Abstract
Cystic Fibrosis (CF) is the most common fatal human genetic disease, which is caused by a defect in an anion channel protein (CFTR) that affects ion and water transport across the epithelium. We devised an apparatus to enable the measurement of concentration changes of sodium, potassium, chloride, pH, and transepithelial potential difference by means of ion-selective electrodes that were placed on both sides of a 16HBE14σ human bronchial epithelial cell line that was grown on a porous support. Using flat miniaturized ISE electrodes allows for reducing the medium volume adjacent to cells to approximately 20 μL and detecting changes in ion concentrations that are caused by transport through the cell layer. In contrast to classic electrochemical measurements, in our experiments neither the calibration of electrodes nor the interpretation of results is simple. The calibration solutions might affect cell physiology, the medium composition might change the direction of actions of the membrane channels and transporters, and water flow that might trigger or cut off the transport pathways accompanies the transport of ions. We found that there is an electroneutral transport of sodium chloride in both directions of the cell monolayer in the isosmotic transepithelial concentration gradient of sodium or chloride ions. The ions and water are transported as an isosmotic solution of 145 mM of NaCl.
Highlights
Epithelial tissue that is made of a single cell layer bound together by tight junctions lines all the wet surfaces of the body
The defect in ion and water transport is the cause of many different human disorders, including the most common fatal inherited one—cystic fibrosis (CF) [1]
It has been found that a defect in a single gene coding Cystic Fibrosis Transport Regulator (CFTR)—an anion channel that is present in the apical face of epithelial cell is responsible for CF [2,3]
Summary
Epithelial tissue that is made of a single cell layer bound together by tight junctions lines all the wet surfaces of the body. The tissue forms a barrier for the diffusive transport of water and solutes. Epithelial cells are polarized, i.e., they have different ion-transporting molecules on apical and basolateral faces. The difference in membrane compositions allows for the directional transport of ions. Water follows transported ions due to osmosis. The functioning of the ion transporters of epithelial cells is under external and intracellular control. The defect in ion and water transport is the cause of many different human disorders, including the most common fatal inherited one—cystic fibrosis (CFTR)—an anion channel that is present in the apical face of epithelial cell is responsible for CF [2,3]
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