Figure 10. Model of the embryonic heart ETC.

A. Components of the ETC; the complexes are labeled with Roman numerals. B. At E9.5, the complexes are arranged randomly and do not participate in electron transport, although Cx-1 and -2 have NADH and FADH₂ oxidase activity. The mPTP, represented by a not-fully-assembled Cx-5, is open. C. At E11.5, Cx-2, but not Cx-1, participates in electron transport (red line) and oxygen consumption. The mPTP is open or closed. D. At E13.5, the ETC exists in both the fluid (left two panels) and solid (right panel) assembly states, while the mPTP is closed.