Thallium inhibition of ouabain-sensitive sodium transport and of the (Na+ plus K+)-ATPase in human erythrocytes.

The influence of Tl+ on Na+ transport and on the ATPase activity in human erythrocytes was studied. 0.1-1.0 mM Tl+ added to a K+-free medium inhibited the ouabain-sensitive self-exchange of Na+ and activated both the ouabain-sensitive 22Na outward transport and the transport related ATPase. 5-10mM external Tl+ caused inhibition of the ouabain-sensitive 22Na efflux as well as the (Na+ plus Tl+)-ATPase. Competition between the internal Na+ and rapidly penetrating thallous ions at the inner Na+-specific binding sites of the erythrocyte membrane could account for the inhibitory effect of Tl+. An increase of the internal Na+ concentration in erythrocytes or in ghosts protected the system against the inhibitory effect of high concentration of Tl+. A protective effect of Na+ was also demonstrated on the (Na+ plus Tl+)-ATPase of fragmented erythrocyte membranes studied at various Na+ and Tl+ concentrations.