Nitric oxide, a physiological modulator of mitochondrial function.

The effect of nitric oxide (NO) on the energy transfer reactions of mitochondria was examined under different oxygen tensions. Mitochondrial functions, such as respiration, ATP synthesis and regulation of membrane potential, were inhibited by NO in a concentration-dependent manner. In the presence of various substrates, NO also inhibited uncoupled respiration in an oxygen concentration-dependent manner. The inhibited function recovered completely at certain times after adding NO. When added to mitochondrial suspensions, NO disappeared rapidly from the medium and more rapidly at high oxygen tensions than at low oxygen tensions as determined by the formation of methemoglobin and EPR methods. From these results it is concluded that NO might play an important role in the regulation of mitochondrial functions particularly under low oxygen concentrations.