bluuebunny/crossref_metadata_2025 huggingface dataset:
Ontogeny of renal mineralocorticoid receptors and urinary electrolyte responses in the rat
Authors: Stephenson G. , Hammet M. , Hadaway G. , Funder J. W.
Published: December 2017

We examined the ontogeny of cytosol mineralocorticoid receptors in renal inner medulla-papilla (IM-PAP) and outer medulla-cortex (OM-CX) and of a biological response to administered corticosteroids (urinary K+/Na+ ratio). Rats at early (7-9 days), intermediate (13-15 days), and late (23-30 days) stages of maturation were used. Young rats were found to be essentially insensitive to aldosterone, in contrast to rats aged 13-15 days and older. Scatchard analysis of IM-PAP and OM-CX cytosol showed equivalent high-affinity aldosterone binding sites at all ages. The affinity of these sites was constant (Kd, 4 degrees C approximately 0.5 nM) and their concentration varied only slightly over maturation. In a series of in vivo nuclear transfer studies, the hyposensitivity to aldosterone in young rats did not seem to be due to a difference in the nuclear binding of aldosterone-receptor complexes. The resistance of the immature (7-9 days) rat kidney to aldosterone thus appears to be a postreceptor phenomenon. The maturational events allowing expression of mineralocorticoid-inducible genes in the kidney remain to be determined.
Salt depletion inhibits cerebral-induced natriuresis in the dog
Authors: Gilmore J. P. , Nemeh M. N.
Published: December 2017

Experiments were carried out in the conscious dog to determine whether renal responses to intracarotid (IC) infusion of hypertonic NaCl are altered in the sodium-depleted state. In the sodium-replete animal, both IC and IV infusion of hypertonic NaCl produced significant increases in sodium excretion and significant decreases in free water clearance. However, both of these renal responses were more rapid in onset with IC infusion. Both IC and IV infusion decreased free water clearance. In the sodium-deplete animal, IC hypertonic NaCl infusion had no effect on sodium excretion but did decrease free water clearance. It is concluded that total body sodium is a determinant of the gain of the cerebral sodium-sensing mechanism and that this mechanism is different from the osmosensitive mechanism.
Isolation of calcium oxalate crystal growth inhibitor from rat kidney and urine
Authors: Nakagawa Y. , Abram V. , Coe F. L.
Published: December 2017

Glycoproteins that slow the growth rate of calcium oxalate monohydrate crystals were purified from rat kidney homogenate and urine by selective heat denaturation (for rat kidney homogenate), DEAE-cellulose column chromatography, and gel permeation column chromatography. Both kidney and urine inhibitors were glycoproteins with an apparent mol wt of 1.4 X 10(4), as determined by high-performance liquid chromatography. They contained gamma-carboxyglutamic acid and a high percentage of aspartic acid and glutamic acid but had few aromatic amino acid residues. Both inhibitors contained fucose, mannose, glucose, galactose, glucosamine, galactosamine, and N-acetylneuraminic acid but no glucuronic acid. Kinetic studies suggest that purified inhibitors bind to calcium oxalate monohydrate seed crystals according to a Langmuir adsorption isotherm with similar dissociation constants of 14 X 10(-8)M for rat urine inhibitor and 8.7 X 10(-8) M for rat kidney inhibitor. The isolation of similar glycoproteins from kidney and urine suggests that urinary crystal growth inhibitor may be produced in the kidneys.
Does calcium couple the apical and basolateral membrane permeabilities in epithelia?
Authors: Chase H. S.
Published: December 2017

Tight epithelial cells actively transport sodium against steep electrochemical gradients. To maintain a constant internal ionic content and volume, they must continuously adjust the passive cation permeabilities of their membranes as the rate of transport varies. There is evidence suggesting that changes in cell calcium may accomplish this task. An increase in cell calcium reduces the luminal sodium permeability and increases basolateral potassium permeability. There is basolateral sodium-calcium exchange through which changes in the rate of sodium transport, reflected in the cell sodium activity, are translated into changes in cell calcium. To demonstrate that cell calcium couples the permeability of the cell membrane requires obtaining measurements of cell calcium activity under physiologically relevant conditions, and, to date, there are no measurements during spontaneous changes in the rate of transport. However, there are measurements following ouabain inhibition of the pump indicating that the increase is sufficient to account for the reduction in luminal sodium permeability observed in intact tissues.
Abnormal pressure-diuresis-natriuresis response in spontaneously hypertensive rats
Authors: Roman R. J. , Cowley A. W.
Published: December 2017

