bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential regulation of CHIF mRNA by potassium intake and aldosterone
Authors: Wald H. , Popovtzer M. M. , Garty H.
Published: December 2017

The channel-inducing factor (CHIF) is an epithelial-specific transmembrane protein, which is induced by aldosterone in distal colon (but not in kidney) and can evoke K+ conductance in Xenopus oocytes. The current study examined the possibility that CHIF participates in maintaining K+ balance by assessing its regulation during variations in K+ intake. In adrenal-intact rats, high-K+ diet stimulated, whereas K+ deficiency downregulated, CHIF mRNA both in kidney and colon. The downregulation of CHIF observed in rats fed a low-K+ diet for different periods of time closely correlated with a decrease in plasma K+ but also with changes in aldosterone levels. To differentiate between the two, modulation of CHIF has been studied in adrenalectomized rats with and without corticosteroid supplementation. These experiments have demonstrated that a low-K+ intake suppresses CHIF mRNA, irrespective of aldosterone level. On the other hand, the upregulation evoked by a high-K+ load is apparent only in adrenal-intact rats. This is despite the fact that infusing rats with aldosterone and corticosterone does not increase the expression of this mRNA in kidney. These findings may suggest a role for CHIF in preserving K+ balance.
Expression of bcl-2 and bax in regenerating rat renal tubules following ischemic injury
Authors: Basile D. P. , Liapis H. , Hammerman M. R.
Published: December 2017

To define potential roles for bcl-2 and bax in adult kidney as regulators of regeneration, their expressions were characterized postischemic injury. A 2.1-fold increase in levels of renal bcl-2 mRNA occurred within 24 h of injury relative to levels in kidney of sham-operated control rats. The levels of bcl-2 mRNA remained elevated for 3 days but returned to baseline by day 5 postischemia. In situ hybridization of kidneys from sham-operated rats demonstrated faint expression of bcl-2 mRNA localized diffusely throughout the nephron. After renal injury, the expression of bcl-2 mRNA was markedly enhanced in regenerating proximal tubule cells relining the basement membrane. Immunohistochemistry showed a similar localization for bcl-2 protein. Levels of bax mRNA in kidney were elevated beginning at 24 h postischemia and remained elevated for 7 days postinjury. Bax mRNA and bax protein were colocalized to regenerating proximal tubules postischemia and were prominently expressed in papillary proliferations. We conclude that the expressions of bcl-2 and bax in kidney are enhanced in a predictable pattern following acute ischemic injury. Our findings suggest that these regulators of apoptosis play key roles in the process of repair of the damaged proximal tubule postischemia.
Effect of chronic metabolic acidosis on thyroid hormone homeostasis in humans
Authors: Brungger M. , Hulter H. N. , Krapf R.
Published: December 2017

The effects of metabolic acidosis on thyroid function are unknown. We investigated the effects of chronic extrarenal acidosis on the hypothalamic-pituitary-thyroid axis. Chronic metabolic acidosis was induced by administering NH4Cl (4.2 mmol.kg body wt-1.day-1) to six normal male volunteers during metabolic balance conditions. Plasma bicarbonate concentration decreased from 25.0 +/- 0.4 to 15.5 +/- 0.9 mmol/l (P < 0.001). Metabolic acidosis significantly decreased serum-free 3,5,3'-triiodothyronine (T3) concentrations from 373 +/- 18 (control) to 251 +/- 13 pg/dl (P < 0.001) and decreased serum-free L-thyroxine (T4) from 1.55 +/- 0.42 to 1.25 +/- 0.37 ng/dl (P < 0.002), whereas serum total reverse T3 did not change significantly. Consequently, the reverse T3-to-free T4 ratio increased. Serum thyroid-stimulating hormone (TSH) levels increased significantly from 0.70 +/- 0.07 during control to 1.30 +/- 0.12 mU/l during acidosis (P < 0.003). The TSH response to thyrotropin (TRH, 2 mg intranasally) was exaggerated in acidosis: the partial area under the concentration curve for the TSH response (210 min post-TRH) was 902 +/- 167 during control compared with 1.394 +/- 209 mU.min.l-1 during acidosis (P = 0.0139). Chronic metabolic acidosis, as produced by the model employed here, induces a decrease in thyroid hormone secretion and might exert additional effects on thyroid hormone metabolism in humans. The acidosis-induced decrease in thyroid function might modulate some of the reported effects of metabolic acidosis, such as on nitrogen balance, protein synthesis, lean body mass, insulin-like growth factor I levels, renal acidification, and cardiac contractile function.
Albumin endocytosis in OK cells: dependence on actin and microtubules and regulation by protein kinases
Authors: Gekle M. , Mildenberger S. , Freudinger R. , Schwerdt G. , Silbernagl S.
Published: December 2017

We used proximal tubule-derived opossum kidney (OK) cells to determine the dependence of albumin endocytosis on regulation by protein kinases and on the cytoskeleton. Uptake was observed only across the apical but not the basolateral membrane and exceeded uptake in collecting duct-derived Madin-Darby canine kidney cells 14-fold. Inhibition of endocytosis via clathrin-coated vesicles but not via caveolae abolished uptake. Cytochalasin D reduced uptake to < 5% of control, and inhibition of microtubule polymerization by nocodazole reduced uptake to approximately 55% of control. Activation of protein kinase A (PKA) by adenosine 3',5'-cyclic monophosphate, forskolin, or parathyroid hormone (PTH) reduced uptake to approximately 65% of control. Protein kinase C (PKC) activation did affect uptake to a similar extent as PKA activation but with a certain delay. Stimulation of PKG by guanosine 3',5'-cyclic monophosphate did not affect albumin endocytosis. The inhibitor of tyrosine kinases (TRK), genistein, induced an increase of uptake to approximately 160% of control. Reexocytosis of albumin was enhanced by PKC activation but not by PKA activation. TRK inhibition reduced the rate of reexocytosis. We conclude that albumin endocytosis in OK cells requires the integrity of the actin cytoskeleton. Microtubules facilitate endocytosis. Uptake is regulated by PKA, PKC, and TRK, yet with different time course and by different mechanisms, e.g., reexocytosis. Possibly TRK activity serves in a negative feedback loop to limit albumin endocytosis via a stimulation of reexocytosis.
Insulin-like growth factor I increases renal 1,25(OH)2D3 biosynthesis during low-P diet in adult rats
Authors: Wong M. S. , Sriussadaporn S. , Tembe V. A. , Favus M. J.
Published: December 2017

