Extracellular ATP increases NH4+ permeability in human lymphocytes by opening a P2Z purinoceptor operated ion channel.
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.
Chen
J R
JR
Department of Haematology, Austin Hospital, Heidelberg, Vic., Australia.
Jamieson
G P
GP
Wiley
J S
JS
D000255:Adenosine Triphosphate / Q000502:physiology*; D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000588:Amines / Q000494:pharmacology; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism; D002463:Cell Membrane Permeability; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007473:Ion Channels / Q000502:physiology*; D008214:Lymphocytes / Q000378:metabolism*; D010084:Oxidation-Reduction; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D011983:Receptors, Purinergic / Q000502:physiology*
D000588:Amines; D005452:Fluoresceins; D005456:Fluorescent Dyes; D007473:Ion Channels; D000644:Quaternary Ammonium Compounds; D011983:Receptors, Purinergic; C057360:5-(N,N-hexamethylene)amiloride; D000584:Amiloride; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein; D000255:Adenosine Triphosphate; D002118:Calcium