Intense receptor-mediated endocytosis in nephrocytes of myriapoda

Nephrocytes were investigated in species from several groups of Diplopoda and Chilopoda. Ultrastructurally diplopod and chilopodnephrocytes are characterized by the following features: They are completely surrounded by a basal lamina. The plasma membrane is deeply infolded. Narrow slits between the resulting pedicels are bridged by diaphragmata. The plasma membrane is the site of a very intense receptor-mediated endocytosis the elements of which could be demonstrated for the first time in Myriapoda. Coated pits and vesicles, endosomes, tubular elements, and lysosomes are present. Formerly, nephrocytes were recognized by their ability to absorb dyes from the hemolymph. Therefore, they were regarded as excretion stores. The basal lamina and diaphragmata represent the extracellular sites of filtration for hemolymph components before they are taken up by these cells by receptor-mediated endocytosis. Positively charged particles with a diameter of up to 5-10 nm permeate the basal lamina and reach the cell plasma. Nephrocytes do not only import substances but also export material. However, their ability to transform or even synthesize substances cannot be discerned until it is possible to isolate and culture the cells.