Renal inter-alpha-trypsin inhibitor heavy chain 3 increases in calcium oxalate stone-forming patients

Inter-alpha-trypsin inhibitor heavy-chain proteins bind to the protease inhibitor bikunin and to hyaluronan, stabilizes extracellular matrix in various tissues, and also inhibits calcium oxalate crystallization in vitro. In both normal and stone-forming patients, we found heavy chain 3 and hyaluronan in the interstitial matrix of the kidney. Osteopontin was found in the collecting duct, thin loop of Henle, and urothelial cells. In stone formers, heavy chain 3 was also present in collecting duct, thin loop, and interstitial cells. Heavy chain 3 and osteopontin colocalized in plaque matrix and urothelial cells. Within individual plaque spherules, heavy chain 3 was found in the matrix layer while osteopontin was located along the crystal-matrix interface. Bikunin was present only in the collecting duct apical membranes and the loop cell cytoplasm of stone formers colocalizing with osteopontin and heavy chain 3. Widespread heavy chain 3 was only present in stone formers, whereas osteopontin was similarly expressed in normal and stone-forming subjects except for its localization in plaques of the stone formers. This is consistent with studies linking inter-alpha-trypsin inhibitor components to human stone disease, although their role is still unclear. Heavy chain 3 may also play a role in stabilizing hyaluronan in the renal interstitial matrix.

Changes in subcellular distribution of the ammonia transporter, Rhcg, in response to chronic metabolic acidosis

The primary mechanism by which the kidneys mediate net acid excretion is through ammonia metabolism. In the current study, we examined whether chronic metabolic acidosis, which increases ammonia metabolism, alters the cell-specific and/or the subcellular expression of the ammonia transporter family member, Rhcg, in the outer medullary collecting duct in the inner stripe (OMCDi). Chronic metabolic acidosis was induced in normal SD rats by HCl ingestion for 7 days; controls were pair-fed. The subcellular distribution of Rhcg was determined using immunogold electron microscopy and morphometric analyses. In intercalated cells, acidosis increased total Rhcg, apical plasma membrane Rhcg, and the proportion of total cellular Rhcg in the apical plasma membrane. Intracellular Rhcg decreased significantly, and basolateral Rhcg was unchanged. Because apical plasma membrane length increased in parallel with apical Rhcg immunolabel, apical plasma membrane Rhcg density was unchanged. In principal cells, acidosis increased total Rhcg, apical plasma membrane Rhcg, and the proportion of total cellular Rhcg in the apical plasma membrane while decreasing the intracellular proportion. In contrast to the intercalated cell, chronic metabolic acidosis did not significantly alter apical boundary length; accordingly, apical plasma membrane Rhcg density increased. In addition, basolateral Rhcg immunolabel increased in response to chronic metabolic acidosis. These results indicate that in the rat OMCDi 1) chronic metabolic acidosis increases apical plasma membrane Rhcg in both the intercalated cell and principal cell where it may contribute to enhanced apical ammonia secretion; 2) increased apical plasma membrane Rhcg results from both increased total protein and changes in the subcellular distribution of Rhcg; 3) the mechanism of Rhcg subcellular redistribution differs in intercalated and principal cells; and 4) Rhcg may contribute to regulated basolateral ammonia transport in the principal cell.

Apatite plaque particles in inner medulla of kidneys of calcium oxalate stone formers: osteopontin localization

BACKGROUND

We have previously shown that interstitial plaque particles appear first in the basement membranes of thin loops of Henle and then in the interstitial space. However, it is not known if the plaque in the basement membrane of thin loops of Henle is of the same or different form than the interstitial plaque. Thus our purpose here is to detail the structure of the interstitial and membrane-bound plaque and explore the relationship of plaque apatite to osteopontin, a well-known crystal-associated urine protein.

METHODS

Deep papillary biopsy tissue was studied from all 15 calcium oxalate stone formers and four nonforming subjects that we previously reported on [Evan et al, J Clin Ivest, 2003]. Routine light and transmission electron microscopy (TEM) as well as light microscopy and TEM immunohistochemical localization of osteopontin antibody were performed on all 19 subjects.

RESULTS

In the basement membrane, plaque particles are individual and appear laminated with alternating light regions of crystal and electron-dense organic layers. In the interstitium, individual particles are not abundant but are instead aggregated to form regions of attached particles and in some regions what appears to be a fusion or syncytium in which crystal islands float in an organic sea. By light microscopy immunohistochemistry, osteopontin was localized to cells of the loops of Henle and collecting ducts as well as on sites of plaque. By immunoelectron microscopy, osteopontin immunogold label was found mainly on the surfaces of apatite crystal phase, at the junction of the crystal/organic layers. A similar immunogold labeling pattern was seen in the particles forming the syncytial islands of interstitial plaque.

CONCLUSION

If indeed we accept the hypothesis that apatite plaque may be an anchored site on which calcium oxalate stones form and grow, the present work makes clear that it is unlikely that the surface of plaque presented to the final urine will be apatite crystal per se. However, our findings clearly show osteopontin is one of the crystal-associated urine proteins involved in the formation of the organic layers of the plaque particles.

Exercise-induced apoptosis in renal tubular cells of the rat

A number of studies have shown that acute physical exercise is associated with the induction of apoptosis not only in skeletal muscle but also in many distant organs. One of the pathogenic agents responsible for exercise-induced damage in many tissues is the generation of oxygen free radicals. The aim of the present study was to examine the influence of exercise-induced oxidative stress on the rat kidney. The analysis was performed on the kidneys of rats subjected to treadmill running until exhaustion. Our results demonstrated that acute exercise led to apoptotic damage of the renal distal tubular cells, although this was not a result of oxidative stress.

1,25-Dihydroxyvitamin D3 stimulates osteopontin expression in rat kidney

Osteopontin (OPN) is a secreted phosphoprotein expressed constitutively in the descending thin limb (DTL) and papillary surface epithelium (PSE) of the kidney. Although its function is not fully established, a role for OPN in the regulation of calcium-mediated or calcium-dependent processes has been proposed. The aim of this study was to examine the effects of 1,25-dihydroxyvitamin D(3) (vitD), a hormone involved in the regulation of calcium homeostasis, on renal OPN expression. Four groups of rats were studied: acute vehicle (single intraperitoneal [i.p.] injection of 0.1 ml 10% ethanol-90% propylene glycol, 12 h before being killed); acute vitD (single injection of vitD, 2 ng/g i.p., 12 h before being killed); chronic vehicle (daily subcutaneous [s.c.] injection of 0.1 ml 10% ethanol-90% propylene glycol for 7 days); and chronic vitD (daily s.c. injection of vitD, 0.5 ng/g, for 7 days). Kidneys were processed for light and electron microscope immunocytochemistry, in situ hybridization, and Western blot analysis. In vehicle-treated animals, OPN mRNA and protein were expressed primarily in the DTL and PSE. In the acute vitD group, OPN mRNA and immunoreactivity appeared in the thick ascending limb (TAL) of the inner stripe of the outer medulla, and increased slightly in the DTL and PSE. The proximal tubules exhibited strong OPN immunoreactivity, but no hybridization signal. In the chronic vitD group, there was a marked increase in OPN mRNA and immunoreactivity in the distal tubule, including the TAL, as well as in the DTL and PSE. A weak hybridization signal and immunostaining were also observed in some proximal tubules. Administration of vitD causes a marked increase in OPN mRNA and protein in the rat kidney, mainly in the distal nephron, but also in the DTL, PSE, and proximal tubules. These results indicate that vitD is involved in the regulation of OPN expression in the kidney.

