Kinetics of erythromycin uptake into Ehrlich mouse ascites tumor cells

The uptake was studied with freshly isolated Ehrlich ascites tumor (EMAT) cells and with 14C-labelled erythromycin. Erythromycin was accumulated by EMAT cells. The uptake rates and quotes of erythromycin increased with increasing temperature and with increasing pH value (alkaline pH). The uptake was reduced by SH-group reagents, by inhibitors of electron transport and of oxidative phosphorylation and by ouabain. The uptake was saturable (Km = 6.0 X 10(-4) mol/l). The release of the accumulated erythromycin followed first order kinetics (k = 4.5 X 10(-2) min-1). The uptake and accumulation of erythromycin cannot be explained by non-ionic partition. An active uptake mechanism is suggested.