Distribution of intramembrane particles and filipin-sterol complexes in plasma membranes of kidney. I. Corpuscle of Malpighi.

A quantitative study was performed on glomerular cell types from the rat kidney freeze fractured after conventional fixation or following exposure to the sterol-specific antibiotic, filipin. The results reveal a considerable variation on the size and number of intramembrane particles, as well as in the number of filipin-sterol complexes present on plasma membranes of the different cell types present in the glomerulus. These differences in membrane structure probably reflect specialized functions of the individual plasma membranes within the glomerulus. The most striking observation, however, was the low particle content and poor filipin labeling of podocyte foot process bases (which lie against the basal lamina) compared with the rest of the podocyte plasma membrane. The presence of distinct membrane domains in podocytes may be a factor involved in maintaining their specific architecture that is critical for the normal functioning of the kidney filtration barrier.