NH4+ and NH3 permeabilities of Henle's loop segments.
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Ammonia↗
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A hormonal mosaic modulating the function of the thick ascending limb of Henle's loop.
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Animals↗
[Characteristics of electrolyte transport in the ascending limb of the Henle's loop].
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Biological Transport, Active↗
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.
Animals↗
Computer simulation of flow-dependent absorption in microperfused short Henle's loop of rats.
With computer simulation we examined the extent to which current theories and experimental data explain function of single microperfused superficial Henle's loops in rats. In the model standard phenomenological equations describe transport; two sets of transport parameters labeled rat and rabbit were taken from published experiments; Michaelis-Menten kinetics in the ascending thick limb were adjusted arbitrarily; tubular radius is either constant or depends on luminal pressure with compliance based on experimental observations; the interstitium is an infinite sink with salt and urea concentrations constant in the cortex and exponentially increasing in the outer medulla; concentrations resemble those found in hydropenic or saline diuretic rats. The following predictions were obtained. The model with rabbit parameters does not recirculate urea and will not operate with high medullary urea concentrations; with rat parameters too much urea recirculates an the results of perfusion with equilibrium solution are not reproduced. Using a compromise between rat and rabbit parameters, the model reproduces water absorption, salt reabsorption, and urea recirculation as observed in vivo in rat loops perfused at 5-40 nl/min. It also simulates perfusion with saline, equilibrium solution, saline plus furosemide, and 300 mM mannitol. When the model includes a short early distal segment, effluent salt concentration reaches a minimum at a 15 nl/min perfusion rate as observed in vivo; however, concentration at the macula densa is a monotonically increasing function of flow. When permeation rate is a function of wall surface area and thickness a better fit to experimental results is produced. However, the effect is small: water absorption alters by 4% or less and effluent salt concentration is reduced by up to 10% at low perfusion rates. Comparison of rigid and compliant loops shows no relationship between transit time per se and reabsorption.
Animals↗
Effect of protamine on cation-selective permeability in hamster medullary thick ascending limb of Henle's loop.
To estimate the contribution of the paracellular shunt pathway to cation-selective permeability in the hamster medullary thick ascending limb of Henle's loop, we observed the effect of protamine, a selective blocker of paracellular conductance, on salt-diffusion voltage (dVT) in the isolated nephron segment perfused in vitro. When 300 microg/ml protamine was added to the lumen, the lumen-positive dVT generated upon reduction of the lumen NaCl concentration was decreased from 5.1 +/- 0.9 to 0.8 +/- 0.8 mV and the calculated Na+/Cl- permeability ratio was decreased from 1.40 +/- 0.14 to 0.86 +/- 0.08. Although the effect of protamine persisted after removal of the agent from the lumen, addition of 30 U/ml heparin, which neutralizes protamine, returned the dVT toward the control level. This effect was almost the same when the orientation of the imposed NaCl gradient was reversed. Protamine exhibited a similar effect on dVT in the presence of ouabain added to the bath. Protamine was without effect from the bath. Protamine did not affect the basel VT perfused with the control solution. Increased VT by decreasing perfusion pressure was inhibited by adding protamine from the lumen. These observations suggest that the paracellular pathway contributes to the cation selectivity of the medullary thick ascending limb. The cation selectivity of the paracellular shunt pathway may mainly account for the changes in VT which are either dependent on the luminal flow rate or transmural NaCl concentration gradient, while it may not contribute to the basal level of VT.
Animals↗
Inhibition of heme oxygenase decreases sodium and fluid absorption in the loop of Henle.
We previously demonstrated that carbon monoxide (CO) stimulates the apical 70-pS K+ channel in the thick ascending limb (TAL) of the rat kidney (Liu HJ, Mount DB, Nasjletti A, and Wang WH. J Clin Invest 103: 963-970, 1999). Because the apical K+ channel plays a key role in K+ recycling, we tested the hypothesis that heme oxygenase (HO)-dependent metabolites of heme may affect Na+ transport in the TAL. We used in vivo microperfusion to study the effect of chromium mesoporphyrin (CrMP), an inhibitor of HO, on fluid absorption (Jv) and Na+ absorption (JNa) in the loop of Henle and renal clearance methods to examine the effect of CrMP on renal sodium excretion. Microperfusion experiments demonstrated that addition of CrMP to the loop of Henle decreased Jv by 13% and JNa by 20% in animals on normal rat chow and caused a decrease in Jv (39%) and JNa (40%) in rats on a high-K+ (HK) diet. The effect of CrMP is the result of inhibition of HO because addition of MgPP, an analog of CrMP that does not inhibit HO, had no effect on Jv. Western blot analysis showed that HO-2 is expressed in the kidney and that the level of HO-2 was significantly elevated in animals on a HK diet. Renal clearance studies demonstrated that the infusion of CrMP increased the excretion of urinary Na+ (ENa) and volume (UV) without changes in glomerular filtration rate. The effect of CrMP on ENa and UV was larger in HK rats than those kept on normal chow. We conclude that HK intake increases HO-2 expression in the kidney and that HO-dependent metabolites of heme, presumably CO, play a significant role in the regulation of Na+ transport in the loop of Henle.
