The effect of extracellular sodium concentration on α-methyl-d-glucoside transprot by rat kidney cortex slices

Abstract

The kinetics of α-methyl-d-glucoside accumulation by rat kidney cortex slices under conditions of varying extracellular sodium concentration were investigated. Extracellular sodium reduction below 144 mequivi/l resulted in a diminished initial uptake and reduced influx calculated by steady-state analysis of a two-compartment system. At 72 mequiv/l extracellular sodium efflux was decreased to the same extent as influx resulting in the same steady state concentration that was observed at 144 mequiv/l sodium. At 36 mequiv/l the steady state concentration was below that observed at 144 mequiv/l sodium because of a disproportionate decrease of influx. In the complete absence of extracellular sodium, no concentration gradient was achieved and efflux had become increased. Low extracellular sodium was associated with an increase in the apparent Km of transport without affecting the V. The apparent Ki for sodium appeared to be in th e 40 to 59 mequiv/l range. The presence of 20 mM α-methyl-d-glucose prompted the accelerated efflux of the sugar from the tubule cells in a normal fashion despite a low extracellular sodium concentration.