Effect of cortisol on the physiology of cultured pavement cell epithelia from freshwater trout gills

Cortisol had dose-dependent effects on the electrophysiological, permeabili ty, and ion-transporting properties of cultured pavement cell epithelia der ived from freshwater rainbow trout gills and grown on cell culture filter s upports. Under both symmetrical (L15 media apical/L15 media basolateral) an d asymmetrical (freshwater apical/L15 media basolateral) culture conditions , cortisol treatment elevated transepithelial resistance, whereas permeabil ity of epithelia to a paracellular permeability marker (polyethylene glycol -4000) decreased. Cortisol did not alter the Na+-K+-ATPase activity or the total protein content of the cultured preparations. During 24-h exposure to asymmetrical conditions, the net loss rates of both Na+ and Cl- to the wat er decreased with increasing cortisol dose, an important adaptation to dilu te media. Unidirectional Na+ and Cl- flux measurements and the application of the Ussing flux-ratio criterion revealed cortisol-induced active uptake of both Na+ and Cl- under symmetrical culture conditions together with an i ncrease in transepithelial potential (positive on the basolateral side). Un der asymmetrical conditions, cortisol did not promote active ion transport across the epithelium. These experiments provide evidence for the direct ac tion of cortisol on cultured pavement cell epithelia and, in particular, em phasize the importance of cortisol for limiting epithelial permeability.