Complexity in Valinomycin Effects on Amino Acid Port Trans-

3H-labeled dibenzyldimethylammonium ion, applied as an indicator for the potential differences across the plasma membrane, enters the Ehrlich ascites-tumor cell during 2 h to an apparent steady-state concentration about twice that of the suspending medium. In the presence of valinomycin, the distribution ratio reached was increased to about four, the cells meanwhile undergoing a substantial loss of K + and a corresponding gain of Na ÷. Valinomycin decreased the extent to which four model amino acids, selected to represent the uplfill operation of the three transport system, were accumulated by the respiring cell. Simultaneously, the cellular level of ATP was sharply decreased. These observations indicate as expected that the ATP is not a direct factor in the accumulation of the dibenzyldimethylammonium ion. They further indicate that the diminution of cellular ATP by valinomycin handicaps uphill transport more than the accompanying increase in the transmembrane potential may possibly stimulate it.