24Na+-efflux from kidney cortex slices under the effect of indomethacin

24Na+-efflux from kidney cortex slices previously saturated with 24Na+ in vivo was studied in vitro under control conditions and in the presence of 4 micrograms per ml of indomethacin. The radioactivity washout curves obtained in the effluent from cortex slices superfused with Krebs-Ringer medium at 37 degrees C indicated that Na was localized in three compartments in the cortex. Indomethacin did not influence 24Na+-efflux from the compartment that exhibited the fastest efflux; this compartment is thought to be extracellular. Indomethacin potently increased 24Na+-efflux from Na+-compartments localized intracellularly and showing a lower efflux rate (lambda 2 control = 0.156 +/- 0.042, lambda 2 indomethacin = 0.21 +/- 0.064, p less than 0.05; lambda 3 control = 0.031 +/- 0.013 lambda 3 indomethacin = 0.063 +/- 0.020 min-1, p less than 0.001). Since on the basis of earlier findings the direct effect of indomethacin on the enzymes of the active transport system can be ruled out, the present results suggest that indomethacin increases the permeability of cell membranes.