bluuebunny/crossref_metadata_2025 huggingface dataset:
Physiological processes revealed through an analysis of inborn errors
Authors: Gargus J. J. , Mitas M.
Published: December 2017

To develop the significance of human inborn errors of membrane function in terms of their potential for the elucidation of physiological processes, an overview of the genetics of inherited metabolic disorders is first presented, concisely covering classical Mendelian inheritance and progressing to molecular applications currently being used in the isolation of a number of disease-causing genes. Second, approaches to the isolation of several genes implicated in inherited disorders of membrane function are discussed. Examples are drawn from studies of the Shaker/IA K+ channel mutants of Drosophila and human inborn errors in the low-density lipoprotein receptor and Kidd antigen/urea transporter. These examples illustrate the techniques of "reverse" genetics, restriction fragment-length polymorphism analysis, chromosomal walking, and cDNA library screening with oligonucleotides and antibodies. Finally, the need to develop a physiological functional analysis of the protein structures derived from isolated human disease-causing genes is presented as a necessary direction for future research.
Effect of intrarenal volume expansion on proximal sodium reabsorption
Authors: Haas J. A. , Granger J. P. , Knox F. G.
Published: December 2017

The objective of the present study was to examine the effect of direct expansion of the renal interstitial volume on sodium reabsorption by proximal tubules of superficial and deep nephrons in the absence of systemic extracellular volume expansion. Renal interstitial volume expansion was achieved by injection of 50 microliter of 2.5% albumin in 0.9% saline into the renal interstitium via a polyethylene matrix that was chronically implanted in the interstitium of the rat kidney. Renal interstitial volume expansion increased renal interstitial hydrostatic pressure from 3.8 +/- 0.5 to 6.8 +/- 1.1 mmHg, P less than 0.05 (n = 5 rats). Fractional reabsorption of sodium by the superficial late proximal tubule decreased from 45.7 +/- 5.6 to 34.2 +/- 5.4%, P less than 0.05, and by the proximal tubule and descending limb of Henle's loop of deep nephrons it decreased from 73.9 +/- 2.9 to 57.2 +/- 6.3%, P less than 0.05 (n = 8 rats). Thus expansion of the renal interstitial volume increased renal interstitial hydrostatic pressure and decreased sodium reabsorption by the proximal tubules of superficial and deep nephrons.
Effect of ureteral excision on inner medullary solute concentration in rats
Authors: Pallone T. L. , Jamison R. L.
Published: December 2017

To elucidate the role of the ureter in urinary concentration we studied the effect of partial and complete ureteral excision on urinary osmolality and papillary interstitial osmolality and on sodium, potassium, and urea concentrations in the antidiuretic rat. Urine and descending vasa recta (DVR) plasma samples were obtained by micropuncture of the left renal papilla before (period 1) and 45 min after (period 2) complete (group 1, n = 10 rats) or partial (group 2, n = 10 rats) ureteral excision. Urine osmolality fell from 2,063 +/- 156 (mean +/- SE) to 736 +/- 116 mosmol/kgH2O after complete ureteral excision (P less than 0.01). After partial ureteral excision, the fall was less than half as great, from 2,038 +/- 167 to 1,551 +/- 162 mosmol/kgH2O (P less than 0.01). Vasa recta plasma osmolality decreased from 1,742 +/- 133 to 860 +/- 119 mosmol/kgH2O after complete excision (P less than 0.01) but only from 1,830 +/- 146 to 1,504 +/- 154 mosmol/kgH2O after partial excision (P less than 0.05). Mean DVR plasma sodium concentration declined from 339 +/- 25 to 211 +/- 25 meq/l (P less than 0.01) in group 1 but did not change in group 2 (348 +/- 21 to 347 +/- 28 meq/l). The fraction of DVR plasma osmolality accounted for by urea decreased significantly from 0.59 +/- 0.01 to 0.46 +/- 0.02 mM/(mosmol/kgH2O) in group 1 and from 0.59 +/- 0.02 to 0.49 +/- 0.03 mM/(mosmol/kgH2O) for group 2 (P less than 0.01, both groups). We interpret these findings to show that the remnant ureter moderates the fall in interstitial osmolality at least in part through preservation of the corticomedullary sodium chloride gradient.
Adaptation of distal tubule and collecting duct to increased Na delivery. II. Na+ and K+ transport
Authors: Stanton B. A. , Kaissling B.
Published: December 2017

This study was conducted to determine whether a chronic increase in sodium delivery to, and sodium uptake by, the distal tubule stimulates the transport capacity of this tubular segment. To increase the rate of sodium delivery to the distal tubule, furosemide (12 mg/day) was administered continuously to rats by osmotic minipump for 6 days. Volume depletion was prevented by giving the animals a drinking solution containing 0.8% NaCl and 0.1% KCl. Control animals were given vehicle (0.9% NaCl) by osmotic minipump and tap water to drink. All animals were adrenalectomized and given replacement doses of aldosterone (0.5 microgram.100 g-1.day-1) and dexamethasone (1.2 microgram.100 g-1.day-1) to eliminate changes in adrenal corticosteroid levels. Furosemide was withdrawn 12 h before sodium and potassium transport rates were measured in distal tubules by in vivo microperfusion. We found that increased sodium uptake dramatically enhanced the transport capacity of the distal tubule. Sodium absorption rose from 71.7 to 316.7 pmol.min-1.mm-1, and potassium secretion increased from 30.7 to 73.7 pmol.min-1.mm-1. This response was accompanied by an increase in cell and mitochondrial volume and by proliferation of the basolateral membrane of distal convoluted cells, connecting tubule cells, and principal cells in the distal tubule. We conclude that a chronic increase in sodium uptake by the distal tubule, independent of alterations in extracellular fluid volume and aldosterone levels, stimulates the transport capacity of this nephron segment in part by inducing specific alterations in cell ultrastructure.
Atrial natriuretic factor and salt adaptation in the teleost fish Gila atraria
Authors: Westenfelder C. , Birch F. M. , Baranowski R. L. , Rosenfeld M. J. , Shiozawa D. K. , Kablitz C.
Published: December 2017