The renal responses to changes in perfusion pressure (RPP) were studied in spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) to determine whether an abnormality in the pressure-diuresis phenomenon could be involved in the resetting of kidney function in hypertension. Differences in the neural and endocrine background to the kidneys were minimized by denervating the kidney and by holding plasma vasopressin, aldosterone, corticosterone, and norepinephrine levels constant by intravenous infusion. In WKY, increasing renal perfusion pressure 54 mmHg, from 103 to 157 mmHg, produced a ninefold increase in urine flow and sodium excretion with no measurable change in renal blood flow (RBF) or glomerular filtration rate (GFR). In SHR, increasing renal perfusion pressure 54 mmHg, from 133 to 187 mmHg, produced only a fourfold increase in urine flow and sodium excretion. GFR, RBF, and peritubular capillary pressures were well autoregulated and were similar in the SHR and WKY at pressures above 110 mmHg. These results indicate the presence of intrinsic changes in the kidney of SHR that enhance fractional tubular reabsorption and impair the pressure-diuresis response. This blunting of the renal pressure-diuresis phenomenon in SHR may represent the functional resetting of the kidney that is necessary for sustained hypertension.
Effects of aldosterone on potassium recycling in the kidney of adrenalectomized rats
Authors: Higashihara E. , Kokko J. P.
Published: December 2017

Recent studies have suggested that potassium, like urea, undergoes medullary recycling. The present cortical and papillary micropuncture studies were designed to confirm the existence of medullary potassium recycling and to determine whether acute infusions of aldosterone affected this phenomenon. Thus, nephron segmental analysis of potassium and sodium transport was conducted in adrenalectomized Munich-Wistar rats and similarly prepared rats that received aldosterone acutely to achieve physiological blood levels. The clearance results demonstrated that aldosterone has an acute antinatriuretic and a kaliuretic effect, whereas the micropuncture studies demonstrated that 1) aldosterone increases potassium secretion between early and late distal tubule punctures; 2) aldosterone causes an increase in delivery of potassium to the papillary collecting duct; 3) aldosterone does not increase potassium secretion across the papillary collecting duct; and 4) aldosterone significantly increases medullary potassium recycling as evidenced by increased quantities of potassium present at the bend of the loop of Henle in response to aldosterone infusions. Thus, the studies confirm the existence of potassium recycling and suggest that this phenomenon is a feedback system that, in part, regulates urinary potassium excretion.
Electrophysiological evidence for Cl secretion in shark renal proximal tubules
Authors: Beyenbach K. W. , Fromter E.
Published: December 2017

The electrophysiology of shark proximal tubules (Squalus acanthias) was investigated using conventional microelectrodes and cable analysis. Under in vitro perfusion with symmetrical Ringer solutions, tubule transepithelial resistance was 36.3 +/- 2.3 omega X cm2 (means +/- SE, n = 44). Other electrophysiological variables varied widely under control conditions. In unstimulated tubules (n = 16) the transepithelial voltage (VT,o) was lumen positive (1.2 +/- 0.2 mV), the basolateral membrane potential (Vbl,x) was -61.3 +/- 1.6 mV, and the fractional resistance of the apical membrane (fRa) was 0.67 +/- 0.02. Spontaneously stimulated tubules (n = 28) had lumen-negative VT,o values (-1.5 +/- 0.4 mV), low Vbl,x values (-41.3 +/- 1.7 mV), and low fRa values (0.30 +/- 0.02). The stimulated state can be induced in unstimulated tubules via treatment with cAMP. Multiple microelectrode impalements in a single tubule revealed epithelial cells sharing similar electrophysiological properties. Selective ion substitutions in the tubule lumen and peritubular bath uncovered an increased Cl conductance in the apical membrane of spontaneously and cAMP-stimulated tubules. Anthracene-9-carboxylic acid tended to reverse the stimulated state, and furosemide hyperpolarized Vbl,x. These results constitute the first evidence for secretory Cl transport in a renal proximal tubule. The electrophysiological responses to ion substitutions, stimulators, and inhibitors are strikingly similar to those of known Cl-transporting epithelia.
An improved bioassay method for determining natriuretic activity of atrial extracts
Authors: Johnson M. D.
Published: December 2017

Extracts of mammalian atrial tissue contain potent natriuretic substances known collectively as atrial natriuretic factor (ANF). The purposes of the present experiments were: 1) to improve on existing bioassay methodology for the detection of ANF activity in atrial extracts, and 2) to compare the ANF activity of atrial extracts prepared from Brattleboro-stain diabetes insipidus (DI) rats with that from normal and water-deprived Long-Evans (LE) rats. A pool of atrial tissue extract (AE) was prepared from normal Sprague-Dawley rats for use as a standard against which unknown AE samples could be compared. Five doses, ranging from 27 to 432 micrograms of AE protein, were assayed in the Sprague-Dawley bioassay rats. Phosphate-buffered saline (PBS) vehicle and ventricular tissue extracts were also assayed. Statistical analysis of several log dose-response relationships revealed that the bioassay response most appropriate in determining relative natriuretic activity of AE was the log of the experimental/control ratio for sodium excretion. The bioassay was used to demonstrate that PBS atrial extracts from both water-deprived LE rats and DI rats contain more natriuretic activity than do PBS atrial extracts from LE rats.
Interactions between adenosine and angiotensin II in controlling glomerular filtration
Authors: Hall J. E. , Granger J. P. , Hester R. L.
Published: December 2017

