[Ultrastructural organization of the inner medullary zone of the kidney of the water vole Arvicola terrestris].

Papillary component ultrastructure and acid mucopolysaccharide distribution have been investigated in the kidney of the water vole A. terrestris. Structural differences between the descending and ascending parts of the Henle's loop are rather small, cell cytoplasm of these segments being poor in organells. Unusual ultrastructure of the collecting duct epithelium with high level of cytoplasmic organization (elongated thin mitochondria, fairly developed Golgi complex, numerous phagosomes and pinocytotic vesicles, long branching microvilli) was described. Apical membrane of the epithelium is covered by rich glycocalix layer. Heil-positive substrances are located intracellularly inside phagosomes and on vesicle membranes, as well as on the membranes of cisternae of endoplasmic reticulum. Interstitium is abundant, but no close contacts between papillary components were found. Acid mucopolysaccharide content of the interstitium is low, "gel" filter being not formed. The described peculiarities are discussed in relation to water and salt metabolism of the rodents investigated.