Transport of 3-O-methylglucose in isolated rat retinal pigment epithelial cells

The uptake of 3-O-methylglucose in isolated rat retinal pigment epithelial cells exhibits complex kinetics as revealed by a plot of the Lineweaver-Burke transformation of the Michaelis-Menten equation. Conventional analysis of the linear portion of the double-reciprocal plot yields a Km of 7 . 69 mM and a Vmax of 1 . 95 nM/mg protein/min. If data are analyzed to take into account the existence of two carrier-mediated processes, a high affinity system (Km = 1 . 94 mM, Vmax = 0 . 012 nM/mg protein/min) and a low affinity system (Km = 640 mM, Vmax = 12 . 20 nM/mg protein/min) for 3-O-methylglucose uptake results. Three-O-methylglucose accumulation over a 10-min period was insensitive to phloridzin (0 . 1 mM), ouabain (1 mM) and dinitrophenol (1 mM), but was inhibited by mercuric chloride (1 mM). Phloretin (0 . 1 mM) increased the accumulation of both glucose and 3-O-methylglucose, which may indicate the existence of carrier-mediated efflux system. These findings demonstrate that glucose transport in rat retinal pigment epithelial cells is a complex process involving carrier mediation.