This study examined interactions between adenosine (Ado) and angiotensin II (ANG II) in controlling renal blood flow (RBF) and glomerular filtration rate (GFR). In six normal dogs, intrarenal Ado infusion (1.0 mumol/min) transiently decreased RBF, but during sustained Ado infusion RBF increased to 122 +/- 7% of control, although GFR remained at 75 +/- 6% of control. Blockade of ANG II formation with the converting enzyme inhibitor SQ 14225 (n = 6) almost abolished the transient decrease in RBF but did not prevent the sustained fall in GFR caused by Ado. When circulating ANG II was held constant by intravenous infusion of SQ 14225 and 20 ng . kg-1 . min-1 of ANG II (n = 6), Ado transiently decreased RBF but the return of RBF was much slower than in normal dogs and RBF did not increase above control. Maintenance of constant circulating ANG II did not prevent Ado-mediated decreases in GFR. These observations suggest that Ado-mediated reductions in GFR do not depend entirely on ANG II and may be due to dilation of efferent arterioles by Ado. However, the transient renal vasoconstriction caused by Ado depends on ANG II, and data from this study suggest that part of the waning constrictor response to Ado is due to suppression of renin secretion and endogenous ANG II formation. In circumstances where high ANG II levels are maintained (i.e., ischemic renal failure), Ado may be capable of causing sustained renal vasoconstriction.
Abnormalities in kallikrein excretion in spontaneously hypertensive rats
Authors: Ader J. L. , Pollock D. M. , Butterfield M. I. , Arendshorst W. J.
Published: December 2017

Experiments were conducted to examine kallikrein excretion in 12-wk-old anesthetized and conscious Okamoto-Aoki spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). Urinary excretion of active and total kallikrein was determined at spontaneous pressures and in response to acute decreases in renal perfusion pressure (RPP; suprarenal aortic constriction). Under basal conditions, active kallikrein excretion was lower in SHR compared with WKY whether conscious (4.4 +/- 1.7 vs. 9.4 +/- 1.3 pkat . min-1 . g kidney wt-1) or anesthetized (5.7 +/- 1.3 vs. 10.4 +/- 1.7). In both anesthetized SHR and WKY, excretion of active and total kallikrein was directly related to RPP after 20 mmHg decrements in RPP and was depressed in SHR at each pressure level. The slope of the relation between active kallikrein excretion and pressure was less in SHR (0.06 +/- 0.01 vs. 0.14 +/- 0.05 pkat . min-1 . g kidney wt-1 . mmHg-1). Thus kallikrein excretion is set at a lower level in SHR and is less responsive to changes in RPP. These strain differences are not related to urine flow, Na excretion, or glomerular filtration rate (GFR) since the values were the same in both strains at each pressure level. Analysis of covariance indicated a significant correlation between active kallikrein excretion and RPP in WKY and SHR, with RPP accounting for 92% of the variation in the kallikrein data. GFR, Na excretion, and urine flow rate were not significantly correlated to active kallikrein and were responsible for only 2% of the variation.(ABSTRACT TRUNCATED AT 250 WORDS)
Prostaglandin inhibitors alter loop segment chloride uptake during furosemide diuresis
Authors: Kirchner K. A.
Published: December 2017

Prostaglandin synthesis inhibition antagonizes the chloruretic effect of furosemide. To identify the site of this interaction, cortical micropuncture was performed in furosemide-treated rats during meclofenamate or indomethacin infusion. Control rats received the vehicle for prostaglandin synthesis inhibition. The fractional excretion of chloride decreased from 10.6 +/- 1.0% in control rats to 6.5 +/- 0.93% in indomethacin-treated rats (P less than 0.01) and to 5.7 +/- 0.7% in meclofenamate-treated rats (P less than 0.001). Mean arterial pressure, inulin clearance, renal blood flow, and single nephron glomerular filtration rate were not different among the groups. Chloride delivery out of the late proximal tubule was also not different among the groups. Early distal tubule chloride delivery was greater (P less than 0.001) in control rats than in either prostaglandin-inhibited group. Late distal chloride delivery was also greater in control rats. Calculated loop segment chloride uptake was 9 +/- 2% in furosemide-treated control rats but 18 +/- 2% in both indomethacin- and meclofenamate-treated rats (P less than 0.05). Distal tubule chloride uptake was greater in control than in prostaglandin-inhibited rats. Thus, the attenuated chloruretic response to furosemide observed in indomethacin- or meclofenamate-treated animals may in part result from increased chloride uptake in the loop segment of superficial nephrons.
Measurement of glomerular filtration rate in conscious unrestrained rats with inulin infused by implanted osmotic pumps
Authors: Jobin J. , Bonjour J. P.
Published: December 2017

