Ca²⁺-linked upregulation and mitochondrial production of nitric oxide in the mouse preimplantation embryo

Previous studies have demonstrated a role for the signalling agent nitric oxide in regulating preimplantation embryo development. We have now investigated the biochemical mode of action of nitric oxide in mouse embryos in terms of mitochondrial function and Ca²⁺ signalling. DETA-NONOate, a nitric oxide donor, decreased day 4 blastocyst cell number and oxygen consumption, consistent with a role for nitric oxide in the inhibition mitochondrial cytochrome c oxidase. Using live cell imaging and the nitric-oxide-sensitive probe DAF-FM diacetate, nitric oxide was detected at all stages of preimplantation development and FRET analysis revealed a proportion of the nitric oxide to be colocalised with mitochondria. This suggests that mitochondria of preimplantation embryos produce nitric oxide to regulate their own oxygen consumption. Inhibiting or uncoupling the electron transport chain induced an increase in nitric oxide and [Ca²⁺]_i as well as disruption of Ca²⁺ deposits at the plasma membrane, suggesting that mitochondrial disruption can quickly compromise cellular function through Ca²⁺-stimulated nitric oxide production. A link between antimycin-A-induced apoptosis and nitric oxide signalling is proposed.