Figure 1. Human airway epithelia cultured at the air–liquid interface have cation‐selective tight junctions that are not affected by low physiological pH.

Red is pH 6.0, black is pH 7.4, squares are Na⁺ data and triangles are Cl⁻ and all error bars represent standard deviations of the mean. One donor was omitted because a 11.43 mS cm⁻² baseline conductance was identified as an outlier; Grubb's test α ≤ 0.01. A, representative dilution potential experiment not corrected for junction potentials. B, junction potential‐corrected dilution potential summary data for experiments containing identical solutions titrated to pH 7.4 or 6.0; n = 7 donors. The dashed lines represent theoretical dilution potentials calculated by substituting average relative permeability data from panel C into the Goldman–Hodgkin–Katz equation. C, relative paracellular permeability, each circle represents a single human donor. P = 0.54; two‐tailed paired Student's t test; n = 7 donors. D, bilateral 150 mm NaCl paracellular conductance. Each circle represents a single human donor. P = 0.63; paired Student's t test; n = 7 donors. E, relative paracellular permeability vs. paracellular conductance, each circle represents a single human donor. We cannot reject the null hypothesis that the slopes were zero; pH 7.4 P = 0.15, pH 6.0 P = 0.25; F test; n = 7 donors each. F, paracellular ion permeability vs. paracellular conductance. Data were fit with linear regressions, r ² > 0.98. We cannot reject the null hypothesis that the slopes were equal; P = 0.12; F test; n = 7 donors each ion and pH value.