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

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Abstract
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. The entry of C14-L-valine is not significantly affected by L-lysine and, conversely, L-lysine entry is not affected by L-valine. L-valine is concentrated against a gradient in experiments of 40 minute duration. 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 the inhibition is competitive. 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. Quantitative analyses of free amino acids of the dogfish intestinal lumen showed variability in the absolute concentrations but great stability in relative concentrations. The data are discussed in terms of the host-parasite relationship.