Support of Thyroxine-induced Swelling of Liver Mitochondria by Generation of High Energy Intermediates at Any One of Three Sites in Electron Transport

Swelling of liver mitochondria induced by thyroxine in isotonic KCl medium can be prevented by uncoupling phosphorylation or by blocking the electron transport chain. Experiments with inhibitors for different points in electron transport (cyanide, antimycin A, Amytal, rotenone), with oxidation-reduction dyes which create bypasses of these blocked points (2,6-dichlorophenolindophenol, methylene blue, and phenazine methosulfate), and with other artificial electron donors and acceptors have demonstrated that any one of the three energy conservation sites associated with electron transport can by itself support swelling induced by thyroxine. The requirement would appear to be for formation of a high energy intermediate and not specific for any particular point, such as the cytochrome b segment. Induction of swelling with thyroxine shows certain similarities to that with gramicidin, such as inhibition by sucrose. Further work is needed to determine whether ion transport is involved.