It is unknown whether atrial natriuretic factor (ANF) is a mediator of environmental salt tolerance in euryhaline teleost fish. This was investigated in anesthetized Gila atraria, a euryhaline teleost native to springs of pleistocene Lake Bonneville. Plasma levels of immunoreactive (ir) ANF [using anti-human ANF-(99-126) antibodies] in fish obtained from a "fresh water" spring were significantly lower (146 +/- 27) than those in fish obtained from a "1% NaCl" spring (347 +/- 21 pg/ml, P less than 0.01). Electron micrographs of fish atrial and ventricular cardiocytes demonstrated many perinuclear granules, which closely resembled ANF-containing secretory granules seen in mammalian atriocytes. Fish heart extract contained ANF-like material of 3 kDa, which caused a marked diuresis and natriuresis in rats. In a second study, fish from a 1% NaCl spring were kept in tanks. One-third of the fish were maintained in 1% NaCl and one-third each were either adapted to fresh- or high-salt water. After 12 days, plasma irANF levels in 1% NaCl fish were 343 +/- 55, in fresh water fish 213 +/- 20 and in high-NaCl fish 691 +/- 79 pg/ml. These values differed significantly from each other (P less than 0.01). There was a close correlation between plasma irANF levels and both environmental and internal salt concentration. These data suggest that piscine ANF is an as yet unrecognized mediator of salt tolerance in this teleost and that ANF in these animals closely resembles mammalian ANF.
Correlation of structure and function in developing proximal tubule of guinea pig
Authors: Welling L. W. , Evan A. P. , Gattone V. H. , Rollins S. , Saunders R. , Kaskel F. J. , Spitzer A.
Published: December 2017

Unlike the case in rat, rabbit, and other species in which nephron formation continues into the newborn period, nephrogenesis in the guinea pig is completed well before the time of birth. Therefore, the marked increase in proximal tubule reabsorption that occurs during the postnatal period in that species can be attributed entirely to an increase in the absorptive capacity of existing nephron units. The purpose of the present morphometric studies was to correlate that change in proximal tubule function with changes in the apical and basolateral cell membrane surface areas. The apical and basolateral membrane surface densities were found to be approximately equal to each other and to remain constant throughout development. Because of increasing tubule volume, however, both membranes doubled in size between 1 and 3 wk of age and eventually increased by a factor of 3.5 in the adult. At the same time, there was little change in the length of tight function complexes measured in the plane of the luminal surface. Using previously published functional data and tubule length data, a good correlation was found between absolute absorption and total basolateral membrane surface area throughout the entire period of development in proximal tubules. Absorption per unit area of basolateral membrane was approximately 0.55, 0.41, 0.56, and 0.42 X 10(-6) nl.min-1.micron-2 in the 1st, 2nd, and 3rd wk, and in adult animals, respectively, and thus was similar to that reported for proximal tubule segments of adult rabbit and juvenile to adult rat.
Glomerular responses to platelet-activating factor in the rat: role of thromboxane A2
Authors: Badr K. F. , DeBoer D. K. , Takahashi K. , Harris R. C. , Fogo A. , Jacobson H. R.
Published: December 2017

In view of its role as a pro-inflammatory mediator in glomerular injury, we investigated the renal cortical microcirculatory responses to the intrarenal arterial administration of platelet-activating factor (PAF) in the anesthetized euvolemic Munich-Wistar rat. Close arterial administration of PAF led to dose-dependent reductions in renal plasma flow rate (RPF), glomerular filtration rate (GFR), and filtration fraction (FF), in the absence of hypotension or hemoconcentration. Single-nephron (SN) plasma flow rate (QA), SNGFR and SNFF also fell [126 +/- 7 to 101 +/- 6 nl/min (P less than 0.005), 40.6 +/- 2.1 to 21.5 +/- 2.5 nl/min (P less than 0.005), and 0.33 +/- 0.03 to 0.21 +/- 0.03 (P less than 0.025)]. PAF increased pre- and postglomerular arteriolar resistances [2.32 +/- 0.14 to 2.73 +/- 0.19 (P less than 0.005) and 1.32 +/- 0.13 to 1.45 +/- 0.10(10)dyn.s.cm-5 (P less than 0.05)]. PAF infusion also led to a dramatic reduction in the mean value for the glomerular capillary ultrafiltration coefficient, Kf [0.058 +/- 0.012 to 0.020 +/- 0.003 nl.s-1.mmHg (P less than 0.025)]. PAF-induced changes in renal hemodynamics were abolished in the presence of the cyclooxygenase inhibitors, indomethacin and ibuprofen. When administered concomitantly with a thromboxane A2 (TxA2) receptor antagonist, PAF led to significant increases in RPF and GFR. In isolated glomeruli, PAF stimulated the biosynthesis of TxB2 in a dose-dependent manner. Thus PAF depresses rat glomerular function by inducing contraction of arteriolar and mesangial smooth muscle. These effects are likely mediated via the secondary release of TxA2.
Role of renal interstitial hydrostatic pressure in the pressure diuresis response
Authors: Garcia-Estan J. , Roman R. J.
Published: December 2017

