CFTR and cystic fibrosis: NPD values before treatment were typical of CF patients, i.e., highly negative basal NPD, strong depolarisation in response to inhibition of sodium current by 100 μM amiloride (Δamiloride) and no significant response to CFTR activation by isoproterenol 10 μM in chloride-free solution (ΔCl-free-isoproterenol) [13] (Figure 2a, Tables 3 and 5).