Ultrastructure of the thick ascending limb of henle in the rat kidney

Abstract

The thick ascending limb of Henle (TAL) in the rat until recently has been considered a morphologically homogeneous structure despite physiologic and biochemical evidence to the contrary. The present study was designed to examine the ultrastructural characteristics of the TAL in the inner cortex and the outer and inner stripes of the outer medulla using qualitative and quantitative transmission electron microscopy. Kidneys of male Sprague-Dawley rats were preserved by in vivo perfusion with glutaraldehyde for light and electron microscopy. The peritubular diameter and cell height were determined by direct measurements on tubule cross sections. Morphometric analyses were performed on montages of tubule cross sections. The peritubular diameter of the TAL was similar in the three regions under investigation, but the TAL cells were taller in the inner stripe than in the inner cortex and outer stripe. Morphometry revealed significant differences between the three regions with respect to the mean tubular cross-sectional area (AT), the surface density (SV), and the surface area per mm of tubule (ST) of apical and basolateral plasma membranes, and the volume density (VV) of mitochondria. The major morphologic division appeared to be between the inner stripe segment and the remainder of the TAL. These findings document the presence of significant morphologic heterogeneity of the rat TAL.

Regulation by adrenal corticosteroids of sodium and potassium transport in loop of Henle and distal tubule of rat kidney.

“…Adrenalectomy had no apparent effect on the ultrastructure of the loop of Henle when examined both qualitatively and by morphometric analysis. Cell structure in the control state was similar to that reported by Kone et al (29).…”

“…Because of the increase in tissue osmolality in the outer medulla, 0.4 M sodium chloride was added to the fixative solution when cells from the inner and outer stripe ofthe outer medulla were examined (28). Fixation was considered as acceptable when the tubule lumina were patent and the cytological architecture was comparable with previous studies in the rat, and a normal appearance of mitochondria and nuclei was observed (29). 5-7 thick ascending limbs from each region of the kidney (cortex and outer and inner stripes of the outer medulla) were photographed with a Zeiss lOB electron microscope and enlarged during printing to a final magnification of 10,000 times.…”

Reactive oxygen species as important determinants of medullary flow, sodium excretion, and hypertension

“…A large proportion (25-30%) of the filtered Na ϩ is absorbed by the mTAL, a function that is critical for body Na ϩ homeostasis and survival. The active transport of Na ϩ in the mTAL results in high levels of mitochondrial oxygen utilization further enabled by levels of mitochondrial cell density, which are among the highest in the body, including the heart (7,20,45,94). Since ROS levels within mitochondria are 5-to 10-fold higher than other cytosolic and nuclear compartments, mTAL mitochondria would be expected to have developed strong systems to protect from the highly damaging effects of oxidant stress.…”

Renal Cyclooxygenase-2

“…Several authors have described the presence of COX-2 in cTAL cells interspersed with COX-2-negative cells, suggesting a subpopulation on cells in cTAL. 8,5,19 The possibility that the uneven distribution of COX-2 in the cTAL could correspond to the smooth and rough surface subtypes of TAL cells 20,21 is under study in our laboratory with immunoelectron microscopy.…”

“…Several authors have described the presence of COX-2 in cTAL cells interspersed with COX-2-negative cells, suggesting a subpopulation on cells in cTAL. 8,5,19 The possibility that the uneven distribution of COX-2 in the cTAL could correspond to the smooth and rough surface subtypes of TAL cells 20,21 is under study in our laboratory with immunoelectron microscopy.It is interesting to note that COX-2-positive cells were close to but not in the macula densa. Thus, the present results in microdissected nephron segments from neonates are in agreement with previous works in kidney sections from neonate rats 6,22 in which COX-2 was not observed in the macula densa cells themselves but in the cTAL cells in the proximity of the macula densa.…”