Arsenical and mercurial inhibition of tyrosine transport by the flounder intestine

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Abstract
The effects of mercurials and arsenicals on tyrosine absorption by the winter flounder Pseudopleuronectes americanus were studied using isolated intestinal strips mounted in Ussing chambers. The mercurials mercuric chloride (HgCl2), p‐chloromercuriphenyl sulfonic acid (PCMBS), and phenylmercuric acetate (PMA) and the arsenicals oxophenylarsine and arsenamide were chosen for their different chemical properties. The transmural absorptive fluxes (mucosa to serosa, M ? S) were inhibited by mucosal additions of 0.1 mM HgCl2 (64% inhibition), 1.0 mM PCMBS (41% inhibition), and 0.25 mM oxophenylarsine (48% inhibition). Tyrosine tissue accumulation was inhibited 68% by 0.1 mM HgCl2, 42% by 1.0 mM PCMBS, and 62% by 0.25 mM oxophenylarsine. Serosal addition of 1.0 mM PCMBS inhibited M ? S flux by 45%. Transepithelial potential (TEP) was measured to monitor changes in ionic gradients across the epithelial membrane. Mucosal addition of 0.1 mM HgCl2, and of 0.25 and 0.05 mM oxophenylarsine significantly changed the TEP. Serosal additions of 0.1 mM HgCl2, 1.0 mM PCMBS, and 0.25 mM oxophenylarsine also altered the TEP significantly. These results indicate that Na+‐dependent tyrosine uptake is inhibited by arsenicals and mercurials, but it is unclear whether the Na+‐tyrosine cotransport system or the transmembrane ionic gradients were affected by these heavy metals.