bluuebunny/crossref_metadata_2025 huggingface dataset:
Parathyroid hormone inhibits Na(+)-K(+)-ATPase through a cytochrome P-450 pathway
Authors: Ribeiro C. M. , Dubay G. R. , Falck J. R. , Mandel L. J.
Published: December 2017

We have previously shown that parathyroid hormone (PTH)-(1-34) or its analogue PTH-(3-34) inhibits proximal tubule (PT) Na(+)-K(+)-adenosinetriphosphatase (Na(+)-K(+)-ATPase) activity independently of adenosine 3',5'-cyclic monophosphate generation. The present study used PT suspensions to investigate the signaling pathway responsible for this hormonal action. PTH-(1-34) and PTH-(3-34) significantly increased the release of arachidonic acid (AA) compared with control tubules, suggesting activation of phospholipase A2 (PLA2). AA, 10(-6) M, mimicked the inhibition of the pump by 10(-8) M PTH-(3-34), and together were not additive. Eicosatetraynoic acid, 3 microM, a general inhibitor of AA metabolism, blocked the PTH action. Indomethacin, 10 microM, an inhibitor of AA-dependent cyclooxygenase, did not prevent the PTH action, but 2 microM 7-ethoxyresorufin, a cytochrome P-450 inhibitor, prevented the PTH effect. 20-Hydroxyeicosatetraenoic acid (20-HETE), the main product of P-450 metabolism in PT, inhibited Na(+)-K(+)-ATPase activity to the same extent as 10(-8) M PTH-(3-34), was not additive with PTH, and was maximally inhibitory at 10(-7) M. To further investigate the signaling pathway responsible for PTH-activated PLA2, we tested the effect of PTH on cytoplasmic free Ca2+ ([Ca2+]i). PTH-(1-34), 10(-7) M, did not affect [Ca2+]i, although 10(-8) M angiotensin II promoted a Ca2+ transient. Treatment of PT with pertussis toxin (PTX) did not prevent the PTH action.(ABSTRACT TRUNCATED AT 250 WORDS)
Na pump defects in chronic uremia cannot be attributed to changes in Na-K-ATPase mRNA or protein
Authors: Greiber S. , England B. K. , Price S. R. , Medford R. M. , Ebb R. G. , Mitch W. E.
Published: December 2017

We have found abnormalities in Na-K-adenosine-triphosphatase (Na-K-ATPase) function in different tissues of rats with chronic renal failure (CRF). A potential mechanism for these findings is a change in Na-K-ATPase alpha- and/or beta-gene expression. To evaluate this possibility, we compared CRF with pair-fed, sham-operated rats to determine whether chronic uremia changes the expression of Na-K-ATPase alpha 1-, alpha 2-, beta 1-, and beta 2-isoform mRNAs or protein in different types of skeletal muscle, heart, liver, adipose, and kidney tissue. In CRF rats, alpha 1-mRNA in heart tended to be higher and beta 2-mRNA was lower in fat and kidney. There were no other statistically significant differences in isoform mRNAs in tissues of CRF compared with the control rats. Western blot analysis revealed a 38% increase in alpha 1-protein in adipocytes and a 61% decrease in kidney of CRF rats but no significant differences in the amounts of isoform protein in other tissues. Thus, in uremia, posttranslational events or inhibitors of the enzyme are more likely causes of defects in Na-K-ATPase than changes in mRNA or protein abundance.
Macrophage Fc receptor activity modulates mesangial cell proliferation and matrix synthesis
Authors: Mattana J. , Singhal P. C.
Published: December 2017

Substantial in vivo evidence exists to implicate the macrophage (M phi) in modulating mesangial expansion and glomerulosclerosis (GS) following renal injury. We studied in an in vitro system how M phi activation via Fc-receptor-mediated endocytosis, such as occurs in immune complex-mediated disease states, may influence the effect of M phi secretory products (MSP) on mesangial cell (MC) proliferation and matrix synthesis. MSP from M phi incubated with immunoglobulin G (IgG) complexes caused significantly greater (P < 0.001) enhancement of MC [3H]thymidine incorporation compared with MSP from unstimulated M phi or from M phi activated via nonspecific endocytosis (P < 0.001). MSP from M phi incubated with IgG complexes plus the inhibitor of endocytosis cytochalasin B showed an attenuated effect on MC proliferation (P < 0.02). MSP were also found to enhance MC matrix synthesis (P < 0.001). These data demonstrate that MSP can play a direct role in mesangial expansion by increasing both MC proliferation and matrix synthesis. Surface binding alone of IgG complexes may not be sufficient to activate M phi and enhance their mitogenic effect on MC as endocytosis appears to be required. These findings lend in vitro support to a potential role for the M phi in the process of mesangial expansion and GS following renal injury.
Combined K+ and Cl- repletion corrects augmented H+ secretion by distal tubules in chronic alkalosis
Authors: Wesson D. E.
Published: December 2017

NaCl administration enhances HCO3 secretion in the distal tubule of animals with chronic metabolic alkalosis but does not correct the augmented H+ secretion characteristic of this disorder. The present studies used in vivo microperfusion micropuncture to investigate whether combined repletion of K+ and Cl- corrected the augmented H+ secretion in the distal tubule of rats with chronic furosemide-induced metabolic alkalosis. Correction of alkalosis was induced in one group of animals with NaCl and in another group with a similar amount of Cl- as NaCl + KCl for 24 h; each group was compared with animals with maintained alkalosis. Total 24-h urine HCO3 excretion by each Cl(-)-repleted group comprised > or = 70% of the calculated HCO3 loss necessary to induce the respective decrease in plasma total CO2. Alkalotic animals given NaCl+KCl had significantly lower H+ secretion in the distal tubule compared with animals with maintained alkalosis (15.5 +/- 1.2 vs. 34.6 +/- 1.8 pmol.mm-1.min-1, P < 0.01) but those given only NaCl did not (28.3 +/- 1.5 pmol.mm-1.min-1, P = 0.14). H+ secretion was not different among control animals given similar amounts of Na+, K+, and Cl-. These studies demonstrate that Cl- repletion corrects chronic furosemide-induced metabolic alkalosis predominantly by a renal mechanism and that combined administration of K+ and Cl-, but not of Cl- alone, corrects the augmented H+ secretion in the distal tubule in this model of chronic alkalosis.
Activation of acid-secreting intercalated cells in rabbit collecting duct with ammonium chloride loading
Authors: Verlander J. W. , Madsen K. M. , Cannon J. K. , Tisher C. C.
Published: December 2017