Dietary P restriction increases renal 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] biosynthesis through stimulation of proximal tubule 25-hydroxyvitamin D3-1 alpha-hydroxylase (1-OHase). Because insulin-like growth factor I (IGF-I) is required for 1-OHase stimulation by low-P diet (LPD) and because 1-OHase stimulation by low-Ca diet and parathyroid hormone is lost with aging, studies were undertaken to determine whether 1-OHase activity during LPD is impaired with age and whether IGF-1 can increase 1-OHase activity in adult rats. Five days of LPD increased in vitro 1-OHase activity in young (97.3 +/- 13.5 vs. 49.7 +/- 6.8 pg.mg protein-1.5 min-1, P < 0.005) but not adult (42.3 +/- 5.37 vs. 41.2 +/- 8.9) rats. In LPD-fed adult rats, recombinant human IGF-I (rhIGF-I, 1.4 mg.kg body wt-1.day-1) for 72 h increased 1-OHase (65.2 +/- 5.88 vs. 95.1 +/- 7.26 pg.mg protein-1.5 min-1, P < 0.005). The results show that the rise in 1-OHase activity during LPD is lost in adult rats and that rhIGF-I can overcome the inhibition and stimulate renal 1-OHase activity to levels observed in young animals. The studies indicate that the age-related loss of 1-OHase activity is reversible.
Involvement of phospholipase A2 in gentamicin-induced rat mesangial cell activation
Authors: Martinez-Salgado C. , Rodriguez-Barbero A. , Rodriguez-Puyol D. , Perez de Lema G. , Lopez-Novoa J. M.
Published: December 2017

The role of the phospholipase A2 (PLA2) activation in the gentamicin (Gent)-induced rat mesangial cell activation has been studied. Gent (10(-5) M) induced a time-dependent mesangial planar cell surface area reduction that was significantly inhibited by the PLA2 inhibitors aristolochic acid (AA) and quinacrine, by the platelet-activating factor (PAF) blocker BN-52021 (BN), and by verapamil. These substances also inhibited Gent-induced [3H]thymidine incorporation into DNA (AA, 504 +/- 20; quinacrine, 555 +/- 66; BN, 1,126 +/- 120; and verapamil, 896 +/- 109; vs. 1,818 +/- 35 cpm/well in cells treated with Gent alone) and the Gent-induced increase in cell number (AA, 20,116 +/- 2,696; quinacrine, 24,687 +/- 1,481; BN, 26,122 +/- 1,016; and verapamil, 27,566 +/- 1,214; vs. 47,486 +/- 1,124 cells/well in cells treated with Gent alone). Gent induced a twofold increase in [3H]acetate incorporation into PAF (27 +/- 3 vs. 12 +/- 2 cpm/microgram protein in control conditions) that was completely blocked by AA, BN, or verapamil. Gent increased thromboxane B2 and prostaglandin E2 (PGE2) production, with both increases inhibited by either AA or verapamil. BN only inhibited the Gent-induced mesangial PGE2 production. In addition, Gent increased PLA2 activity (measured as [3H]arachiodonic acid release, 29,849 +/- 2,151 vs. 20,104 +/- 2,308 cpm/well in basal conditions), an effect that was blocked by AA (11,804 +/- 684 cpm/well). These data suggest a major role for PLA2 activation in Gent-induced mesangial cell contraction, proliferation and prostanoid secretion.
Morphological heterogeneity of renal glomerular arterioles and distinct [Ca2+]i responses to ANG II
Authors: Helou C. M. , Marchetti J.
Published: December 2017

The present study compares cytosolic calcium concentration ([Ca2+]i) responses to angiotensin II (ANG II) of afferent (AA) and efferent arterioles (EA) by taking account of the localization and morphological differences of EA. In outer cortex, 1 nM ANG II induced smaller [Ca2+]i increases in thin EA than in AA[48 +/- 10 (n = 12) vs. 94 +/- 7 nM (n = 11); P < 0.001]. In inner cortex, two types of EA were considered, i.e., thin and muscular ones. The response to 1 nM ANG II was 35% lower in thin than in muscular EA (P < 0.05) but did not differ from that obtained with corresponding AA. In EA of the outer cortex, 1 microM nifedipine, a dihydropyridine blocker of voltage-operated channels (VOCC), did not affect calcium influx, which was suppressed by 1 mM NiCl2, a nonselective calcium entry blocker. In other arterioles, nifedipine inhibited by approximately 40% calcium entry, and remaining influx was blocked by NiCl2. These results indicate a relationship between the magnitude of [Ca2+]i responses, activation of dihydropyridine-sensitive VOCC by ANG II, and the muscular morphology in renal glomerular arterioles. They suggest that ANG II regulates differently local renal microcirculation. They do not, however, support the hypothesis of a greater sensitivity to ANG II of EA compared with the AA of a given nephron.
Downregulation of aquaporin-2 parallels changes in renal water excretion in unilateral ureteral obstruction
Authors: Frokiaer J. , Christensen B. M. , Marples D. , Djurhuus J. C. , Jensen U. B. , Knepper M. A. , Nielsen S.
Published: December 2017

