Palytoxin binds to and inhibits kidney and erythrocyte Na+, K+-ATPase.

Hog kidney Na+, K+-ATPase, purified to the microsomal stage and activated with detergent, binds palytoxin, as shown by the nearly complete competition of the toxin with 3H-ouabain. The Ki-values of palytoxin, but not of ouabain, depend on the protein concentration; this indicates additional binding sites for the toxin on kidney membranes. - Palytoxin inhibits the enzymatic activity of the detergent-activated preparation nearly completely (IC50 8 X 10(-7) mol/l). Inhibition of ATPase activity and of ouabain binding are promoted by borate, a known activator of palytoxin. - Palytoxin also inhibits the Na+,K+-ATPase of erythrocyte ghosts in the same dose range. The data are discussed in context with the hypothesis (Chhatwal et al. 1983) that palytoxin raises the cellular permeability by altering the state of Na+,K+-ATPase or its environment.