Mitochondrial swelling induced by valinomycin, calcium chloride and Pi was studied after potassium permanganate fixation in suspension. Valinomycin induces a rapid K+ influx, increase of the matrix space and out-folding of the cristae, with good preservation of the matrix material. This swelling is reversible but the cristae do not completely re-form and have a blebbed appearance. On repeated swelling and contraction cycles there is a gradual loss of matrix material. Calcium chloride and Pi produce a slow swelling of the matrix space. Shrinkage induced by ATP was partial and not associated with return to the original structure.