In bilateral ureteral obstruction, both aquaporin-2 (AQP2) levels and urinary concentrating capacity are markedly reduced. However, the mechanisms involved in AQP2 downregulation are unknown. In rats with unilateral ureteral obstruction (UUO) the relative role of intrarenal and systemic factors can be evaluated. Semiquantitative immunoblotting revealed a marked decrease in AQP2 in obstructed kidneys to 23 +/- 7% (n = 9) of sham levels. This downregulation persisted 24 h after release of UUO. Furthermore, there was a significant but less extensive downregulation of AQP2 in the nonobstructed kidneys to 75 +/- 7% (n = 9) of sham levels. Consistent with impairment of collecting duct water reabsorption, free water clearance was greatly elevated in the obstructed kidneys (-2 +/- 1 microliter-min-1.kg-1, determined immediately after release) and only moderately elevated in nonobstructed kidneys (-44 +/- 5 microliters.min-1.kg-1) compared with sham-operated controls (-59 +/- 3 microliters.min-1.kg-1). Also AQP2 mRNA levels were reduced in obstructed kidneys. Immunocytochemistry confirmed the marked decrease in AQP2 expression in obstructed kidneys. In nonobstructed kidneys AQP2 was predominantly found in intracellular vesicles, which together with the reduced expression and elevated free water clearance strongly suggests a role of AQP2 in the observed compensatory diuresis from nonobstructed kidneys. The much lower AQP2 protein and mRNA levels in obstructed vs. nonobstructed kidneys are consistent with intrarenal factors playing a major role for downregulation of AQP2.
Adhesion of hydroxyapatite crystals to anionic sites on the surface of renal epithelial cells
Authors: Lieske J. C. , Norris R. , Toback F. G.
Published: December 2017

Adhesion of microcrystals that nucleate in tubular fluid to the apical surface of renal tubular cells could be a critical step in the formation of kidney stones, 20% of which contain hydroxyapatite (HA). HA crystals bound rapidly to monolayer cultures of monkey kidney epithelial cells (BSC-1 line), used to model the surface of the nephron, in a concentration-dependent manner. Adhesion was blocked by diverse polyanions including heparin, pentosan polysulfate, polyaspartate, and polyglutamate, as well as many found in tubular fluid such as chondroitin sulfates A and B, heparan sulfate, citrate, nephrocalcin, and osteopontin. The polycations cetylpyridinium chloride and cationized ferritin, as well as the cationic dyes alcian blue, polyethylenimine, and brilliant blue R, also inhibited adhesion of HA crystals, as did specific lectins including Triticum vulgaris (wheat germ agglutinin). Anions that inhibited adhesion of crystals appeared to act on the crystal surface, whereas cations and lectins exerted their effect on the cell. Treatment of cells with neuraminidase inhibited binding of crystals, suggesting that anionic cell surface sialic acid residues function as HA crystal receptor sites that can be blocked by specific cations or lectins. Adherence of HA crystals to cells of another renal line (MDCK) and, to 3T3 fibroblasts was also inhibited by heparin, polyaspartate, alcian blue, and T vulgaris lectin, suggesting that these crystals bind to analogous molecules on the surface of different types of cells. These results suggests that the structure, quantity, and/or function of soluble anions in tubular fluid, as well as those anchored to the cell surface, could be critical determinants of HA crystal retention in the nephron and the subsequent formation of a renal stone.
Proximal tubular fluid, kidney, and plasma levels of angiotensin II in hypertensive ren-2 transgenic rats
Authors: Mitchell K. D. , Jacinto S. M. , Mullins J. J.
Published: December 2017

The present study was performed to assess the plasma and kidney levels of angiotensin I (ANG I) and ANG II during prehypertensive (4- to 5-wk old), development (6- to 8-wk old), and maintenance (10- to 12-wk old) phases of hypertension in pentobarbital-anesthetized transgenic rats [TGR; strain name: TGR(mRen2)27] and age-matched transgene-negative Hannover Sprague-Dawley rats (HanSD). At 4-5 wk, mean arterial pressures of TGR were not different from those of HanSD (110 +/- 5 vs. 114 +/- 4 mmHg). However, mean arterial pressures of 6-8 wk and 10-12 wk TGR were higher than those of HanSD (179 +/- 3 vs. 110 +/- 6 and 173 +/- 5 vs. 116 +/- 3 mmHg, respectively; P < 0.01 in both cases). Plasma ANG II levels in 4-5 wk and 6-8 wk TGR were not different from those in HanSD (70 +/- 11 vs. 66 +/- 7 and 60 +/- 8 vs. 48 +/- 12 fmol/ml, respectively). However, plasma ANG II levels in 10-12 wk TGR were higher than those in HanSD (125 +/- 26 vs. 38 +/- 12 fmol/ml, P < 0.01). Kidney ANG II levels in 4-5 wk, 6-8 wk, and 10-12 wk TGR averaged 370 +/- 57, 247 +/- 16, and 562 +/- 86 fmol/g, respectively, values not different from those in HanSD. In additional studies performed on 6-8 wk TGR and HanSD, multiple free-flow proximal tubular fluid collections were obtained and pooled for each animal. In these experiments, mean arterial pressures of the 10 TGR and 7 HanSD studied averaged 178 +/- 9 and 129 +/- 3 mmHg (P < 0.01), respectively. The ANG II concentration in proximal tubular fluid obtained from TGR averaged 5.6 +/- 2.1 pmol/ml (n = 10), a value not different from that in proximal tubular fluid collected from HanSD (5.3 +/- 2.8 pmol/ml, n = 7). However, the ANG II contents of the micropunctured left kidney and the nonmicropunctured right kidney of TGR were lower than those in HanSD (690 +/- 95 vs. 1,374 +/- 210 and 659 +/- 119 vs. 1,303 +/- 196 fmol/g, respectively; P < 0.01 in both cases). The present findings indicate that proximal tubular fluid of hypertensive TGR contains nanomolar concentrations of ANG II and that proximal tubular fluid, plasma and kidney ANG II levels in anesthetized hypertensive TGR are not markedly suppressed compared with those in normotensive control rats.
Urea transporters in kidney and erythrocytes
Authors: Sands J. M. , Timmer R. T. , Gunn R. B.
Published: December 2017

