Figure 1

The Known Signaling Functions of Extracellular NAD(P). NAD acts as a substrate for ectoenzymes on the extracellular surface of the plasma membrane. ADP-ribosylation by ARTs regulates the function of a wide range of cell surface enzymes, receptors and channels while CD38 produces a number of active metabolites from NAD(P). The Ca²⁺-releasing CD38 metabolites cADPR and NAADP are transported across the plasma membrane to reach their intracellular sites of action while NAD can be released or transported out of the cell. In addition, NADP and NAADP have been shown to act on P2X receptors, while ADPR and NAD act directly on yet unidentified plasma membrane receptors/channels. CD38 plays a central role in these processes by regulating the concentrations of all of the nucleotide players. Adapted from (10).