Effects of monovalent cations on (Na⁺ + K⁺)-ATPase in rat brain slices

The influence of monovalent cations on membrane (Na⁺ + K⁺)-ATPase was estimated in vitro in intact cells from the oxygen consumption of rat brain cortical slices. High concentrations of K⁺, Rb⁺ or Cs⁺ stimulated the respiration in the presence of Na⁺. This stimulation was antagonized by ouabain in a concentration- and time-dependent manner. Additionally, only combinations of monovalent cations, that stimulate (Na⁺ + K⁺)-ATPase, increased oxygen consumption, indicating that the stimulated portion of respiration is related to the (Na⁺ + K⁺)-ATPase activity. Low concentrations of Rb⁺ and Cs⁺, however, failed to affect oxygen consumption. Li⁺ slightly and transiently stimulated oxygen uptake at low concentrations and inhibited it at higher concentrations. Low concentrations of Tl⁺ also stimulated respiration in a K⁺-free medium. However, the inhibitory effects of Tl⁺ were predominant at higher concentrations or in the presence of K⁺. Thus, monovalent cations can alter (Na⁺ + K⁺)-ATPase activity. While Rb⁺ and Li⁺ produce opposite effects on this enzyme system under certain conditions, these actions do not seem to be related to the antidepressant action of Rb⁺ and the antimanic action of Li⁺.