Mitochondrial superoxide flashes in cultured articular chondrocytes.

<p><b>A</b>, Colocalization of the superoxide biosensor – mitochondrial circularly permuted yellow fluorescent protein (mt-cpYFP) and tetramethylrhodamine methyl ester (TMRM) in chondrocyte mitochondria revealed by tri-wavelength excitation imaging. Chondrocytes were isolated from mt-cpYFP transgenic mice and cultured as described in the Methods. Only chondrocytes from the first passage were used for experiments. <b>B</b>, Mitochondrial superoxide flashes in articular chondrocytes. Enlarged (top panel) and pseudo-color contrast-enhanced (middle panel, scale bar shown to the bottom left) snapshots of a representative mitochondrial superoxide flash in chondrocyte are shown to the right. The lower panel shows the time course of the corresponding mt-cpYFP fluorescence intensity at 488 nm excitation. <b>C</b>, Histogram analysis of amplitude (ΔF/F₀) and full duration at half maximum (FDHM) of chondrocyte superoxide flashes. <b>D</b>, Kinetics of superoxide flashes. Note the characteristic lack of fluorescence change at 405 nm excitation. Superoxide flash coincided with transient mitochondrial depolarization (ΔΨ_m, TMRM at 543 nm excitation).