Mercury and zinc differentially inhibit shark and human CFTR orthologues: Involvement of shark cysteine 102

Gerhard J. Weber, Ali Poyan Mehr, Jeffrey C. Sirota, Stephen G. Aller, Sarah E. Decker, David C. Dawson, John N. Forrest

Research output: Contribution to journalArticlepeer-review

17 Scopus citations

Abstract

The apical membrane is an important site of mercury toxicity in shark rectal gland tubular cells. We compared the effects of mercury and other thiol-reacting agents on shark CFTR (sCFTR) and human CFTR (hCFTR) chloride channels using two-electrode voltage clamping of cRNA microinjected Xenopus laevis oocytes. Chloride conductance was stimulated by perfusing with 10 μM forskolin (FOR) and 1 mM IBMX, and then thio-reactive species were added. In oocytes expressing sCFTR, FOR + IBMX mean stimulated Cl- conductance was inhibited 69% by 1 μM mercuric chloride and 78% by 5 μM mercuric chloride (IC50 of 0.8 μM). Despite comparable stimulation of conductance, hCFTR was insensitive to 1 μM HgCl2 and maximum inhibition was 15% at the highest concentration used (5 μM). Subsequent exposure to glutathione (GSH) did not reverse the inhibition of sCFTR by mercury, but dithiothreitol (DTT) completely reversed this inhibition. Zinc (50-200 μM) also reversibly inhibited sCFTR (40-75%) but did not significantly inhibit hCFTR. Similar inhibition of sCFTR but not hCFTR was observed with an organic mercurial, p-chloromercuriphenylsulfonic acid (pCMBS). The first membrane spanning domain (MSD1) of sCFTR contains two unique cysteines, C102 and C303. A chimeric construct replacing MSD1 of hCFTR with the corresponding sequence of sCFTR was highly sensitive to mercury. Site-specific mutations introducing the first but not the second shark unique cysteine in hCFTR MSD1 resulted in full sensitivity to mercury. These experiments demonstrate a profound difference in the sensitivity of shark vs. human CFTR to inhibition by three thiol-reactive substances, an effect that involves C102 in the shark orthologue.

Original languageEnglish (US)
Pages (from-to)C793-C801
JournalAmerican Journal of Physiology - Cell Physiology
Volume290
Issue number3
DOIs
StatePublished - Mar 2006

Keywords

  • Chloride transport
  • Cystic fibrosis transmembrane regulator
  • Dithiothreitol
  • Glutathione
  • Xenopus laevis oocytes
  • p-chloromercuriphenylsulfonic acid

ASJC Scopus subject areas

  • Physiology
  • Cell Biology

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