Inhibition of Na (+) -K (+) -2Cl (-) cotransport by mercury
Jacoby, S.C.; Gagnon, E.; Caron, L.; Chang, J.; Isenring, P.
American Journal of Physiology 277(4): C684-C692
1999
ISSN/ISBN: 0002-9513 PMID: 10516098 Document Number: 510459
Mercury alters the function of proteins by reacting with cysteinyl sulfhydryl (SH-) groups. The inorganic form (Hg2+) is toxic to epithelial tissues and interacts with various transport proteins including the Na+ pump and Cl- channels. In this study, we determined whether the Na+-K+-Cl cotransporter type 1 (NKCC1), a major ion pathway in secretory tissues, is also affected by mercurial substrates. To characterize the interaction, we measured the effect of Hg2+ on ion transport by the secretory shark and human cotransporters expressed in HEK-293 cells. Our studies show that Hg2+ inhibits Na+-K+-Cl- cotransport, with inhibitor constant (Ki) values of 25 mM for the shark carrier (sNKCC1) and 43 mM for the human carrier. In further studies, we took advantage of species differences in Hg2+ affinity to identify residues involved in the interaction. An analysis of human-shark chimeras and of an sNKCC1 mutant (Cys-697-->Leu) reveals that transmembrane domain 11 plays an essential role in Hg2+ binding. We also show that modification of additional SH- groups by thiol-reacting compounds brings about inhibition and that the binding sites are not exposed on the extracellular face of the membrane. Reprinted by permission of the publisher.