Fig. 2.

Increased Na⁺-dependent intracellular pH (pH_i) regulation across the apical membrane of cilium-deficient vs. cilium-competent cortical collecting duct (CCD) principal cell monolayers. Initial pH_i experiments were performed without a BCECF calibration, and results are presented as the ratio of 495-nm to 440-nm excitation (I₄₉₅/I₄₄₀). A: cilium-competent monolayer. Removing external Na⁺ on both sides of the monolayer elicited an I₄₉₅/I₄₄₀ decrease (bc), which was unaffected by first returning apical Na⁺ (cd) but was reversed by then returning basolateral Na⁺ (de). n = 17. B: cilium-deficient monolayer. The experimental protocol was identical to that described in A. Returning apical Na⁺ in the continued absence of basolateral Na⁺ caused the ratio to increase more than halfway back to the initial value (cd). Subsequently returning basolateral Na⁺ elicited a further increase in the ratio (de) to the initial value. n = 24.