EXTRACELLULAR ATP INCREASES NH4+ PERMEABILITY IN HUMAN-LYMPHOCYTES BY OPENING A P-2Z 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 InM NH4Cl produced a rapid phase of alkalinization. This was followed by a slow return to resting pH(i) 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 P-2Z 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. (C) 1994 Academic Press, Inc.