The present study examines the role of renal interstitial hydrostatic pressure (RIHP) in the pressure-diuretic and -natriuretic response. The relationships between RIHP, sodium excretion, and renal perfusion pressure (RPP) were determined in antidiuretic and volume-expanded (VE) rats with an intact or decapsulated kidney. RIHP was measured by use of the implanted capsule technique. RIHP increased significantly from 7.5 +/- 0.8 to 12.0 +/- 1.4 mmHg in VE animals and from 3.3 +/- 0.4 to 5.2 +/- 0.7 mmHg in antidiuretic rats after RPP was varied from 100 to 150 mmHg. The pressure-natriuretic response of the antidiuretic rats was blunted compared with that observed in the VE rats. Decapsulation of the kidney in VE rats lowered RIHP and reduced, but did not eliminate, the pressure-natriuretic response. To determine whether this residual response was related to changes in interstitial pressure in the medulla, cortical (CIHP) and medullary interstitial hydrostatic pressures (MIHP) were simultaneously measured in VE rats with an intact or decapsulated kidney. In control rats CIHP and MIHP were similar at all levels of RPP studied. In rats with the renal capsule removed MIHP was higher than CIHP and rose significantly from 6.7 +/- 0.8 to 9.2 +/- 0.8 mmHg when RPP was varied from 100 to 150 mmHg. These results indicate that pressure diuresis and natriuresis is accompanied by changes in RIHP and the response is modulated by the basal level of RIHP. These findings suggest that changes in MIHP may serve as an intrarenal signal for this response.
Cyclosporine nephrotoxicity: blood volume, sodium conservation, and renal hemodynamics
Authors: Devarajan P. , Kaskel F. J. , Arbeit L. A. , Moore L. C.
Published: December 2017

Glomerular filtration rate (GFR) and renal blood flow (RBF) are depressed by chronic cyclosporine treatment. We examined the hypothesis that depletion of extracellular or intravascular fluid volume contributes to the renal vasoconstriction of early cyclosporine nephrotoxicity (CCN). Control and CCN rats were given 10 mg/kg cyclosporine A or vehicle intramuscularly daily for 7 days. The effects of extracellular volume expansion, both acute (AVE, 10% body wt saline) and chronic (CVE, 10% body wt/day saline ip, 10 days including cyclosporine A treatment period), on renal hemodynamics were measured. In CCN, AVE completely normalized GFR and RBF, whereas CVE partially prevented the development of CCN. Renal autoregulatory ability was depressed in CCN but was largely restored by AVE. Intravascular volumes were measured with Evans blue and 51Cr-labeled red cells. Plasma and red cell volumes were reduced by 24% in CCN, indicating circulatory hypovolemia. Acute repletion of the deficit in blood volume by acute administration of an isoncotic solution (1.8 ml/100 g body wt of 5% albumin in isotonic saline) restored GFR and RBF to levels similar to those in control rats. Extracellular fluid volume, estimated as inulin space, was similar in both CCN and control groups. A metabolic study (7 day) showed stool Na loss in CCN to be twice that in controls but both groups remained in sodium balance. We conclude that the renal vasoconstriction produced in the rat by short-term cyclosporine treatment is, at least in part, prerenal in origin and related to the development of circulatory hypovolemia.
Leukotriene D4 inhibits atrial natriuretic factor-dependent cGMP production in rat glomerulus
Authors: Terada Y. , Tomita K. , Yoshiyama N. , Shiigai T. , Marumo F.
Published: December 2017

The effects of leukotriene D4 (LTD4) on guanosine 3',5'-cyclic monophosphate (cGMP) production induced by atrial natriuretic factor (ANF) or sodium nitroprusside (SNP) were investigated in isolated rat glomeruli. First, the isolated glomeruli were preincubated in Krebs-Ringer buffer containing 3-isobutyl-1-methylxanthine for 10 min, then incubated with varying concentrations of ANF, SNP, and LTD4 for 3 min. cGMP content was determined by radioimmunoassay. cGMP production (fmol.glomerulus-1.3 min-1) was not increased by LTD4. cGMP accumulation was increased by ANF (1 microM) and SNP (100 microM) remarkably from 0.19 +/- 0.09 to 3.24 +/- 0.21 (n = 7, mean +/- SE), and from 0.19 +/- 0.09 to 3.67 +/- 0.47 (n = 4), respectively. The increase in cGMP production by ANF was significantly and dose-dependently inhibited by LTD4 (P less than 0.05). Maximum suppression was observed at the concentration of 100 nM (from 3.06 +/- 0.33 to 1.43 +/- 0.09; P less than 0.05). However, LTD4 caused no significant change in the level of cGMP production induced by SNP. Second, particulate or soluble guanylate cyclase from glomeruli were similarly investigated. ANF selectively activated particulate guanylate cyclase and the response was selectively inhibited by LTD4 from 9.07 +/- 1.79 fmol.micrograms-1.3 min-1 (n = 6) to 4.70 +/- 0.70 (n = 6, P less than 0.05). These results suggest the site where LTD4 has effect on cGMP production induced by ANF was the particulate guanylate cyclase system, but not the soluble guanylate cyclase system.
Control of magnesium transport in the thick ascending limb
Authors: Quamme G. A.
Published: December 2017

The mammalian renal thick ascending limb of Henle (TAL) reabsorbs approximately 55% of the filtered magnesium; accordingly, it is the major segment involved in control of renal Mg balance. This review discusses recent evidence for passive and active transport of Mg through the paracellular and transcellular pathways of the TAL, respectively. The properties of these pathways provide a basis for understanding the factors influencing magnesium reabsorption and hormonal controls regulating Mg balance. Normally, Mg absorption is load dependent, whether delivery is altered by increasing luminal Mg concentration or increasing the flow rate into the thick ascending limb. In contrast to the luminal concentration, elevation of peritubular (plasma) Mg and Ca inhibit divalent cation absorption by mechanisms that are not entirely clear. Magnesium reabsorption in the TAL is also closely associated with NaCl absorption so that factors that influence NaCl also affect magnesium. Magnesium deficiency results in a specific and apparently intrinsic cellular adaptation to increase Mg absorption in the TAL. Our greatest understanding of hormonal controls for Mg absorption have come from recent studies using a "hormone deprived" animal model. Parathyroid hormone, calcitonin, glucagon, and antidiuretic hormone act through a common second messenger, adenosine 3',5'-cyclic monophosphate, to limit Mg excretion by enhancing active Mg transport in the TAL. The integrated actions of these hormones and possibly others provide a sensitive means of control. Clearly, recent observations, using in vivo and in vitro microperfusion studies, have altered our thinking of TAL function and indicate that Mg transport is sensitively and specifically controlled within this segment.
Renal potassium adaptation: role of the Na+-K+ pump in rat cortical collecting tubules
Authors: Fujii Y. , Mujais S. K. , Katz A. I.
Published: December 2017

