Expression and properties of recombinant P2X₁WT and P2X_1delreceptors in 1321-N1 cells. (A) ATP and ADP (both 100 μM, application indicated by bar) had no effect on the holding current in 1321-N1 cells stably transfected with either (i) P2X₁WT (1321-N1 G P2X₁ WT) or (ii) P2X_1del (1321-N1 G4 P2X_1del) receptors.¹³  When transiently transfected with P2X₁WT receptors (iii), these cells gave a transient inward current in response to ATP (100 μM) but not to ADP (100 μM). (B) Western blot showing that no P2X₁ receptor signal was detected in 1321-N1 G5 P2X_1del, 1321-N1 G4 P2X_1del, or 1321-N1 G P2X₁WT cell clones¹³  and in nontransfected native 1321-N1 or HEK293 cells (NT). We used HEK293 cells transiently transfected with P2X₁ WT as a positive control of expression of the P2X₁ receptor. (C) However, bands corresponding to P2X₁ receptors were detected when P2X₁WT (WT), P2X_1del (del), or P2X₁ WT + P2X_1del (WT + del) receptors (ratio 1:9) were transiently expressed in 1321-N1 G P2X₁WT cells.