Meeting Abstract
Many elasmobranchs are considered top predators with worldwide distribution, and in general these fish play an important role in the transfer of energy from the lower to the upper trophic levels within the marine ecosystem. Despite this, little research regarding the rates of prey digestion and processes of energy and nutrient absorption have been explored. Specifically understudied is enzymatic digestion within the intestinal brush border that functions to breakdown macromolecules to smaller subunits for absorption across the gastrointestinal epithelium. Given their carnivorous diet, the present study sought to expand knowledge on nutrient intake in elasmobranchs by focusing on the uptake of products of protein metabolism. To accomplish this, Peptide Transporter 1 (PEPT1), a protein found within the brush border membrane of higher vertebrates that is responsible for the translocation and absorption of small peptides released during digestion by membrane- bound proteases, was molecularly identified in the bonnethead shark(Sphyrna tiburo) using degenerate primers based on conserved portions of known PEPT1 sequence. The transporter was localized by immunocytochemistry, and vesicle studies were used to identify the apparent affinity of the transporter, and to quantify the rate of uptake by its H+-dependent cotransporter properties, using 3H-glycylsarcosine as a model dipeptide. Such results provide insight into the rate and properties of food passage within S. tiburo, and can lead to topics like physiological regulation of protein metabolism and absorption, and how it may vary in elasmobranchs that exhibit different feeding strategies, thereby helping us assess different life history characteristics that contribute to elasmobranch vulnerability of overfishing.
