Evidence for a sodium ion exchange carrier linked with glucose transport across the brush border of a flatworm (Hymenolepis diminuta, Cestoda)

The manner in which the flatworm, Hymenolepis diminuta (Cestoda), regulates the transport of glucose and Na⁺ across the brush border was examined. While the presence of an unstirred region in the brush border may favor the reabsorption of leaked glucose, some leaked glucose was lost to the ambient medium. This loss was markedly enhanced by preloading the worms with glucose and by removing Na⁺ from the incubation medium. Since glucose and Na⁺ influxes are coupled, glucose leakage stimulated the influx of ²²Na⁺. However, this ²²Na⁺ influx was balanced by a simultaneous increased ²²Na⁺ efflux. The presence of phlorizin inhibited both unidirectional fluxes of ²²Na⁺ indicating that efflux of ²²Na⁺ occurred by counter-transport; countertransport of [¹⁴C]glucose appeared to be negligible. A model has been proposed in which the transport of glucose and compensating transfers of Na⁺ across the membrane occur via the same carrier.