A method is described for determining glomerular filtration rate (GFR) in conscious unrestrained rats without extracellular volume expansion. The glomerular marker used was 14C-labeled inulin infused in the minimal fluid volume of 1 microliter/h by intraperitoneally implanted osmotic minipumps. The workability, reproducibility, and precision of the technique was evaluated in sham-operated (sham) and uninephrectomized (UNI-NX) rats for 6 days. In six sham-operated rats the clearance of [14C]-inulin calculated from the plasma value obtained in a blood sample taken at 10 A.M. before food consumption was (means +/- SE): day 1 after pump implantation: 1.38 +/- 0.05; day 2: 1.27 +/- 0.05; day 3: 1.46 +/- 0.16; day 4: 1.45 +/- 0.15; day 5: 1.33 +/- 0.08; day 6: 1.38 +/- 0.11 ml/min. In six UNI-NX rats the corresponding values were: day 1: 0.88 +/- 0.04; day 2: 0.79 +/- 0.05; day 3: 0.91 +/- 0.03; day 4: 0.91 +/- 0.03; day 5: 0.83 +/- 0.06; day 6: 0.87 +/- 0.05 ml/min. When determined on day 2, 3, or 6 at 6 P.M., i.e., at the end of the food consumption period, [14C]inulin clearance was increased in all animals compared with the value determined at 10 A.M. in the fasted state. The use of implanted osmotic minipumps for delivering a glomerular marker such as [14C]inulin allows the determination of GFR in conscious unrestrained rats with normal fluid balance conditions. This method appears to be particularly appropriate for studying the influence of the intake and composition of food on GFR in physiological conditions.
Kinin stimulation of renin release in isolated rat glomeruli
Authors: Beierwaltes W. H. , Prada J. , Carretero O. A.
Published: December 2017

Numerous studies have suggested that a functional relationship exists between the renal kallikrein-kinin and renin-angiotensin systems. We used an in vitro preparation of isolated glomeruli to study the effect of kinins on renin release. Glomeruli were harvested from the dissected cortices of rat kidneys by a passive sieving technique. They were then placed in chambers and superfused with aerated modified Krebs buffer, and the chamber effluent was collected during two sequential 10-min periods. Bradykinin at 10(-6) M increased renin release from 2.17 +/- 0.34 to 4.05 +/- 0.72 ng ANG I/min, and 10(-5) M bradykinin increased renin release from 3.51 +/- 0.64 to 8.94 +/- 1.27 ng ANG I/min. With albumin-modified buffer, 10(-5) M bradykinin stimulated renin release from 7.11 +/- 0.79 to 14.03 +/- 2.36 ng/min. Lys-bradykinin at 10(-5) M also increased renin release from 5.69 +/- 1.11 to 14.50 +/- 2.65 ng ANG I/min. However, neither of the inactive kinin analogues, [Tyr8]bradykinin or des-Arg9-bradykinin, had any effect on renin release. We found that isolated glomeruli were relatively free of kininase activity, in contrast to the high activity found in the kidney slice preparation or in rat plasma. These results suggest that biologically active kinins can stimulate renin release in an in vitro preparation that is free of degradative kininases and independent of hemodynamic and neural influences.
Role of citrate excretion in acid-base balance in diuretic-induced alkalosis in the rat
Authors: Kaufman A. M. , Brod-Miller C. , Kahn T.
Published: December 2017

Studies were performed to assess the role of changes in the excretion of citrate, a metabolic precursor of bicarbonate, in acid-base balance in diuretic-induced metabolic alkalosis. Rats on a low-chloride diet with sodium sulfate added were studied during a base-line period, 3 days of furosemide administration, and 4 days post-furosemide. During the period of furosemide administration, net acid excretion and plasma bicarbonate concentration increased. In the post-furosemide period, net acid excretion remained higher than base line but plasma bicarbonate concentration did not increase further. Citrate excretion was significantly higher in the post-furosemide period than in base line. Studies substituting sodium neutral phosphate or sodium bicarbonate for dietary sodium sulfate demonstrated greater increases in net acid excretion post-furosemide and, again, no increase in plasma bicarbonate concentration during this period. Citrate excretion was greater than in the sulfate group. The increment in citrate excretion was proportional to the base “load,” defined with respect to changes in net acid excretion and/or dietary bicarbonate. Thus, in these studies alterations of base excretion in the form of citrate play an important role in acid-base balance during diuretic-induced metabolic alkalosis.
Renal sodium reabsorption, oxygen consumption, and gamma-glutamyltransferase excretion in the postischemic rat kidney
Authors: Herminghuysen D. , Welbourne C. J. , Welbourne T. C.
Published: December 2017