Physiological and molecular data demonstrate that urea transport in kidney and erythrocytes is regulated by specific urea transporter proteins. The urea transporter in the terminal inner medullary collecting duct permits very high rates of regulated transepithelial urea transport and results in the delivery of large amounts of urea into the deepest portions of the inner medulla, where it is needed to maintain a high interstitial osmolality for concentrating the urine maximally. The urea transporter in erythrocytes permits these cells to lose urea rapidly as they ascend through the ascending vasa recta, thereby preventing loss of urea from the medulla. Urea lost from the medulla would decrease concentrating ability by decreasing the efficiency of countercurrent exchange, as occurs in individuals who lack the Kidd antigen. The recent cloning of cDNAs for these two urea transporters has begun to yield new insights into the mechanisms underlying acute and long-term regulation of urea transport and should permit exciting new insights in the future. This review focuses on the physiological and biophysical evidence that established the concept of urea transporters, the subsequent cloning of cDNAs for urea transporters, and the recent integrative studies into the regulation of urea transport. We also propose a new systematic nomenclature and a new structural model for urea transporters.
Intracellular pH regulation in the rabbit cortical collecting duct A-type intercalated cell
Authors: Milton A. E. , Weiner I. D.
Published: December 2017

The A cell may possess multiple H+ transporters, including H(+)-adenosinetriphosphatase (H(+)-ATPase) and H(+)-K(+)-ATPase. The current study examines the relative roles of proton transporters in the A cell by observing their contribution to both basal intracellular pH (pHi) regulation and pHi recovery from an intracellular acid load. CCD were studied using in vitro microperfusion, and pHi was measured in the individual A cell using the fluorescent, pH-sensitive dye, 2',7'-bis(carboxyethyl)-5(6)-carboxy-fluorescein (BCECF). Inhibiting H(+)-ATPase with luminal bafilomycin A1 decreased basal pHi, whereas inhibiting apical H(+)-K(+)-ATPase with either luminal Sch-28080 or luminal potassium removal did not. The predominant mechanism of pHi, recovery from an intracellular acid load was peritubular sodium dependent and peritubular ethylisopropylamiloride (EIPA) sensitive, identifying basolateral Na+/H+ exchange activity. In the absence of peritubular sodium, pHi recovery was inhibited by luminal bafilomycin A1 but not by luminal Sch-28080 addition or by luminal potassium removal. However, when Na+/H+ exchange was inhibited with EIPA, both bafilomycin A1 sensitive and potassium dependent, Sch-28080-sensitive components of pHi recovery were present. Quantitatively, the rate of H(+)-ATPase proton secretion was greater than the rate of H(+)-K(+)-ATPase proton secretion. We conclude that basolateral Na+/H+ exchange is the predominant mechanism of A cell pHi recovery from an intracellular acid load. An apical H(+)-ATPase is the primary apical transporter contributing to A cell pHi regulation. An apical H(+)-K(+)-ATPase, while present, plays a more limited role under the conditions tested.
Reduction in renin release and renal vascular resistance by H(+)-K(+)-ATPase inhibition
Authors: Lin H. , Young D. B.
Published: December 2017

Results from previous experiments in our laboratory suggested that a H(+)-K(+)-adenosinetriphosphatase (H(+)-K(+)-ATPase) was present in vascular smooth muscle. Here we analyzed the effects on regulation of renal vascular function in anesthetized dogs of inhibition of the H(+)-K(+)-ATPase by a highly specific inhibitor, NC-1300-B. The compound was injected intravenously, 15 mg/kg (5.8 x 10(-5) mol wt/kg), into one group of six dogs, whereas saline was given to a control group of eight. Renal function was measured at controlled levels of renal perfusion pressure ranging from 110 to 60 mmHg. Renal blood flow (RBF) was higher in the treated group at all levels of perfusion pressure; at 70 mmHg, the treated group RBF was 5.85 +/- 1.00 ml.min-1.g kidney wt-1, 71% greater than that of the control group. Glomerular filtration rate (GFR) mean values of the two groups were not significantly different at any perfusion pressure level. Renin release was inhibited (P < 0.01) by H(+)-K(+)-ATPase inhibition; at 90 mmHg, the control group mean was 14.3 +/- 4.3 units, 4.47 times greater than the treated group mean of 3.2 +/- 1.6 units. H(+)-K(+)-ATPase inhibition with NC-1300-B causes profound renal vasodilation and inhibition of renin release without affecting regulation of GFR.
EGF receptor ligands are a large fraction of in vitro branching morphogens secreted by embryonic kidney
Authors: Sakurai H. , Tsukamoto T. , Kjelsberg C. A. , Cantley L. G. , Nigam S. K.
Published: December 2017

Much attention has recently focused upon hepatocyte growth factor (HGF) as a potential regulator of epithelial branching morphogenesis. However, since neither the HGF nor c-met "knockout" mice show abnormal kidney branching morphogenesis, we sought to analyze the relative importance of HGF in in vitro branching morphogenesis compared with other factors secreted by the embryonic kidney. Exploiting an assay that employs kidney epithelial cells (murine inner medullary collecting duct, mIMCD3) seeded in collagen cocultured with the embryonic kidney, we found that a tyrosine kinase inhibitor that is highly specific for the epidermal growth factor (EGF) receptor (EGFR), tyrphostin AG1478, inhibited mIMCD3 cell process formation (an early step in branching tubulogenesis) by 40%, whereas high concentrations of neutralizing anti-HGF antibodies had a lesser effect (20% inhibition), suggesting that EGFR ligands account for a larger fraction of branching morphogens secreted by the embryonic kidney than HGF. In addition, when an embryonic epithelial cell line derived from c-met (-/-) mice was cocultured with the embryonic kidney, these c-met (-/-) cells underwent process formation. EGFR ligands but not HGF were able to induce branching tubulogenesis in these cells. All EGFR ligands tested, including EGF, transforming growth factor-alpha, heparin-binding EGF, betacellulin, and amphiregulin, induced mIMCD3 cell tubulogenesis. EGFR ligands caused upregulation of urokinase, urokinase receptor, and matrix metalloprotease-1, and tubulogenesis could be inhibited by the metalloprotease inhibitor 1,10-phenanthroline. Our results support the notion that multiple parallel and potentially redundant growth factor-dependent pathways regulate branching tubulogenesis.
A quantitative description of the Na-K-2Cl cotransporter and its conformity to experimental data
Authors: Benjamin B. A. , Johnson E. A.
Published: December 2017

