Figure 4. Diazoxide failed to induce swelling of brain mitochondria as judged by transmission electron microscopy (TEM) (A and B). A low dose of valinomycin produced a distinct expansion of the mitochondrial matrix (C).

A, mitochondria were incubated in the KCl-based incubation medium supplemented with 3 mm succinate and 3 mm glutamate before fixation. B and C, mitochondria were incubated for 5 min in the same medium additionally containing 50 μm diazoxide (B) or 0.4 nm valinomycin (C). Higher or lower doses of diazoxide (10 and 100 μm) produced similar results (not shown). In all these experiments, BSA was omitted from the medium to avoid possible interference with diazoxide or valinomycin. Frames, representative examples of condensed (c), intermediate (i) and swollen (s) mitochondria. D, morphometric analysis of mitochondria incubated with and without 50 μm diazoxide (+Diazo) or 0.4 nm valinomycin (+Val). The percentages of the mitochondrial populations in the respective groups are given in parentheses. *P < 0.05, **P < 0.01 versus corresponding morphological group in the control without pretreatments. Data are means ±s.e.m., n = 4.