Sieve structure of slit diaphragms of podocytes and pore cells of gastropod molluscs.

The ultrastructure of the slit diaphragms between the pedicels of the podocytes of the prosobranch Viviparus viviparus and between the cytoplasmic tongues of the haemocyanin producing pore cells of the pulmonate Lymnaea stagnalis was investigated. In both cell types 2 diaphragms are present in the slits. They form a 3-dimensional sieve structure with holes of respectively 90 x 110 A (podocyte) and 200 x 220 A (pore cell). Injection experiments showed that the size of the holes of the pore cell sieve matches that of particles which can be ingested by theis cell type. The substructure of the sieves of the molluscs is compared to that of the 2-dimensional sieve of the podocytes of the mouse and the rat.