Absorption↗
Cyclooxygenase inhibitors increase Na-K-2Cl cotransporter abundance in thick ascending limb of Henle's loop.
Cyclooxygenase inhibitors, such as indomethacin and diclofenac, have well-described effects to enhance renal water reabsorption and urinary concentrating ability. Concentrating ability is regulated in part at the level of the thick ascending limb of Henle's loop, where active NaCl absorption drives the countercurrent multiplication mechanism. We used semiquantitative immunoblotting to test the effects of indomethacin and diclofenac, given over a 48-h period, on the expression levels of the ion transporters responsible for active NaCl transport in the thick ascending limb. Both agents strongly increased the expression level of the apical Na-K-2Cl cotransporter in both outer medulla and cortex. Neither agent significantly altered outer medullary expression levels of other thick ascending limb proteins, namely, the type 3 Na/H exchanger (NHE-3), Tamm-Horsfall protein, or alpha1- or beta1-subunits of the Na-K-ATPase. Administration of the EP3-selective PGE(2) analog, misoprostol, to indomethacin-treated rats reversed the stimulatory effect of indomethacin on Na-K-2Cl cotransporter expression. We conclude that cyclooxygenase inhibitors enhance urinary concentrating ability in part through effects to increase Na-K-2Cl cotransporter expression in the thick ascending limb of Henle's loop. This action is most likely due to elimination of an EP3-receptor-mediated tonic inhibitory effect of PGE(2) on cAMP production.
Animals↗
Anoxia-induced increases in intracellular calcium concentration in primary cultures of rabbit thick ascending limb of Henle's loop.
The effect of anoxia on intracellular Ca2+ concentration ([Ca2+]i) in primary cultures of medullary (mTAL) and cortical (cTAL) thick ascending limb of Henle's loop was investigated. Previously, we reported a method to monitor [Ca2+]i continuously in cultured proximal tubule cells during 1 h of anoxic incubation in the absence of glycolytic substrates [1]. Complete absence of O2 was realised by inclusion of a mixture of oxygenases in an anoxic chamber. As a result of substrate-free anoxia, [Ca2+]i started to rise in individual cells of mTAL and cTAL monolayers and reached maximal levels within 60 min after starting the anoxic incubation. Anoxia induced significant increases in [Ca2+]i from 76 +/- 1 (n = 176) to 469 +/- 18 nM (n = 203) in mTAL monolayers and from 58 +/- 1 (n = 91) to 442 +/- 27 nM (n = 106) in cTAL monolayers (P < 0.05). At the re-introduction of oxygen and glucose, elevated [Ca2+]i rapidly declined to 110 +/- 4 (n = 167) and 105 +/- 5 nM (n = 87) in mTAL and cTAL, respectively (P < 0.05). Removal of extracellular Ca2+ and addition of 0.1 mM La3+ partially prevented anoxia-induced increases in [Ca2+]i in both cell types. The L-type Ca2+ channel blocker D600 (1 microM) was as effective as Ca2+ removal and La3+ addition. Comparing mTAL and cTAL cells, only one difference was consistently observed. Prevention of Ca2+ influx by exposure to La3+ combined with Ca2+ removal or addition of 1 microM D600 had a greater inhibitory effect on anoxic [Ca2+]i values in mTAL than in cTAL monolayers, indicative of a larger role of Ca2+ influx through L-type Ca2+ channels in anoxia-induced increases in [Ca2+]i in the former cell type. In conclusion, substrate-free anoxia reversibly increases [Ca2+]i in primary cultures of cTAL and mTAL, which results from Ca2+ release from stores as well as from Ca2+ influx via D600-sensitive Ca2+ channels.
Animals↗
Localization of diuretic effects along the loop of Henle: an in vivo microperfusion study in rats.
