Effect of nicotinamide-adenine dinucleotides on Ca2+ transport system in rat liver nuclei: stimulation of Ca2+ release by NAD+.

The effect of nicotinamide-adenine dinucleotides (NAD+ and NADP+) on Ca2+ transport in rat liver nuclei was investigated. Ca2+ uptake and release were determined with a Ca2+ electrode. Ca2+ uptake was dependent on adenosine triphosphate (ATP; 2 mM). The presence of NAD+ (2 mM) or NADP+ (1 and 2 mM) caused a significant inhibition of Ca2+ uptake following addition of 2 mM ATP. Ca2+, which accumulated in the nuclei during 6 min after ATP addition, was significantly released by the addition of NAD+ (0.5-2 mM) or NADP+ (0.1-2 mM). However, the effect of NADH (2 mM) or NADPH (2 mM) on Ca2+ uptake and release clearly weakened in comparison with the effects of NAD+ and NADP+. Meanwhile, ryanodine (10 microM), thapsigargin (10 microM) or oxalate (0.5 mM) had no effect on Ca2+ uptake and release in rat liver nuclei. These reagents did not significantly alter the effects of 2 mM NAD+ on Ca2+ uptake and release. Thus, NAD+ and NADP+ had a potent effect on Ca2+ transport in rat liver nuclei. The present findings suggest that the liver cytosolic NAD+ (NADP+) is a factor in the regulation of the nuclear Ca2+ concentration.