Estimation of the lifespan of amiloride binding sites in the membranes of toad bladder epithelial cells.

1. Sodium entry sites in the membranes of isolated epithelial cells prepared from bladders of toads (Bufo marinus) have been labelled with amiloride. The number of binding sites remained constant in suspensions for up to 100 hr. 2. In the presence of a protein synthesis inhibitor (cycloheximide, 0-5 mug/ml.) there was a decline in the density of binding sites was approximately exponential. Regression analysis gave a half-life of approximately 60 hr. 3. Aldosterone (5 X 10(-8) M) caused a significant (P less than 0-001) increase (50%) in the density of amiloride binding sites. Cells which had been treated with aldosterone had populations of binding sites which declined, in the presence of cycloheximide, at rates indistinguishable from those of untreated cells.