To evaluate the mechanism of renal potassium adaptation we explored several facets of Na+-K+-ATPase function during K loading in rat cortical collecting tubule (CCT). Urinary K excretion increased within the 1st day after initiation of dietary loading to a level matching intake, indicating the early onset of K adaptation. CCT Na+-K+-ATPase activity after 1 and 2 days on the high-K diet was not different from that observed in control animals, whereas it increased to threefold base line after 7 days. Similarly, the specific binding of ouabain was unchanged by 2 days of high-K diet, but was increased on the 7th day. In contrast, there was an early increase in Rb uptake that persisted throughout the period of observation. Acute (60 min) KCl infusion into control rats led to a significant increase in Rb uptake, whereas Na+-K+-ATPase hydrolytic activity remained unchanged. In the isolated perfused kidney, increasing perfusate K led to an increase in CCT Rb uptake similar to that observed in vivo, again without altering the hydrolytic activity of the enzyme. We conclude that K adaptation is an early event developing rapidly after initiation of dietary change. In its early phase the Na+-K+ pump responds by increasing K-transport rate to accommodate the acute homeostatic need; when the requirement for increased K secretion is sustained, a different adaptive pattern emerges characterized by an increase in the number of pumps. The adaptive response to an acute K load appears to be an intrinsic property of the pump independent of hormonal influences.
Effect of acute metabolic acidosis on ammonia metabolism in kidney
Authors: Bogusky R. T. , Dietrich R. L.
Published: December 2017

To understand the mechanisms that initiate the increase in ammonia formation during acute acidosis in kidney [amino-15N]- and [amino-15N]glutamine were used as substrates in isolated perfused rat kidney experiments. Perfused kidneys from methionine sulfoximine-treated rats take up glutamine nitrogen at the rate of 1.50 +/- 0.08 mumol.g kidney-1.min-1 while forming ammonia at a rate of 0.65 +/- 0.09 mumol.g.kidney-1.min-1. Mass spectrometer analysis of the perfusate and urine reveals that ammonia is formed from the amide nitrogen of glutamine at the rate of 0.32 +/- 0.06 mumol.g kidney-1.min-1 and ammonia is formed from glutamate derived from glutamine at the rate of 0.21 +/- 0.04 mumol.g kidney-1.min-1. The balance of the ammonia formed is from unidentified endogenous sources. Addition of HCl to the perfusate to lower perfusate pH increases ammonia formation to 1.09 +/- 0.10 mumol.g kidney-1.min-1. The results exclude a role for the purine nucleotide cycle during acute acidosis and confirm that ammonia formation from glutamate derived from glutamine is via glutamate dehydrogenase. Lowering perfusate pH increases the rate of glutamine deamidation significantly by 0.33 +/- 0.06 mumol.g kidney-1.min-1 and increases the rate of ammonia formation via glutamate dehydrogenase insignificantly by only 0.08 +/- 0.04 mumol.g kidney-1.min-1, whereas ammonia formation from endogenous sources remains unchanged. The results demonstrate that regulation of glutamine deamidation is an important controlling step in ammonia formation during acute metabolic acidosis in kidney.
Axial heterogeneity of rabbit proximal tubule luminal H+ and basolateral HCO3- transport
Authors: Baum M.
Published: December 2017

The present in vitro microperfusion study examined whether the rates of the apical membrane Na+-H+ antiporter and basolateral membrane Na(HCO3)3 symporter vary along the length of the proximal tubule. Initial proximal convoluted tubules (PCT obtained within 0.5 mm from the glomerulus), mid-PCT (PCT without glomerular attachments) and cortical proximal straight tubules were examined. The rate of either the apical or basolateral membrane acidification mechanism was measured from the initial rate of change of intracellular pH after a change in either the luminal or bathing solution. Intracellular pH was measured fluorometrically using the pH-sensitive dye (2',7')-bis(carboxyethyl)-(5,6)-carboxyfluorescein. The rate of bicarbonate exit across the basolateral membrane was examined by imposing either a sodium or bicarbonate gradient. There was no difference between initial and mid-PCT, but the rate of change in cell pH was 30% slower in PST in both series. The rate of sodium-dependent apical proton secretion was examined by changing the sodium concentration in the lumen. There was no difference in sodium-dependent apical proton secretion in initial vs. mid-PCT, but the rate fell by 70% in the proximal straight tubule (PST). These differences were not due to a difference in buffer capacity in these segments. These data are consistent with a homogeneous rate of apical Na+-H+ antiporter and basolateral Na(HCO3)3 activity along the rabbit PCT, but a lower rate in the PST.
Na+-K+-ATPase is an effector protein for protein kinase C in renal proximal tubule cells
Authors: Bertorello A. , Aperia A.
Published: December 2017

