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 (T3; 10 or 100 ng ml(-1)), alone or combined with cortisol (500 ng ml(-1)), on the physiological properties of cultured pavement cell epithelia from freshwater rainbow trout gills were assessed. T3 had dose-dependent effects on electrophysiological, biochemical, and ion transporting properties of cultured epithelia in both the absence and the presence of cortisol. These included reduced transepithelial resistance (TER), increased net Na(+) and Cl(-) movement (basolateral to apical) under asymmetrical culture conditions (freshwater apical/L15 media basolateral), and elevated Na(+)-K(+)-ATPase activity. However, paracellular permeability was elevated only in high-dose T3-treated preparations. In T3 + cortisol-treated epithelia, similar T3-induced alterations in TER, net Na(+) and Cl(-) movement, and paracellular permeability were observed, whereas the activity of Na(+)-K(+)-ATPase was further elevated. Under symmetrical culture conditions (L15 medium apical/L15 medium basolateral), T3 had no effect on transepithelial Na(+) and Cl(-) transport, which was passive. However, T3 + cortisol treatment resulted in active Na(+) extrusion (basolateral to apical). Under asymmetrical conditions, hormone treatment did not change the pattern of ion movement (active Na(+) extrusion, active Cl(-) uptake). These experiments demonstrate that cultured pavement cell epithelia from freshwater rainbow trout are T3-responsive and provide evidence for the direct action of T3 and the interaction of T3 and cortisol on the physiology of this preparation.