EXTRACELLULAR ATP INCREASES NH4-LYMPHOCYTES BY OPENING A P-2Z PURINOCEPTOR OPERATED ION-CHANNEL( PERMEABILITY IN HUMAN)

The permeability of lymphocytes to NH4+ was examined by measuring intr acellular pH using the fluorescent pH-sensitive dye BCECF. Addition of 20 InM NH4Cl produced a rapid phase of alkalinization. This was follo wed 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 sh owed features consistent with NH4+ being a permeant for the P-2Z purin oceptor operated ion channel. Cytosolic pH measurements showed monomet hylammonium(+) and dimethylammonium(+) were also permeants, but trimet hylammonium(+) (69 Dalton) was excluded by this channel. Since our pre vious data showed ethidium(+) (314 Dalton) is a permeant it appears th at molecular conformation rather than molecular weight determines entr y of cationic solutes through the channel. (C) 1994 Academic Press, In c.