Ultrastructural markers of tubular transport within the rat nephron in experimental diabetes insipidus.

Using stereological methods mitochondrial energy states and intercellular spaces with basal infolded channels were evaluated in proximal and distal tubules in rats. The studies were performed on animals with experimental diabetes insipidus and on control rats by means of electron microscopy. No significant differences were found in mitochondrial energy states and sizes of intercellular spaces with basal infolded channels in the proximal tubules, which indicates undisturbed transport in this nephron segment. However, significant differences of these parameters were found in the distal tubules. In diabetes insipidus mitochondrial energy states approximated the condensed state, while in the control animals they were similar to the orthodox state. Intercellular spaces became significantly narrowed in diabetes insipidus in comparison with these in the controls. These observations suggest that mitochondrial energy states may be considered as ultrastructural markers of active tubular transport, while intercellular spaces with basal infolded channels may reflect ultrastructural counterparts of water transport.