A perchlorate sensitive iodide transporter in frogs

Abstract

Nucleotide sequence comparisons have identified a gene product in the genome database of African clawed frogs (Xenopus laevis) as a probable member of the solute carrier family of membrane transporters. To confirm its identity as a putative iodide transporter, we examined the function of this sequence after heterologous expression in mammalian cells. A green monkey kidney cell line transfected with the Xenopus nucleotide sequence had significantly greater (125)I uptake than sham-transfected control cells. The uptake in carrier-transfected cells was significantly inhibited in the presence of perchlorate, a competitive inhibitor of mammalian Na(+)/iodide symporter. Tissue distributions of the sequence were also consistent with a role in iodide uptake. The mRNA encoding the carrier was found to be expressed in the thyroid gland, stomach, and kidney of tadpoles from X. laevis, as well as the bullfrog Rana catesbeiana. The ovaries of adult X. laevis also were found to express the carrier. Phylogenetic analysis suggested that the putative X. laevis iodide transporter is orthologous to vertebrate Na(+)-dependent iodide symporters. We conclude that the amphibian sequence encodes a protein that is indeed a functional Na(+)/iodide symporter in X. laevis, as well as R. catesbeiana.

Lifecycle exposure to perchlorate differentially alters morphology, biochemistry, and transcription as well as sperm motility in Silurana tropicalis frogs

“…Perchlorate contamination has been reported in ground and surface waters across North America (ASTSWMO 2011; Blount et al 2010;GAO 2010;Parker et al 2008;Backus et al 2005;Reviewed in Trumpolt et al 2005) and the anion has been found to compete with iodide at the sodium-iodide symporter in the thyroid (Carr et al 2008). However, few studies have examined the effects of prolonged exposure to the thyroid hormone disrupting chemical particularly at environmentally relevant concentrations in lower vertebrates, such as amphibians.…”

“…Amphibian development and growth is dependent on thyroid hormones, and thus we examined the effects of environmentally relevant concentrations of KClO 4 on thyroid hormonerelated gene expression. ClO 4 competitively inhibits the uptake of Ivia the NIS limiting the synthesis of the iodine-rich thyroid hormones (T4 and T3) by the thyroid gland (Carr et al 2008). Mukhi et al 2007;X.…”

“…The primary mechanism of ClO 4 is the competitive inhibition of iodide (I -) uptake via the Na + /Isymporter (NIS) limiting the synthesis of the iodine-rich thyroid hormones, tetraiodothyronine (T4) and triiodothyronine (T3), by the thyroid gland (Carr et al 2008).…”