Increase of plasma membrane oxidoreductase activity is not correlated with the production of extracellular Superoxide radicals in human Namalwa cells

We have considered the regulatory interrelationship of the plasma membrane oxidoreductase (PMOR) system and the mitochondrial respiratory capacity of human Namalwa (lymphoblastoid) cells. To this end, we made use of mitchondrially respiratory competent (ρ{variant}⁺) cells and ρ{variant}⁰ cells, which lack mitochondrial DNA (mtDNA) and consequently mitochondrial respiratory activity. NADH-fer-ricyanide reductase activity of the PMOR system is increased 3-fold in ρ{variant}⁰ Namalwa cells compared to ρ{variant}⁺ cells. It is also shown for the first time that addition of coenzyme Q₁₀ and coenzyme Q₁₀-ana-logues, which can rescue ρ{variant}⁰ Namalwa cells in the absence of pyravate, gives rise to a further 2-3-fold increase in plasma membrane NADH-ferricyanide reductase activity. These systems were examined to determine if there exists a correlation between the regulation of the PMOR system and extracellular Superoxide radical formation as measured with the fluorescence probe L-012. No correlation was found between NADH-ferricyanide reductase activity and extracellular Superoxide radical production. PMOR function in cellular proliferation appears therefore not to involve extracellular Superoxide radical production.