Ultrastructural, optical and volume changes in brain mitochondria during gramicidin-induced ion uptake.

Gramicidin-induced swelling of rat brain mitochondria was followed spectrophotometrically with a parallel analysis of changes in the ultrastructure, volume and eccentricity ratio of the mitochondria. Under the effect of gramicidin the expansion of the inner compartment occurs with an overall increase in volume. Mitochondria tend to be rounded although not entirely spherical in shape. The reversal of swelling with respiratory inhibitor (KCN, rotenone) results in a shrinkage of the inner compartment and is not accompanied by a proportional reduction of the outer compartment. Mitochondria fail to regain their original shape. It can be concluded that in the course of energy-dependent swelling the ability to contract might be retained, whereas other factors controlling the shape of the mitochondrion are irreversibly affected.