In order to clarify the effects on sodium reabsorption in the loop of Henle of methazolamide (a carbonic anhydrase inhibitor), chlorothiazide and the loop diuretics frusemide and bumetanide, superficial loops were perfused in vivo in anaesthetized rats and the individual diuretics were included in the perfusate. Differentiation between effects in the pars recta and in the thick ascending limb of Henle (TALH) was achieved by comparing responses to the diuretics when using a standard perfusate, designed to mimic native late proximal tubular fluid, and a low-sodium perfusate, designed to block net sodium reabsorption in the pars recta. With the standard perfusate, methazolamide caused decreases in sodium reabsorption (J(Na)) and water reabsorption (J(V)); with the low-sodium perfusate, a modest effect on J(Na) persisted, suggesting that carbonic anhydrase inhibition reduces sodium reabsorption in both the pars recta and the TALH. The effects of chlorothiazide were very similar to those of methazolamide with both the standard and low-sodium perfusates, suggesting that chlorothiazide also inhibits sodium reabsorption in the pars recta and TALH, perhaps through inhibition of carbonic anhydrase. With the standard perfusate, both frusemide and bumetanide produced the expected large decreases in J(Na), but J(V) was also lowered. With the low-sodium perfusate, the inhibitory effects of the loop diuretics, particularly those of frusemide, were substantially reduced, while net potassium secretion was found. These observations indicate that a significant component of the effect of frusemide (and possibly of bumetanide) on overall sodium reabsorption is located in the pars recta, and that loop diuretics induce potassium secretion in the TALH.
Absorption↗
Lack of inhibition of vasopressin-stimulated NA+K+ATPase by atrial natriuretic factor in the rat renal medullary thick ascending limb of Henle's loop.
The anti-diuretic hormone, arginine vasopressin (AVP) stimulates the activity of Na+K+ATPase in the rat renal medullary thick ascending limb of Henle's loop (mTAL). Atrial natriuretic factor (ANF) has been suggested to exert a tubular effect on the mammalian nephron, perhaps in part, by interacting with other hormones. In the present study, we investigated the effect of rat ANF with and without AVP upon mTAL Na+K+ATPase activity using cytochemical methods. ANF alone failed to inhibit or stimulate Na+K+ATPase activity in mTAL at any of the concentrations tested (10 nmol-0.1 pmol l-1). Unlike the rat hypothalamic digitalis-like factor, ANF (10 nmol-10 fmol l-1) did not inhibit Na+K+ATPase activity after stimulation with AVP (1 fmol l-1) for either 4 or 10 min. The results suggest that ANF does not exert an effect on mTAL, either alone or in conjunction with AVP.
Analysis of Variance↗
Periodic disk-like structures of the loop of Henle: description of a newly recognized anatomic network.
A light-microscopic examination of sections of kidneys from 35 patients was performed utilizing the PAS stain. A previously unrecognized anatomic network of the basement membrane of the loop of Henle is described. The network consists of 10-to 15-mu-diameter, round-to-ovoid, disk-like areas of thickening of the basement membrane occurring along most loops of Henle and appearing to be present on both thin and thick portions. These disks are present around the entire circumference of the tubule and are separated by areas of 5 to 10 mu of nonthickened basement membranes. Their function, if any, is not presently understood.
Adolescent↗
Regulation of Cl- conductance in the thin ascending limb of Henle's loop.
Characteristics of the ion transport of the ascending thin limb of Henle's loop (ATL) were reviewed with special reference to the regulatory mechanisms of the putative Cl- channel. The ATL is highly permeable to NaCl, moderately permeable to urea, and virtually impermeable to water. The Cl- permeability is extremely high, having saturation kinetics and being inhibited by halogens. The Cl- conductances exist in series in both apical and basolateral membranes. They are inhibited by anion transport inhibitors including DIDS, phloretin, and NPPB. The Cl- conductance is pH sensitive and activated by Ca2+. NEM exhibits dual action on this conductance: irreversible inhibition and reversible stimulation. This highly effective Cl- transport system is favorable for the operation of the countercurrent multiplication system in the renal medulla.
Animals↗
Calcium and magnesium transport in the cortical thick ascending limb of Henle's loop: influence of age and gender.
Previous studies from our laboratory have shown that Ca2+ and Mg2+ absorption in the mouse cortical thick ascending limb of Henle's loop (cTAL) is a passive, paracellular process driven by the transepithelial voltage. The passive permeability of the epithelium is enhanced by peptide hormones. The present study investigated whether divalent cation absorption in the cTAL is influenced by cell maturation and/or gender. For this purpose, mouse cTAL segments were microdissected from kidneys of female and male animals aged 4 and 8 weeks. The microdissected tubules were perfused in vitro at a luminal flow rate of 1.5 to 2.5 nl/min. Transepithelial Na+, Cl-, Ca2+ and Mg2+ net fluxes (JX, pmol.min-1.mm-1) were measured using electron microprobe analysis, and the transepithelial potential difference (PDte) was measured continuously. No differences were found in the PDte, JNa and JCl of the various animal groups but the transepithelial Ca2+ and Mg2+ transport capacity of the cTAL was higher in adults (8 weeks) than in young animals (4 weeks). Furthermore, irrespective of age, transepithelial Ca2+ net absorption was greater in male than in female animals. In contrast, the NaCl transport was maximal at 4 weeks in both genders. We conclude therefore that transepithelial divalent cation absorption in the mouse cTAL is an inductive process influenced by cell maturation and gender. The molecular basis of these inductions remains to be elucidated.
