Figure 1. NAD⁺ enters neurons through P2X₇-gated channels.

(A) Neurons incubated with ¹⁴C NAD⁺, radiolabeled on the adenine moiety, exhibited a time-dependent accumulation of ¹⁴C that was abolished in the presence of 1 U / ml NADase.

(B) 30 minute incubations with NAD⁺ produced a saturable increase in neuronal NAD⁺ content. The increase was blocked by pre-incubation with oxidized ATP (OxATP; 100 µM) or by co-incubation with brilliant blue G (BB; 10 µM), both of which block P2X₇ receptors.

(C) Neuronal NAD⁺ depletion induced by MNNG (75 µM, 30 minutes) was prevented by co-incubation with the PARP inhibitor DPQ (25 µM), and reversed by the addition of 5 mM NAD⁺ to the medium after washout of the MNNG. NAD⁺ content was measured 30 minutes after washout of the MNNG. n = 3–4; * p<0.01, ** p<0.001.