Activators of protein kinase C (PKC) inhibit sodium transport in proximal tubules (PT) (M. Baum and S. R. Hays. Am. J. Physiol. 254 (Renal Fluid Electrolyte Physiol. 23): F9-F14, 1988. In this study we have evaluated the effect of PKC activators on the enzyme responsible for active sodium transport, Na+-K+-ATPase. Both endogenous (diacylglycerol, DAG) and exogenous (phorbol esters, PE) activators were used. Enzyme activity was determined in permeabilized single PT segments. In vehicle-incubated PT, Na+-K+-ATPase activity (pmol Pi.mm tubule-1.-1 h) was 1,403 +/- 128. The synthetic DAG, L-alpha-l-oleoyl-2-acetoyl-sn-3-glycerol (10(-4) M) significantly inhibited Na+-K+-ATPase activity to 673 +/- 51, P less than 0.05. The PE-phorbol 12,13-dibutyrate (PDBu), induced a time- and dose-dependent inhibition of Na+-K+-ATPase activity. Inhibition was significant at 15 and maximal at 20 min. Na+-K+-ATPase activity in PT incubated with PDBu was 796 +/- 171 (10(-8) M), 570 +/- 198 (10(-7) M), and 484 +/- 130 (10(-6) M). A PE that does not activate PKC, 4-alpha-phorbol didecanoate, did not inhibit Na+-K+-ATPase activity. PDBu 10(-7) M had no effect on purified Na+-K+-ATPase. Sphingosine (SP), a PKC inhibitor, abolished the inhibitory effect of PDBu (10(-7) M) on Na+-K+-ATPase activity. Dopamine (DA) is a physiological inhibitor of Na+-K+-ATPase activity in PT [A. Bertorello, T. Hokfelt, M. Goldstein, and A. Aperia Am. J. Physiol. 254(Renal Fluid Electrolyte Physiol. 23): F795-F801, 1988].(ABSTRACT TRUNCATED AT 250 WORDS)
Mechanism of neuropeptide Y inhibition of vasopressin action in rat cortical collecting tubule
Authors: Dillingham M. A. , Anderson R. J.
Published: December 2017

Neuropeptide Y (NPY) is a unique 36-amino acid peptide found in high concentrations in brain and peripheral neurons. Although NPY is present in kidney tissue, its role in regulation of renal function has not been delineated. We found that NPY significantly decreases arginine vasopressin (AVP) but not adenosine 3',5'-cyclic monophosphate (cAMP)-stimulated hydraulic conductivity (Lp) in perfused rat cortical collecting tubules (CCT). Either alpha 2-adrenergic receptor blockade (yohimbine) or occupancy (clonidine) prevent NPY inhibition of AVP-stimulated Lp. By contrast, alpha 1-adrenergic receptor blockade with prazosin did not alter NPY inhibition of AVP action. Pretreatment of CCT with pertussis toxin also abolishes NPY inhibition of AVP-stimulated Lp. These data suggest that NPY acts via an alpha 2-adrenergic receptor coupled to a pertussis toxin-sensitive protein to inhibit AVP-stimulated cAMP formation and Lp in the rat CCT.
Ketoacid production in acute respiratory and metabolic acidosis and alkalosis in rats
Authors: LaGrange B. M. , Hood V. L.
Published: December 2017

Metabolic acidosis inhibits and alkalosis enhances ketoacid production in ketotic humans and animals. To compare these effects with those of superimposed respiratory acid-base disturbances, ketone output was evaluated in awake ketotic rats during metabolic (intravenous infusions of HCl or NaHCO3) or respiratory (hyper or hypocapnia) disorders. With decreases in blood pH of 0.1-0.2 units over 3 h, blood ketone concentrations significantly decreased an average of 1.9 mM (metabolic) and 1.1 mM (respiratory) and urinary ketone excretion rates significantly decreased by 1.3 mumol/min (metabolic). With increases in systemic pH, blood ketone concentrations and urinary ketone excretion rates were significantly increased. Changes in blood pH correlated with changes in urinary ketone excretion rates in both metabolic (r = 0.87) and respiratory (r = 0.67) acid-base disturbances. The alterations occurred promptly and were rapidly reversible. These findings indicate that modest changes in systemic pH from metabolic or respiratory acid-base disturbances modify net ketoacid production in ketotic rats, confirm pH control of endogenous acid output as an acid-base regulator, and show that systemic pH, not bicarbonate concentration, mediates the process.
Voltage dependence and barium sensitivity of colonic K secretion in renal failure
Authors: Siga E. L. , Martin R. S. , Ibarra C. , Veron D. , Ibarra F. , Gimenez M. , Parisi M. , Arrizurieta E.
Published: December 2017

Net colonic K secretion (JKnet) is increased in rats and humans with chronic renal failure (CRF). To study whether transepithelial potential difference (PD), active transport forces and/or luminal K conductance play a role in this adaptation, experiments were performed in the colon of control, K-adapted, and CRF rats. Under basal conditions the PD in vivo in CRF was greater than in controls and not different from K-adapted rats. JKnet was comparable in vivo in CRF and K-adapted rats and was greater than in controls. Amiloride (10 microM) reduced PD and JKnet in K-adapted and CRF rats to levels comparable to controls. Under in vitro short-circuited conditions serosal-to-mucosal K flux (JKs----m) in distal colon was significantly increased in K-adapted and CRF animals compared with control, whereas barium caused a significant reduction in JKs----m in all groups of animals. The barium-sensitive component of K secretion was greater, however, in the two experimental groups (-0.2 +/- 0.02 and -0.2 +/- 0.07 in K-adapted and CRF animals, respectively, vs. -0.08 +/- 0.02 microeq.h-1.cm-2 in controls, P less than 0.05). However, luminal barium failed to completely inhibit the increase in K secretion observed in the experimental groups. These data suggest that an increase in PD that results in a rise in luminal negativity, stimulation of active transport, and an increase in barium-sensitive K channels and barium-insensitive pathways in apical membrane of distal colon participate in the mechanism by which net K secretion is increased in the large intestine of subjects with CRF.
Control of bicarbonate transport in collecting tubules from normal and remnant kidneys
Authors: Hamm L. L. , Hering-Smith K. S. , Vehaskari V. M.
Published: December 2017

