Phosphorylation of p56lck by external ATP in intact cells

Recent studies have suggested a role for extracellular ATP. In this report we show that extracellular labelled ATP crosses the plasma membrane of intact lymphoma cells and peripheral blood lymphocytes and phosphorylates p56lck a tyrosine protein kinase specific of lymphoid cells. Two other phosphoproteins of 92Kd and 35Kd become detectable on alkali treated gels. Phosphorylation occurs within minutes following addition of ATP. ATP, GTP, ADP and an ATP analog prevent phosphorylation but not AMP nor Pi; trypsinization of cells abolishes labelling. The possible involvement of P2 purinergic receptors is discussed.