Uptake of creatine by cultured cells

Abstract We have examined the uptake of creatine by cultured monolayers of human IMR-90 flbroblasts, human uterine smooth muscle cells, calf aortic smooth muscle cells, and myoblasts and myotubes of the L 6 E 9 rat skeletal muscle cell line. Creatine uptake is dependent on temperature and sensitive to the presence of Na + in the extracellular medium. It is saturable, apparently concentrative, and inhibited by ouabain and structural analogs of creatine. In these respects, it resembles the process of creatine uptake by isolated preparations of skeletal muscle and brain tissues. Lineweaver-Burk plots of the data for variation in rate of uptake with concentration of creatine in the medium are nonlinear, suggesting that the process of uptake may be heterogeneous. Assuming the operation of two saturable processes of uptake, we calculated two values for apparent K m and V for each cell line. Kinetic parameters of creatine uptake by the different cell types are similar. The lower values of K m (0.02–0.04 m m ) are in the physiological range of creatine concentration in mammalian plasma.