In epithelia, the Na-K-2Cl cotransporter cooperates with other transport mechanisms to produce transepithelial NaCl transport. The reaction cycle for the Na-K-2Cl cotransporter has been established experimentally, but whether it accounts, quantitatively, for experimental findings has yet to be established. The differential equations that describe the reaction cycle were formulated, and the steady-state solutions were obtained by digital computation. Conformity between this description and the experimental data obtained from the literature was explored by automatic searches for the sets of rate constants that yielded statistical best-fits to the experimental data. Fits were obtained from renal epithelial cell lines, HeLa cells, and duck erythrocytes. Results show that the reaction cycle for the Na-K-2Cl cotransporter conforms well, quantitatively, with the experimental data.
Simultaneous recording of tissue ion content and blood flow in rat renal medulla: evidence on interdependence
Authors: Sadowski Janusz , Kompanowska-Jezierska Elz˙bieta , Dobrowolski Leszek , Walkowska Agnieszka , Ba̧dzyńska Boz˙ena
Published: December 2017

The relationship of renal medullary tissue ion concentration and medullary blood flow (MBF) has never been closely evaluated because of limitations of available measuring methods. In an attempt to overcome this difficulty, an integrated probe was developed for simultaneous recording in rat renal medulla of tissue electrical admittance ( Y), an index of interstitial ion concentration, and tissue perfusion with blood (laser-Doppler method). During spontaneous-selective MBF variations tissue Y showed inverse changes ( r = −0.77, P < 0.001). The inverse correlation of the two variables was also seen after MBF has been reduced (−43%) by indomethacin, 5 mg/kg body wt iv ( r = −0.77, P < 0.01). A modest selective MBF reduction (15%) induced by glibenclamide, an inhibitor of ATP-dependent K channels, did not alter medullary tissue admittance. The data support experimentally the concept that the rate of medullary tissue perfusion with blood is one determinant of interstitial solute concentration; however, changes in the latter were demonstrable only with major alterations of the MBF.
Localization of endothelin-converting enzyme-1 in human kidney
Authors: Pupilli C. , Romagnani P. , Lasagni L. , Bellini F. , Misciglia N. , Emoto N. , Yanagisawa M. , Rizzo M. , Mannelli M. , Serio M.
Published: December 2017

The distribution of endothelin-converting enzyme-1 (ECE-1) mRNA and protein was investigated in human kidney excised because of renal tumors. ECE-1 immunoreactivity was detected by immunohistochemistry throughout the different areas of the kidney in the vascular and tubular structures. In the cortex, ECE-1 immunostaining was present in the endothelial surface of arcuate and interlobular arteries and in arterioles. Weak specific immunoreactivity was present over some proximal and distal tubules. Few endothelial glomerular cells contained ECE-1 protein. In the medulla, ECE-1 immunoreactivity was observed in the vasa recta bundles and capillaries. ECE-1 immunostaining was also detected in the outer and inner medullary collecting ducts and thin limbs of Henle’s loops. Immunohistochemical detection of the von Willebrand factor on adjacent sections confirmed the endothelial nature of the vascular cells that exhibited ECE-1 immunostaining. The distribution patterns of ECE-1 mRNA, investigated by in situ hybridization, appeared similar to that obtained by immunohistochemistry in the cortical and medullary vasculature and in different portions of the nephron. Northern blot and densitometric analyses demonstrated that ECE-1 mRNA levels were quantitatively similar in both the renal cortex and medulla. These results demonstrate that vascular endothelial and tubular epithelial cells in the cortex and medulla of the human kidney synthesize ECE-1, which, in turn, may play an important role in regulating endothelin production in physiological and pathological conditions.
Ureteric bud cells secrete multiple factors, including bFGF, which rescue renal progenitors from apoptosis
Authors: Barasch Jonathan , Qiao Jizeng , McWilliams Glenn , Chen De , Oliver Juan A. , Herzlinger Doris
Published: December 2017

Kidney development requires reciprocal interactions between the ureteric bud and the metanephrogenic mesenchyme. Whereas survival of mesenchyme and development of nephrons from mesenchymal cells depends on signals from the invading ureteric bud, growth of the ureteric bud depends on signals from the mesenchyme. This codependency makes it difficult to identify molecules expressed by the ureteric bud that regulate mesenchymal growth. To determine how the ureteric bud signals the mesenchyme, we previously isolated ureteric bud cell lines (UB cells). These cells secrete soluble factors which rescue the mesenchyme from apoptosis. We now report that four heparin binding factors mediate this growth activity. One of these is basic fibroblast growth factor (bFGF), which is synthesized by the ureteric bud when penetrating the mesenchyme. bFGF rescues three types of progenitors found in the mesenchyme: precursors of tubular epithelia, precursors of capillaries, and cells that regulate growth of the ureteric bud. These data suggest that the ureteric bud regulates the number of epithelia and vascular precursors that generate nephrons by secreting bFGF and other soluble factors.
Identification of a new gene product (diphor-1) regulated by dietary phosphate
Authors: Custer María , Spindler Benjamin , Verrey François , Murer Heini , Biber Jürg
Published: December 2017

