DUAL REGULATION OF ARACHIDONIC-ACID RELEASE BY P(2U) PURINERGIC RECEPTORS IN DIBUTYRYL CYCLIC AMP-DIFFERENTIATED HL-60 CELLS

ATP promoted biphasic effects on both basal and fMLP-stimulated arachi donic acid (AA) release in neutrophil-like HL60 cells: stimulation in the micromolar range (EC50 = 3.2 +/- 0.9-mu-M) and inhibition at highe r concentrations (EC50 = 90 +/- 11-mu-M). ATP also inhibited UTP- and platelet activating factor-stimulated AA release. Only stimulatory eff ects of ATP on basal or fMLP-stimulated phospholipase C were observed. The inhibitory effect of ATP on AA release was not due to reacylation of released AA, chelation of extracellular Ca2+, cell permeabilizatio n, or changes in the rise of [Ca2+]i induced by agonist. The inhibitio n was rapid, being detected within 5-15 s. The inhibitory effect of AT P on fMLP-stimulated AA release could be desensitized by pretreatment of the cells with 2 mM ATP, but not 20-mu-M ATP, the concentration tha t resulted in maximal release of AA and inositol phosphates. The inhib ition by ATP was neither dependent on generation of adenosine by ATP h ydrolysis nor the result of direct interaction of ATP with P1 purinerg ic receptors. Among other nucleotides tested (CTP, GTP, ITP, TTP, XTP, adenosine 5'-(beta,gamma-methylene)triphosphate (AMP-PCP), adenyl-5'- yl imidodiphosphate (AMP-P(NH)P, ADP, adenosine 5'-O-(3-thiotriphospha te) (ATP(gamma)S), and UTP), only UTP and ATP(gamma)S displayed biphas ic effects with potencies and efficacies almost identical to those of ATP. The other nucleotides only exhibited stimulatory effects (EC50 = 60-300-mu-M). The results are consistent with a model of dual regulati on of AA release by two distinct subtypes of P2U receptors in HL60 cel ls.