Inhibition of cytochrome c release in rat hippocampal neurons by dissipation of mitochondrial potassium and proton gradients. Cultured rat hippocampal neurons were exposed to vehicle (a), 10 nm Val (b), 10 μm FCCP (c), 300 nm STS (d), Val + STS (e), or FCCP + STS (f) for 6 hr. Distribution of cytochrome c is shown by immunofluorescence analysis. Only cultures exposed to 300 nm STS showed a diffuse cytochrome c staining pattern (d). Scale bar, 50 μm.