Kinetics of erythromycin uptake and release by human lymphocytes and polymorphonuclear leucocytes

The uptake of 14C-labelled erythromycin by human lymphocytes and polymorphonuclear leucocytes was studied. Erythromycin was concentrated by the cells. The amount of accumulated erythromycin was correlated with the cell count and was found to increase with alkaline pH and with increasing temperature of the incubation medium. The uptake of erythromycin could be reduced by compounds which inhibit cell respiration, glycolysis and (Na+-K+)membrane ATPase. Furthermore, the uptake was saturable and followed Michaelis-Menten kinetics (Km = 0.7 and 1.6 mM for lymphocytes and polymorphonuclear leucocytes, respectively). The intracellular concentrations cannot be explained by the principle of non ionic diffusion. It is suggested that erythromycin is actively transported via the nucleoside transport system. The accumulated erythromycin was rapidly released when the cells were washed and re-incubated in antibiotic-free medium. Probably, no strong intracellular binding takes place.