Identification of mitochondria-rich cells in unstained vital preparations of epithelia by autofluorescence

To recognize mitochondria-rich cells in unstained vital preparations of heterogeneously composed epithelia we report here the use of an autofluorescence technique. Upon illumination with wavelengths of 400-440 or 450-490 nm mitochondria-rich cells emit fluorescence light of wave-lengths of greater than 470 or greater than 520 nm respectively, which probably arises from flavoproteins. Illumination does not seem to impair cell function and the fluorescence does not show any sign of fading over observation times of 20 min or greater. The method allows us to identify parietal cells from chief cells in gastric glands and obviously also intercalated cells from principal cells in renal collecting ducts. It might also be useful in other epithelia.