Hymenolepis diminuta and Hymenolepis microstoma: Effect of ouabain on active nonelectrolyte uptake across the “epithelial” syncytium

Abstract

The effect of ouabain on the unidirectional uptake of glucose, galactose, and alanine by Hymenolepis diminuta and glucose uptake by H. microstoma was examined in vitro. Both intact cestodes and those worms that were sliced along the length of their flat surface in order to expose the underlying tissues to ouabain were employed in these studies. Uptake via the exposed parenchyma cells accounted for less than 25% of the uptake by the sliced worms as demonstrated with worms in which uptake across the brush border was inhibited by treating the worms with HgCl 2 prior to slicing. Similarly, the tissue hexose transport pools were derived primarily from uptake across the brush border. Ouabain did not alter uptake by intact worms but diminished the influx of all three absorbates when the sliced worms were used. The minimum concentration of ouabain required to inhibit uptake was 1.0 m M for galactose, 0.1 m M for glucose, and 0.01 m M for alanine. These results suggest a number of possible effects of ouabain on uptake systems. Na +-free conditions did not immediately alter hexose uptake and upon returning the worms to Na +-containing fluids, inhibition of hexose uptake was not immediately reversible, suggesting that the sole site of Na + action is not on the external side of the brush border membrane. Na +-free conditions were more effective in inhibiting hexose influx than ouabain, DNP, or iodoacetate used in combination with Na +-free preincubations, suggesting that under these conditions substantial Na +-dependent uptake occurred. Ouabain, DNP, and iodoacetate were more effective inhibitors of galactose uptake in the presence of Na + than in its absence. Although the tegument is polarized with respect to the action of ouabain, it is concluded that hexose and amino acid uptake by H. diminuta consists of both primary and secondary active transport.