The effect of 30 min of renal artery occlusion on renal sodium reabsorption, oxygen consumption, and brush border integrity was studied in the immediate 1-h reflow period. Rats were studied using clearance and renal extraction measurements. Glomerular filtration rate and renal plasma flow were measured over four consecutive 15-min periods; renal venous samples were drawn via an indwelling catheter. Renal oxygen consumption (QO2) was calculated from renal blood flow, corrected for urine flow, and from blood oxygen content measured with a fuel cell analyzer. Brush border integrity was assessed by the excretion of the brush border marker enzyme gamma-glutamyltransferase as well as by morphologic observation. Ischemia induced a 10-fold rise in fractional sodium excretion in the initial 0- to 15-min period, rose to 20-fold during the subsequent two periods, 15-45 min, and then returned to the initial reflow period level. The progressive deterioration of renal function with reflow could not be attributed to an increase in the filtered Na+ load. Rather, Na+ reabsorption appeared to be related to the presence of intact brush borders at 0-15 min, their removal from the luminal surface between 15 and 45 min, and their return at 60 min of reflow. Renal QO2 was coupled to Na+ reabsorption in the initial 15-min and final 45- to 60-min reflow periods. However QO2 was significantly increased over the control level at 30-45 min of reflow. The results point to a significant role of brush border uptake in the development of functional impairment following renal ischemia and suggest that the associated rise in renal O2 consumption may be coupled to the reparation of this organelle.
Effects of vasopressin on phosphoinositides and prostaglandin production in cultured mesangial cells
Authors: Troyer D. A. , Kreisberg J. I. , Schwertz D. W. , Venkatachalam M. A.
Published: December 2017

We studied the effects of vasopressin on phospholipid metabolism in mesangial cells and the temporal relationship of these changes to prostaglandin production. The changes included: 1) increased breakdown of phosphatidylinositol (PI), 2) increased breakdown of diphosphoinositide (PI-P) and triphosphoinositide (PI-P2), 3) an increase in the mass of diglyceride and phosphatidic acid, 4) increased synthesis, first of PI-P and PI-P2, then phosphatidic acid, and, finally, PI, and 5) increased water-soluble inositol phosphates. Vasopressin treatment resulted in a significant increase (90%) in the mass of phosphatidic acid and a smaller (13%) decline in the mass of PI. Changes in diglyceride were seen following 45 s of treatment with vasopressin. Alterations of phosphoinositide metabolism were seen as early as 45 s and continued for up to 5 h following hormone exposure. By contrast, prostaglandin production declined after 30 min. These observations on vasopressin-stimulated metabolism in cultured mesangial cells may provide a basis for an understanding of the functional changes that follow hormone exposure.
Renal handling of aluminum in the rat: clearance and micropuncture studies
Authors: Burnatowska-Hledin M. A. , Mayor G. H. , Lau K.
Published: December 2017

Previous uncertainty regarding glomerular ultrafilterability (UF) of aluminum has limited the definition of renal Al handling. Glomerular micropuncture was therefore performed in hydropenic Munich-Wistar rats infused with AlCl3 to achieve plasma (P) Al levels between 2 and 10 mg/liter. Glomerular fluid, P, and urine Al concentrations were measured by flameless atomic-absorption spectrophotometry. UFA1 was inversely correlated with PA1 [%UFA1 = 10.3 - 8.4 (log PA1), r = -0.90, P less than 0.01]. When this equation was used to calculate the filtered load (FLA1), A1 excretion (UA1V, ng/min) in simultaneously collected samples was found to be a direct function of FLA1 [UA1V = 5.7 + 0.37 (FLA1), r = 0.93, P less than 0.01]. Fractional excretion (FE) of A1 was 39.4 +/- 4.2% in these hydropenic experiments (FENa = 0.3 +/- 0.1%). We next evaluated the tubular handling of A1 (using these UF data) during step-wise extracellular fluid volume expansion with isotonic saline (2.5, 5.0, 7.0, and 7.0% body wt) and during the infusion of increasing doses (2.7, 5.3, 8.0, and 8.0 mg X kg-1 X h-1) of furosemide as urinary losses were quantitatively replaced. The natriuresis produced by volume expansion (FENa = 1.0, 3.0, 8.4, and 7.9%) and furosemide (FENa = 4.2, 6.0, 6.6, and 6.7%) were comparable. At similar FLA1, 7% volume expansion but not furosemide (at any dose) increased UA1V (240 and 95 ng/min, respectively, vs. 116 ng/min in hydropenia) and FEA1 (84.5 and 29.4 vs. 37.4%, respectively). These data indicate that at pharmacological PA1 levels, less than 8.4% of PA1 is ultrafilterable, suggesting extensive plasma protein binding.(ABSTRACT TRUNCATED AT 250 WORDS)
Contractile properties of cultured glomerular mesangial cells
Authors: Kreisberg J. I. , Venkatachalam M. , Troyer D.
Published: December 2017

The glomerular mesangium is composed of matrix material and at least two cell types. One is a bone marrow-derived phagocyte and the other is a smooth muscle-like cell. The phagocytic cell represents approximately 3-7% of the total mesangial cell population. The other, more abundant, cell type appears to be contractile and therefore has been proposed to play a role in regulating the surface area for filtration, one component of the ultrafiltration coefficient, Kf. In this review we discuss the contractile properties of cultured mesangial cells as well as the phenotypic alterations that lead to loss of isotonic contraction after prolonged culture.
Cl-HCO3 exchange in choroid plexus: analysis by the DMO method for cell pH
Authors: Johanson C. E. , Parandoosh Z. , Smith Q. R.
Published: December 2017