Arachidonic acid inhibits K channels in basolateral membrane of the thick ascending limb

We have used the patch-clamp technique to study the effect of arachidonic acid (AA) on the basolateral K channels in the medullary thick ascending limb (mTAL) of rat kidney. An inwardly rectifying 50-pS K channel was identified in cell-attached and inside-out patches in the basolateral membrane of the mTAL. The channel open probability (P(o)) was 0.51 at the spontaneous cell membrane potential and decreased to 0.25 by 30 mV hyperpolarization. The addition of 5 microM AA decreased channel activity, identified as NP(o), from 0.58 to 0.08 in cell-attached patches. The effect of AA on the 50-pS K channel was specific because 10 microM cis-11,14,17-eicosatrienoic acid had no significant effect on channel activity. To determine whether the effect of AA was mediated by AA per se or by its metabolites, we examined the effect of AA on channel activity in the presence of indomethacin, an inhibitor of cyclooxygenase, or N-methylsulfonyl-12,12-dibromododec-11-enamide (DDMS), an inhibitor of cytochrome P-450 monooxygenase. Inhibition of cyclooxygenase increased channel activity from 0.54 to 0.9. However, indomethacin did not abolish the inhibitory effect of AA on the 50-pS K channel. In contrast, inhibition of cytochrome P-450 metabolism not only increased channel activity from 0.49 to 0.83 but also completely abolished the effect of AA. Moreover, addition of DDMS can reverse the inhibitory effect of AA on channel activity. The notion that the effect of AA was mediated by cytochrome P-450-dependent metabolites of AA is also supported by the observation that addition of 100 nM of 20-hydroxyeicosatetraenoic acid, a main metabolite of AA in the mTAL, can mimic the effect of AA. We conclude that AA inhibits the 50-pS K channel in the basolateral membrane of the mTAL and that the effect of AA is mainly mediated by cytochrome P-450-dependent metabolites of AA.

Properties of an inwardly rectifying K(+) channel in the basolateral membrane of mouse TAL

We investigated the properties of K(+) channels in the basolateral membrane of the cortical thick ascending limb (CTAL) using the patch-clamp technique. Approximately 34% of cell-attached patches contained an inwardly rectifying K(+) channel (K(+)-to-Na(+) permeability ratio approximately 22), having an inward conductance (G(in)) of 44 pS and an outward conductance (G(out)) of approximately 10 pS (G(in)/G(out) approximately 4). Channel activity (NP(o)) increased with depolarization. When the cytosolic sides of inside-out patches were exposed to an Mg(2+)-free medium, the channel had a G(in) of 50 pS and was weakly inwardly rectifying (G(in)/G(out) approximately 1). Cytosolic Mg(2+) reduced G(out), yielding a G(in)/G(out) of 3.8 at 1.3 mM Mg(2+). Internal Na(+) also yielded a G(in)/G(out) of 1.6 at 20 mM Na(+). Spermine reduced NP(o) on inside-out membrane patches. Sensitivity to spermine at depolarizing voltages [half-maximal inhibitory concentration (K(i)) = 0.2 microM] was much greater than at hyperpolarizing voltages (K(i) = 26 microM). Half-inactivation by 0.5 microM spermine occurred at a clamp potential of 43 mV, with an effective valence of 1.25. A sigmoid relationship between bath pH and NP(o) of inside-out membrane patches was observed, with a pK of 7.6 and a Hill coefficient of 1.8. Intracellular acidification also reduced the NP(o) of cell-attached patches. This channel is probably a major component of K(+) conductance in the CTAL basolateral membrane.

Expression of urea transporters in the developing rat kidney

Urea transport in the kidney is mediated by a family of transporter proteins that includes renal urea transporters (UT-A) and erythrocyte urea transporters (UT-B). Because newborn rats are not capable of producing concentrated urine, we examined the time of expression and the distribution of UT-A and UT-B in the developing rat kidney by light and electron microscopic immunocytochemistry. Kidneys from 16-, 18-, and 20-day-old fetuses, 1-, 4-, 7-, 14-, and 21-day-old pups, and adult animals were studied. In the adult kidney, UT-A was expressed intensely in the inner medullary collecting duct (IMCD) and terminal portion of the short-loop descending thin limb (DTL) and weakly in long-loop DTL in the outer part of the inner medulla. UT-A immunoreactivity was not present in the fetal kidney but was observed in the IMCD and DTL in 1-day-old pups. The intensity of UT-A immunostaining in the IMCD gradually increased during postnatal development. In 4- and 7-day-old pups, UT-A immunoreactivity was present in the DTL at the border between the outer and inner medulla. In 14- and 21-day-old pups, strong UT-A immunostaining was observed in the terminal part of short-loop DTL in the outer medulla, and weak labeling remained in long-loop DTL descending into the outer part of the inner medulla. In the adult kidney, there was intense staining for UT-B in descending vasa recta (DVR) and weak labeling of glomeruli. In the developing kidney, UT-B was first observed in the DVR of a 20-day-old fetus. After birth there was a striking increase in the number of UT-B-positive DVR, in association with the formation of vascular bundles. The intensity of immunostaining remained strong in the outer medulla but gradually decreased in the inner medulla. We conclude that the expression of urea transporters in short-loop DTL and DVR coincides with the development of the ability to produce a concentrated urine.

Reduced expression of Na-K-2Cl cotransporter in medullary TAL in vitamin D-induced hypercalcemia in rats

Chronic hypercalcemia (HC) is accompanied by urinary concentration defects, and functional studies indicate defects in the thick ascending limb (TAL). We hypothesize that dysregulation of renal sodium transporters may play an important role in this. Vitamin D-induced HC in rats resulted in polyuria, natriuresis, and phosphaturia. Immunoblotting revealed a marked reduction in the abundance of rat type 1 bumetanide-sensitive Na-K-2Cl cotransporter (BSC-1) in inner stripe of the outer medullary (ISOM; 36 +/- 5%) and whole kidney (51 +/- 11%) in HC. Consistent with this finding, immunocytochemistry and immunoelectron microscopy demonstrated reduced BSC-1 labeling of the apical plasma membrane. Immunoblotting and immunohistochemical labeling of the K channel Kir 1.1 (ROMK) was also reduced in HC. In contrast, there were no reductions in the expression of Na/H exchanger (NHE)3 and Na,K-ATPase in ISOM. The abundance of the proximal tubule type II Na-P(i) cotransporter (NaPi-2) (but not Na,K-ATPase and NHE3) was significantly reduced (25 +/- 4%), consistent with a dramatic increase in urinary phosphate excretion. In conclusion, 1) the reduced abundance of BSC-1 and ROMK in TAL is likely to play a major role in the urinary concentration defects associated with HC and 2) the reduced abundance of NaPi-2 is likely to play a role in the increased urinary phosphate excretion.

Reduced water permeability and altered ultrastructure in thin descending limb of Henle in aquaporin-1 null mice

It has been controversial whether high water permeability in the thin descending limb of Henle (TDLH) is required for formation of a concentrated urine by the kidney. Freeze-fracture electron microscopy (FFEM) of rat TDLH has shown an exceptionally high density of intramembrane particles (IMPs), which were proposed to consist of tetramers of aquaporin-1 (AQP1) water channels. In this study, transepithelial osmotic water permeability (Pf) was measured in isolated perfused segments (0.5-1 mm) of TDLH in wild-type (+/+), AQP1 heterozygous (+/-), and AQP1 null (-/-) mice. Pf was measured at 37 degrees C using a 100 mM bath-to-lumen osmotic gradient of raffinose, and fluorescein isothiocyanate (FITC)-dextran as the luminal volume marker. Pf was (in cm/s): 0.26 +/- 0.02 ([+/+]; SE, n = 9 tubules), 0.21 +/- 0.01 ([+/-]; n = 12), and 0.031 +/- 0.007 ([-/-]; n = 6) (P < 0.02, [+/+] vs. [+/-]; P < 0.0001, [+/+] vs. [-/-]). FFEM of kidney medulla showed remarkably fewer IMPs in TDLH from (-/-) vs. (+/+) and (+/-) mice. IMP densities were (in microm-2, SD, 5-12 micrographs): 5,880 +/- 238 (+/+); 5,780 +/- 450 (+/-); and 877 +/- 420 (-/-). IMP size distribution analysis revealed mean IMP diameters of 8.4 nm ([+/+] and [+/-]) and 5.2 nm ([-/-]). These results demonstrate that AQP1 is the principal water channel in TDLH and support the view that osmotic equilibration along TDLH by water transport plays a key role in the renal countercurrent concentrating mechanism. The similar Pf and AQP1 expression in TDLH of (+/+) and (+/-) mice was an unexpected finding that probably accounts for the unimpaired urinary concentrating ability in (+/-) mice.

