Fig. 3. Functional evidence for use-dependent tyrosine dephosphorylation of P2X₇ receptor. (A) Currents in response to successive applications of 100 µM BzATP (4 s duration, indicated by bars) at 2 min intervals; note the marked change in kinetics of the current. (B) Currents recorded from another cell in response to successive applications of 100 µM BzATP in the presence of the tyrosine phosphatase inhibitor bpV (100 µM). (C) Summary of results from all experiments as illustrated in (A) and (B) (n = 43 for each point in control and 7–13 for each point in any of the phosphatase inhibitors). (D) Similar experiments performed on P2X₂-expressing HEK cells. Minimal run-down occurs with successive stimuli and is unaltered by bpV (100 µM; n = 6–12 for each point). All results were obtained from HEK cells stably expressing P2X₇ (A–C) or P2X₂ (D) receptors.