In normal rabbit, immunolabeling of intercalated cells in the outer medullary collecting duct (OMCD) demonstrates band 3-like protein in the basolateral plasma membrane (15) and H(+)-adenosinetriphosphatase (H(+)-ATPase) in the apical plasma membrane and cytoplasmic vesicles (30). However, in type A intercalated cells in the cortical collecting duct (CCD), band 3-like protein is located primarily in multivesicular bodies and cytoplasmic vesicles (15), whereas H(+)-ATPase is present in cytoplasmic vesicles only in most intercalated cells (30). In this study, we observed the effect of chronic acid loading on immunolocalization of these transporters in the collecting duct. Adult New Zealand White rabbits received either normal tap water (controls) or 75 mM NH4Cl for 12 days plus eight daily gavages of 2-6 meq NH4Cl/kg body wt. At time of death, mean urine pH of acid-loaded animals was 5.96 (SD = 0.69), vs. 8.47 (SD = 0.07) in controls. Kidneys were fixed by in vivo perfusion and processed for light and electron microscopic immunoperoxidase localization of band 3-like protein and immunogold localization of H(+)-ATPase. In controls, band 3-like protein was largely confined to multivesicular bodies in the majority of positive-staining intercalated cells in the CCD and to the basolateral plasma membrane of intercalated cells in the OMCD. In acid-loaded rabbits, band 3 protein-positive intercalated cells in the inner CCD and the in the outer stripe of the OMCD (OMCDo) were strikingly stellate in form. Basolateral plasma membrane label was intensified, while the number of labeled multivesicular bodies was diminished. Morphometric analysis demonstrated an increase in the amount of basolateral plasma membrane in these intercalated cells. In control rabbits, H(+)-ATPase immunoreactivity in intercalated cells in the CCD was located predominantly over cytoplasmic vesicles. A minority of intercalated cells exhibited basolateral plasma membrane label, and only an occasional cell displayed apical plasma membrane label. In acid-loaded rabbits, H(+)-ATPase immunoreactivity was enhanced along the apical plasma membrane of intercalated cells in the inner CCD, and morphometric analysis demonstrated increased apical plasma membrane in band 3-positive intercalated cells in this segment. These results suggest that rabbits respond to acid loading via enhancement of both electrogenic proton secretion and Cl-/HCO3- exchange in intercalated cells in the inner CCD and the OMCDo.
Interleukin-1 inhibits sodium and water transport in rabbit cortical collecting duct
Authors: Sakairi Y. , Ando Y. , Tabei K. , Kusano E. , Asano Y.
Published: December 2017

Interleukin-1 (IL-1) induces natriuresis and diuresis. In the present study, the effect of basolateral IL-1 on sodium and water transport was examined in the cortical collecting duct (CCD) perfused in vitro. IL-1, 10 pg/ml and 10 ng/ml, inhibited lumen-to-bath sodium flux (JNa, peq.min-1.mm tubule-1), depolarizing transepithelial voltage (Vt) in a time- and dose-dependent manner. The inhibitory effect of 10 ng/ml but not 10 pg/ml IL-1 on Vt and JNa was mitigated by 5 microM indomethacin (IND) in bath. Also, 10 ng/ml IL-1, which did not affect the basal hydraulic conductivity (Lp, x10(-7) cm.atm-1.s-1) by itself, inhibited the hydrosmotic effect of 20 pM basolateral arginine vasopressin, and 5 microM IND abolished this inhibitory effect of 10 ng/ml IL-1. The present study demonstrated direct inhibitory effect of basolateral IL-1 on sodium and water reabsorption in the rabbit CCD. The effect of IL-1 is suggested to be mediated, in part, by a cyclooxygenase metabolite(s).
A simplified device for injection of paraffin wax blockades
Authors: Pallone T. L.
Published: December 2017

Microperfusion of renal tubules and microvessels in vivo requires occlusion of the lumen with a reliable blockade. Paraffin wax serves this purpose but requires specialized hydraulic or mechanical devices to stably hold a micropipette while this solid material is extruded through micron-sized tips. This communication describes the construction of a simple and very inexpensive wax injector from commercially available parts. The rear of an aluminum holder is threaded so that a thumbscrew can be used to push a stiff wire into the lumen of a micropipette. A solder cast of the micropipette lumen is employed as a tight-fitting piston to generate the high pressures required for wax extrusion. Several wax injectors can be made at negligible cost. This device has been used in this laboratory to introduce over 1,000 wax blocks into papillary vasa recta.
Sodium excess aggravates hypertension and renal parenchymal injury in rats with chronic NO inhibition
Authors: Fujihara C. K. , Michellazzo S. M. , de Nucci G. , Zatz R.
Published: December 2017