Ultrastructural localization of Na-K-2Cl cotransporter in thick ascending limb and macula densa of rat kidney

A bumetanide-sensitive Na-K-2Cl cotransporter, BSC-1, is believed to mediate the apical component of transcellular NaCl absorption in the thick ascending limb (TAL) of Henle's loop. To study its ultrastructural localization in kidney, we used an affinity-purified, peptide-derived polyclonal antibody against rat BSC-1. Immunoblots from rat kidney cortex and outer medulla revealed a solitary 161-kDa band in membrane fractions. Immunocytochemistry of 1-micrometer cryosections demonstrated strong BSC-1 labeling of the apical and subapical regions of medullary and cortical TAL cells. Notably, macula densa cells also exhibited distinct labeling. Distal convoluted tubules and other renal tubule segments were unlabeled. Immunoelectron microscopy demonstrated that BSC-1 labeling was associated with the apical plasma membrane and with subapical intracellular vesicles in medullary and cortical TAL and in macula densa cells. Smooth-surfaced TAL cells, in particular, had extensive BSC-1 labeling of intracellular vesicles. These results support the view that BSC-1 provides the apical pathway for NaCl transport across the TAL and that an extensive intracellular reservoir of BSC-1 is present in a subpopulation of TAL cells. Furthermore, the BSC-1 localization in the apical plasma membrane of macula densa cells is consistent with its proposed role in tubuloglomerular feedback.

Localization of ROMK channels in the rat kidney

Renal potassium secretion occurs in the distal segments of the nephron through apically located secretory potassium (SK) channels. SK may correspond to the ROMK channels cloned from rat kidney. In this study, the localization of ROMK at the cellular level in the rat kidney was examined using an affinity-purified polyclonal antibody raised against a C-terminal peptide of ROMK. The specificity of the antibody was demonstrated by immunoblots of membranes of Xenopus oocytes expressing ROMK2. Immunoblots of homogenates from rat renal outer medulla and cortex revealed predominant bands of 70 to 75 kD, which were ablated by preadsorption with an excess of peptide. These bands were specific for the rat kidney. Immunolocalization studies revealed that ROMK is expressed in specific nephron segments in both the cortex and medulla. In the cortex, ROMK was found in the apical domain of the thick ascending limb of Henle's loop, the connecting tubule, and in some, but not all, cells of cortical collecting tubules. In the medulla, expression in the apical membrane of the thick ascending limbs of Henle's loop was strong, whereas outer medullary collecting ducts were weakly stained. Expression in the thick ascending limb was also heterogeneous; some cells that expressed the Na-K-Cl cotransporter were weakly stained with the anti-ROMK antibody. No staining of glomeruli, proximal tubules, or inner medullary collecting ducts was found. The localization of ROMK agrees well with the findings of SK in patch-clamp studies and supports the view that ROMK is the SK channel of the distal segments of the nephron.

Role of apoptosis in development of the ascending thin limb of the loop of Henle in rat kidney

At birth, the rat renal papilla has the structural composition of the mature inner stripe of the outer medulla. All loops of Henle have the configuration of short loops, and there are no ascending thin limbs. This study examines the role of apoptosis in the differentiation of the loop of Henle and the development of the ascending thin limb in the rat kidney. Kidneys of 20-day-old fetuses and 1-, 3-, 5-, 7-, 14-, and 21-day-old pups were preserved for immunohistochemistry and electron microscopy. Using a preembedding immunoperoxidase method, we identified thick ascending limbs by labeling with antibodies to the serotonin receptor, 5-HT1A, and descending thin limbs were identified by labeling with antibodies to aquaporin-1. Three methods were used to identify apoptotic cells as follows: 1) in situ nick end labeling using the ApopTag kit, 2) toluidine blue staining on plastic sections followed by etching, and 3) transmission electron microscopy. At birth, tubules with 5-HT1A immunoreactivity were present throughout the renal papilla, and there were no ascending thin limbs. From 1 to 14 days of age, staining for apoptosis was observed in numerous cells in the 5-HT1A-positive epithelium, beginning at the papillary tip and ascending to the border between outer and inner medulla. This was associated with transformation from a cuboidal to a squamous epithelium and subsequent disappearance of 5-HT1A immunostaining from the transformed cells. Electron microscopy confirmed the presence of apoptotic cells and phagocytosed apoptotic bodies in the thick ascending limb in the renal papilla. We conclude that the ascending thin limb is derived from the 5-HT1A-positive thick ascending limb by apoptotic deletion of thick ascending limb cells and transformation of the remaining tubule cells into the 5-HT1A-negative ascending thin limb.

Tamm-Horsfall glycoprotein in streptozotocin diabetic rats: a study of kidney in situ hybridization, immunohistochemistry, and urinary excretion

Tamm-Horsfall glycoprotein, present only in the kidney thick ascending limb of Henle's loop, was studied here in streptozotocin diabetic rats. Tamm-Horsfall glycoprotein mRNA in situ hybridization was performed on snap-frozen left kidneys; the right kidneys were perfusion-fixed with 4% paraformaldehyde and embedded either in paraffin, for Tamm-Horsfall glycoprotein immunohistochemistry, or in Epon for stereologic measurements. The length of the thick ascending limb of Henle's loop and the amount of glycogen were measured and the ultrastructure of the cells was evaluated. Urinary excretion of Tamm-Horsfall glycoprotein, calcium, magnesium and albumin was measured. After 10 and 50 days' duration of diabetes, kidney weight increased 20 and 41%, respectively and the length of the thick ascending limb of Henle's loop increased 28 and 56%, respectively, compared with controls. Substantial glycogen accumulations were present in the thick ascending limb of Henle's loop, and electron microscopy revealed a significant decrease in organelles and basolateral membranes. After 10 and 50 days' duration of diabetes, in situ hybridization of Tamm-Horsfall glycoprotein mRNA revealed a fourfold decrease, and the immunostaining for Tamm-Horsfall glycoprotein showed a threefold decrease as measured by densitometry. However, urinary Tamm-Horsfall glycoprotein excretion rate was increased fivefold and urinary concentration about twofold. Urinary calcium excretion increased three-fold and magnesium twofold, but urinary albumin excretion was not significantly increased. The increased amount of Tamm-Horsfall glycoprotein, calcium and magnesium in the urine in diabetes occurs here concomitant with severe cellular damage in the thick ascending limb of Henle's loop.

Quantitative immunoelectron microscopic analysis of the localization and induction of 25-hydroxyvitamin D3 24-hydroxylase in rat kidney

25-Hydroxyvitamin D3 24(R)-hydroxylase (24-hydroxylase) is involved in the metabolism and regulation of vitamin D3 and is markedly induced by administration of vitamin D3. We detected this enzyme by electron microscopy and an immunogold technique along nephrons of normal and vitamin D3-administered rats. After the rats were administered vitamin D3, 50,000 IU/day for 1 week, they were perfusion-fixed with a paraformaldehyde solution. The fixed kidneys were then removed and embedded in LR White resin. Ultrathin sections were prepared and labeled by the immunogold technique using a mouse anti-rat 25-hydroxyvitamin D3 24-hydroxylase monoclonal antibody. We counted the number of gold particles bound per micron 2 of the mitochondria (particle density) of the tubule epithelial cells along the nephrons. In normal and vitamin D3-administered rats, gold particles were observed in the mitochondria of epithelial cells along the tubules. In normal rats, gold labeling for 24-hydroxylase was statistically significant (p < 0.05), in the S1-S2 segments, the S3 segment of the proximal tubules, and in the distal convoluted tubules. In the rats administered vitamin D3, the particle density increased significantly (p < 0.05) by about 12-fold in the S1-S2 segments of the proximal tubules, whereas it increased less markedly in other parts of the nephron. The marked induction of the S1-S2 segments of the proximal tubules suggests that these segments play an important role in the regulation of vitamin D3 metabolism.

