Figure 5.

Respiratory mucins promote and potentiate PMA-induced neutrophil membrane depolarization. (A) Neutrophils were exposed to graded K⁺ concentrations. Membrane depolarization is indicated by the shift in the intensity of DiBAC4(3) fluorescence. Graded potassium solutions were made by increasing the KCl concentration in the solution. For graded K⁺ solutions, the KCl concentration was set to 1, 5, 10, 25, 38, 50, 75, and 100 mM. (B) Human neutrophils were incubated in the presence of respiratory mucins (•, 0.5–4 mg/ml) or stimulated with 200 nM PMA in the presence of respiratory mucins (<). After a 20-min incubation, the cells were stained with 100 nM DiBAC₄(3). The transmembrane potential was determined by flow cytometry as described in Materials and Methods and is presented as mean fluorescence intensity (MFI) of the DiBAC₄(3) probe. Means ± s.e.m. of four independent experiments are shown. (C) Representative flow cytometric histograms showing a concentration-dependent increase in DiBAC4(3) fluorescence in resting neutrophils incubated with mucins, indicating plasma membrane depolarization. (D) Exposure of neutrophils to increasing concentrations of respiratory mucins potentiated membrane depolarization in PMA-stimulated neutrophils. The data are representative of four separate experiments in four donors. (**p < 0.01 vs. no mucin).