Figure 6.

Inhibition of S1141K/E1371Q-CFTR by intracellular ATP. (A) Example macroscopic currents carried by S1141K/E1371Q during hyperpolarizing voltage steps to between +60 and −100 mV recorded under conditions of low extracellular Cl⁻ concentration (4 mM). Currents were recorded before (control) and immediately after the addition of 10 mM Na₂ATP to the intracellular solution in the absence of PKA and PPi. (B) Mean fractional current remaining after the addition of different concentrations of ATP under these conditions, measured at membrane potentials of −100 mV (•) and 0 mV (○). Fits are to Eq. 3, giving K_d = 1.92 ± 0.08 mM and n_H = 1.11 ± 0.05 at −100 mV, and K_d = 41.9 ± 19.1 mM and n_H = 0.91 ± 0.23 at 0 mV. Also shown are the effects of 10 mM ATP on E1371Q (▴) and K95S/S1141K/E1371Q (▾) at −100 mV. (C) Example macroscopic S1141K/E1371Q currents during voltage steps to between +60 and −100 mV recorded with a high extracellular Cl⁻ concentration (154 mM) before (control) and after the addition of 10 mM Na₂ATP to the intracellular solution in the absence of PKA. (D) Mean fractional current remaining after the addition of different concentrations of ATP under these conditions, measured at a membrane potential of −100 mV. The data are fit to Eq. 3, giving K_d = 36.3 ± 18.2 mM when n_H was constrained to unity. (E) Voltage dependence of K_d estimated from fits such as those shown in B and D, with 4 mM Cl⁻ (•) and 154 mM Cl⁻ (○) in the extracellular solution. Data at 4 mM Cl⁻ have been fit by Eq. 2, suggesting a zδ of −1.17 ± 0.11. In both A and C, the dotted line represents the 0 current level. Mean of data from three to six patches in B and D.