Effects of salt depletion on the kidney: changes in medullary oxygenation and thick ascending limb size

Previous studies have shown that salt depletion enhances the susceptibility of the kidney to nephrotoxins (amphotericin, cyclosporine, and contrast). To study the renal response to salt depletion, Sprague-Dawley rats were fed a sodium-deficient diet (N = 12) with pair-fed controls (N = 13) for 4 wk. In addition, rats from each group underwent 24-h water deprivation studies (N = 9; four salt deprived, five normal). Plastic 1-micron horizontal sections of mid-inner stripe were examined, and cross-sectional areas of the medullary thick ascending limb (mTAL) were analyzed. The mTAL of the salt-deprived rats were smaller (P = 0.04) and showed greater variance in size (P = 0.02) than control (618 +/- 106 versus 693 +/- 50 microns2). However, mean glomerular and collecting duct cross-sectional areas were unaffected by salt intake. Cross-sectional areas of long- and short-loop mTAL were significantly different, regardless of group (518 +/- 78 versus 732 +/- 92 microns2). Maximal urinary concentrating ability was found to correlate with mTAL cross-sectional area (r = 0.85; P = 0.004) and with long-loop mTAL size (r = 0.77; P = 0.016). However, it did not significantly correlate with short loop mTAL size (r = 0.53; P = 0.14).(ABSTRACT TRUNCATED AT 250 WORDS)

Structural-functional correlation in chinchilla long loop of Henle thin limbs: a novel papillary subsegment

The ultrastructural characteristics of thin limb subsegments from chinchilla long loops of Henle were studied in perfusion-fixed kidneys and in isolated perfused tubules. In sections from the perfusion-fixed kidneys, we noted types I, II, III, and IV thin limb epithelia similar to those previously identified in other rodent species. Sections from the deepest 20% of the papillary tip, however, revealed only a single thin limb epithelial type, which had a combination of structural characteristics distinct from previously identified thin limb subtypes. This "papillary type" epithelium had relatively tall cells and a complex cellular organization with extensive interdigitation, numerous shallow tight junctions, and microvilli. In single-tubule studies, thin limb segments dissected from different levels of the outer and inner medulla were perfused in vitro for osmotic water permeability (Pf) measurements and were fixed for ultrastructural examination. Long-loop thin descending limbs (LDL) dissected from the outer medulla (Pf, 2,637 +/- 336 micron/s) had type II epithelium. LDL dissected from the middle of the inner medulla (Pf, 1,570 +/- 76 microns/s) had a type III epithelium. LDL segments dissected from the deepest 20% of the inner medulla had a low but nonzero Pf (68 +/- 9 micron/s) and had the same novel papillary type epithelium seen in sections from fixed kidneys. Thin ascending limbs dissected from inner 50% of the inner medulla had essentially zero Pf (8 +/- 4 micron/s) and had a type IV epithelium. Immunohistochemical localization of CHIP28 water channel protein confirmed the presence of CHIP28 in thin descending limbs throughout the outer 75% of the inner medulla, whereas labeling was essentially absent in the deep inner medulla where the low-PfLDL (novel papillary type epithelium) is located.

Immunohistochemical mapping of cellular and subcellular distribution of 5-HT1A receptors in rat and human kidneys

Northern blotting studies have demonstrated mRNA for the serotonin 5-HT1A receptor in human neonatal kidney (B. K. Kobilka, T. Frielle, S. Collins, T. Yang-Feng, T. S. Kobilka, U. Francke, R. J. Lefkowitz, and M. G. Caron. Nature Lond. 329: 75-79, 1987). To confirm expression of receptor protein in kidney, we raised antibodies to two peptides derived from the third intracellular loop of the human 5-HT1A receptor. Specific immunoglobulin G (IgG) was purified sequentially on protein A-Sepharose and peptide-Affigel 10 columns. Each IgG was able to: 1) quantitatively immunoprecipitate [3H]8-OH-2-(di-n-propylamino)1,2,3,4-tetrahydronaphthalene ([3H]8-OH-DPAT)-labeled human and rat receptors; 2) immunoblot a new protein in cells transfected with human 5-HT1A receptor DNA; and 3) immunoautoradiographically label areas of rat brain (frontal cortex, hippocampus, and lateral septum) in a highly characteristic pattern similar to that labeled by 125I-Bolton-Hunter-8-methoxy-2-(N-propyl-N-propylamino)Tetralin, a specific 5-HT1A receptor autoradiography ligand. By use of a light microscopic immunoperoxidase labeling technique, incubation of each IgG antibody with sections of rat and human kidney demonstrated an identical pattern of immunoreactivity. Specific labeling of basolateral plasma membranes was detected throughout medullary and cortical thick ascending limbs (TAL), in distal convoluted tubules (DCT), in connecting tubule cells of the connecting tubule, and in principal cells of the initial collecting tubule. There was no labeling in the inner medulla, glomeruli, or blood vessels. The labeling was blocked by preincubation with the corresponding peptide, but not with noncorresponding peptide or carrier protein. There was no labeling with preimmune IgG. Electron microscopic immunoperoxidase labeling confirmed the specific localization of the IgG antibody along the basolateral plasma membrane in all positively staining cells in rat kidney. Radioligand binding studies with the specific 5-HT1A receptor ligand [3H]8-OH-DPAT confirmed the presence of 5-HT1A receptor binding sites in bulk-isolated rat medullary TAL. These studies provide the first evidence that the 5-HT1A receptor is expressed on the basolateral surface of TAL and DCT cells of human and rat kidney. The specific localization to these cells suggests a possible role for the 5-HT1A receptor in the regulation of salt and water transport in mammalian kidney.

Vasopressin regulates apical and basolateral Na(+)-H+ antiporters in mouse medullary thick ascending limbs

We assessed in isolated perfused mouse medullary thick ascending limb (MTAL) segments Na(+)-H+ antiporter activity in both apical and basolateral membranes and the effects of arginine vasopressin (AVP) on the activities of these antiporters under isotonic conditions using 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein to monitor intracellular pH (pHi). When the apical Na(+)-H+ antiporter was inhibited in the absence of AVP with removal of luminal Na+ plus addition of 0.5 mM amiloride, a small but significant increase in pHi was observed after luminal NH4Cl-induced acidification of MTAL cells to pHi less than 6.7. This increase in pHi was dependent on basolateral Na+ and inhibited with 0.5 mM basolateral amiloride, consistent with the function of a basolateral Na(+)-H+ antiporter. Basolateral AVP (100 microU/ml) enhanced the rate of pHi recovery due to the basolateral Na(+)-H+ antiporter by more than twofold. In contrast, AVP decreased the apical Na(+)-H+ antiporter activity by 50%. In the absence of AVP, addition of 0.5 mM amiloride to the luminal perfusate reduced steady-state pHi by 0.40 +/- 0.07 units, whereas exposure of the basolateral membrane to the same concentration of amiloride had no effect on pHi (delta pHi = 0.01 +/- 0.01 units). AVP reduced the magnitude of cell acidification on exposure of apical membranes to amiloride (delta pHi = 0.16 +/- 0.03) but increased the pHi response to basolateral amiloride (delta pHi = 0.09 +/- 0.00). Thus Na(+)-H+ antiporters are present on both apical and basolateral membranes of the mouse MTAL in the absence of AVP. AVP stimulates the basolateral, while inhibiting the apical, Na(+)-H+ antiporter.(ABSTRACT TRUNCATED AT 250 WORDS)

