ATP stimulation of currents mediated by ΔR-CFTR. (A) Current recordings from an inside-out patch upon perfusion with control internal solution (left), and with solutions containing ATP as indicated in the panels. Voltage pulses are from −80 to 80 mV in 20-mV increments. Capacity transients are not subtracted. (B) ATP dependence of currents measured at 80 mV normalized to currents measured in 1 mM ATP. Error bars indicate SD (the data point at 1 mM has no error bar because it was used for the normalization). The solid line is the best fit of Eq. 2 with Kd = 38 μM and n = 0.63.