Hymenolepis diminuta: Chloride fluxes and membrane potentials associated with sodium-coupled glucose transport

Abstract

Glucose transport by Hymenolepis diminuta was inhibited when Cl − in the bathing medium was replaced with acetate (C 2H 3O 2 Post−), but was unaffected when Cl − was replaced with SCN −. The relative effectiveness of the anions to inhibit influx of 7.4 m M Cl − in the presence of 1 m M glucose was SCN − > Cl − > C 2H 3O 2 Post−. Glucose stimulated the influxes of 120 m M Cl − and SCN −, but had little effect on 120 m M C 2H 3O 2 Post− influx. While the diffusion rates of the anions were C 2H 3O 2 Post− > SCN − = Cl −, the preference of the glucose transport system for the anions was SCN − > Cl − > C 2H 3O 2 Post−. Efflux of Cl − was not affected by the rate of glucose influx. Finally, microelectrode recordings of worms anesthetized with 2 m M arecoline revealed a transmembrane potential (TMP) of −45 ± 3.6 mV (inside negative). Three to four minutes after addition of glucose (5 m M) there was a progressive hyperpolarization of the TMP to −58 mV. A revised model of the glucose transport system that is consistent with previous observations on this organism is proposed.