Non-granulated peripolar cells exist in the rat glomerulus

The emergence of the glomerular parietal epithelial cell

Glomerular diseases are the leading causes of chronic and end-stage kidney disease. In the 1980s and 1990s, attention was focused on the biology and role of glomerular endothelial and mesangial cells. For the past two decades, seminal discoveries have been made in podocyte biology in health and disease. More recently, the glomerular parietal epithelial cell (PEC)-the fourth resident glomerular cell type-has been under active study, leading to a better understanding and definition of how these cells behave normally, and their potential roles in glomerular disease. Accordingly, this Review will focus on our current knowledge of PECs, in both health and disease. We discuss model systems to study PECs, how PECs might contribute to glomerulosclerosis, crescent and pseudocrescent formation and how PECs handle filtered albumin. These events have consequences on PEC structure and function, and PECs have potential roles as stem or progenitor cells for podocytes in glomerular regeneration, which will also be described.

A comparative study of the glomerular peripolar cell and the renin-secreting cell in twelve mammalian species

The peripolar cell is a glomerular epithelial cell situated within Bowman's capsule at its vascular pole. It is believed to be a secretory cell which forms part of the juxtaglomerular apparatus. Scanning electron microscopy was used to perform a comparative study of the morphology and number of peripolar cells in twelve mammalian species. The number of renin-secreting cells in kidney sections stained by renin antibodies and immunocytochemistry was counted. There was a marked inter-species variation in the number, size and appearance of peripolar cells. They were largest and most abundant in sheep and goat and fewest in dog, cow and human. There was no correlation between the numbers of peripolar cells and renin-secreting cells. This does not support the view that the peripolar cell is part of the juxtaglomerular apparatus.

Scanning and transmission electron-microscopic study of peripolar cells in the newborn lamb kidney

Scanning and transmission electron microscopy were used to study the ultrastructural characteristics and positions of granulated peripolar cells in newborn lamb kidney. Following tissue fixation by vascular perfusion in situ, the vascular pole region of the glomerulus was exposed for examination by scanning electron microscopy following removal of the glomerular tuft. Peripolar cells were recognized by their surface morphology enabling their quantification and an assessment of the relationship of their position in the renal cortex. The prominent expression of peripolar cells in this species was confirmed. Almost every vascular pole examined revealed peripolar cells (405 out of 407; 99.5%) and thus, throughout the cortex, the distribution of peripolar cells was the same as the distribution of renal corpuscles. Larger, more protruding peripolar cells were observed in the outer cortical renal corpuscles. The numbers of peripolar cells encircling each vascular pole ranged from 1 to 10. There was no correlation between number of granulated peripolar cells at the vascular pole and the position of the renal corpuscle within the renal cortex. As viewed by transmission electron microscopy, organelles of protein synthesis were abundant in the cytoplasm of peripolar cells. Exocytosis of cytoplasmic granules was observed by both scanning and transmission electron microscopy implying that a process of regulative secretion occurs from these cells. The use of ultrastructural techniques has provided evidence supporting the concept that peripolar cells are prominent in the cuff region of each renal corpuscle of the newborn lamb and furthermore that peripolar cells in this species most likely have a secretory function.