FIGURE 5.

Supramaximal CCK stimulation (10 nm) induces a large exocytic response; the consequent acid load in the lumen with HEPES buffer is significantly smaller with HCO₃⁻ buffer. A, two-photon live-cell imaging in HEPES buffer before (C, i) and after (C, ii) supramaximal CCK stimulation showing a large exocytic response (SRB) and significant luminal acidification (A, C, and D; see also supplemental Movies 9 and 10). In the presence of HCO₃⁻ buffer (B), the exocytic response is similar, but the luminal acidification is much less (B–D, see also supplemental Movies 11 and 12). Scale bars = 5 μm. n ≥ 9 lumens, n ≥ 3 mice. Student's t test; **, p < 0.01.