Nicotinamide adenine dinucleotides permeate through mitochondrial membranes in human Epstein-Barr virus-transformed lymphocytes

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Human cultured cells are widely used for the investigation of respiratory chain disorders. Oxidative properties are generally investigated by means of polarographic studies carried out on detergent-permeabilized cells. By studying the oxidative properties of Epstein- Barr virus-transformed B lymphocytes, we found that the respiration was significantly decreased after 3–4 days of cell culture. Simultaneously, we observed decreased NAD+-dependent oxidations (malate, glutamate, pyruvate) that became dependent upon the addition of exogenous NAD+. The effect of NAD+ was shown to be related to an influx of catalytic amount of NAD+ into the mitochondrial matrix. A full ability to oxidize NAD+-dependent substrates was restored less than 2 h after a change of the culture medium.

These observations suggested: (a) the occurrence of fluxes of catalytic amounts of NAD+ through the mitochondrial inner membrane in human cells; (b) an early control of mitochondrial metabolism by matrix NAD+ content in cells grown under limiting growth conditions; (c) the possible confusion between complex I deficiency and a decrease content of matrix NAD+ when using human cultured cells. (Mol Cell Biochem 174: 115–119, 1997)