Chronic nitric oxide (NO) inhibition promotes hypertension and ischemic glomerular injury with only minor glomerulosclerosis (GS). We evaluated the effect of superimposed salt overload, which has been shown to aggravate GS in other models. Fifteen days of treatment with the NO inhibitor N omega-nitro-L-arginine methyl ester (L-NAME) promoted marked arterial and glomerular hypertension, hyporeninemia, and slight renal interstitial expansion, but no glomerular injury. Salt overload slightly exacerbated systemic and glomerular hypertension, promoted albuminuria, interstitial expansion, and glomerular ischemia, and paradoxically reversed hyporeninemia. The angiotensin II inhibitor losartan attenuated glomerular and systemic hypertension and prevented renal injury in these rats. Thirty days of treatment with L-NAME resulted in marked hypertension, hyperreninemia, interstitial expansion, and glomerular ischemia. Concomitant salt overload exacerbated hypertension, interstitial expansion, and ischemia and promoted massive albuminuria, GS, and creatinine retention. Losartan attenuated these effects. Sodium overload aggravates the renal and systemic consequences of chronic NO inhibition by mechanisms that may include paradoxical activation of renin secretion. Interstitial expansion and glomerular ischemia, rather than GS, constitute the chief modalities of renal injury in this model.
Long-term regulation of collecting duct water permeability: freeze-fracture analysis of isolated perfused tubules
Authors: Wade J. B. , Nielsen S. , Coleman R. A. , Knepper M. A.
Published: December 2017

Terminal inner medullary collecting duct (IMCD) segments from water-restricted rats have high osmotic permeabilities despite the absence of vasopressin (AVP). We performed freeze-fracture analysis of individual IMCD segments from such animals following measurement of their water permeability (Pf). IMCD segments from control rats did not have a high Pf in the absence of AVP (88 +/- 15 microns/s) and had a low incidence of E-face intramembrane particle (IMP) clusters (9.6 +/- 2.7 clusters/100 microns 2). Segments exposed to 0.1 nM AVP in vitro had enhanced Pf (1,060 +/- 210 microns/s) and cluster incidence (122 +/- 33 clusters/100 microns 2). IMCD segments isolated from rats dehydrated for 48 h and perfused without AVP exposure had an elevated Pf (605 +/- 71 microns/s) and a high incidence of clusters (166 +/- 36 clusters/100 microns 2). There also was an increase in the number of single particles between clusters in tubules from dehydrated rats (2.5-fold) and in AVP-treated tubules (3.6-fold). These findings indicate that IMP clusters are associated with high water permeability in tubules from dehydrated animals independent of continued AVP exposure. The increased incidence of particles between clusters suggests that water channels may also occur outside of cluster domains.
Role of renal nerves for the expression of renin in adult rat kidney
Authors: Holmer S. , Rinne B. , Eckardt K. U. , Le Hir M. , Schricker K. , Kaissling B. , Riegger G. , Kurtz A.
Published: December 2017

Utilizing a combination of mechanical and chemical unilateral denervation, we have examined the relevance of renal innervation for the expression of renin in kidneys of adult rats. Renal denervation led to a reduction by 57 +/- 4% of renin-containing areas in denervated kidneys as quantitated by morphometry of kidney sections immunoreactive against a polyclonal antirenin antibody. Preprorenin mRNA content in the denervated kidneys fell to 46 +/- 7% of the contralateral innervated kidneys. Treatment of rats with the beta 1-adrenoreceptor antagonist metoprolol (100 mg.kg-1.day-1) for 2 days decreased renal renin mRNA levels to 71% of control levels. Unilateral renal denervation led to a further decrease of renin mRNA levels also in metoprolol-treated animals to 60% of the values found in the contralateral kidneys. Hypotensive hemorrhage led to a 1.4-fold increase of renin mRNA in the kidneys of sham-treated animals. In unilaterally denervated rats renin mRNA increased to levels similar to those in sham-operated animals in both denervated and in contralateral innervated kidneys in response to bleeding. As a consequence, the ratio of abundance of renin mRNA in the denervated to the innervated kidneys rose to 86 +/- 7%. Pretreatment of the animals with metoprolol, on the other hand, prevented the rise of renin mRNA in response to hypotensive hemorrhage. Our findings suggest that in the adult organism renal neural input significantly contributes to the expression of renin under basal conditions, while it appears to be of less importance for stimulation of renin gene expression by severe blood loss.
Protein restriction sequentially induces new urea transport processes in rat initial IMCD
Authors: Isozaki T. , Gillin A. G. , Swanson C. E. , Sands J. M.
Published: December 2017

We reported that feeding rats 8% protein for 4 wk induces two new urea transport processes in initial inner medullary collecting ducts (IMCD); neither is present in rats fed 18% protein. In this study, we measured the time course of induction of these transporters in perfused initial IMCD segments from rats fed 8% protein. Net urea flux was induced after 3 wk, whereas vasopressin-stimulated passive urea permeability (P(urea)) was induced after 2 wk. 8-Bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP) significantly increased P(urea)); adding vasopressin did not increase P(urea) further. In fact, there was no difference in vasopressin-stimulated cAMP production in initial or terminal IMCD segments from rats fed 18% or 8% protein, suggesting that the adaptive response was not due to increased cAMP production. Glucagon did not change cAMP production or P(urea). Specificity of the response was suggested because neither aldose reductase nor sorbitol dehydrogenase activity changed with feeding 8% protein. Thus 1) in initial IMCD segments, vasopressin-stimulated P(urea) is induced after 2 wk, but net urea flux requires 3 wk of feeding 8% protein; 2) this adaptation is not solely due to a higher rate of cAMP production; and 3) specificity of the adaptive response is suggested because activities of enzymes responding to decreases in concentrating ability are unchanged. These results suggest that two distinct urea transporters may be involved in the adaptation to a low-protein diet.
Inhibition of nitric oxide causes exaggerated natriuresis in spontaneously hypertensive rats
Authors: Khraibi A. A.
Published: December 2017

