Regulation of human airway ciliary beat frequency by intracellular pH

pH i affects a number of cellular functions, but the influence of pH i on mammalian ciliary beat frequency (CBF) is not known. CBF and pH i of single human tracheobronchial epithelial cells in submerged culture were measured simultaneously using video microscopy (for CBF) and epifluorescence microscopy with the pH‐sensitive dye BCECF. Baseline CBF and pH i values in bicarbonate‐free medium were 7.2 ± 0.2 Hz and 7.49 ± 0.02, respectively ( n = 63) . Alkalization by ammonium pre‐pulse to pH i 7.78 ± 0.02 resulted in a 2.2 ± 0.1 Hz CBF increase ( P < 0.05) . Following removal of NH 4 Cl, pH i decreased to 7.24 ± 0.02 and CBF to 5.8 ± 0.1 Hz ( P < 0.05) . Removal of extracellular CO 2 to change pH i resulted in similar CBF changes. Pre‐activation of cAMP‐dependent protein kinase (10 μ m forskolin), broad inhibition of protein kinases (100 μ m H‐7), inhibition of PKA (10 μ m H‐89), nor inhibition of phosphatases (10 μ m cyclosporin + 1.5 μ m okadaic acid) changed pH i ‐mediated changes in CBF, nor were they due to [Ca 2+ ] i changes. CBF of basolaterally permeabilized human tracheobronchial cells, re‐differentiated at the air–liquid interface, was 3.9 ± 0.3, 5.7 ± 0.4, 7.0 ± 0.3 and 7.3 ± 0.3 Hz at basolateral i.e., intracellular pH of 6.8, 7.2, 7.6 and 8.0, respectively ( n = 18) . Thus, intracellular alkalization stimulates, while intracellular acidification attenuates human airway CBF. Since phosphorylation and [Ca 2+ ] i changes did not seem to mediate pH i ‐induced CBF changes, pH i may directly act on the ciliary motile machinery.