PERMEATION AND MEMBRANE TRANSPORT IN PARASITISM: STUDIES ON A TAPEWORM-ELASMOBRANCH SYMBIOSIS

¹ Marine Biological Laboratory, Woods Hole, Massachusetts; Department of Pathobiology, School of Hygiene and Public Health, Johns Hopkins University, Baltimore, Maryland; and Department of Biology, The Rice Institute, Houston, Texas

1. The entry of C14-L-valine into the tapeworm, Calliobothrium verticillatum, is competitively inhibited by L-serine, L-threonine, and L-alanine. Conversely, L-valine competitively inhibits the entry of C14-L-serine.

2. The entry of C14-L-valine is not significantly affected by L-lysine and, conversely, L-lysine entry is not affected by L-valine.

3. L-valine is concentrated against a gradient by Calliobothrium in experiments of 40-minute duration.

4. The entry of C14-L-valine into mucosal tissues of the dogfish host, Mustelus canis, is competitively inhibited by L-serine and, conversely, C14-L-serine entry is competitively inhibited by L-valine. L-leucine, L-isoleucine, L-methionine, L-threonine, and L-lysine also inhibit C14-L-valine entry but it has not been shown that inhibition is competitive.

5. In experiments of 30-minute duration, L-histidine uptake by dogfish mucosa was not affected by L-alanine, L-proline, L-valine, L-serine, or L-aspartic acid at the concentrations tested.

6. Quantitative analyses of free amino acids of the dogfish intestinal lumen showed variability in the absolute concentrations but great stability in the relative concentrations.

7. The data are discussed in terms of differences in amino acid entry systems of host and parasite, the significance of stability of amino acid ratios in the nutrition of host and parasite, and the necessity for evaluating host-parasite competitions in terms of entry of single components from complex mixtures.