[14C]DMO distribution was used to measure steady-state intracellular pH (pHi) and [HCO3]i in adult rat choroid plexus (CP) incubated in synthetic cerebrospinal fluid (CSF) for 30 min. In controls at 37 degrees C, mean pHi (6.95 at PCO2 = 30 mmHg) was close to corresponding in vivo values; and [HCO3]i/[HCO3]csf, i.e., rHCO3, was 0.37. At normal [HCO3]csf = 18 mM, cell HCO3 was accumulated threefold above electrochemical equilibrium (as estimated from Em = -50 mV). [HCO3]i decreased proportionally with [HCO3]csf, as the latter was altered from 47 to 9 mM; in severe extracellular acidosis [( HCO3]csf = 3.7 mM), [HCO3]i was not reduced further and so rHCO3 rose to 0.66. Except in low [HCO3]csf, acetazolamide and ouabain (10(-4) M) caused small depletion of cell HCO3. 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid lowered [HCO3]i by 60%, thus decreasing rHCO3 (0.16) and rCl (0.25) to values close to estimated equilibrium distribution (0.15). Substitution of CSF Cl with isethionate resulted in marked alkalinization of pHi when [Cl]csf was depleted to 12 mM. Augmented PCO2 associated with temperature reduction to 15 degrees C elevated [HCO3]i, thereby increasing rHCO3 (to 0.66) as well as rCl. Anion distribution ratios indicate heteroanion exchange in mammalian CP.
Peritubular uptake and brush border transport of 28Mg by flounder renal tubules
Authors: Renfro J. L. , Shustock E.
Published: December 2017

The uptake of 28Mg by isolated renal tubules of winter flounder, Pseudopleuronectes americanus, was studied by compartmental analysis. Two phases of uptake were seen in steady-state conditions. The slow-exchanging compartment was 46% of the total Mg content, and uptake into this compartment was saturable (Km = 0.36 mM) and inhibited by 10 mM CaCl2, dinitrophenol, and ouabain but not by furosemide, Na-free medium, or cytochalasin B. The fast-exchanging compartment was 5% of the total Mg, and uptake into this compartment showed sigmoid saturation kinetics (K 1/2 = 1.62 mM). The fast uptake rate was inhibited by dinitrophenol, ouabain, Na-free medium, 10 mM CaCl2, and furosemide but stimulated by cytochalasin B. 28Mg efflux from brush border membrane vesicles (BBMV) was stimulated by both an inside positive electrical potential generated by 100 mM KCl (out greater than in, in the presence of valinomycin) and by 100 mM NaCl (out greater than in). The latter effect was still present when the membrane electrical potential was short-circuited with 100 mM KCl (in = out) in the presence of valinomycin. Uptake of Mg by BBMV was stimulated by reversal of the aforementioned gradients. Both uptake and efflux were stimulated by A23187. BBMV uptake was inhibited by 10 mM CaCl2 and unaffected by furosemide. The relationship of electrical gradient-driven and Na gradient-driven Mg transport to the Mg secretory function of these tubules is discussed.
Transport of citrate across renal brush border membrane: effects of dietary acid and alkali loading
Authors: Jenkins A. D. , Dousa T. P. , Smith L. H.
Published: December 2017

Dietary acid or alkali loading was given to rats by providing 150 mM NH4Cl or 150 mM NaHCO3 in place of drinking water for 6 days; control animals received 150 mM NaCl. After 6 days, the citrate clearance was 0.04 +/- 0.01 ml/min (mean +/- SE) in the acid-loaded group, 0.9 +/- 0.1 ml/min in the control group, and 2.5 +/- 0.2 ml/min in the alkali-loaded group. At the end of the experiment, the rats were killed, and the Na+ gradient-dependent (Nao+ greater than Nai+) citrate uptake (pmol/mg protein) was measured in brush border membrane (BBM) vesicles prepared from each group. At 0.3 min, the [14C]citrate uptake was 198 +/- 8 pmol/mg protein (mean +/- SE) in the acid-loaded group, 94 +/- 16 pmol/mg protein in the control group, and 94 +/- 13 pmol/mg protein in the alkali-loaded group. The rate of Na+-independent (NaCl in medium replaced by KCl) [14C]-citrate uptake by BBM vesicles was the same for acid-loaded, control, and alkali-loaded animals. Thus, the increased capacity of the proximal tubular BBM to transport citrate from the tubular lumen into the cell interior may be an important factor that contributes to decreased urinary citrate in the presence of metabolic acidosis induced by chronic dietary acid loading.
Effect of insulin on renal phosphorus handling in the rat: interaction with PTH and nicotinamide
Authors: Guntupalli J. , Rogers A. , Bourke E.
Published: December 2017