Competitive inhibition of the conversion of L-arginine to nitric oxide by a high dose of NG-monomethyl-L-arginine (L-NMMA) leads to significant increases in arterial pressure, natriuresis, and diuresis in Sprague-Dawley rats. The purpose of this study was to determine the extent of the natriuretic and diuretic responses and the possible role of arterial pressure and renal interstitial hydrostatic pressure (RIHP) elevations with the infusion of L-NMMA in anesthetized spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. Intravenous infusion of L-NMMA (15 mg/kg bolus followed by 500 micrograms.kg-1.min-1 continuous infusion) in WKY rats (n = 8) resulted in a significant increase in mean arterial pressure (MAP, 122 +/- 3 to 152 +/- 2 mmHg), RIHP (4.7 +/- 0.4 to 6.7 +/- 0.5 mmHg), fractional excretion of sodium (FENa, 0.76 +/- 0.21 to 4.74 +/- 0.70%), and urine flow rate (V, 27.7 +/- 5.0 to 161.3 +/- 19.6 microliters/min). Increases in RIHP and sodium and water excretions are abolished when renal perfusion pressure is prevented from increasing with L-NMMA infusion in a group of WKY rats (n = 6). In SHR (n = 6) administration of the same dose of L-NMMA resulted in no significant changes in MAP (172 +/- 3 to 178 +/- 2 mmHg) or RIHP (3.3 +/- 0.4 to 3.5 +/- 0.6 mmHg), but significantly higher increases in FENa (1.19 +/- 0.26 to 7.52 +/- 0.68%) and V (47.1 +/- 10.0 to 248.3 +/- 25.7 microliters/min) compared with WKY rat.(ABSTRACT TRUNCATED AT 250 WORDS)
Role of intracellular Ca2+ in modulation of tight junction resistance in A6 cells
Authors: Jovov B. , Lewis S. A. , Crowe W. E. , Berg J. R. , Wills N. K.
Published: December 2017

The role of intracellular Ca2+ in the development and maintenance of epithelial tight junctional integrity is poorly understood. We assessed tight junctional resistance (Rj) in confluent monolayers of A6 cells that were treated with mucosal amiloride such that the transepithelial resistance (Rt) reflects Rj. Solution Ca2+ concentration [Ca2+] was reduced by ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) addition to the bathing solutions. Reduction of mucosal [Ca2+] to 1 microM or reduction of serosal Ca2+ to 100 microM did not significantly alter Rt. However, a further decrease of serosal Ca2+ to 40 microM caused the resistance to fall to < 12% of the control value. Following restoration of serosal [Ca2+], Rt increased to a new steady-state value within approximately 15 min. The magnitude of recovery of Rt was inversely correlated with the length of time the epithelium was exposed to low serosal [Ca2+]. To further test the effects of asymmetric Ca2+ removal, the serosal [Ca2+] was chelated using EGTA to reduce Rt. When the Ca2+ ionophore A-23187 was subsequently added to the mucosal solution, Rt increased from 20% to 60% of the control level. In addition, cells were loaded with the fluorescent Ca2+ indicator, Calcium Green, and the temporal relationship between changes in Rt and intracellular Ca2+ was determined. Following removal of serosal Ca2+, cell Ca2+ decreased, followed by a decrease in Rt. In contrast, returning Ca2+to the serosal bathing solution resulted in a parallel increase of both Rt and cell [Ca2+]. These data strongly suggest that changes in intracellular [Ca2+] play an important role in the regulation of Rj.
Adenosine A1 receptor-mediated inhibition of vasopressin action in inner medullary collecting duct
Authors: Edwards R. M. , Spielman W. S.
Published: December 2017

We examined the effects of adenosine and adenosine analogues on arginine vasopressin (AVP)-induced increases in osmotic water permeability (Pf; micron/s) and adenosine 3',5'-cyclic monophosphate (cAMP) accumulation in rat inner medullary collecting ducts (IMCDs). When added to the bath, the A1 receptor agonist N6-cyclohexyladenosine (CHA) produced a rapid and reversible inhibition of AVP-stimulated (10 pM) Pf (1,781 +/- 195 to 314 +/- 85 microns/s at 0.3 microM CHA; n = 9). The inhibitory effect of CHA was concentration dependent, with a 50% inhibitory concentration of 10 nM. The effect of CHA was inhibited by prior exposure of IMCDs to the A1 receptor antagonist 1,3-dipropylxanthine-8-cyclopentylxanthine (DP-CPX; 1 microM) or by preincubation with pertussis toxin. CHA had no effect on cAMP-induced increases in Pf. In addition to CHA, adenosine and the nonselective agonist 5'-(N-ethylcarboxamido)-adenosine (NECA) inhibited AVP-dependent Pf by > or = 70%, whereas the A2 receptor agonist CGS-21680 had no effect. Luminal adenosine (0.1 mM) had no effect on basal or AVP-stimulated Pf. CHA, NECA, and adenosine but not CGS-21680 inhibited AVP-stimulated cAMP accumulation in a concentration-dependent manner (50% inhibitory concentrations 0.1–300 nM). The inhibitory effect of CHA on AVP-stimulated cAMP accumulation was attenuated by DPCPX. We conclude that adenosine, acting at the basolateral membrane, inhibits AVP action in the IMCD via interaction with A1 receptors. The inhibition occurs proximal to cAMP generation and likely involves an inhibitory G protein.
Urate transport in brush-border membrane of human kidney
Authors: Roch-Ramel F. , Werner D. , Guisan B.
Published: December 2017

Mechanisms of urate transport were investigated in human renal brush-border membrane vesicles. The imposition of an outwardly directed Cl- gradient, in voltage-clamp and pH-clamp conditions, stimulated [14C]urate uptake. Organic anions, including pyrazinoate (PZA), probenecid, lactate, ketone bodies, succinate, and alpha-ketoglutarate in their monovalent forms, cis-inhibited [14C]urate uptake. The affinity order was PZA> urate > probenecid > other anions. Vesicle preloading with these anions trans-stimulated urate uptake. These observations demonstrate the presence of a urate/anion exchanger. p-Aminohippurate and OH- were not substrates for this exchanger. In the presence of an inwardly directed K+ gradient and valinomycin (intravesicular positive potential) [14C]urate uptake was stimulated. Voltage-sensitive [14C]urate uptake was cis-inhibited by organic anions in the following affinity order: urate > probenecid > PZA. The differences in affinity orders for the urate exchanger and the urate voltage-sensitive transport suggest different pathways for apical transport. The anion exchanger might be the main mechanism involved in urate tubular reabsorption in humans.
The emerging role of transforming growth factor-beta in kidney diseases
Authors: Sharma K. , Ziyadeh F. N.
Published: December 2017

