105a] Energy-linked low amplitude mitochondrial swelling

Abstract

Reversible swelling-shrinkage associated with metabolic states is an energy-linked function of mitochondria. Similar to other energy-dependent processes, volume changes are affected by reagents, which interact with the energy transfer pathway. Thus, mitochondrial swelling is supported by electron flow through the respiratory chain and it requires the presence of an anion-like phosphate. Another distinguishing feature of this energy-linked process is the action of oligomycin, which does not inhibit swelling, but abolishes the shrinkage effect of ADP. Packed volume (or mitocrit) determinations can be employed to detect swelling successfully by pretreating the reaction mixture with O2 and performing the experiment rapidly, 5 or by redesigning centrifuge tubes to contain a well in the bottom, where mitochondria are collected from the bulk solution and their volume determined. The Coulter counter technique is also valuable for measuring particle volumes, and it has been used to detect high amplitude mitochondrial swelling. The types of methods needed to assess the occurrence of energy-linked volume changes are those providing great sensitivity at low mitochondrial concentration. The most convenient and simplest to use—light scattering and transmission (or absorbency) determinations—are described in detail.