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, Thirty minute incubations with NAD⁺ produced a saturable increase in neuronal NAD⁺ content. The increase was blocked by preincubation with oxidized ATP (ox-ATP) (100 μm) or by coincubation with brilliant blue G (B.B.) (10 μm), both of which block P2X₇ receptors. C, Neuronal NAD⁺ depletion induced by MNNG (75 μm; 30 min) was prevented by coincubation 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 min after washout of the MNNG. n = 3–4; *p < 0.01, **p < 0.001. Error bars indicate SEM.