Extracellular NAD+ regulates intracellular calcium levels and induces activation of human granulocytes

beta-NAD(e)(+) (extracellular beta-NAD(+)), present at nanomolar levels in human plasma, has been implicated in the regulation of [Ca2+](i) (the intracellular calcium concentration) in various cell types, including blood cells, by means of different mechanisms. Here, we demonstrate that micromolar NAD(e)(+), (both the alpha and the beta extracellular NAD(+) forms) induces a sustained [Ca+](i) increase in human granulocytes by triggering the following cascade of causally related events: (i) activation of adenylate cyclase and overproduction of cAMP; (ii) activation of protein kinase A; (iii) stimulation of ADP-ribosyl cyclase activity and consequent over-production of eADP-ribose, a universal Ca2+ mobilizer; and (iv) influx of extracellular Ca2+. The NAD(e)(+)-triggered [Ca2+](i) elevation translates into granulocyte activation, i.e. superoxide and nitric oxide generation, and enhanced chemotaxis in response to 0.1-10 mu M NAD+,. Thus extracellular beta-NAD(e)(+), behaves as a novel pro-inflammatory cytokine, stimulating human granulocytes and potentially recruiting them at sites of inflammation.