Abstract
Ciliated lung epithelial cells and the airway surface liquid (ASL) comprise one of the body's most important protective systems. This system is finely tuned, and perturbations to ASL rheology, ASL depth, ASL pH, the transepithelial potential, and the cilia beat frequency are all associated with disease pathology. Further, these apparently distinct properties interact with each other in a complex manner. For example, changes in ASL rheology can result from altered mucin secretion, changes in ASL pH, or changes in ASL depth. Thus, one of the great challenges in trying to understand airway pathology is that the properties of the ASL/epithelial cell system need to be assessed near-simultaneously and without perturbing the sample. Here, we show that nanosensor probes mounted on a scanning ion conductance microscope make this possible for the first time, without any need for labeling. We also demonstrate that ASL from senescence-retarded human bronchial epithelial cells retains its native properties. Our results demonstrate that by using a nanosensor approach, it is possible to pursue faster, more accurate, more coherent, and more informative studies of ASL and airway epithelia in health and disease.
Highlights
The airway surface liquid (ASL) is a very shallow (∼10 μm), viscoelastic gel that covers the upper airways
We have developed a fast and simple approach to the measurement of ASL and epithelial cell function that uses just a single apparatus consisting of nanoprobes mounted on a scanning ion conductance microscope (SICM)
scanning ion conductance microscopy (SICM) imaging relies on current flowing between a ground electrode and a nanopipette probe that is filled with normal, physiological solution
Summary
The airway surface liquid (ASL) is a very shallow (∼10 μm), viscoelastic gel that covers the upper airways. It used to be believed that the PCL was a “watery” layer to allow free motion of the cilia, whilst the mucus layer was much more viscous, important for its role in trapping pathogens. This idea is not consistent with the fact that 40 nm particles cannot penetrate the PCL layer, and recently, a revised ‘gel on a brush’ model has redefined thinking about these two layers.[2] In this new model, the PCL layer consists of membrane-spanning mucins and mucopolysaccharides tethered to the airway surface, including the cilia themselves.[2]
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