Energetics of Ehrlich ascites mitochondria: membrane potential of isolated mitochondria and mitochondria within digitonin-permeabilized cells.

Ehrlich ascites tumour cells were treated with digitonin so that they became permeable for low-molecular-weight compounds but, at certain concentrations of digitonin, retained most of their cytoplasmic proteins. Respiration of mitochondria with exogenous substrates and their membrane potential could thus be measured in situ by means of oxygen electrode and tetraphenylphosphonium-sensitive electrode, respectively. The results were compared with data from similar measurements on mitochondria isolated from such digitonin-permeabilized cells. Isolated mitochondria and mitochondria in situ oxidized succinate at similar rates and developed membrane potential of comparable magnitude. Both preparations also exhibited an identical nonlinear relationship between resting state respiration (titrated with a respiratory inhibitor) and the membrane potential. In the cells permeabilized with low concentrations of digitonin (i.e., retaining most of cytoplasmic proteins) and suspended in medium containing NaCl and other major anions and cations at concentrations close to those in mammalian plasma, anaerobiosis did not produce a decrease in the mitochondrial membrane potential, which was collapsed only after a subsequent addition of oligomycin. In this medium, glucose had little effect on either respiration or the membrane potential.

Changes in the mitochondrial surface potential during cuprizone-induced formation of megamitochondria.

The formation of megamitochondria upon treatment of mice with cuprizone was studied in relation to the surface potential of mitochondria. The latter was monitored by binding of 8-anilino-1-naphthalene sulphonate to membranes, by kinetics of monoamine oxidase and by free-flow electrophoresis of the particles. It was found that the surface potential of megamitochondria was by about 20 mV less negative than that of normal mitochondria whereas no change of the surface potential upon cuprizone treatment was observed in microsomes. It is suggested that a partial neutralization of the negative surface charge of mitochondrial membranes may promote fusion or inhibit division of mitochondria, thus resulting in formation of giant structures.

Mitochondria from the lamprey (Lampetra fluviatilis). Oxidative phosphorylation and related processes.

1. High efficiency of oxidative phosphorylation and a good respiratory control in liver, heart and somatic muscle mitochondria of the lamprey (Lampetra fluviatilis) were observed when the particles were isolated in a complex sucrose medium containing EDTA, heparin and nicotinamide. The coupling properties of these mitochondria were further improved by including serum albumin in the incubation medium. 2. The content of total adenine nucleotides in lamprey mitochondria was between 4 and 6 nmoles/mg protein. The translocation of these nucleotides across mitochondrial membrane was stimulated by serum albumin. 3. Lamprey mitochondrial phospholipids contain a large proportion (64-72%) of polyunsaturated fatty acids. 4. Electron micrographs of mitochondria from lamprey liver, heart and somatic muscle are presented.