Three-dimensional visualization of renal cells by NaOH maceration

The three-dimensional fine structure of cells composing the renal tissue was demonstrated by SEM after the removal of extracellular matrices by NaOH maceration. This paper focuses on glomerular mesangial cells, Goormaghtigh's cells (extraglomerular mesangial cells), and epithelial cells in the thin limbs of Henle's loop in the rat, rabbit and dog. Mesangial cells reveal rough surfaces covered with short microvilli. The cells extend long branching processes in close association with the glomerular capillary, suggesting a role for them of regulating the capillary caliber. The mesangial cells interdigitate with each other by their microvilli, forming an intercellular labyrinth. Goormaghtigh's cells at the glomerular hilus are also covered with microvilli, which form narrow labyrinthine spaces between the cells. The labyrinth among the mesangial cells and that among Goormaghtigh's cells connect with each other at the hilus, giving rise to a channel system leading from the periphery of the glomerulus through the hilus to the interstitial space outside the glomerulus. Renal tubule cells display complicated intra- and intercellular interdigitations on the basal aspect. The pattern of epithelial interdigitation is specific to each tubular segment. The descending and ascending thin limbs of the long loops demonstrate a striking contrast to each other. The former is characterized by moderate intercellular interdigitation and by numerous microvilli on the lateral and basal surfaces; the latter is marked by elaborate, pectineal interdigitations, and by smooth basolateral surfaces.

Expression of epidermal growth factor in the rat kidney. An immunocytochemical and in situ hybridization study

The renal localization and the site of synthesis of epidermal growth factor (EGF) were investigated in the rat kidney by immunohistochemistry and in situ hybridization techniques. EGF was localized in the cells of the thick ascending limb of Henle (TAL) and distal convoluted tubule (DCT). At the ultrastructural level, EGF immunoreactivity was distributed on the apical membrane and trans-Golgi complex of the TAL and DCT cells. These segments of the rat nephron also hybridized to prepro-EGF cRNA probes in a specific manner, indicating that TAL and DCT are the sites of EGF synthesis in the rat kidney.

A potassium channel in the apical membrane of rabbit thick ascending limb of Henle's loop

We used the patch-clamp technique to study the activity of single potassium channels in the apical membrane of isolated thick ascending limbs of Henle's loop (TAL) of rabbit kidneys. In cell-attached patches with NaCl Ringer or high-K+ solution in the bath and 140 mM K+ in the pipette, an inwardly rectifying K+ channel was observed with an inward slope conductance of 22.0 +/- 0.5 pS and outward slope conductance of 10.2 +/- 0.3 pS at 22 degrees C (n = 15). The channel was highly selective for K+, with a calculated permeability ratio for K(+)-to-Na+ of 20:1 (n = 4). The open probability (Po) of the channel was 0.89 +/- 0.03 (n = 15) and was not voltage dependent. In inside-out patches with 140 mM K+ in both the bath and the pipette solutions, both Po and conductance of the channel were similar to that in cell-attached patches. Addition of 0.1 mM Ba2+ to the pipette solution reduced Po of the channel in a voltage-dependent manner. Lowering the pH of the bath solution from 7.4 to 6.9 or increasing Ca2+ concentration from 0 to 0.5 mM in inside-out patches did not alter either Po or conductance of the channel. Addition of 2 mM ATP to the bath solution completely inhibited channel activity. This ATP-induced inhibition was fully reversible and was found to be dependent on the ratio of ATP to ADP, since adding 1 mM ADP to the bath solution relieved the ATP-induced blockade. The property of this small-conductance K+ channel make it a likely candidate for recycling of K+ across the apical membrane of TAL of the rabbit kidney. ATP and ADP are possible intracellular regulators of the channel's activity.

The histotopography and ultrastructure of the thin limb of the Henle's loop: a scanning electron microscopic study of the rat kidney

The three-dimensional construction of the thin limb epithelium was demonstrated in all four segments previously determined by transmission electron microscopy. Special reference was given to the pattern and extent of both intercellular and intracellular interdigitation. In the thin limb of short-looped nephrons, epithelial cells were simple polygonal in shape. The cells showed fine intercellular and intracellular interdigitations of basolateral microprojections. The upper descending thin limb of long-looped nephrons was characterized by well-developed intercellular and intracellular interdigitations. Both types of interdigitations showed a double structure, as they were composed of primary lateral processes or deep basal grooves, with numerous secondary microprojections on their walls. This segment additionally revealed apical interdigitations of small laminar processes, which caused the fine undulation of luminal cell boundaries. In the lower descending thin limb of long-looped nephrons, the intercellular and intracellular interdigitations also showed the double structure, though diminished in degree. This segment lacked the fine apical interdigitations. The ascending thin limb was characterized by an elaborate pectineal pattern of intercellular interdigitations, and by the absence of intracellular interdigitations. The intercellular interdigitations in this segment were formed by thin primary processes oriented parallel to each other. No secondary microprojections were found on their lateral surfaces.

Membrane stretch: a physiological stimulator of Ca2+-activated K+ channels in thick ascending limb

The effects of membrane stretch on Ca2+-activated (maxi) K+ channels were examined in the apical membrane of cultured medullary thick ascending limb (MTAL) cells. Using cell-attached patchclamp technique, we found that negative pressure (-33 +/- 5 cmH2O) applied to the patch membrane increased fractional open probability (NPo) from 0.3 +/- 0.2 to 29.9 +/- 7.6% (n = 12) in the presence of 1.8 mM Ca2+ in the pipette. The activity returned to control on releasing the negative pressure. Reduction of extracellular osmolality from 293.2 +/- 1.6 to 219.8 +/- 1.1 mosmol/kg also activated K+ channels (NPo = 43.8 +/- 12.2%, n = 8) in cell-attached patches. Removal of Ca2+ from both pipette and bathing solution inhibited osmotic activation of K+ channels. K+ channels were shown to be Ca2+-activated K+ channels by their conductance (146 +/- 7 pS, n = 5) and Ca2+ dependence. Our data suggest that membrane stretch caused by swelling or possibly by tubular flow enhances Ca2+ entry across the apical cell membrane of MTAL cells activating maxi K+ channels.

Cells in culture from rabbit medullary thick ascending limb of Henle's loop

Freshly isolated cells obtained from the medullary segment of the rabbit thick ascending limb of Henle's loop (mTALH) metabolize arachidonic acid (AA) primarily by the cytochrome P-450 monooxygenase pathway forming several products; a vasorelaxant and an inhibitor of Na+-K+-ATPase have been identified. These studies have been extended to mTALH cells in culture. The ability of cells isolated from 1-mo-old rabbits to grow in culture far surpassed that of cells isolated from adult rabbits, whereas similar cytochrome P-450-dependent AA metabolites were produced by freshly isolated cells from rabbits of both ages. Three-week-old mTALH cultures formed ouabain-sensitive "domes" when grown on plastic surfaces and developed transepithelial voltages (4.7 + 1.2 mV, n = 6) when grown on gas-permeable surfaces. Electron microscopy of the cells showed typical mTALH cell characteristics. The presence of Tamm-Horsfall protein, a surface membrane protein of mTALH cells, in 90-95% of the cells confirmed the homogeneity of the cultures. Although several environmental manipulations were tested, mTALH cells in culture did not produce the same cytochrome P-450-dependent AA metabolites as those produced by mTALH cells before culture. However, a cytochrome P-450-dependent AA metabolite that differs from the AA metabolites formed by freshly isolated mTALH cells was produced by hemin-treated mTALH and heterogenous cell cultures.

