Treatment of Friend-erythroleukemia cells with 1.5% dimethylsulfoxide (DMSO) caused a decrease in ouabain sensitive 86Rb+-uptake beginning six to seven hours after DMSO addition indicating a reduced function of the Na+, K+-pump. However, analysis of the ouabain sensitive 86Rb+-uptake after Na+-preloading of the cells as well as measurements on the Na+, K+-ATPase activity in isolated membrane fragments revealed that no inhibition of the Na+, K+-ATPase occurred during the first 12 hours. On the contrary the Na+, K+-ATPase activity was initially enhanced and then returned to control levels during the early phase of induction by DMSO. On the other hand, 22Na+-transport into DMSO-treated cells was reduced similar to the ouabain sensitive 86Rb+ uptake in cells without Na+ preloading. The piretanide sensitive 86Rb+-uptake, due to the Na+, K+, 2Cl - cotransport system was inhibited after seven hours exposure to DMSO. Some three hours after DMSO addition the incorporation of 35S-methionine into proteins began to decrease, which was accompanied with or followed by a reduction in the methionine uptake of DMSO treated cells. Membrane-potential-dependent tetraphenylphosphonium cation uptake was not altered relative to the controls in the first 12 hours following DMSO addition. These results suggest that the reduced activity of the Na+, K+-pump in Friend cells after DMSO exposure is not due to inhibition of the Na+, K+-ATPase, but most probably due to a smaller Na+-influx, which results from inhibition of Na+-cotransport processes (amino acid uptake, Na+, K+, 2Cl - cotransport system).

Components of the 86Rb+-influx in HeLa cells were investigated in Joklik minimal essential medium, or in Earle's balanced salt solution with and without medium amino acids. The presence of amino acids led to the stimulation of the ouabain sensitive 86Rb+-uptake and inhibition of the diuretic-sensitive and residual 86Rb+-fluxes. These results show that the presence of amino acids is an important regulator of the K+/Rb+-fluxes under normal conditions in growth medium.