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Extracellular ATP increases NH4+ permeability in human lymphocytes by opening a P2Z purinoceptor operated ion channel.

Chen JR, Jamieson GP, Wiley JS

  • Journal Biochemical and biophysical research communications

  • Published 12 Sep 1994

  • Volume 202

  • ISSUE 3

  • Pagination 1511-6

  • DOI 10.1006/bbrc.1994.2102


The permeability of lymphocytes to NH4+ was examined by measuring intracellular pH using the fluorescent pH-sensitive dye BCECF. Addition of 20 mM NH4Cl produced a rapid phase of alkalinization. This was followed by a slow return to resting pHi due to NH4+ influx. The rate of NH4+ was increased many fold by extracellular ATP and the increment showed features consistent with NH4+ being a permeant for the P2Z purinoceptor operated ion channel. Cytosolic pH measurements showed monomethylammonium+ and dimethylammonium+ were also permeants, but trimethylammonium+ (69 Dalton) was excluded by this channel. Since our previous data showed ethidium+ (314 Dalton) is a permeant it appears that molecular conformation rather than molecular weight determines entry of cationic solutes through the channel.