Previous studies suggested an antiphosphaturic action of insulin. However, effects of parathyroid hormone (PTH), anti-natriuresis, or other variables were not vigorously controlled. Recently it has been suggested that nicotinamide restores phosphaturia in several antiphosphaturic states. Clearance studies were therefore performed in acutely parathyroidectomized rats to test the hypothesis that insulin abolishes the phosphaturic action of PTH and that this effect is prevented by nicotinamide. Superimposition of euglycemic hyperinsulinemia on PTH infusion (plasma insulin 19.1 +/- 2.7 vs. 9.8 +/- 1.1 microU/ml, P less than 0.05) during steady-state Pi excretion decreased fractional excretion (FE) of Pi compared with PTH-infused controls (3.16 +/- 0.61 vs. 18.02 +/- 0.81%, P less than 0.001). Renal cortical NAD+ was lower in the former than the latter group (455 +/- 22 vs. 689 +/- 30 pmol/mg, P less than 0.01). Nicotinamide pretreatment prevented the antiphosphaturic action of insulin and the decrease in cortical NAD+ in both the presence and absence of exogenous PTH. These studies offer direct evidence that in acutely parathyroidectomized rats insulin can abolish the phosphaturic action of PTH, independent of glomerular filtration rate, the filtered loads of Pi and glucose, FENa+, and cAMP excretion, an effect that is prevented by nicotinamide pretreatment. In the absence of nicotinamide pretreatment, superimposition of insulin on PTH infusion was associated with a decrease in renal cortical NAD+. A role for intracellular NAD+, probably indirect, in the antiphosphaturic action of insulin is suggested.
Sensitivity of rat renal luminal and contraluminal sulfate transport systems to DIDS
Authors: Bastlein C. , Burckhardt G.
Published: December 2017

4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) was tested as an inhibitor of the sulfate transport systems in rat renal brush border and basolateral membrane vesicles. Na+-driven sulfate uptake into brush border membrane vesicles was half-maximally inhibited at 350 microM DIDS. Proton gradient-driven sulfate uptake into basolateral membrane vesicles was competitively inhibited by DIDS with a Ki of 2.4 microM. The Km for delta pH-driven sulfate uptake was 5.4 microM. The different affinities of the sulfate transport systems for DIDS correlated with different substrate specificities. The luminal transport system accepted a smaller range of anions than the contraluminal system and did not operate as a Na+-independent anion exchanger. After treatment of basolateral membrane vesicles with 50 microM DIDS at pH 8.4 for 30 min, an irreversible inhibition of sulfate uptake was observed. With brush border membranes, only a small irreversible inhibition was obtained. Lack of inhibition after treatment of basolateral membranes with DIDS at pH 6.4 indicated that DIDS reacted with deprotonated amino groups of the transport protein. Sulfate was protected from the irreversible inhibition by DIDS. Sodium-driven uptake of L-glutamate and methylsuccinate into basolateral membrane vesicles was not irreversibly inhibited by DIDS, indicating a specific action of DIDS on the contraluminal sulfate transport system. Irreversible and substrate-protectable inhibition of sulfate transport render DIDS suitable for future affinity labeling studies on the sulfate transport system in basolateral membranes.
Effects of dietary alteration of bicarbonate and magnesium on rat bone
Authors: Burnell J. M. , Liu C. , Miller A. G. , Teubner E.
Published: December 2017

To study the effects of bicarbonate and magnesium on bone, mild acidosis and/or hypermagnesemia were produced in growing rats by feeding ammonium chloride and/or magnesium sulfate. Bone composition, quantitative histomorphometry, and mineral x-ray diffraction (XRD) characteristics were measured after 6 wk of treatment. The results demonstrated that both acidosis (decreased HCO3) and hypermagnesemia inhibited periosteal bone formation, and, when combined, results were summative; and the previously observed in vitro role of HCO3- and Mg2+ as inhibitors of crystal growth were confirmed in vivo. XRD measurements demonstrated that decreased plasma HCO3 resulted in larger crystals and increased Mg resulted in smaller crystals. However, the combined XRD effects of acidosis and hypermagnesemia resembled acidosis alone. It is postulated that the final composition and crystal structure of bone are strongly influenced by HCO3- and Mg2+, and the effects are mediated by the combined influence on both osteoblastic bone formation and the growth of hydroxyapatite.
Phosphorylation of type II cAMP-dependent protein kinase in renal brush border membranes
Authors: Hammerman M. R.
Published: December 2017

We have previously demonstrated cAMP-dependent 32P phosphorylation and dephosphorylation of a 62,000 relative molecular weight (Mr) protein in autoradiograms of sodium dodecyl sulfate polyacrylamide gels originating from canine renal brush border membranes. In the current studies 32P phosphorylation of the 62,000 Mr protein that was independent of cAMP was noted in the presence of Zn2+. Under these conditions, cAMP inhibited the 32P phosphorylation of this protein. Concentration-dependent photoaffinity labeling of a band with Mr 60,000 in autoradiograms of gels resulted from incubation of membranes with cyclic 8-azidoadenosine-3',5'-monophosphate (8-N3-[32P]cAMP) followed by exposure to light. In the presence of Zn2+ and ATP, an apparent shift in the Mr of a portion of the photoaffinity-labeled band to 62,000 was seen. The 62,000 Mr phosphoprotein in detergent-solubilized supernatants of brush border membranes was immunoprecipitated with antibodies directed against the regulatory subunit of type II cAMP-dependent protein kinase. Our observations strongly suggest that the 62,000 Mr protein is the regulatory subunit.
Increases of cell ATP produced by exogenous adenine nucleotides in isolated rabbit kidney tubules
Authors: Weinberg J. M. , Humes H. D.
Published: December 2017