Polyethylene glycol effect on the oxygenated and hypoxic isolated perfused rat kidney

Polyethylene glycol protects against O2 deprivation after clamping of the renal artery or norepinephrine infusion and in hypoxic primary cell culture. Isolated perfused kidneys under hypoxic conditions develop morphological alterations in all segments of the proximal tubule and medullary thick ascending limb. In an attempt to ameliorate the effect of hypoxia, rat kidneys were perfused for 90 min with regularly oxygenated (95% O2 + 5% CO2) or hypoxic perfusate (95% N2 + CO2) supplemented with 8-12% polyethylene glycol (MW approximately 8000). In oxygenated and hypoxic kidneys, polyethylene glycol produced similar changes in S1-S2 segments consisting of reduction of cell thickness and organelle compaction with internalization of brush border into the tubulo-vesicular system. In the S3 segment, the cellular volume loss was more limited; the brush border was transformed to membranous whorls and the cytoplasm contained large, irregular, clear zones. Mitochondrial swelling was pronounced in the hypoxic proximal tubules. Polyethylene glycol quantitatively increased and emphasized the damage in the medullary thick ascending limb. Inclusion of 10(-2) M ouabain preserved the medullary thick ascending limb from hypoxic injury and polyethylene glycol had no effect on this undamaged epithelium. Thus, polyethylene glycol affects renal tubules on the basis of their known water permeability and does not protect against but rather worsens hypoxic injury in the medullary thick ascending limb.

Ultrastructure of the nephron of the one-humped camel, Camelus dromedarius

The nephron of the one-humped camel Camelus dromedarius was investigated by light and transmission electron microscopy. Besides the many features common to other mammalian kidneys, the nephron of the camel is unique in having an unusually thick basal lamina underlying the epithelial cells of the nephron, the thickest being found in part of the parietal layer of Bowman's capsule and the thin limb of the loop of Henle. In the latter, the membrane usually appears lamellated and contains numerous tiny vesicles. In other parts of the nephron, the basal lamina usually has a homogenous appearance. The possible significance of the thickening of the basal lamina is discussed in relation to the general high renal efficiency of the camel.

Structure of avian loop of Henle as related to countercurrent multiplier system

The ultrastructural detail of the avian loop of Henle was examined, and comparisons were made to the loop of Henle of mammalian kidneys. Birds are the only group of vertebrates other than mammals that have the capability of elaborating a urine more concentrated than the plasma. Therefore, a comparison of the principal tubular element responsible for this phenomenon was made. Gambel's quail (Callipepla gambelii) were used as experimental animals. The animals were anesthetized with Inactin, and the kidneys were perfused-fixed in situ. The results show that the transition from the pars recta of the proximal tubule to the thin descending limb of Henle's loop (DLLH) is very abrupt. The upper part of the DLLH appears to be composed of type 2 and the lower part of type 3 epithelia, a condition somewhat similar to mammals. The junctions of the upper portion of DLLH are of the zonula adherens type and those of the lower portion of DLLH are of the macula adherens type. The epithelium of the loop always thickens before the formation of the hairpin turn with the thick descending limb being approximately 15% of the total DLLH. The structure of the avian renal medulla, in particular that of the loop of Henle, appears to parallel quite closely that postulated by the original formulation of the countercurrent multiplier system for the mammalian kidney.

Lectin-gold labeling of glycoconjugates in normal and Brattleboro rat papilla: effect of vasopressin

Some reports suggest that the plasma membrane glycocalyx of collecting duct epithelial cells, as well as interstitial glycoconjugates, may be involved in vasopressin action and urinary concentration. In view of this, we have used the lectin-gold technique to map and quantify Helix pomatia lectin (HPL)-binding sites in the inner medulla of kidneys from normal Long-Evans rats, vasopressin-deficient Brattleboro rats, and Brattleboro rats treated for up to 5 wk with exogenous vasopressin. The results show that the labeling of epithelial cell plasma membranes from collecting ducts and thin limbs of Henle is not different between normal and Brattleboro rats, and the labeling is not modified by chronic vasopressin treatment. In contrast, the heavy interstitial labeling seen in normal rats is virtually absent from Brattleboro rats, but it is progressively restored by chronic vasopressin treatment of Brattleboro rats. These results show that vasopressin does not modify HPL-binding glycoconjugates on epithelial cell plasma membranes, but that vasopressin treatment has a major effect on HPL-binding glycoconjugates in the medullary interstitium.

Effects of dextran-containing perfusion fixatives on intraluminal compounds in rat kidney tubules

In the present study on rat kidney tubules an intraluminal, electron-dense granular substance was found in animals perfusion-fixed with dextran-containing fluids. Most findings were made in thick ascending limbs of Henle and distal convoluted tubules. The incidence decreased from 50% to zero when intravascular rinsing time was increased from zero to 70 sec. In animals fixed without dextran no such substance was found. In some thick ascending limbs of Henle and distal convoluted tubules a similar electron-dense substance was found along the apical plasmalemma of some cells. The origin of the observed substances is at present not defined, but may represent a coprecipitation of dextran and (glyco)proteins caused by glutaraldehyde.

Differentiation in vitro of primary cultures and transfected cell lines of epithelial cells derived from the thick ascending limb of Henle's loop

The use of primary cell cultures derived from defined locations of the kidney has enabled the study of certain kidney cell type-specific characteristics under defined environmental conditions. The use of primary cell cultures, however, has a number of inherent disadvantages, many of which may be overcome by the use of differentiated cell lines of defined origin. In this paper I describe in detail an approach to: (a) the isolation and culture of primary cultures derived from the thick ascending limb of Henle's loop (TALH), and (b) the production of differentiated cell lines by the transfection of these primary cell cultures with early region SV40 virus genes. The characteristics of these cultures and other TALH-derived cell lines are described.

Differences in glycocalyx composition between cells of the cortical thick ascending limb of Henle and the macula densa revealed by lectin-gold cytochemistry

The glycocalyx composition of cells from the macula densa and the cortical thick ascending limb of Henle was examined in rabbit kidney by means of the lectin-gold technique. A quantitative evaluation at the ultrastructural level showed that macula densa cells had a considerably greater affinity for Helix pomatia lectin than adjacent cells of the thick ascending limb. Wheat germ lectin and concanavalin A bound equally well to both cell types. This difference in plasma membrane glycocalyx composition may be an important aspect of the functional differentiation of cell types in this specialized nephron segment.

Segmental variations in the organization of the endoplasmic reticulum of the rat nephron. A stereomicroscopic study

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.

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

Studies were conducted to examine the effects of adrenalectomy (ADX) and selective, physiological adrenal corticosteroid replacement on sodium and potassium transport by the superficial loop of Henle and distal tubule of rat kidney in vivo. In the loop of Henle, ADX inhibited sodium reabsorption by 33%. Whereas dexamethasone had no effect on reabsorption, aldosterone increased sodium transport to control levels. Thus, physiological levels of mineralocorticoids, but not glucocorticoids, control a fraction of sodium reabsorption in the loop of Henle. ADX also inhibited potassium reabsorption in the loop of Henle. Both dexamethasone and aldosterone reversed the inhibition, although only aldosterone increased reabsorption to control levels. In the distal tubule, ADX reduced sodium reabsorption by 44%. Both aldosterone and dexamethasone stimulated reabsorption: however, only aldosterone increased transport to control. Potassium secretion by the distal tubule was also reduced 34% by ADX. Aldosterone, but not dexamethasone, stimulated secretion. Thus, physiological levels of aldosterone regulate a fraction of sodium reabsorption and potassium secretion in the distal tubule.

