Transepithelial Impedance Analysis of Chloride Secretion

Transepithelial chloride secretion requires the activation of both apical membrane chloride channels and basolateral membrane potassium channels. Chloride channels are needed for the apical membrane exit of chloride and potassium channels are needed to repolarize the cell and thereby provide the driving force for chloride exit. Chloride entry on the basolateral membrane Na:K:2Cl^- cotransporter must be carefully matched with the apical membrane exit of chloride to maintain cell volume integrity and to achieve a sustained level of chloride secretion. Endogenous secretory agonists acting via intracellular signal transduction cascades (e.g., cAMP, Ca²⁺ ) coordinate the activities of the apical and basolateral membrane channels and transporters by mechanisms that are still poorly understood. Moreover, several different types of chloride and potassium channels are thought to contribute to the secretion of chloride. In an effort to better understand the mechanisms that regulate the coordinated activation of apical and basolateral membrane channels and to investigate the relative contribution of various candidate chloride and potassium channels in chloride secretion we have begun to utilize transepithelial impedance analysis.