Absorption↗
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.
Adenosine Triphosphate↗
Characterization of aldose reductase from the thick ascending limb of Henle's loop of rabbit kidney.
BACKGROUND: The organic osmolyte sorbitol plays an important role in the osmoregulation of immortalized epithelial cells of the thick ascending limb of Henle's loop (TALH) of rabbit. The intracellular sorbitol content seems to depend strongly on the extracellular osmolarity. To investigate the nature of the osmotic regulation we characterized the aldose reductase. METHODS: We determined aldose reductase activity enzymatically and the content of organic osmolytes by HPLC. RESULTS: The aldose reductase activity correlates with the extracellular tonicity. Elevating the osmolarity of the medium from 300 to 600 mosm/l by addition of NaCl or sucrose resulted in a significant increase of maximal velocity (V(max)) of the adapted cells from 8 +/- 1 micromol/g x min (300 mosm/l) to 322 +/- 28 micromol/g x min (600 mosm/l, NaCl) or 54 +/- 9 micromol/g x min (600 mosm/l, sucrose), respectively, while affinity (K(m)) remained unchanged. But we found no rise of aldose reductase activity when extracellular urea concentration was elevated. Similar alterations in V(max) were observed when the activity of the highly enriched enzyme was determined with glucose as substrate. Elevation of the extracellular osmolarity by NaCl and sucrose strongly induced the expression of aldose reductase protein with an apparent molecular weight of 39 kD. The affinity of glucose is characteristically low with a K(m) above 300 mmol/l. Aldose reductase utilizes both NADPH and with lower affinity NADH as coenzymes. In vitro sulfate ions (0.4 mol/l) results in a two-fold activation of the aldose reductase activity whereas sodium (200-400 mmol/l) decreased the activity significantly (22-33%). Potassium and chloride up to 400 mmol/l did not alter the aldose reductase activity in vitro. CONCLUSIONS: These results indicate that the aldose reductase of TALH cells of the outer medulla is osmotically regulated and has many similarities with aldose reductase in renal inner medulla. Therefore, intracellular sorbitol synthesis seems to be of similar importance in the osmoregulation of TALH cells as in the inner medulla.
Adaptation, Physiological↗
Effect of Etozolin on whole kidney function and fluid and electrolyte reabsorption in rat proximal convoluted tubules and loops of Henle.
The effects of ethyl (Z)-(3-methyl-4-oxo-5-piperidino-thiazolidin-2-ylidene) acetate (etozolin, Elkapin) on whole kidney function and on fluid, sodium and potassium reabsorption in proximal convoluted tubules and loops of Henle of superficial nephrons were studied in rats using clearance and micropuncture techniques. Etozolin (50 mg/kg i.v. initial dose; 50 mg/kg per hour i.v.) markedly increased urinary fluid and sodium excretion and decreased glomerular filtration rate. Fractional tubular sodium reabsorption fell by 8.7%. Fluid and electrolyte reabsorption in the proximal convolution was not significantly influenced by etozolin. The substance significantly increased flow rate, sodium and potassium concentration and decreased tubular fluid/plasma inulin ratio of the early distal tubular, indicating an inhibitory effect on fluid and electrolyte reabsorption in the loop of Henle. Although etozolin is chemically different its site of diuretic action is the same as that of furosemide and ethacrynic acid.
Animals↗
Effect of potassium depletion on chloride transport in the loop of Henle in the rat.
Microperfusion of the superficial loop segment (latest proximal to earliest distal tubule) was performed in potassium-depleted and control rats. Potassium depletion was confirmed by analysis of muscle content (control 45 +/- 2, potassium depletion 33.5 +/- 0.9 meq/100 g dry solids). During perfusion at 20 nl/min net chloride absorption was decreased (66 +/- 3 vs. 77 +/- 2%, P less than 0.01) and early distal chloride concentration increased (70 +/- 5 vs. 50 +/- 4 meq/liter, P less than 0.01) in the potassium-depleted rats. In separate paired experiments in potassium-depleted rats, indomethacin infusion increased net chloride absorption (P less than 0.05) and lowered early distal chloride concentration (P less than 0.05) toward, but not to, normal. A similar effect of indomethacin to decrease early distal chloride concentration was seen in rats ingesting a normal diet and in control rats. We conclude that in potassium-depleted rats there is impaired net chloride absorption in the loop segment, most likely in the thick ascending limb, and that this effect is not produced by an altered response to prostaglandins. This defect in chloride transport may be responsible, at least in part, for the impaired concentrating capacity seen in potassium-depleted rats.
Animals↗