Expression and properties of recombinant P2X₁WT and P2X_1delreceptors in HEK293 cells. (A) ATP (100 μM; drug application is indicated by bar) induced a transient inward current in HEK293 cells transiently transfected with P2X₁ WT receptors, whereas ADP (100 μM) was ineffective. (B) ATP or ADP (both 100 μM) failed to evoke a change in holding current from HEK293 cells transiently transfected with P2X_{1 del} receptors. (C) When P2X₁ WT and P2X_{1 del} receptors were transiently coexpressed, ATP (100 μM) induced inward currents; however, ADP (100 μM) was ineffective. (D) Western blot analysis on nontransfected HEK293 cells (NT) and cells transiently transfected with either P2X₁ WT (WT), P2X_{1 del} (del)_, or both receptors (WT + del). Total cell protein analysis (left panel) showed that P2X₁WT and P2X_1del receptors were expressed. However, only P2X₁ WT receptor was detected at the cell surface (right panel). A weak nonspecific band was observed around 60 kDa in nontransfected HEK293 cells.