Glucose and Sodium Fluxes Across the Brush Border Ofhymenolepis Diminuta(cestoda)

When Hymenolepis diminuta was preincubated in Na+-free KRT (tris-maleate buffered Krebs-Ringer saline) for varying time intervals, followed by incubation in 14C-glucose in Na+-fee KRT, the influx of glucose in worms was lowered significantly. This effect of Na+ deletion on glucose influx was totally reversible by incubating worms in KRT ([ Na+] = 154 meq/l).When Na+ in the medium was replaced with K+, tris, or choline, a similar decrease in glucose influx in worms was noted; replacement of Na+ with Li+ resulted in a glucose influx rate significantly higher than that obtained with K+, tris, or choline as the replacement cation. In media with a suboptimal Na+ concentration (25 meq/l), influx of 0.5 mM glucose in worms was unaffected by varying concentrations of K+ (0-100 meq/l).Apparent Michaelis-Menten kinetics were observed when glucose influx as a function of glucose concentration was determined in media with Na+ concentrations of 154, 50, 25, and 10 meq/l. There was a slight decrease in the apparent transport constant (Kt) for glucose influx and a marked decrease in maximal glucose influx (JiGmax with decreasing Na+ concentration. Glucose influx in H. diminuta as a function of the Na+ concentration displayed apparent Michaelis-Menten kinetics, and the Na+ concentration necessary to attain JiGmax/2 lowered significantly at lower glucose concentrations.A large Na+ influx was associated with glucose influx in H. diminuta, and the influxes of Na+ and glucose exhibited first order kinetics for at least 2 min. In media with Na+ concentrations of 5, 25, and 50 meq/l, coupling coefficients (JiNa/ JiG) were 1.90, 1.60, and 0.87, respectively, or inversely related to the Na+ concentration. Coupling coefficients were independent of the glucose concentration over a 50-fold range. Glucose-coupled Na+ influx in worms was a hyperbolic function of glucose concentration. In the absence of glucose, Na+ influx in H. diminuta apparently occurred, in part, by a mediated process which was unaffected by phlorizin. There was a small mediated glucose influx in worms in the absence of external Na+, 70% of which was abolished by phlorizin.The cotransport of Na+ and glucose in H. diminuta is (1) compared with other similar systems in both tapeworms and mammals, (2) presented in support of Crane's Na+-gradient hypothesis for transport and accumulation of sugars, (3) tentatively explained in the form of a hypothesized model, and (4) discussed briefly in relation to the evolution of parasitic flatworms.