A transport mechanism for NAADP in a rat basophilic cell line

Abstract

NAADP is a second messenger that releases Ca2+ from intracellular stores. Surprisingly, it has been recently shown that extracellular application of NAADP is capable of inducing intracellular Ca2+ release. This is particularly important since the only mammalian enzymes known to catalyze the synthesis of this second messenger are located extracellularly. In the present manuscript, we have investigated whether mammalian cells possess a transport system capable of transporting this highly charged molecule into cells. Indeed, in RBL-2H3 cells, a rat basophilic cell line, and in SK-N-BE cells, a neuroblastoma cell line, [32P]NAADP is efficiently transported inside cells. NAADP transport is Na+ and Ca2+ dependent, is partially blocked by dipyridamole, but is unaffected by nitrobenzylthioinosine. RBL-2H3 cells also transport [32P]cADPR, but the differences in the pharmacological profile suggest that NAADP transport proceeds by a novel mechanism. Lastly, extracellular application of NAADP, but not NADP, induced a raise in intracellular Ca2+. This is the first demonstration that NAADP is transported into cells and highlights the possibility that, alongside a second messenger, NAADP might also act as an autocrine/paracrine signal.

Autocrine/Paracrine Function of Nicotinic Acid Adenine Dinucleotide Phosphate (NAADP) for Glucose Homeostasis in Pancreatic β-Cells and Adipocytes

“…That NAADP can be efficiently transported into cells has been shown in a rat basophilic cell line and a neuroblastoma cell line, resulting in elevation of intracellular Ca 2ϩ (24). We have also observed that ␤-cells are permeable to exogenous NAADP, such that external application can induce a pattern of Ca 2ϩ signals similar to that stimulated by GLP-1 (3).…”

Generation of Cyclic ADP-ribose and Nicotinic Acid Adenine Dinucleotide Phosphate by CD38 for Ca2+ Signaling in Interleukin-8-treated Lymphokine-activated Killer Cells

“…To investigate this possibility, we examined whether there is any interdependence between cADPR and NAADP production by taking advantage of transporting cADPR and NAADP to LAK cells (supplemental Fig. S1) like other cells known to be transported (35)(36)(37). The addition of exogenous cADPR to LAK cells enhanced intracellular NAADP levels, whereas the addition of NAADP failed to increase intracellular cADPR levels (Fig.…”

Involvement of P2X receptors in the NAD+-induced rise in [Ca2+]i in human monocytes

“…It is difficult to envision how cADPR and NAADP can function inside the cell if they are generated by ectoenzymes. Several studies suggest that cADPR and NAADP are directly transported by CD38 or more likely by nucleotide transporters into the cytosol [10][11][12][13][14]. So far, in many cell types, responding to extracellular NAD + with an increase in [Ca 2+ ] i , conversion of NAD + to the Ca 2+ mobilizer cADPR [14][15][16][17][18] has been implicated as the principal mechanism leading to the rise in [Ca 2+ ] i .…”