Extracellular application of nicotinic acid adenine dinucleotide phosphate induces Ca2+ signaling in astrocytes in situ

Nicotinic acid adenine dinucleotide phosphate (NAADP(+)) has been identified as a novel second messenger triggering Ca2+ release from intracellular stores. Here we report that murine cortical astrocytes in culture and in acute slices respond with transient intracellular Ca2+ increases to extracellularly applied NAADP(+) and express the NAADP(+)-producing enzyme CD38. The Ca2+ transients triggered by NAADP(+) occurred with an average delay of 35 s as compared with ATP-triggered Ca2+ signaling, suggesting that NAADP(+) may have to enter the cell to act. Blockage of connexin hemichannels (a possible entry route for NAADP(+) into the cell) reduced the number of astrocytes responding to NAADP(+). Disruption of lysosomes as the suggested site of NAADP(+) receptors reduced the number of astrocytes responding to NAADP(+) strongly. The NAADP(+)-triggeredCa(2+) signal also depended on intact endoplasmic reticulum Ca2+ stores linked to activation of inositol 1,4,5-risphosphate receptors and on the activity of voltage-gated Ca2+ channels. Adenosine receptor-mediated signaling contributes to the NAADP+evoked signal, since it is strongly reduced by the adenosine receptor blocker CGS-15943. Moreover, NAADP(+) triggered responses in all other cell types (cultured cerebellar neurons, microglia, and oligodendrocytes) of the central nervous system.