Transforming growth factor-beta (TGF-beta) is a prototypical multifunctional cytokine, with growth being only one of its many functions. Its receptors and actions are germane to almost every cell in the body involved in tissue injury and repair, and its effects are best understood in the context of a cellular response to a changing environment. The broad areas in which TGF-beta plays a crucial role include cell proliferation and extracellular matrix production. TGF-beta is a key regulatory molecule in the control of the activity of fibroblasts and has been implicated in several disease states characterized by excessive fibrosis. In the kidney, TGF-beta promotes tubuloepithelial cell hypertrophy and regulates the glomerular production of almost every known molecule of the extracellular matrix, including collagens, fibronectin, tenascin, and proteoglycans, as well as the integrins that are the receptors for these molecules. Furthermore, TGF-beta blocks the destruction of newly synthesized extracellular matrix by upregulating the synthesis of protease inhibitors and downregulating the synthesis of matrix-degrading proteases such as stromelysin and collagenase. As will be discussed, there is a strong body of in vitro and in vivo evidence suggesting that persistent overproduction of TGF-beta 1 in glomeruli after the acute inflammatory stage of glomerulonephritis causes glomerulosclerosis. TGF-beta may also be important in a variety of other chronic renal disorders characterized by hypertrophy and sclerosis, such as diabetic nephropathy. In this review we will attempt to offer a basic understanding of the cellular and molecular biology of TGF-beta and its receptors, with special focus on the role of the TGF-beta system in the kidney during development, growth, and disease.
Exogenous aldosterone antagonizes distal tubular effects of calcium entry blocker felodipine
Authors: Van Hamersvelt H. W. , Wetzels J. F. , Kloke H. J. , Koene R. A. , Huysmans F. T.
Published: December 2017

Calcium entry blockers, such as felodipine, increase natriuresis without increasing kaliuresis. Since these drugs acutely increase plasma renin activity without a concomitant change of aldosterone, inhibition of such stimulated aldosterone release might explain the absence of kaliuresis. In a randomized crossover study in 12 male volunteers, we compared the effects of simultaneously administered exogenous aldosterone and felodipine with the effects of either felodipine or aldosterone alone. Felodipine infusion decreased blood pressure, increased renal plasma flow, and induced natriuresis without kaliuresis. Aldosterone alone reduced sodium excretion and increased potassium excretion without influencing hemodynamics. Addition of aldosterone to felodipine attenuated its natriuretic effect and induced a kaliuresis, which clearly exceeded the rise of potassium excretion during aldosterone alone [delta% fractional excretion of K+ +42 +/- 12 with felodipine+aldosterone and +7 +/- 8% with aldosterone alone; means +/- SE, P < 0.02]. Our data suggest that felodipine-mediated inhibition of stimulated aldosterone release is essential for the absence of kaliuresis with felodipine. In addition, the pronounced kaliuresis with aldosterone during felodipine is in keeping with increased distal sodium delivery due to a proximal tubular action of felodipine.
Vasoconstriction of outer medullary vasa recta by angiotensin II is modulated by prostaglandin E2
Authors: Pallone T. L.
Published: December 2017

Vasa recta were dissected from outer medullary vascular bundles in the rat and perfused in vitro. Examination by transmission electron microscopy reveals them to be only outer medullary descending vasa recta (OM-DVR). To establish a method for systematic examination of vasoconstriction, OMDVR were perfused at 5 nl/min with collection pressure increased to 5 mmHg. Under these conditions, transmembrane volume flux was found to be near zero, and the transmural hydraulic pressure gradient was found to be < 15 mmHg. Over a concentration range of 10(-12) to 10(-8) M, abluminal application of angiotensin II (ANG II) caused graded focal vasoconstriction of OMDVR that is blocked by saralasin. Luminal application of ANG II over the same concentration range was much less effective. Abluminal application of prostaglandin E2 (PGE2) shifted the vasoconstrictor response of OMDVR to higher ANG II concentrations. PGE2 reversibly dilated OMDVR that had been preconstricted by ANG II. These results demonstrate that OMDVR are vasoactive segments. Their anatomical arrangement suggests that they play a key role in the regulation of total and regional blood flow to the renal medulla.
Endothelin modulates the mitogenic effect of PDGF on glomerular mesangial cells
Authors: Kohno M. , Horio T. , Yokokawa K. , Yasunari K. , Kurihara N. , Takeda T.
Published: December 2017

We showed that two isoforms of platelet-derived growth factor (PDGF), AB and BB, stimulate the secretion of endothelin (ET)-1 from cultured rat mesangial cells. Then, we examined whether PDGF AB and BB stimulate mesangial cell proliferation through the modulation of the endogenous production of ET-1 in these cells. Mitogenesis experiments were assessed by tritiated thymidine incorporation into DNA under highest concentrations (10 ng/ml) of PDGF AB and BB in the presence and absence of anti-ET-1 antiserum or a selective A-type endothelin receptor (ETA receptor) antagonist, BQ-123. PDGF AB and BB potently stimulate thymidine incorporation. This stimulation was significantly attenuated in the presence of either anti-ET-1 antiserum or BQ-123 (10(-7)-10(-5)M). Results suggest that PDGF AB and BB stimulate ET-1 secretion in rat mesangial cells through PDGF beta-receptors, and endogenously produced ET-1 serves to modulate the mitogenic effect of PDGF AB and BB, probably via ETA receptors in these cells.
Rat models for clinical use of insulin-like growth factor I in acute renal failure
Authors: Miller S. B. , Martin D. R. , Kissane J. , Hammerman M. R.
Published: December 2017