Bicarbonate transport in the rabbit cortical collecting tubule (CCT) and outer medullary collecting tubule (MCT) in vitro was studied under two types of conditions that were anticipated to alter distal tubule bicarbonate transport: 1) reduction of renal mass, and 2) acid and base loading in vivo. Bicarbonate secretion (both total and acetazolamide sensitive) and bicarbonate reabsorption (studied separately) in CCT and bicarbonate reabsorption in the MCT were not different between tubules from normal and remnant kidneys. The control or conditioning of the separate processes of bicarbonate secretion and bicarbonate reabsorption was also studied in CCT from normal and remnant kidneys. Bicarbonate secretion was not increased by base-loading animals with either normal or remnant kidneys. In contrast, bicarbonate secretion was consistently decreased by acid loading (studied in CCT from remnant kidneys). Bicarbonate reabsorption in the CCT was not altered by acid or base loads given to animals with normal kidneys. And bicarbonate reabsorption in MCT was not increased by acid loading of animals with remnant kidneys. These studies demonstrate that bicarbonate transport (and its conditioning by acid or base loads in vivo) in both CCT and MCT in vitro is not altered by reduction of renal mass in rabbits. The predominant conditioning effect of acid or base loads in vivo is for acid loads to inhibit CCT bicarbonate secretion.
Extra- and intracellular metabolism of platelet-activating factor by cultured mesangial cells
Authors: Neuwirth R. , Ardaillou N. , Schlondorff D.
Published: December 2017

Metabolism of platelet-activating factor (PAF) was examined in cultured mesangial cells from human and rat glomeruli. Human mesangial cells, similar to those from rat, generated PAF after A23187. Both human and rat mesangial cells rapidly hydrolyzed [3H]PAF to lyso-[3H]PAF, and reacylated it into 1-alkyl-2-acyl glycerophosphocholine. Extra- and intracellular metabolism of PAF was then analyzed separately. The majority of [3H]PAF metabolism occurred extracellularly and generated Lyso-[3H]PAF. Intracellularly generated lyso-PAF was rapidly converted to 1-alkyl-2-acyl glycerophosphocholine. Cells prelabeled with [3H]PAF released some [3H]PAF within minutes and then rapidly converted it to lyso-PAF extracellularly. Under control conditions no acetylhydrolase activity was released from cells into the buffer. Acetylhydrolase activity could, however, be released from cell surface into buffer by limited trypsinization, supporting its location on the outer cell membrane. The acetylhydrolase activity was different from phospholipase A2, since phosphatidylcholine was not a substrate for the enzyme. In summary our results show that both rat and human mesangial cells can generate and metabolize PAF. Acetylhydrolase for PAF is present intracellularly, but also and predominantly on the outer cell surface of cells. This ectoenzymatic acetylhydrolase activity may be important in the rapid inactivation of PAF presented to cells, thus protecting cells from deleterious effects of PAF.
Characteristics of ANP-sensitive guanylate cyclase in inner medullary collecting duct cells
Authors: Gunning M. , Silva P. , Brenner B. M. , Zeidel M. L.
Published: December 2017

Our previous characterization of equilibrium binding kinetics of atrial natriuretic peptide (ANP) to the surface of inner medullary collecting duct (IMCD) cells suggested the existence of a single class of high-affinity receptors, functionally coupled to increases in cellular guanosine 3',5'-cyclic monophosphate (cGMP). We have now sought to understand the mode of regulation of this signal transduction system by studying the particulate guanylate cyclase (PGC) enzyme from these cells. PGC activity with and without ANP in membranes, made by homogenization and high-speed centrifugation of suspensions of IMCD cells, was linear up to 5 min and was stimulated by ANP [143 +/- 21 (ANP) vs. 38 +/- 7 (control) pmol/mg protein, n = 3, P less than 0.02]. Vmax increased more than threefold with ANP [130 +/- 19 (ANP) vs. 35 +/- 4 (control) pmol.mg protein-1.min-1, n = 4, P less than 0.005] without significant change in the Km [0.68 +/- 0.17 (ANP) vs. 0.55 +/- 0.08 (control) mM] of the enzyme. Half-maximal stimulation of guanylate cyclase activity occurred at 5 x 10(-10) M ANP, a concentration consistent with our binding data, and with physiological effect. PGC required divalent cations for basal activity and for ANP-stimulated activity; Mg2+ and Mn2+ were most potent in this respect, and Ca2+ was without effect. Both basal and stimulated PGC activities were inhibited in response to changes in the NaCl, but not urea concentration of the assay system. We conclude that binding to the single 120-130 kDa ANP receptor in IMCD cells results in stimulation of PGC by increasing its Vmax and thereby elevating intracellular cGMP, the likely mediator of ANP action in these cells.
Hemodynamic, renal, and hormonal responses to incremental ANF infusions in humans
Authors: Groban L. , Ebert T. J. , Kreis D. U. , Skelton M. M. , Van Wynsberghe D. M. , Cowley A. W.
Published: December 2017