Structural-functional relationship along the distal nephron

The distal tubule, which includes the thick ascending limb (TAL), the macula densa, and the distal convoluted tubule (DCT), and the collecting duct are structurally heterogeneous, thus reflecting the functional heterogeneity that is also present. As the TAL ascends from medulla to cortex, the surface area of the apical plasma membrane increases while that of the basolateral membrane decreases. The structure of the DCT resembles that of the medullary TAL. An excellent correlation exists between structure, Na-K-ATPase activity, and NaCl reabsorptive capacity in the distal tubule. The collecting duct is subdivided into the initial collecting tubule (IC), and cortical (CCD), outer medullary (OMCD), and inner medullary (IMCD) collecting ducts. Between the distal tubule and the collecting duct is a transition region termed the connecting segment or connecting tubule (CNT). Considerable structural heterogeneity exists along the collecting duct within the two major cell populations, the intercalated cells and the principal cells. In the CNT, the ICT, and the CCD, potassium loading and mineralocorticoids stimulate Na-K-ATPase activity and cause proliferation of the basolateral membrane of CNT cells and principal cells, thus identifying the cells responsible for mineralocorticoid-stimulated potassium secretion in these regions. Finally, at least two morphologically distinct populations of intercalated cells exist, types A and B. In the rat, type A predominates in the CNT and the OMCD and is believed to be responsible for H+ secretion, at least in the OMCD. Type B predominates in the CCD, where it may be involved in bicarbonate secretion.

Scanning electron microscopy of basolateral surfaces of rat renal tubules isolated by sequential digestion

Renal tubular cells and segments isolated by a trypsin, pepsin, pronase E digestion procedure were studied with scanning electron microscopy. The basal and lateral surfaces of S1, S2, S3 proximal tubular (PT) segments, descending and ascending thin limbs of Henle (TL), distal ascending thick limb of Henle, or distal straight tubule (DST) and distal convoluted tubule (DCT) segments, connecting tubules (CNT), and collecting ducts (CD) were identified and characterized. The basal processes of the S1 and S2 PT cells were fan shaped, were oriented in a circumferential direction, and terminated in microvilli at the basement membrane. S3 PT cells had microvillous basal processes mainly on the lateral edges of the cells. The basal processes of DST and DCT were similar to PT in orientation but terminated on the basement membrane with flattened, thin attachments. The long-loop descending TL and the ascending TL exhibited distinctive interdigitating cell processes. TL segments with simple contours were present in smaller numbers and were characteristic of short-loop descending limbs. CNT showed some cells with basal surfaces resembling DCT cells and others resembling CD cells. Both cortical and medullary CD segments exhibited intercalated cells with round basal contours and a sparse pattern of basal infolding clefts. The cortical CD principal cells revealed a much more elaborate mosaic of plicae, clefts, and microvilli than those of the medullary CD. These observations extend the previous knowledge gained from transmission electron microscopy and assist in the interpretation of that knowledge.

Direct visualization of the isolated and perfused macula densa

Direct examination of the structure and function of the macula densa is compromised by the relative inaccessibility and small size of this cell plaque. We report the isolation and perfusion of rabbit nephron segments with attached glomeruli and the direct visualization of the macula densa with differential interference-contrast microscopy. We used this technique to examine the structural sensitivity of the macula densa to perturbations in luminal osmolality and NaCl concentration. Reducing luminal osmolality from 290 to 70 mosmol/kg by removing NaCl resulted in a dilation of the lateral intercellular spaces that was both reversible and specific to the region of the macula densa. Associated with the dilation of the intercellular spaces was a small (congruent to 10%), but statistically significant, increase in the height of the macula densa cells. These structural events were related to the reduction in luminal osmolality, since isosmotic replacement of NaCl with mannitol resulted in no detectable structural changes. Thus, the macula densa may represent a small water-permeable plaque of cells within the remaining water-impermeable thick ascending limb of Henle's loop.

Physiological and morphological responses of the rat kidney to reduced dietary protein

Renal physiological and morphological adjustments to a reduced protein diet were studied in young Munich-Wistar rats. Two groups of animals were used for the correlative physiological-morphological studies: normal protein (NP, 24% dietary protein) rats and reduced protein (LP, 8% dietary protein) rats. Both groups were fed their respective diets for 4-5 wk and had free access to drinking water. Physiological measurements of GFR and urea clearance were made on five animals from each group. These data showed that the changes in renal function specifically and almost exclusively affected the handling of urea. There was no difference in GFR between the NP and LP rats. Urea clearance was substantially reduced in LP rats. Morphological analyses were made on perfusion-fixed kidneys of five animals from each group. Selected slices were examined and photographed by light and electron microscopy. These data showed no difference in size and number of elements within the vascular bundles but showed significantly smaller lumina of the thin limbs of the short-looped nephrons and a significant thinning of the wall of the thin descending limbs of the long-looped nephrons. These morphological changes may in part be responsible for the observed physiological adjustments to a reduced protein diet. An additional group of rats (6 NP and 5 LP, all dehydrated) were analyzed for distribution of solutes within the inner medulla. The data showed that the concentration of urea, but not that of Na+, was reduced at the papillary tip in LP rats.

Functional heterogeneity of the descending limbs of Henle's loop. I. Internephron heterogeneity in the hamster kidney

By using the in vitro microperfusion technique, were examined functions of the descending limbs of Henle's loop obtained from either the short-loop nephron (SDL) or the upper portion of the long-loop nephron of hamsters (LDLu). Morphological distinctions between these segments were confirmed by light and electron microscopic observations. Both segments were highly permeable to water. The LDLu was highly permeable to sodium and to chloride: efflux coefficients (10(-7) cm2 x s-1) for 22Na and 36Cl were 41.0 +/- 5.4 and 3.8 +/- 0.6, respectively. The SDL were less permeable to sodium and to chloride: efflux coefficient for 22Na and 36Cl were 2.9 +/- 1.4 and 0.9 +/- 0.2, respectively. In contrast, the SDL was more permeable to urea as compared to the LDL, efflux coefficients for urea being 5.1 +/- 1.4 vs 1.4 +/- 0.3, respectively. When composition of the perfusate was identical to that of the bathing fluid, no transepithelial voltage was demonstrated. The volume flux was very small or undetectable. From these observations, we propose that the internephron heterogeneity must be taken into consideration for constructing a model of countercurrent system in the renal medulla.

Suspension of medullary thick ascending limb tubules from the rabbit kidney

A procedure for isolating a suspension of tubules derived from the rabbit medullary thick ascending limb is described. The purity of the preparation was assessed by microscopy and enzyme assays and the viability of the preparation was assessed by measuring oxygen consumption. Microscopy revealed that the suspension contains 95% thick ascending limbs and that the isolation procedure preserves the structure of the epithelium except for the loss of the basement membrane. The preparation had a high activity of calcitonin-sensitive adenylate cyclase, a marker enzyme for the medullary thick ascending limb. Control oxygen consumption was considerably higher than that reported for proximal tubules in the literature, and nystatin or carbonyl cyanide p-trifluoromethoxyphenylhydrazone addition produced a more than 100% increase in oxygen consumption. Furosemide inhibited the oxygen consumption by 43% and ouabain inhibited it by 42%. Furosemide inhibited sodium chloride entry without directly affecting the Na-K-ATPase or cellular metabolism. Chloride removal depressed oxygen consumption to the same extent as furosemide, but some of this action was through direct inhibition of cellular metabolism.

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

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.

Periodic disklike structures of the adult human loop of Henle. Light and electron microscopic studies

A total of 51 adult human kidneys was examined for the presence of the periodic disklike thickenings recently described by Belliveau in the basement membrane of the loop of Henle. These "Belliveau bodies" formed a PAS-positive rectangular lattice within the basement membrane and appeared limited to the loop of Henle. The bodies were seen in the medulla of every kidney examined but varied considerably in the frequency of their appearance from case to case. This variability did not correlate with predominant illness, organ weight, or time interval between death and autopsy. They averaged 9 to 14 micron in diameter with a horizontal and vertical periodicity of 12 and 16 micron, respectively. Although the bodies were PAS positive and diastase resistant, they did not stain with Congo red, mucicarmine, reticulin, or elastin staining techniques. Ultrastructurally, they consisted of multilaminated areas of basement membrane material. The constancy of their appearance in the material examined suggests that they are a normal anatomic feature or possibly an age-related change of the basement membrane of Henle's loop in the human kidney.

