Segmental variations in the organization of the endoplasmic reticulum of the rat nephron

Abstract

The spatial organization of endoplasmic reticulum (ER) was examined in all segments of rat nephron. Tissues were fixed with glutaraldehyde, impregnated "en bloc" with osmium tetroxide, prepared for and examined by standard (80-100 kV) and high voltage (1 mEV) transmission electron microscopy. In all proximal tubule cells, ER forms a continuous and extensive network of canaliculi and abundant fenestrated saccules which surround mitochondria and cytoplasmic bodies; the cage-like structure of the fenestrated saccules was most evident around the spherical mitochondria of the S3 segment. In the cells of the distal straight and convoluted tubules, the network consists mostly of canaliculi with rare non-fenestrated saccules. The ER network of canaliculi is particularly rich in intercalated cells, in contrast with its rudimentary appearance in the adjacent principal cells of the collecting tubule. In fact, in these cells there are few isolated ER cisternae and they are rarely impregnated. The nuclear envelope is well impregnated in most cells throughout the various segments. Segmental variations in ER organization and its relative abundance are most likely related to the well, established functional heterogeneity of the nephron segments. Moreover, the extensive and unique organization among mitochondria, ER and the basolateral membrane suggests that these three organelles function as a unit which is related to active electrolyte transport. In addition, because of its transepithelial organization, ER may well constitute a transcellular pathway for molecules.

Maleate modifies apical endocytosis and permeability of endoplasmic reticulum membranes in kidney tubular cells

“…1). The extensive ER network in the renal cells had its normal characteristics in a few cells: abundant fenestrated saccules in the proximal nephron and tubular canaliculi organized as a continuous network throughout the cytoplasm in both distal and proximal convoluted cells (Bergeron and Thiéry 1981;Bergeron et al 1987). Early stages of cell damage included dilation of the ER cisternae (Figs.…”

“…The polymorphism of the ER in epithelial cells with different transport functions suggests that this organelle plays a role in the transcellular movement of molecules (Bergeron et al 1978(Bergeron et al , 1987(Bergeron et al , 1988Mollgard and Rostgaard 1978;Bergeron and Thiéry 1981;Thiéry et al 1983;Danechi and Bergeron 1989;McLeese and Bergeron 1990;Danechi et al 1994). If such is the case, then changes in the characteristics of the ER would also be expected to accompany changes in transport function following maleate administration.…”

Altered Expression Pattern of Polycystin-2 in Acute and Chronic Renal Tubular Diseases

“…We were able to detect an intracellular membrane immediately below the plasma membrane in injured cells, which probably corresponds to the membrane of the endoplasmic reticulum. Normal thick ascending limb cells are connected by lateral interdigitations, into which the endoplasmic reticulum extends (48,49). Upon thallium-induced injury, the lateral interdigitations disappear, and with them the infoldings of the endoplasmic reticulum.…”

Molecular basis of autosomal-dominant polycystic kidney disease

“…Distal tubular cells are connected by extensive lateral interdigitations, which contain many mitochondria. The endoplasmic reticulum lies between the mitochondria, which are arranged with their longitudinal axis parallel to the apical-to-basal axis of the cell and the plasma membrane [78,79]. Such a complex relationship between adjacent cells, mitochondria, the endoplasmic reticulum, and the plasma membrane must be carefully maintained, and the peculiar distribution of polycystin-2 in the kidney may also tell us something about its function.…”

“…Polycystin-1 could therefore very well be located in the plasma membrane and participate in cell-cell contacts, whereas polycystin-2 serves as an endoplasmic reticulum-bound calcium channel. Due to the close apposition of the plasma membrane and the endoplasmic reticulum in the distal tubule [78,79], such a scenario can be easily envisioned. In such a model, polycystin-1 as a component of cell-cell contacts would sense the width of the tubular lumen, and the signal would be transduced via polycystin-2 and local Ca 2+ currents.…”