Intercellular fibrillar skeleton in the basal interdigitations of kidney tubular cells

Abstract

The tubular cells from the thick ascending limb of the loop of Henle in rabbit kidney medulla contain in their basal-lateral surfaces a complex system of interdigitations. Within these interdigitations, the plasma membranes are separated by extracellular spaces of relatively constant width that contain a previously undescribed fibrillar system. The structural organization and distribution of this intercellular fibrillar skeleton was studied using freeze-fracture etch and then section electron microscopy. The skeleton is comprised of discrete strands with a density of 300 to 400 per micron 2 evenly distributed along the entire basal-lateral region. Each strand has the shape of a brace and it is constructed from up to eight finer filaments each having a width of about 2 nm. The filaments are tightly joined together along their shafts for about 30 nm but they separate at both ends for about 10 nm before contacting the external surface of the plasma membrane. We propose that this intercellular fibrillar skeleton is responsible for maintaining the wide (about 50 nm) and uniform plasma membrane separation along the entire length of the basal-lateral region of the tubular cells of the thick ascending limb.

Routes and Mechanism of Fluid Transport by Epithelia

“…On the other hand, morphological studies of the rabbit renal proximal tubule were consistent with a poorly deformable LIS of relatively uniform width from tight junction to basement membrane (60). Recently, the LIS of renal (MDCK) cell monolayers was found to be relatively non-compliant in comparison with gallbladder (55), a result consistent with the observations of multiple cross-bridges in the lateral spaces of renal epithelia (61). Thus a compliant LIS is not a mandatory requirement for isosmotic fluid absorption.…”

Morphology of the Loop of Henle, Distal Tubule, and Collecting Duct

“…The intercellular space between the interdigitated lateral cell processes is bridged by an intercellular skeleton, composed of tightly jointed filaments [ Fig. lIb; (442)]. Apically, the intercellular space is sealed from the luminal space by a tight junctional belt of intermediate apicobasal depth that consists of several parallel, narrowly packed junctional strands [ Fig.…”

Acetonitrile as a substitute for ethanol/propylene oxide in tissue processing for transmission electron microscopy: Comparison of fine structure and lipid solubility in mouse liver, kidney, and intestine

“…Nonetheless, several factors may be involved, such as the duration of post-fixation (Schultz and Karlsson, 19721, and the differential extraction of cellular components and their heavy metal (Os, Pb) derivatives. Indeed, the greater proximity of kidney cells to one another, apparent in AN-but not in EtOHdehydrated tissue, is consistent with the loss1 of intermembrane components, the fibrils that govern the intercellular separation being, perhaps, the most likely candidates (Zampighi and Kreman, 1985). Those features are not highlighted in enlargements of Figure 6A-C.…”