Insulin-like growth factor I (IGF-I) improves kidney function and histopathology, when given within a short time (0.5 or 5 h) after an ischemic renal insult in rats. To examine the effects of IGF-I at times that would be more applicable if it were to be used as a therapeutic agent for acute renal failure in humans, we administered IGF-I to rats 24 h after ischemic injury or prior to the induction of injury (pretreatment). In rats that received IGF-I 24 h postischemia, serum creatinine and blood urea nitrogen (BUN) values were significantly lower during the subsequent 6 days than in vehicle-treated rats, and incorporation of 5-bromo-2'-deoxyuridine into tubular cells of the regenerating cortex, measured 48 h postischemia, was enhanced. When examined 7 days postinjury, kidneys from rats that received IGF-I 24 h postischemia were improved in histopathological appearance compared with kidneys from vehicle-treated animals. Whereas creatinine and BUN values were elevated above baseline in both vehicle and IGF-I-pretreated groups, recovery of normal renal function was accelerated by pretreatment with IGF-I. In addition, although we could detect no differences in histopathology at 24 h postinjury, IGF-I pretreatment resulted in more normal renal histology at 7 days postischemic injury and reduced weight loss after injury. Our data show that IGF-I hastens recovery and accelerates regeneration or repair of damaged epithelia following acute renal failure in rats when administered either 24 h postinjury or prior to induction of acute renal failure.(ABSTRACT TRUNCATED AT 250 WORDS)
Stimulation of total CO2 flux by 10% CO2 in rabbit CCD: role of an apical Sch-28080- and Ba-sensitive mechanism
Authors: Zhou X. , Wingo C. S.
Published: December 2017

These studies examine the effect of ambient PCO2 on net bicarbonate (total CO2) absorption by the in vitro perfused cortical collecting duct (CCD) from K-replete rabbits and the mechanism responsible for this effect. Exposure to 10% CO2 increased net bicarbonate flux (total CO2 flux, JtCO2) by 1.8-fold (P < 0.005), and this effect was inhibited by luminal 10 microM Sch-28080, an H-K-adenosinetriphosphatase (H-K-ATPase) inhibitor. In contrast, exposure to 10% CO2 significantly decreased Rb efflux, and this decrement in Rb efflux was blocked by luminal 2 mM Ba, a K channel blocker. Thus transepithelial tracer Rb flux did not increase upon exposure to 10% CO2 as we have observed in this segment under K-restricted conditions. The observation that 10% CO2 increased net bicarbonate absorption without a change in absorptive Rb flux suggested that 10% CO2 increased apical K recycling. To test this hypothesis, we examined whether luminal Ba inhibited the stimulation of luminal acidification induced by 10% CO2. If apical K exit were necessary for full activation of proton secretion, then inhibiting K exit should indirectly affect the stimulation of JtCO2 by 10% CO2. In fact, the effect of 10% CO2 on JtCO2 in the presence of 2 mM luminal Ba was quantitatively indistinguishable from the effect of 10% CO2 on JtCO2 in the presence of 10 microM luminal Sch-28080.(ABSTRACT TRUNCATED AT 250 WORDS)
Regulation of ion content and cell volume in isolated rat renal IMCD cells under hypertonic conditions
Authors: Grunewald J. M. , Grunewald R. W. , Kinne R. K.
Published: December 2017

The adaptive responses of cell volume and intracellular inorganic electrolytes to hypertonicity were investigated in isolated inner medullary collecting duct (IMCD) cells in vitro. Intracellular water and element content were determined simultaneously by a rapid centrifugation technique and electron-probe microanalysis, respectively. In the absence of adenosine 3',5'-cyclic monophosphate (cAMP), cells isolated at 600 mosM (268 mM NaCl) shrank in 900 mosM buffer (418 mM NaCl) within 100 s to 79 +/- 2% of the control volume and showed no regulatory volume increase (RVI). K+ content decreased steadily during the first 5 min to 18% below control. K+ concentration initially increased 25 +/- 2% above control and was normalized after 5 min to 144 +/- 10 mM (n = 6). Na+ and Cl- content increased slowly during the 60-min incubation period; at this point intracellular Na+ and Cl- concentrations were 97 +/- 6 and 59 +/- 7% (n = 6) above control levels (75 +/- 12 mM Na+ and 143 +/- 29 mM Cl-), respectively. In the presence of 10(-4) M 8-bromo-cAMP (8-BrcAMP; used as a substitute for antidiuretic hormone), IMCD cells showed RVI within 5 min. K+ content initially dropped 18 +/- 2% below control and recovered during the next 4 min but was 12 +/- 4% below control after 60 min. K+ concentration showed similar changes. Na+ and Cl- content increased to a larger extent than in the absence of 8-BrcAMP to 95 +/- 10% (Na+) and 47 +/- 6% (Cl-) above control after 60 min, whereas Na+ and Cl- concentrations were the same as without 8-BrcAMP.(ABSTRACT TRUNCATED AT 250 WORDS)
Acute renal effects of neutral endopeptidase inhibition in humans
Authors: Schmitt F. , Martinez F. , Ikeni A. , Savoiu C. , Natov S. , Laborde K. , Lacour B. , Grunfeld J. P. , Hannedouche T.
Published: December 2017

