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 deviation 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, r²>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.