We have recently characterised the presence of a Ca2+-mobilising receptor for ATP which stimulates exocytosis in differentiated HL60 cells. Here we demonstrate that the Undifferentiated HL60 cells also respond to extracellular ATP by stimulating an increase in inositol phosphates and exocytosis. Of the nucleotides (ATP, UTP, ITP, ATPyS, AppNHp, XTP, CTP, GTP, 8-Br-ATP and GTPγS) that were active in stimulating inositol phosphate formation, only UTP, ATP, ITP, ATPγS and AppNHp were active in stimulating secretion. On differentiation, the extent of secretion due to the purinergic agonists ATP, ITP, ATPγS and AppNHp remained unchanged whilst secretion due to UTP, a pyrimidine, was substantially increased. These results indicate that the effect of ATP and UTP may be mediated via separate purinergic and pyrimidinergic receptors, respectively.