The acute renal effects of neutral endopeptidase 24.11 (E-24.11) inhibition induced by a single oral dose of sinorphan (100 mg) were investigated in 10 healthy normotensive subjects on normal sodium diet. Sinorphan inhibited 90% of E-24.11 activity and increased plasma atrial natriuretic peptide (ANP) and urinary guanosine 3',5'-cyclic monophosphate (cGMP) by 70 and 100%, respectively. Sinorphan increased urinary sodium output by 50% (P < 0.001) and decreased fractional distal reabsorption by 4% (P < 0.01). Sinorphan increased glomerular filtration rate (GFR) and filtration fraction by 10% 1 h after administration and decreased renal plasma flow by 10%. Mean arterial pressure, renal vascular resistance, plasma aldosterone concentration, and renin activity were unmodified. Sinorphan decreased fractional clearance of neutral dextrans over the 34- to 52-A radius range. Applying the changes along with a hydrodynamic isopore with shunt model, sinorphan significantly increased capillary pressure gradient (delta P; 39 +/- 1 vs. 34 +/- 1 mmHg; P < 0.01), whereas ultrafiltration coefficient was unchanged. In conclusion, endopeptidase inhibition increased endogenous plasma ANP and cGMP generation and induced natriuresis through both an increase in filtered load and a decrease in distal tubular reabsorption of sodium. Sinorphan increases GFR, filtration fraction, and delta P, probably through an increase in efferent over afferent arteriolar resistance ratio.
Prostaglandins mediate the defect in AVP-stimulated cAMP generation in immature collecting duct
Authors: Bonilla-Felix M. , John-Phillip C.
Published: December 2017

The immature kidney is characterized by resistance to arginine vasopressin (AVP). In the immature cortical collecting duct (iCCD), AVP-stimulated adenosine 3',5'-cyclic monophosphate (cAMP) generation is decreased, but the mechanisms involved are not known. We examined cAMP production in isolated CCD from immature and mature rabbits. Cellular cAMP levels were measured by radioimmunoassay under basal conditions and after stimulation with hormone. Basal cAMP production in the iCCD was not different from that in the mature CCD (mCCD). In contrast, AVP- and forskolin-stimulated cAMP generation were severely decreased in the iCCD. Inhibition of endogenous prostaglandin production by indomethacin increased AVP-stimulated cAMP generation in the iCCD to levels that were not different from the mCCD. Inhibition of protein kinase C (PKC) by staurosporine and inhibition of Gi by pertussis toxin elicited a mature cAMP response in the iCCD. These data suggest that the defect in AVP-stimulated cAMP production in the iCCD is mediated by prostaglandins via 1) activation of Gi and 2) direct inhibition of the adenylyl cyclase catalytic subunit. In addition, PKC appears to play a significant role.
Regulation of Na(+)-K(+)-2Cl- cotransport activity in rabbit proximal tubule primary culture
Authors: Raat N. J. , Hartog A. , van Os C. H. , Bindels R. J.
Published: December 2017

The presence of Na(+)-K(+)-2Cl- cotransport in rabbit kidney proximal tubule cells in primary culture was demonstrated by bumetanide-sensitive, ouabain-insensitive 86Rb+ uptake studies. After addition of 10 microM bumetanide, 86RB+ uptake was inhibited from 11.1 +/- 0.8 to 1.1 +/- 0.1 nmol.mg protein-1.min-1 under isotonic (300 mosM) conditions. Na(+)-K(+)-2Cl- cotransport activities ranged from 2.2 +/- 0.3 to 13.2 +/- 1.0 nmol.mg protein-1.min-1 depending on the osmolarity of the medium (150-500 mosM). Decreasing extracellular pH to 6.5 inhibited, whereas increasing to 8.5 stimulated, transport at all osmolarities. Decreasing intracellular pH (pHi) by the NH4Cl pulse method showed similar results, suggesting a possible regulatory role of pHi on cotransport activity. Ca(2+)-free medium increased cotransport activity 35 and 20% at iso- and hypertonicity, respectively. At 300 mosM, ionomycin (5 microM) inhibited cotransport by 25%. The combination of forskolin (10 microM) and 3-isobutyl-1-methylxanthine (1 mM) resulted in inhibition of cotransport activity by 38% at hypertonic conditions. Calyculin (1 microM) increased cotransport activity 134 and 128% at 150 and 300 mosM, respectively. In hypertonic medium calyculin did not influence cotransport activity. Okadaic acid (1 microM) had no effect on cotransport activity at all three osmolarities. NaF (10 mM) increased cotransport at all osmolarities tested.
Active lithium transport by rat renal proximal tubule: a micropuncture study
Authors: Leyssac P. P. , Frederiksen O. , Holstein-Rathlou N. H. , Alfrey A. C. , Christensen P.
Published: December 2017

We tested the hypothesis that proximal tubular Li+ reabsorption is due to passive transport. Clearances of [14C]inulin (CIn) and Li+ (CLi), proximal transepithelial electrical potential difference (PD), and tubular fluid-to-plasma Li+ concentration ratios [(TF/P)Li] were measured in anesthetized rats before and after induction of osmotic mannitol diuresis. Late proximal (TF/P)Li was measured after acute intravenous LiCl administration and after addition of LiCl to the diet for 2 days. Glomerular filtration rate (CIn) decreased, whereas CNa and CLi increased during osmotic diuresis. Control early proximal PD was -0.6 mV (lumen negative); late proximal PD (PDLP) was 1.1 mV (lumen positive). PDLP decreased by 1.5 mV to -0.4 mV (lumen negative) after mannitol infusion. Late proximal (TF/P)Li was 1.01 after oral Li+, 1.16 after intravenous Li+ (P < 0.01), and 1.00 during osmotic diuresis. It is concluded that proximal Li+ transfer is distinct from that of Na+, closely parallels proximal water transfer, and involves an active transport mechanism independent of the PD. The data suggest that acute elevation of plasma Li+ concentration may activate a delayed Li+ transport pathway in the proximal convoluted tubule.
PCR localization of C-type natriuretic peptide and B-type receptor mRNAs in rat nephron segments
Authors: Terada Y. , Tomita K. , Nonoguchi H. , Yang T. , Marumo F.
Published: December 2017

