The physiological effects of 3,5 ',3 '-triiodo-L-thyronine alone or combined with cortisol on cultured pavement cell epithelia from freshwater rainbow trout gills

The effects of 3,5',3'-triiodo-L-thyronine (T-3; 10 or 100 ng ml(-1)), alon e or combined with cortisol (500 ng ml(-1)), on the physiological propertie s of cultured pavement cell epithelia from freshwater rainbow trout gills w ere assessed. T-3 had dose-dependent effects on electrophysiological, bioch emical, and ion transporting properties of cultured epithelia in both the a bsence and the presence of cortisol. These included reduced transepithelial resistance (TER), increased net Na+ and Cl- movement (basolateral to apica l) under asymmetrical culture conditions (freshwater apical/L15 media basol ateral), and elevated Na+-K+-ATPase activity. However, paracellular permeab ility was elevated only in high-dose T-3-treated preparations. In T-3 + cor tisol-treated epithelia, similar T-3-induced alterations in TER, net Na+ an d Cl- movement, and paracellular permeability were observed, whereas the ac tivity of Na+-K+-ATPase was further elevated. Under symmetrical culture con ditions (L15 medium apical/L15 medium basolateral), T-3 had no effect on tr ansepithelial Na+ and Cl- transport, which was passive. However, T-3 + cort isol treatment resulted in active Na+ extrusion (basolateral to apical). Un der asymmetrical conditions, hormone treatment did not change the pattern o f ion movement (active Na+ extrusion, active Cl- uptake). These experiments demonstrate that cultured pavement cell epithelia from freshwater rainbow trout are T-3-responsive and provide evidence for the direct action of T-3 and the interaction of T-3 and cortisol on the physiology of this preparati on. (C) 2001 Academic Press.