Morphological alterations in the mitochondria of Amoeba proteus induced by uncoupling agents

Ultrastructural changes in mitochondrial morphology were observed in amoebae exposed to the uncoupling agents dinitrophernol (DNP), pentachlorophenol (PCP), and m-chlorocarbonyl cyanide phenylhydrazone (CCCP). These alterations occurred with rapidity and were present before whole-cell activity changes could be detected. They included changes in profile shape and overall dimensions, matrix density changes, and alterations to the cristal membranes, so that distinction between control Type I and Type II conformations was eliminated and a form with intermediate characters generated. It is proposed that, in producing these altered forms, the uncoupling agents are acting by suppressing the control functional states of the mitochondria. At the end of the uncoupler treatment all alterations were shown to be reversible, i.e. in cells transferred back to normal culture medium, mitochondrial profiles identical to those in control cells were again evident with time. These effects on the mitochondria could be produced whether the uncoupler was introduced externally by total cell exposure, or to the inside of the cell by microinjection. The importance of precisely defining conditions for treatments and at disrupting cell activity was evident. Thus, an uncoupler, which is a weak acid, proved to be more effective in whole cell treatments if applied at a pH near to it pKa - so ensuring its penetration across the outer cell membrane.