Chronic restriction of dietary Pielicits an increased reabsorption of Piin the kidney proximal tubules, which involves a stimulation of apical Na-Picotansport. This adaptation is in part a direct cellular response of which the mechanism(s) are poorly understood. In this study, the impact of dietary Pirestriction on the differential expression of rat kidney cortex mRNAs was visualized to identify gene products regulated by the Pistatus. When kidney cortex mRNAs of rats fed a low- or a high-Pidiet were compared by differential display-polymerase chain reaction (DD-PCR), thirty modulated cDNA bands were observed, of which four were confirmed as being regulated. We focused on one of the upregulated bands, dietary Pi-regulated RNA-1 (diphor-1). A cDNA containing an open reading frame encoding a 52-kDa protein was cloned by library screening. Diphor-1 exhibits a high degree of identity to the Na/H exchanger regulatory factor and to a tyrosine kinase activating protein. Highest expression of diphor-1 mRNA was detected in the kidney (proximal tubules) and in small intestine. Expression experiments showed that diphor-1 specifically increases Na-Picotransport in oocytes of Xenopus laevis coinjected with renal type II Na-Picotransporter cRNA. Further characterizations of diphor-1 will show whether diphor-1 is primarily or secondarily involved in the response to dietary Pi.
Heparin binding domain of insulin-like growth factor binding protein-5 stimulates mesangial cell migration
Authors: Abrass Christine K. , Berfield Anne K. , Andress Dennis L.
Published: December 2017

Insulin-like growth factor I (IGF-I) binding protein-5 (IGFBP-5) is produced by mesangial cells (MCs) and likely functions to modulate glomerular IGF-I activity. Although IGFBP-5 may be inhibitory for IGF-stimulated MC activity, preliminary studies suggested that IGFBP-5 acts directly on MCs. To investigate this further, we evaluated the effects of IGFBP-5 on rat MC migration. We found that the carboxy-truncated fragment, IGFBP-5-(1–169), inhibited IGF-I-stimulated migration, but intact IGFBP-5 simulated migration when IGF-I was not present. Demonstration that125I-labeled IGFBP-5 directly binds to MCs further supports an independent role for IGFBP-5. Because heparin inhibited MC binding of125I-IGFBP-5, we tested the heparin binding peptide, IGFBP-5-(201–218), for stimulatory activity. IGFBP-5-(201–218) stimulated MC migration, and this effect was inhibited by heparin. Because the disintegrin, kistrin, blocked IGF-I-induced migration but not migration induced by IGFBP-5-(201–218), the migratory induction mechanism for the two peptides is different. These data indicate that separate, specific regions of IGFBP-5 are responsible for interactive effects with IGF-I as well as direct effects on MC activity.
Secondary hyperparathyroidism downregulates lipoprotein lipase expression in chronic renal failure
Authors: Vaziri N. D. , Wang X. Q. , Liang K.
Published: December 2017

In a recent study, we found marked downregulation of lipoprotein lipase (LPL) gene expression in fat, myocardium, and skeletal muscle of rats with chronic renal failure (CRF). Recently, hepatic lipase expression was shown to be depressed in CRF rats, and parathyroidectomy (PTX) was shown to reverse this abnormality. This study was undertaken to determine whether downregulation of LPL expression in CRF is due to secondary hyperparathyroidism. Accordingly, LPL mRNA (Northern analysis), protein mass (Western analysis using mouse anti-bovine LPL monoclonal antibody, 5D2), and catalytic activity of the fat pad and soleus muscle were compared in five-sixths-nephrectomized male rats (CRF), parathyroidectomized CRF rats, and sham-operated control animals. The CRF animals exhibited marked hypertriglyceridemia and significant reductions of fat and skeletal muscle LPL mRNA abundance, protein mass, and catalytic activity ( P < 0.05 vs. controls, for all parameters). PTX completely normalized the LPL mRNA, protein mass, and enzymatic activity and partially ameliorated the CRF hypertriglyceridemia ( P < 0.05 vs. CRF group, for all parameters). Thus secondary hyperparathyroidism is responsible for impaired LPL expression in experimental CRF. This abnormality is completely corrected by PTX.
BMP-2 and OP-1 exert direct and opposite effects on renal branching morphogenesis
Authors: Piscione Tino D. , Yager Thomas D. , Gupta Indra R. , Grinfeld Branko , Pei York , Attisano Liliana , Wrana Jeffrey L. , Rosenblum Norman D.
Published: December 2017

The bone morphogenetic proteins, BMP-2 and OP-1, are candidates for growth factors that control renal branching morphogenesis. We examined their effects in embryonic kidney explants and in the mIMCD-3 cell model of collecting duct morphogenesis (mIMCD-3 cells are derived from the terminal inner medullary collecting duct of the SV40 mouse). Osteogenic protein-1 (OP-1), at a dose of 0.25 nM, increased explant growth by 30% ( P = 0.001). In contrast, 100-fold greater concentrations of OP-1 (28 nM) decreased explant growth by 10% ( P < 0.001). BMP-2 was entirely inhibitory (maximum inhibition of 7% at 5 nM, P < 0.0004). In an in vitro model for branching morphogenesis utilizing the kidney epithelial cell line, mIMCD-3, low doses of OP-1 (<0.5 nM) increased the number of tubular structures formed by 28 ± 5% ( P = 0.01), whereas concentrations >0.5 nM decreased that number by 22 ± 8% ( P = 0.02). All concentrations of BMP-2 (0.05–10 nM) were inhibitory (maximum inhibition at 10 nM of 88 ± 3%, P < 0.0001). Stimulatory doses of OP-1 increased tubular length ( P = 0.003) and the number of branch points/structure (3.2-fold increase, P= 0.0005) compared with BMP-2. To determine the molecular basis for these effects, we demonstrated that BMP-2 is bound to mIMCD-3 cells by the type I serine/threonine kinase receptor, ALK-3, and that OP-1 bound to an ∼80-kDa protein using ligand-receptor affinity assays. To demonstrate that OP-1 can exert both stimulatory and inhibitory effects within a developing kidney, embryonic explants were treated with agarose beads saturated with 2 μM OP-1. OP-1 decreased the number of ureteric bud/collecting duct branches adjacent to the beads by 58 ± 1% ( P < 0.0001). In contrast, the number of branches in tissue distal to the OP-1 beads was enhanced, suggesting a stimulatory effect at lower doses of OP-1. We conclude that OP-1 and BMP-2 directly control branching morphogenesis and that the effects of OP-1 are dependent on its local concentration within developing kidney tissue.
Molecular structure and assembly of the tight junction
Authors: Denker Bradley M. , Nigam Sanjay K.
Published: December 2017

