Assessment of chloride secretion in human nasal epithelial cells by X-ray microanalysis

The genetic disease cystic fibrosis (CF) is due to defective epithelial chloride transport. Different treatments have been proposed that could restore chloride transport in CF patients. A new method is proposed for measuring the chloride secretion in easily accessible epithelial cells. Fresh nasal epithelial cells were obtained by nasal brushing and made to attach to titanium grids for electron microscopy. Chloride efflux through the cystic fibrosis transmembrane regulator channel was stimulated by 20 microM forskolin and 100 microM isobutyl-methylxanthine (IBMX), in standard Ringer's solution (SR). Chloride efflux through the calcium-regulated channel was stimulated by 200 microM adenosine triphosphate (ATP) in SR. The cells were rinsed after the exposure, in order to remove the experimental medium, frozen and freeze-dried. The elemental composition of the cells was determined by X-ray microanalysis. Rinsing with distilled water or ammonium acetate appeared to cause damage to the cells, whereas rinsing with isotonic mannitol preserved the ionic composition. Stimulation of cells from healthy controls with forskolin and IBMX in a chloride-containing medium caused a significant (28 +/- 6%) decrease in chloride concentration, which is indicative of net chloride efflux. In similar conditions, stimulation with ATP induced a 29 +/- 5% decrease in the chloride concentration. Stimulation of cells from CF patients with forskolin and IBMX in a chloride-containing medium caused no significant change in the intracellular chloride concentration, whereas ATP stimulation induced a response similar to that obtained in cells from healthy controls. It is concluded that X-ray microanalysis of nasal epithelial cells may be used to determine chloride secretion in CF patients in an easily accessible cell type.