HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 565/1/207    most recent jphysiol.2004.080218v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Capendeguy, O. Articles by Horisberger, J.-D. Search for Related Content PubMed PubMed Citation Articles by Capendeguy, O. Articles by Horisberger, J.-D.

¹ Institut de Pharmacologie et de Toxicologie, Université de Lausanne, Rue du Bugnon 27, CH-1005 Lausanne, Switzerland

Na⁺,K⁺-ATPase is responsible for maintaining the cross-membrane Na⁺ and K⁺ gradients of animal cells. This P-type ATPase works via a complex transport cycle, during which it binds and occludes three intracellular Na⁺ ions and then two extracellular K⁺ ions, which it then releases on the other side of the membrane. The cation pathway through the protein, and the structures responsible for occluding cations inside the protein, have not yet been definitely identified. We used cysteine mutagenesis to explore the accessibility and the role of five conserved residues in the short third extracellular loop, between the fifth and the sixth transmembrane helices. The P801C and L802C mutants were not affected by extracellular sulfhydryl reagents. The presence of cysteine residues at three positions (G803C, T804C and V805C) conferred sensitivity to omeprazole, a known inhibitor of the gastric proton pump, and to [2-(trimethylammonium)-ethyl]methanethiosulphonate bromide (MTSET). The effects of omeprazole and MTSET were modulated by the presence of extracellular K⁺, indicating that the accessibility of these positions depended on the conformational state of the protein. MTSET binding to cysteine at position 803 partially inhibited the Na⁺,K⁺-pump function by decreasing its affinity towards extracellular K⁺, suggesting a restriction of the access of extracellular K⁺ ions to their binding sites. In contrast, MTSET binding to cysteine at position 805 partially inhibited the Na⁺,K⁺-pump function by reducing its maximum turnover rate, probably by slowing a rate-limiting conformational change. These residues occupy positions that are critical for either the cation pathway or the conformational modifications.

(Received 29 November 2004; accepted after revision 10 March 2005; first published online 17 March 2005)
Corresponding author J.-D. Horisberger: Institut de Pharmacologie et de Toxicologie, Université de Lausanne, Rue du Bugnon 27, CH-1005 Lausanne, Switzerland. Email: jean-daniel.horisberger{at}unil.ch

This article has been cited by other articles:

				O. Capendeguy, J. Iwaszkiewicz, O. Michielin, and J.-D. Horisberger The Fourth Extracellular Loop of the {alpha} Subunit of Na,K-ATPase: FUNCTIONAL EVIDENCE FOR CLOSE PROXIMITY WITH THE SECOND EXTRACELLULAR LOOP J. Biol. Chem., October 10, 2008; 283(41): 27850 - 27858. [Abstract] [Full Text] [PDF]

				P. Artigas and D. C. Gadsby Ouabain affinity determining residues lie close to the Na/K pump ion pathway PNAS, August 15, 2006; 103(33): 12613 - 12618. [Abstract] [Full Text] [PDF]

				O. Capendeguy, P. Chodanowski, O. Michielin, and J.-D. Horisberger Access of Extracellular Cations to their Binding Sites in Na,K-ATPase: Role of the Second Extracellular Loop of the {alpha} Subunit J. Gen. Physiol., February 27, 2006; 127(3): 341 - 352. [Abstract] [Full Text] [PDF]