EXTRACELLULAR ATP CAUSES LOSS OF L-SELECTIN FROM HUMAN-LYMPHOCYTES VIA OCCUPANCY OF P(2)Z PURINOCEPTORS

Lymphocytes from normal subjects or patients with chronic lymphocytic leukemia are known to possess receptors for extracellular ATP termed P (2)Z purinoceptors whose physiological role is undefined. Addition of extracellular ATP (50-500 mu M) to both normal and leukemic lymphocyte s caused loss of binding of monoclonal antibodies to L-selectin (CD62L ) on the cell surface. UTP, ADP, and adenosine (all at 500 mu M) had n o effect on L-selectin expression. Several features of the ATP-induced loss of L selectin indicate that this effect is mediated by lymphocyt e P(2)Z purinoceptors. First the loss was attenuated in isotonic NaCl medium compared to 150 mM KCl medium. Second the loss of L-selectin wa s immediately halted by addition of Mg2+ ions in molar excess of ATP. The most potent nucleotide causing L-selectin loss was benzoylbenzoic ATP (>10 mu M) which is also the most potent agonist for the P(2)Z pur inoceptor. Finally preincubation of lymphocytes with oxidized ATP, an irreversible inhibitor of P(2)Z purinoceptors, also inhibited ATP indu ced loss of L-selectin. Extracellular ATP is known to open an ion chan nel associated with the P(2)Z purinoceptor on B-lymphocytes which allo ws influx of Ca2+. However, ATP-induced loss of L-selectin did not req uire extracellular Ca2+. Moreover addition of the calcium ionophore, i onomycin, had minimal effect on L-selectin expression. Staurosporine ( 500 nM), an inhibitor of protein kinase C, inhibited only 10% of ATP i nduced loss of L-selectin but completely inhibited the loss of L-selec tin caused by 50 nM PMA. Thus extracellular ATP interacts with lymphoc yte P(2)Z purinoceptors which leads to shedding of L-selectin via a pa thway which requires neither Ca2+ influx nor activation of protein kin ase C. ATP may have a physiological role in the loss of L-selectin whi ch occurs during the interactions of lymphocytes with other cells. (C) 1996 Wiley-Liss, Inc.