The effects of incremental exogenous alpha-human atrial natriuretic factor (ANF) infusion (10 and 25 ng.kg-1. min-1) on the cardiovascular, renal, and hormonal systems were examined in 22 healthy males. Successive 45-min infusions of ANF increased plasma levels five- and ninefold from a basal 42 +/- 5 pg/ml (P less than 0.01 and P less than 0.001). Hemodynamic responses provoked by ANF consisted solely of progressive reductions in central venous pressure (CVP) (P less than 0.05). Heart rate and mean arterial pressure were unaltered. Plasma renin activity, aldosterone, and vasopressin were not modified by either dose of ANF. However, plasma norepinephrine increased 32% during the 10-ng.kg-1.min-1 infusion (P less than 0.05) and remained elevated during the higher dose of ANF. Renal function was unaltered by the 10-ng.kg-1.min-1 infusion of ANF when compared with base line and placebo responses. The 25-ng.kg-1. min-1 infusion of ANF increased sodium excretion 100% from base line (P less than 0.05), whereas potassium excretion decreased 47% (P less than 0.05). Urine output increased significantly from 7.7 +/- 0.6 to 12.5 +/- 0.7 ml/min (P less than 0.05). These responses were not observed in the placebo group or in an additional group of four volunteers who received a continuous low-dose infusion of ANF (10 ng.kg-1.min-1) for two consecutive 45-min periods. Neither dose of ANF altered creatinine clearance or free water clearance. The data indicate that fivefold elevations (physiological levels) of plasma ANF do not influence renal or hormonal function.(ABSTRACT TRUNCATED AT 250 WORDS)
Glomerular actions of ANG II during reduction of renal artery pressure: a morphometric analysis
Authors: Anderson W. P. , Alcorn D. , Gilchrist A. I. , Whiting J. M. , Ryan G. B.
Published: December 2017

The glomeruli of kidneys subjected to reduced perfusion pressure were examined morphometrically. The left renal artery was narrowed for 30 min in anesthetized dogs with (n = 6) or without (n = 7) converting-enzyme inhibition (captopril). The kidneys were then rapidly fixed by glutaraldehyde perfusion at high flow rate. In a comparison of glomeruli of kidneys subjected to pressure reduction in captopril-treated and untreated dogs, there was significantly greater mesangial contraction in the latter, but morphometric analysis revealed no significant differences in the glomerular surface area available for filtration as evidenced by glomerular capillary volume fractions, surface areas of the filtering basement membrane between epithelial and endothelial cells, or the length densities of the glomerular epithelial slits. In a comparison of the left (pressure reduction) and right (no pressure reduction) kidneys in the captopril-treated dogs, there was no significant effect of reduction of renal perfusion pressure per se on mesangial contraction or glomerular filtration surface area when angiotensin (ANG) II formation was blocked. Thus ANG II caused mesangial cell contraction after renal artery stenosis, but this did not significantly change glomerular ultrafiltration surface area.
Effects of AVP and dDAVP on PGE2 synthesis in superfused cortical collecting tubules
Authors: Jaisser F. , Bugeon L. , Blot-Chabaud M. , Bonvalet J. P. , Farman N.
Published: December 2017

Whereas interactions between antidiuretic hormone (ADH) and prostaglandins (PGs) have been reported in the cortical collecting tubule (CCD), the precise effects of arginine vasopressin (AVP) and its analogue, 1-desamino-8-D-arginine vasopressin (dDAVP) on PGE2 synthesis remain controversial. We examined the dynamic response of PGE2 synthesis to these two analogues in isolated rabbit CCD. Microdissected CCD were superfused, and basal and hormone-induced PGE2 synthesis were determined by enzyme immunoassay. Addition of arachidonic acid (AA) steeply increased basal PGE2 synthesis, in the 0-1 microM-dose range. The presence of AA was necessary to obtain a stimulatory effect of AVP on PGE2 synthesis. AVP induced an immediate, transitory, and dose-dependent stimulation of PGE2 synthesis. A maximal effect was obtained at 10(-8) M; PGE2 synthesis was increased by approximately 150-200% over the basal synthesis. With dDAVP, a very weak response was obtained only at 10(-7) M. From these results, we conclude that PGE2 synthesis in CCD is stimulated by ADH. This effect of ADH does not depend on the V2-receptor pathway and suggests the presence of V1-receptors in CCD.
Role of oxygen free radical species in in vitro models of proximal tubular ischemia
Authors: Borkan S. C. , Schwartz J. H.
Published: December 2017

Lipid peroxidation (LP) of cell membranes by oxygen free radical species (OFRS) during reflow may be a mechanism for progressive proximal tubule injury after ischemia. We examined the relationship between tubule function and an endproduct of LP, malondialdehyde (MDA), in two in vitro models using a suspension of rat proximal tubule segments (PTS). Exposure of PTS to tert-butyl hydroperoxide (tBHP), a potent oxidant, induced dose-dependent decrements in the PTS respiration (QO2) but was associated with a progressive increase in MDA. The relationship between increasing doses of tBHP, QO2, and MDA content, as well as that between MDA and QO2 were highly correlated (r greater than or equal to 0.89, n = 6). Dithiothreitol (1 mM), a sulfhydryl reagent, prevented the tBHP-induced changes in both QO2 and LP. In the second model, 45-min O2 deprivation followed by 30 min of reoxygenation produced similar decrements in QO2 as did 0.75 mM tBHP but without a rise in MDA (n = 9). Mitochondria isolated from ischemic PTS had a 49 +/- 8.2% decrement in state III respiration (P less than 0.006, n = 4) but their MDA content was unchanged. Furthermore, allopurinol, superoxide dismutase, and catalase, agents that reduce tissue OFRS, did not attenuate ischemic tubular injury (n = 9). These results suggest that OFRS do not mediate transient O2 deprivation injury to the proximal tubule.
Theoretical effects of network structure on glomerular filtration of macromolecules
Authors: Remuzzi A. , Deen W. M.
Published: December 2017

A parallel network model was developed to examine the effects of a distribution of capillary lengths on the filtration of macromolecules by the glomerulus. When networks having different distributions of capillary lengths (but similar values of single nephron glomerular filtration rate) were compared, the filtrate-to-plasma concentration ratio (theta s) for neutral macromolecules was found to increase as the vessel lengths became less uniform. Because anatomical studies have demonstrated that the glomerulus is in fact a heterogeneous network, this implies that the conventional modeling assumption of identical capillaries in parallel leads to an overestimation of effective pore sizes. However, simulations employing various pore-size distributions demonstrated that the expected errors in estimating membrane-pore parameters are generally negligible. Furthermore, the dependence of theta s on hemodynamic inputs such as glomerular plasma flow rate and transmembrane hydraulic pressure difference was insensitive to the assumed distribution of capillary lengths. We conclude that models based on dimensionally uniform capillary networks remain valid for interpreting clearance data for macromolecules.
In vivo indicator dilution kinetics of PAH transport in dog kidney
Authors: Silverman M. , Whiteside C. , Lumsden C. J. , Steinhart H.
Published: December 2017