Polarized epithelial cells separate two extremely different cellular milieus. The tight junction (TJ) is the most apical component of the junctional complex and serves as the permeability barrier between these environments. The tight junctional complex appears to be a dynamic and regulated structure. Some of its protein components have been identified and include the transmembrane protein occludin. Nontransmembrane proteins on the cytosolic leaflet including ZO-1, ZO-2, cingulin, 7H6, and several unidentified phosphoproteins are also believed to be part of the TJ. Interactions of some of these proteins with the actin cytoskeleton are a major determinant of TJ structure and may also play a role in the regulation of TJ assembly. Recent progress using the “calcium switch” and the “ATP depletion-repletion” model of TJ formation offers new insight regarding how these structures form. TJ biogenesis appears to be regulated, in part, by classic signal transduction pathways involving heterotrimeric G proteins, release of intracellular Ca2+, and activation of protein kinase C. Although many of the details of the signaling pathways have yet to be defined, these observations may provide insight into how TJs form during tubular development. Furthermore, it may be possible to suggest potential therapeutic targets for intervention in a variety of diseases (e.g., ischemia, toxic injury to the kidney and other epithelial tissue) where TJ integrity has been compromised and reassembly is required.
Angiotensin II induces TNF production by the thick ascending limb: functional implications
Authors: Ferreri Nicholas R. , Escalante Bruno A. , Zhao Yejun , An Shao-Jian , McGiff John C.
Published: December 2017

The effects of angiotensin II (ANG II) on tumor necrosis factor-α (TNF) production were determined in freshly isolated tubules from the medullary thick ascending limb (MTAL). ANG II (10−9M) increased the accumulation of TNF mRNA associated with enhanced production of TNF by approximately five- to sixfold. ANG II also increased prostaglandin E2(PGE2) production by the MTAL in a dose-dependent manner and exerted biphasic differential effects on86Rb uptake, depending on the exposure time of the tubules to the peptide and the doses used. Low-dose ANG II (10−11M) increased86Rb uptake by MTAL tubules after a “short-term” (15 min) challenge, whereas uptake was inhibited after a “long-term” (3 h) incubation period. High-dose ANG II (10−6M) inhibited MTAL86Rb uptake, irrespective of incubation time. Uptake of86Rb was inhibited by ∼60% in MTAL tubules that were challenged for 3 h with ANG II. The inhibitory action of ANG II was prevented by eliminating the participation of either TNF with antisera to the cytokine or PGE2by inhibition of cyclooxygenase with indomethacin. We conclude that ANG II regulates TNF production in the MTAL, an interaction that affects86Rb uptake via an eicosanoid-dependent mechanism in this nephron segment.
Evidence suggesting that nitric oxide mediates iron-induced toxicity in cultured proximal tubule cells
Authors: Chen Liguang , Zhang Bao-Hong , Harris David C. H.
Published: December 2017

The potential role of nitric oxide (NO) in iron-induced toxicity was studied in proximal tubule cells in primary culture. NO production ([Formula: see text]/[Formula: see text]) was significantly increased in iron-treated compared with control cells (3.43 ± 0.08 vs. 1.56 ± 0.08 nmol/dish, P < 0.01). NO synthase (NOS) activity was also induced by iron treatment (16.2 ± 2.0 vs. 0.4 ± 0.2 nmol of [Formula: see text]citrulline/mg protein, P < 0.01).l-Arginine, a substrate for NOS, augmented iron-induced NO production and cell damage [lactate dehydrogenase (LDH) leakage], whereas aminoguanidine, an inhibitor of NOS, reduced iron-induced NO production and LDH leakage. Sodium nitroprusside, an exogenous NO donor, induced LDH leakage in a dose-dependent manner, but no effect on lipid peroxidation {malondialdehyde bis[dimethyl acetal] (MDA) production} was observed. Superoxide dismutase and catalase decreased iron-induced MDA production but did not affect LDH leakage or NO production. Dimethylpyrroline N-oxide and desferal prevented MDA production, LDH leakage, and NO production. We concluded that NO is one of the mediators of iron-induced toxicity in proximal tubule cells. NO-induced toxicity is not dependent on lipid peroxidation. This may explain the variable effect of different antioxidants on cell damage and lipid peroxidation in iron-induced cytotoxicity.
Effect of BNP on renal hemodynamics, tubular function and vasoactive hormones in humans
Authors: Jensen K. T. , Carstens J. , Pedersen E. B.
Published: December 2017

The effect of a continuous infusion of human brain natriuretic peptide (BNP) was studied in 48 healthy men. The study was randomized, placebo controlled, and single blind. BNP was given in doses of 1, 2, or 4 pmol ⋅ kg−1⋅ min−1for 60 min, and peak values of BNP in plasma were 38, 85, and 199 pmol/l, giving increments in plasma as seen in heart or renal failure. BNP infusion increased the urinary flow rate and the excretion of sodium in a dose-dependent way. The maximal effects were +65 and +156%, respectively. GFR increased and RPF decreased, the latter in a dose-dependent manner. Blood pressure, heart rate, angiotensin II, and aldosterone were all unaffected by infusion of BNP, whereas a direct inhibition of renin secretion was seen. With the use of the lithium clearance technique, we concluded that the tubular site of action is in both the proximal and distal segments, and the major effect on sodium handling is in the distal parts of the nephron.
Role of AT1angiotensin II receptors in renal ischemic injury
Authors: Kontogiannis Jimmy , Burns Kevin D.
Published: December 2017