Selective vulnerability of the medullary thick ascending limb to anoxia in the isolated perfused rat kidney

A specific anatomical lesion sharply localized to the cells of the medullary thick ascending limbs (mTAL) and characterized by mitochondrial swelling progressing to nuclear pyknosis and cell death is elicited reproducibly in isolated rat kidneys perfused for 15 or 90 min with cell-free albumin-Ringer's medium gassed with 5% CO2, 95% O2 (O2 content, 1.5 vol/100 ml). The lesion, involving about half of mTALs, appears first in mTALs removed from vascular bundles and near the inner medulla, areas most likely to be anoxic. Hypoxic perfusion (O2 content 0.12 vol/100 ml) exaggerates the lesion, wiping out gradations of damage and extending it to all mTALs. O2-enriched perfusions using rat erythrocytes (O2 content 7.1 vol/100 ml) completely eliminates the lesion (unless gassed with carbon monoxide). Similarly, supplementation of the perfusion medium with a purified hemoglobin (O2 content 5.8 vol/100 ml) prevents mTAL injury. Perfusion with a fluorinated hydrocarbon blood substitute, Oxypherol (O2 content 4.3 vol/100 ml) also attenuates the lesion. These findings suggest that the mTAL is exquisitely susceptible to anoxic damage because of low O2 supply imposed by the medullary vascular system and the high rate of metabolism mandated by active reabsorption of sodium chloride. The vulnerability of the mTAL to anoxic injury could play a key role in the pathogenesis of ischemic renal injury.

Murine globoid cell leukodystrophy: the twitcher mouse. An ultrastructural study of the kidney

Kidneys of 5- to 45-day-old twitcher mice were studied by light and electron microscopy. No abnormalities were detected with the light microscope. However, at the ultrastructural level, several types of cytoplasmic inclusions were found in epithelial cells with increasing frequency with age. The characteristic inclusions of globoid cell leukodystrophy, identical with those observed in the central nervous system, were confined to epithelial cells of the thin limbs of the loop of Henle. They were present on day 5 in epithelial cells of the thin limbs of the loop of Henle in the papillae of developing kidneys and, after day 20, became more widely distributed in both descending and ascending thin limbs of long loops and in descending thin limbs of short loops. Occasionally, these characteristic inclusions were found within the lumen. Thus, although the twitcher mouse is an authentic model of human globoid cell leukodystrophy, the massive increase in renal galactosylceramide and the finding of inclusions in the twitcher mouse's kidney contrast sharply with the lack of similar changes in man.

Influence of altered glomerular permeability on renal tubular immune complex formation and clearance

Proteinuria was induced in rats to determine whether intravenously injected antibodies to a distal tubular antigen would bind to the luminal surfaces of distal tubular cells in vivo. Rats with proteinuria induced by an intravenous injection of sheep antisera to Fx1A (passive Heymann model) were injected 10 days later with rabbit antisera to Tamm-Horsfall protein. Linear rabbit IgG deposits along the luminal cell surfaces in the initial portion of the thick ascending limb of the loop of Henle (ALH) were demonstrated by immunofluorescence microscopy at 4 hours and were maximal 1 to 3 days after injection of antibodies to Tamm-Horsfall protein. The distance that these immune deposits extended along the ALH was directly proportional to the magnitude of proteinuria. Light microscopy showed periodic acid-Schiff-positive luminal deposits and an increased number of mitoses confined to the early ALH. Ultrastructural studies revealed continuous very electron-dense deposits initially covering the luminal surfaces of ALH cells. During the clearance phase, these deposits were surrounded and separated from ALH cell surfaces by a less electron-dense fibrillar material with the ultrastructural characteristics of Tamm-Horsfall protein. The mechanism of immune complex formation in the present study appears to involve the in situ combination of rabbit antibodies to Tamm-Horsfall protein in the glomerular filtrate with a tubular surface membrane antigen, Tamm-Horsfall protein.

Phosphate and the development of nephrocalcinosis in rats fed diets containing alpha protein

It has been suggested that nephrocalcinosis in rats fed diets containing alkali-treated soy protein may be due to a high availability of phosphate in the diet. In the present study, the development of nephrocalcinosis in rats fed a diet containing 20% alpha protein (an alkali-treated soy protein) was compared with that in rats fed the same diet supplemented with additional phosphate. Phosphate supplementation of the alpha protein diet produced a form of nephrocalcinosis that was morphologically different, at both the light- and electronmicroscopic level, from that obtained with the unsupplemented diet but was quite similar to that obtained with a phosphate-supplemented standard commercial laboratory diet. Levels of serum and urinary calcium and phosphorus and urinary cyclic AMP suggested that a phosphate-induced secondary hyperparathyroidism was present in the rats fed either of the phosphate-supplemented diets, but not in the rats fed the unsupplemented alpha protein diet. The results of this study suggest that nephrocalcinosis in rats fed a diet containing 20% alpha protein, without additional phosphate, is not typically phosphate-induced.

Murine globoid cell leukodystrophy (the twitcher mouse). The presence of characteristic inclusions in the kidney and lymph nodes

Ultrastructural investigations were carried out on the kidney, lung, liver, spleen, lymph nodes and adrenal gland of the twitcher mouse, a recently discovered authentic murine model of human globoid cell leukodystrophy (GLD). The characteristic cytoplasmic inclusions identical to those found in the glial and globoid cells in the central nervous system (CNS) were observed in the epithelial cells of the thin limbs of the loops of Henle in the kidney and also in the macrophages in the lymph nodes. Such inclusions were not detected in the systemic organs in a case of human GLD. This fact may indicate an important species difference between the human and murine forms of GLD, although the genetic enzymatic defect is the same.

Insights into intrarenal sites and mechanisms of action of diuretic agents

Effective diuresis requires both sufficient glomerular filtrate and adequate delivery of the diuretic drug to the lumen of the renal tubule. Diuretics will not "force open" the kidney. Diuretics that work primarily in the proximal tubule include osmotic diuretics (e.g., mannitol), diuretics that interfere with the adenyl cyclase system (e.g., xanthines), and those which inhibit carbonic anhydrase (e.g., acetazolamide). Some thiazide and thiazide-like diuretics have a secondary site of action in the proximal tubule based on either carbonic anhydrase inhibition or other mechanisms, such as inhibition of sodium phosphate reabsorption. The diuretics that work primarily in the medullary diluting segment of the loop of Henle, furosemide and ethacrynic acid, block the active reabsorption of chloride and interfere with the tubular reabsorption of free water. The exact mechanism remains unknown. These diuretics tend to have a "high ceiling," to be potent and rapidly acting, and to have a short duration of effect. They are excellent for the treatment of severe fluid overload or pulmonary edema but are not ideal for the treatment of uncomplicated hypertension. Furosemide is a sulfonamide derivative; ethacrynic acid can be used in patients who are allergic to sulfa drugs. Diuretics that work primarily in the cortical diluting segment include the thiazides and thiazide-like drugs. They inhibit sodium transport by an undetermined mechanism. Most of them seem to reach a dose-response plateau beyond which little additional effect is gained by increasing the dose. Most of them appear to lose efficacy as the glomerular filtration rate decreases, except for metolazone and indapamide. The thiazides are most commonly used to treat hypertension. Diuretics that work primarily in the distal tubule and collecting tubule include the aldosterone inhibitor spironolactone and two drugs that impair tubular reabsorption of sodium by direct action, triamterene and amiloride. These drugs are primarily used for their potassium-sparing effect.