HARRISON, K.D.*; ZOZZARO, P.E.; COLLIE, N.L.; CARR, J.A.: Iodide Transport in Xenopus laevis Gut and Skin
Ammonium perchlorate is an important environmental contaminant found at munitions and rocket fuel waste sites. The perchlorate anion is a potent inhibitor of iodide (I–) uptake by the thyroid, thus disrupting thyroid hormone synthesis. However, there are several extrathyroidal sites of I– transport that perchlorate may also inhibit. We characterized I– transport in the gut and skin, as primary sites of environmental I– uptake. Adult male frogs were anesthetized, and the stomach, intestine, and skin patches were removed for study. I– uptake (mucosal-to-cell ) was measured using an everted sleeve technique, with 125I– as the probe and 3H-PEG-4000 as adherent fluid marker. I– uptake was linear for at least 2 min, so all subsequent uptakes employed this time period. Skin I– uptake was about 5-10 fold lower than that in the gut. For the gut, I– uptake was lowest in the stomach, increased slightly in the proximal intestine, and increased steeply in the distal gut. Over a broad concentration range (0.1-500 uM), uptake for both skin and gut appeared approximately linear with mucosal I– concentration. However, at physiological concentrations, the uptake rate best fit a saturable plus a linear component. The 75-uM Km saturable component was similar to that in frog choroid plexus (60 uM). Skin exhibited a 103-uM Km saturable component. Thus, both skin and gut may contain perchlorate-sensitiveI– pathways. Current efforts are aimed at full characterization of these I– uptake components. Supported in part by a Howard Hughes Med. Inst. grant through the Undergrad.Biol.Sci.Edu. Program to Texas Tech Univ.
