Cyanide Insensitive Respiration in Mammalian Cells: An Artifact of Mycoplasmal Contamination

Abstract

Oxygen consumption by mammalian cells occurs primarily in the mitochondria although alternate oxidation pathways are also present. The resistance (often high) of these alternate pathways to metabolic inhibitors like CN⁻ determine the residual oxygen consumption in the presence of the inhibitor. In many plant cells and microorganisms the cyanide insensitive pathway can account for an appreciable fraction of the total oxygen consumption.

We were studying oxidation by electron-affinic drugs in non-mitochondrial pathways and were surprised to find some mammalian cell lines having 10% – 90% residual oxygen consumption in the presence of 1 mM CN⁻. This oxygen consumption was associated with mycoplasmal contaminants (Mycoplasma hyorhinis, Mycoplasma arginini) and disappeared after treatment with appropriate antibiotics. The rate of CN⁻ insensitive oxygen consumption was dependent on the mammalian cell concentration suggesting that the organisms were oxidizing a product of the mammalian cells. In one species (Mycoplasma hyorhinis) lactate may be the oxidative substrate.

Mycoplasnas are known to cause a large number of metabolic alterations in their mammalian cell hosts (Stanbridge et al, 1978) sometimes indirectly due to the metabolism of microorganisms themselves, and sometimes directly due to interference with the normal metabolism of the mammalian cells. It is also known that the respiratory pathways of mycoplasmas are vastly different from those of mammalian cells, (Van Denark and Smith, 1964; see Pollack, 1980 for review) and one might expect alterations of the overall respiratory patterns between infected and non-infected mammalian cell-cultures.

We were studying drug-mediated electron transfer reactions in cells whose normal respiration was inhibited by CN⁻, (see Biaglow, 1981, for review) and found many cell lines whose oxygen consumption rate was quite significant in the presence of 1 mM CN⁻ (10–100% control). In all cases, this atypical resistance to CN⁻ inhibition was traced to mycoplasmal contamination of the mammalian cell cultures. This brief report illustrates same of the respiratory changes which can be expected in such contaminated cultures.