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

Abstract

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 that NAD⁺-dependent oxidations (malate, glutamate, pyruvate) 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 115–119, 1997)