Pages F255–F265: M. Silverman, C. Whiteside, C. J. Lumsden, and H. Steinhart. “In vivo indicator dilution kinetics of PAH transport in dog kidney.” Two important early studies of PAH transport in the kidney were carried out using the pulse-injection, multiple indicator dilution technique (MID). These references were overlooked in our citations. Page F261: the text should read “Probenecid is a known inhibitor of organic ion transport. Chinard et al. (35) noted that probenecid doses of 25 mg/kg body wt, when administered to dogs 20–30 min prior to an MID run, resulted in renal vein outflow curves for hippurate nearly identical to those of simultaneously injected creatinine. Figure 5 illustrates our control and experimental runs using probenecid as an inhibitor of [3H]PAH transport .” Page F263: the text should read “As Chinard showed in the earliest renal MID work on PAH known to us (36), the MID technique as used in this study has the advantage of allowing one to look at events occurring simultaneously at opposing nephron surfaces in the anesthetized dog, under nearly normal physiological conditions (see also Ref. 27).”
Symptomatic hyponatremia in rats: effect of treatment on mortality and brain lesions
Authors: Ayus J. C. , Krothapalli R. K. , Armstrong D. L. , Norton H. J.
Published: December 2017

Hyponatremia was induced in rats over 3 days with dextrose in water and vasopressin. Eighty-five percent of the rats survived for 5 mo after spontaneous correction of mild hyponatremia. However, spontaneous correction of symptomatic hyponatremia (serum sodium less than 120 meq/l) resulted in 32% survival. Rapid correction of symptomatic hyponatremia by hypertonic saline with an absolute change in serum sodium of greater than 14 and less than 25 meq/l in the first 24 h allowed 100% of the rats to survive for 5 mo without brain lesions. On the other hand, correction of symptomatic hyponatremia with an absolute change in serum sodium of greater than 25 meq/l in the first 24 h resulted in 12% survival and development of brain lesions. We conclude that rapid correction of symptomatic hyponatremia improves survival and is safe if the absolute change in serum sodium is between 14 and 25 meq/l in the first 24 h. Increased mortality and brain lesions are associated with an absolute change in serum sodium of greater than 25 meq/l in the first 24 h.
K+ and Rb+ transport by the rabbit CCD: Rb+ reduces K+ conductance and Na+ transport
Authors: Warden D. H. , Hayashi M. , Schuster V. L. , Stokes J. B.
Published: December 2017

We compared transport of K+ and Rb+ across the rabbit cortical collecting duct to gain insight into the mechanisms of K+ secretion. Passive tracer fluxes, active secretory rates, electrophysiological behavior, and the ability of each ion to support Na+-K+-ATPase activity were determined. When active transport was inhibited by amiloride, K+ permeability was twice the Rb+ permeability. Transepithelial conductance (GT) was half as great in solutions where 5 mM Rb+ replaced 5 mM K+. When 4 mM Ba2+ was added to the lumen, both Rb+ and K+ permeability fell to values not different from that expected for paracellular diffusion. The relationship between Ba2+-induced changes in the K+ and Rb+ permeabilities and in the simultaneously measured GT provides strong evidence that K+ transport across the apical membrane is largely, if not exclusively, conductive. We also determined that net K+ secretion is greater than net Rb+ secretion (when each is the abundant ion). The reasons for this difference probably involve several steps in the K+ secretory process and include the following: 1) reduced ATPase activity in the presence of Rb+ (approximately 80%) compared with K+, 2) reduction of Na+ absorption, and 3) partial blockade of the apical (and perhaps basolateral) K+ conductance. Although there were quantitative differences between K+ and Rb+ transport, we found no evidence suggesting that these ions are transported by different mechanisms.
Effect of thyroid hormone on gentamicin accumulation in rat proximal tubule lysosomes
Authors: Cronin R. , Inman L. , Eche T. , Southern P. , Griggs M.
Published: December 2017

T4 decreases gentamicin nephrotoxicity, but the mechanism is unknown. This study investigated whether T4 affects renal processing of gentamicin by examining renal cortical gentamicin accumulation and proximal tubular lysosomal volume after 48 h of gentamicin (30 mg/kg twice daily) in rats (GT4) that had previously received 10 days of T4 (10 micrograms/100 g body wt). The pair-fed control group received only gentamicin. A T4-treated control group and an untreated control group were also pair fed and studied. At the end of the 12-day study the four groups did not differ in food intake, body weight, urine volume, urinary Na+ excretion, or urinary K+ excretion. Plasma creatinine, inulin clearance, and serum clearance of gentamicin were not different among the groups. Gentamicin accumulation was higher in G vs. GT4 (2.1 +/- 0.1 vs. 1.7 +/- 0.1 micrograms/mg protein, P less than 0.01). Blinded, computer-assisted electron microscopic analysis of outer cortical proximal tubules showed that lysosomes occupied a significantly smaller fraction of the cell volume in GT4 (8.1 +/- 0.5 vs. 11.6 +/- 1.1%, P less than 0.02). Thyroxine had no effect on lysosomal volume in non-gentamicin-treated rats. Except for scatter foci of apical vacuolization, proximal tubular cells of both groups were otherwise normal. The results show that chronic T4 administration decreases renal tubular accumulation of gentamicin, and this effect may in part explain its protective effect against gentamicin nephrotoxicity.