Fast and selective ammonia transport by aquaporin-8

Sapar M. Saparov, Kun Liu, Peter Agre, Peter Pohl

Research output: Contribution to journalArticlepeer-review

141 Scopus citations


The transport of ammonia/ammonium is fundamental to nitrogen metabolism in all forms of life. So far, no clear picture has emerged as to whether a protein channel is capable of transporting exclusively neutral NH3 while excluding H+ and NH4+. Our research is the first stoichiometric study to show the selective transport of NH3 by a membrane channel. The purified water channel protein aquaporin-8 was reconstituted into planar bilayers, and the exclusion of NH4 + or H+ was established by ensuring a lack of current under voltage clamp conditions. The single channel water permeability coefficient of 1.2 × 10-14 cm3/subunit/s was established by imposing an osmotic gradient across reconstituted planar bilayers, and resulting minute changes in ionic concentration close to the membrane surface were detected. It is more than 2-fold smaller than the single channel ammonia permeability (2.7 × 10-14 cm 3/subunit/s) that was derived by establishing a transmembrane ammonium concentration gradient and measuring the resulting concentration increases adjacent to the membrane. This permeability ratio suggests that electrically silent ammonia transport may be the main function of AQP8.

Original languageEnglish (US)
Pages (from-to)5296-5301
Number of pages6
JournalJournal of Biological Chemistry
Issue number8
StatePublished - Feb 23 2007
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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