Laser-stimulated fluorescence of submicrometer regions within single mitochondria of rhodamine-treated myocardial cells in culture.

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A focused laser beam of 442 nm was used to stimulate fluorescence in 0.5-micrometer spots in single mitochondria of myocardial and endothelial cells in culture. Cells were treated with rhodamine 6G or 123 in order to render the mitochondria fluorescent. Rhodamine 123-treated cells exhibited a gradual decrease in fluorescence over several minutes, whereas the rhodamine 6G-treated myocardial cells exhibited three distinct patterns of variable fluorescence intensity. These patterns were detected at different points within the same mitochondrion or in different mitochondria. Mitochondria from nonmyocardial endothelial cells did not exhibit any variable intensity patterns of fluorescence. Electron microscopy revealed no ultrastructural damage attributable to laser exposure of the mitochondria. The variable fluorescence patterns are hypothesized to be indicative of localized alterations in molecules or ions at the suborganelle level.