The present studies determined the effect of renal ischemia/reperfusion on components of the intrarenal renin-angiotensin system in rats and evaluated the effect of AT1angiotensin (ANG) II receptor blockade on functional recovery. After bilateral renal pedicle occlusion for 60 min, serum creatinine increased, peaking at 72 h, and returned to sham levels after 120 h. ANG II levels in ischemic kidneys were significantly increased 24 h after reperfusion but did not differ from levels in sham kidneys after 120 h. Both renal cortical angiotensinogen mRNA and proximal tubular AT1receptor mRNA were significantly reduced early after reperfusion, returning to sham levels by 120 and 72 h, respectively. AT2ANG II receptor mRNA was undetectable in proximal tubules from sham rats but was consistently present in ischemic rats at 120 h. By histoautoradiography, we found that binding of125I-labeled ANG II was preserved in glomeruli but was decreased in whole cortex and outer medulla early after reperfusion and was completely blocked by the AT1antagonist losartan. Treatment of rats with losartan (25 mg/kg sc daily), starting at the time of reperfusion, had no effect on expression of proliferating cell nuclear antigen in cortical tubules but caused a significant decrease in serum creatinine at 72 h (ischemia: 334 ± 69 μM vs. ischemia + losartan: 135 ± 28 μM; P < 0.025, n = 6). These data indicate that renal ischemic injury causes an early increase in intrarenal ANG II levels, associated with reduction of mRNA for angiotensinogen and proximal tubular AT1receptors, and maintenance of glomerular ANG II binding. Losartan accelerates recovery of renal function, suggesting that activation of AT1receptors impairs glomerular filtration in the postischemic kidney.
Dietary acid increases blood and renal cortical acid content in rats
Authors: Wesson Donald E.
Published: December 2017

We examined whether dietary acid that increases net acid excretion (NAE) without measurably decreasing plasma pH or total CO2(tCO2) causes net acid retention. Control rats drinking distilled H2O were compared with those drinking 40 mM (NH4)2SO4, 40 mM Na2SO4, or drinking Na2SO4and given aldosterone (Na2SO4+ Aldo) to increase NAE without dietary acid. Systemic plasma tCO2 increased in Na2SO4+ Aldo animals, but systemic and stellate vessel plasma tCO2 and pH were not different from control among remaining groups. NAE increased in (NH4)2SO4and Na2SO4+ Aldo but not in Na2SO4animals. Blood base excess (BBE) decreased compared with its respective baseline in (NH4)2SO4(−0.44 ± 0.06 vs. 0.66 ± 0.04 μmol/ml; P < 0.01, paired t-test), increased in Na2SO4+ Aldo (0.79 ± 0.05 vs. 0.61 ± 0.03 μmol/ml; P < 0.04, paired t-test), but was unchanged in Na2SO4animals. Renal cortical H+ content assessed by microdialysis of the renal cortex in situ increased in (NH4)2SO4, decreased in Na2SO4+ Aldo, but was unchanged in Na2SO4animals. The data show that dietary acid sufficient to increase NAE without decreasing plasma tCO2 or pH nevertheless decreases BBE and increases renal cortical acid content, consistent with net acid retention.
ATP releases HSP-72 from protein aggregates after renal ischemia
Authors: Aufricht Christoph , Lu Ellen , Thulin Gunilla , Kashgarian Michael , Siegel Norman J. , Van Why Scott K.
Published: December 2017

The pattern of 72-kDa heat-shock protein (HSP-72) induction after renal ischemia suggests a role in restoring cell structure. HSP-72 activity in the repair and release from denatured and aggregated proteins requires ATP. Protein aggregates were purified from normal and ischemic rat renal cortex. The addition of ATP to cortical homogenates reduced HSP-72, Na+-K+-ATPase, and actin in aggregates subsequently isolated, suggesting that their interaction is ATP dependent. Altering ATP hydrolysis in the purified aggregates, however, had different effects. ATP released HSP-72 during reflow and preserved Na+-K+-ATPase association with aggregates at 2 h but had no effect in controls or at 6 h reflow and caused no change in actin. These results indicate that HSP-72 complexes with aggregated cellular proteins in an ATP-dependent manner and suggests that enhancing HSP-72 function after ischemic renal injury assists refolding and stabilization of Na+-K+-ATPase or aggregated elements of the cytoskeleton, allowing reassembly into a more organized state.
Na-Pi cotransport sites in proximal tubule and collecting tubule of winter flounder (Pleuronectes americanus)
Authors: Elger M. , Werner A. , Herter P. , Kohl B. , Kinne R. K. H. , Hentschel H.
Published: December 2017

Localization of a recently described and cloned Na-Pi cotransport system from flounder was investigated by reverse transcription-polymerase chain reaction (RT-PCR) of microdissected tubules and by immunocytochemistry of kidney of winter flounder. Histological examination showed a small glomerulus, an extremely short proximal tubule PI with a selective affinity to Lens culinaris agglutinin from lentils, and an extensive second proximal tubule segment PII (>90% of proximal tubules), consisting of cells with numerous apical clear vesicles and extensive amplification of basolateral cell membranes. PII merged with the collecting tubule/collecting duct (CT/CD) system without a distal segment. By RT-PCR, PII cells revealed high levels of NaPi-II related RNA; low levels were also observed in CTs. Previously characterized antisera against different epitopes of flounder NaPi-II specifically labeled the basolateral regions of PII and the apical cell portion of CT/CD cells and of some PII cells. These results suggest that tubular secretion of Pi occurs in PII of teleost fish with modulation of urinary Picontent in the subsequent CT/CD system.