility of the inward P2X2/5 conductance. C, D, Shift in the reversal potential of ATP-evoked currents in NMDG extracellular solution. Currents were measured during repeated voltage ramps protocol in the presence of 100 μm ATP. Two seconds after ATP application, reversal potential of P2X2 current has already changed compared with that of P2X2/5. Note the difference in current rectification between the two types of channels.