The present study was undertaken to investigate the presence of C-type natriuretic peptide (CNP) mRNA and its receptor, natriuretic peptide B-type receptor (ANPR-B) mRNA, in rat renal structures. The microlocalization of mRNAs coding for CNP and ANPR-B was carried out in the rat kidney, using an assay of reverse transcription and polymerase chain reaction (RT-PCR) in individual microdissected renal tubule segments, glomeruli, vasa recta bundle, and arcuate arteries. The PCR signal for CNP was detected in glomerulus, vasa recta bundle, and arcuate artery. The PCR product of ANPR-B was widely present in renal structures. Relatively large amounts of ANPR-B PCR product were detected in glomerulus, vasa recta bundle, arcuate artery, and distal nephron segments. A relatively high concentration of CNP (10(-7) M) stimulated guanosine 3',5'-cyclic monophosphate accumulation in glomerulus, medullary thick ascending limb, cortical collecting duct, and inner medullary collecting duct. Our data demonstrate that CNP can be produced locally in the glomerulus and renal vascular system and that ANPR-B is widely distributed in renal structures. Thus CNP may influence renal function and act in autocrine and paracrine fashions in the kidney.
ATP inhibits the hydrosmotic effect of AVP in rabbit CCT: evidence for a nucleotide P2u receptor
Authors: Rouse D. , Leite M. , Suki W. N.
Published: December 2017

In rabbit renal cortical collecting tubule (CCT), perfused in vitro at 38 degrees C, ATP in concentrations of 10(-7) M and greater inhibits arginine vasopressin (AVP)-stimulated osmotic water permeability (Pf). The P1-purinergic receptor antagonist 8-phenyltheophylline did not attenuate the inhibitory action of ATP, and the poorly hydrolyzable ATP analogue, 5'-adenylylimidodiphosphate (AMP-PNP), mimicked the effect of ATP, arguing against an effect of ATP on a P1 receptor or the "P site." Purinergic receptor agonists inhibited AVP-stimulated Pf with the following rank order efficacy: ATP = ADP = UTP = AMP-PNP = alpha, beta-methylene-ATP > 2-methylthio-ATP >> AMP > adenosine, consistent with the pharmacology of a "nucleotide" receptor subtype. Pertussis toxin pretreatment attenuated the action of 10(-5) and 10(-6) MATP; however, 10(-4) MATP failed to inhibit the hydrosmotic action of forskolin or 8-bromoadenosine 3',5'-cyclic monophosphate. Pretreatment with the phosphodiesterase inhibitor RO20-1724 or indomethacin did not inhibit the action of ATP. Staurosporin and 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester significantly attenuated the inhibition of Pf by lower concentrations of ATP. These data suggest that ATP activates nucleotide receptors on the CCT, mobilizing intracellular Ca2+, which inhibits the hydrosmotic action of AVP.
Expression of mRNA for natriuretic peptide receptor subtypes in bovine kidney
Authors: Yamamoto T. , Feng L. , Mizuno T. , Hirose S. , Kawasaki K. , Yaoita E. , Kihara I. , Wilson C. B.
Published: December 2017

The localization of mRNA for atrial natriuretic peptide (ANP) receptor subtypes (A, B, C) in the kidney was examined. Quantitative analysis of the ribonuclease protection assay showed that the numbers of type A receptor (ANPRA) mRNA were 6.9 x 10(7) in the glomeruli and 10.4 x 10(7) molecules/micrograms of total RNA in the inner medulla, and that of type C receptor (ANPRC) mRNA was 21.7 x 10(7) molecules/micrograms of total RNA in the glomeruli. The type B receptor (ANPRB) mRNA was present in smaller numbers (4.5-4.9 x 10(6) molecules/micrograms of total RNA) evenly throughout the kidney fractions. In situ hybridization demonstrated both ANPRA and ANPRC mRNA selectively in the glomerular epithelial cells and ANPRA mRNA in the collecting duct cells of the inner medulla. ANPRC was also localized on the foot processes of glomerular epithelial cells by immunohistochemistry using a specific antibody against the receptor. These results indicate that ANPRA is the major biologically active receptor for the ANP family of hormones in the kidney and is present selectively on the glomerular epithelial cells and inner medullary collecting duct cells. These cells are presumed to play a role in the regulation of glomerular filtration rate and sodium excretion induced by the family of ANP.
Tyrosine protein phosphorylation in plasma membranes of rat kidney cortex
Authors: Tremblay L. , Beliveau R.
Published: December 2017

The endogenous tyrosine protein kinase activity (TPKA) associated with brush-border (BBM) and basolateral (BLM) membranes of rat kidney cortex was studied with an anti-phosphotyrosine monoclonal antibody (PY20). Distinct major phosphotyrosine-containing proteins were associated with BBM (50, 54, and 120 kDa) and BLM (37, 90, 130, and 170 kDa). For both plasma membranes, tyrosine phosphorylation leveled off after 10 min of incubation. Endogenous phosphotyrosine-specific protein phosphatases (PT-Pases) were active in both membranes, since the presence of sodium vanadate or ammonium molybdate, which are inhibitors of PTPases, was essential to detect endogenous phosphorylation. Substrates and/or tyrosine protein kinases (TPKs) seem to be differently distributed in these plasma membranes, since phosphorylation of endogenous substrates in BLM and BBM was differently sensitive to competitive inhibitors of TPKs. Moreover, insulin- and insulin-like growth factor I-stimulated tyrosine phosphorylation of a 90-kDa substrate was only observed in solubilized BLM proteins. However, similar p60v-src-related TPKs appear to be present in the BBM and BLM, since an antibody raised against p60v-src recognized proteins of 52, 58, and 75 kDa by immunoblotting and could immunoprecipitate the TPKs associated with both plasma membranes. These data provide evidence that the endogenous tyrosine protein phosphorylation observed in the BLM is catalyzed by nonreceptor TPKs as well as receptor TPKs, whereas that observed in the BBM is exclusively due to nonreceptor TPKs.