Figure 8. Effects of apical Na⁺ substitution on I_sc in dDAVP-stimulated cultured CCD cells.

I_sc was measured in confluent cultures of +/+^(L), L/+, L/L, m/m and CFTR−/− (cftr−/−) CCD cells grown on filters, and incubated with apical Na⁺-free solution (Na⁺ was replaced by N-methyl-d-glucamine) and basal HFM. After equilibration of the traces, amiloride (Am, 10⁻⁵m) was added to the apical side of the cells (Δ). Thereafter, the cells were sequentially incubated with basal dDAVP (10⁻⁸m, •) and apical NPPB (10⁻⁴m, δ). Bars represent the relative δI_sc increase caused by dDAVP. Values are means ± s.e.m. from five to eight separate experiments. ***P < 0.001 between groups.