The effects of exogenous nucleotides on adenine nucleotide metabolism and cell cation levels in normal and O2-deprived isolated rabbit kidney tubules were studied to gain insight into ways in which exogenous nucleotides could contribute to ameliorating O2 deprivation-induced injury. In control oxygenated tubules, 250 microM exogenous ATP, ADP, or AMP resulted in two- to threefold increases of cell ATP over 75-90 min of incubation and smaller relative increases of ADP and AMP. GTP was not increased. Exogenous adenosine, inosine, and hypoxanthine were substantially less effective at increasing intracellular nucleotides than equimolar concentrations of exogenous nucleotides. Nucleotide-treated cells had higher levels of Ca2+ and Mg2+ than untreated cells. Treatment of O2-deprived tubules with exogenous Mg-ATP improved recovery of ATP levels following O2 deprivation, and tubules with mild injury increased their ATP levels to supranormal values such as those seen in control oxygenated tubules treated with nucleotides. Increases of tubule cell ATP levels required ongoing oxidative metabolism and thus were not evident until the reoxygenation recovery period. Exogenous ATP produced some improvement of other injury-associated metabolic parameters but did not substantially alter the overall pattern of tubule susceptibility to lethal cell injury. Allopurinol did not affect the behavior of oxygenated or O2-deprived tubules irrespective of the presence of exogenous ATP. These data clarify the potential for manipulating intracellular ATP levels with exogenous nucleotides and the functional consequences of such manipulation in oxygenated and O2-deprived renal tubule cells.
A mathematical model of the rat proximal tubule
Authors: Weinstein A. M.
Published: December 2017

The equations of mass conservation and electroneutrality are used to extend a nonequilibrium thermodynamic model of the rat proximal tubule epithelium to a representation of a 0.5-cm segment of tubule. The output of the tubule model includes the luminal profiles and absolute proximal reabsorption of Na, K, Cl, HCO3, HPO4, H2PO4, glucose, and urea, generated by the epithelial model. Transport rates and permeabilities, chosen in agreement with those of the rat, result in luminal glucose and bicarbonate depletion and a transition from an electronegative to positive lumen. Despite the development of significant transepithelial osmotic driving forces (a transepithelial glucose gradient and Cl-HCO3 asymmetry), intraepithelial solute-solvent coupling remains an important force for water reabsorption along the proximal tubule length. In particular, this means that when osmotic gradients that appear under free-flow conditions are used in the calculation of the epithelial water permeability, a substantial overestimate of this permeability will be obtained. A single first-order differential equation has been derived in conjunction with an approximate nonelectrolyte model of the proximal tubule that represents both coupled and gradient-driven water reabsorption. In the present work, this equation is shown to yield an accurate description of water transport by the comprehensive tubule model.
Mitochondrial alterations in cisplatin-induced acute renal failure
Authors: Gordon J. A. , Gattone V. H.
Published: December 2017

The mild reversible nonoliguric form of acute renal failure is perhaps the most common of many nephrotoxic side effects that occur secondary to cisplatin administration. The present studies were undertaken to gain insight into mitochondria alterations and morphological abnormalities underlying this form of renal failure. Following a single intraperitoneal injection of 5.5 mg/kg body wt of cisplatin changes in renal function, mitochondrial respiration, and calcium accumulation were measured serially over a 9-day period. Results indicate that reversible functional changes secondary to cisplatin are accompanied by changes in mitochondrial respiration and calcium accumulation. A decline in state 3 mitochondrial respiration precedes mitochondrial calcium accumulation. However, calcium accumulation begins to recover before mitochondrial respiration. At the peak of functional and biochemical injury morphological damage is extensive, and mitochondria are strikingly aberrant. The results demonstrate that changes in mitochondrial respiration and calcium accumulation occur secondary to cisplatin administration. Both of these effects may play a role in the renal cellular injury induced by cisplatin.
Morphological changes with Na+-free fluid absorption in isolated perfused snake tubules
Authors: Dantzler W. H. , Brokl O. H. , Nagle R. B. , Welling D. J. , Welling L. W.
Published: December 2017

Snake (Thamnophis spp.) proximal renal tubules were perfused and bathed in vitro either with medium containing sodium or with medium in which the sodium was replaced with choline. Net fluid absorption was measured by changes in volume marker concentration, and cell volumes and cell membrane surface areas were measured by ultrastructural morphometric methods. Net fluid absorption did not differ significantly in the presence or absence of sodium. However, during the 20-25-min perfusion in the absence of sodium, significant morphological changes took place. The volume of the cells, doubled and the volume of the intercellular spaces nearly quintupled. The areas of the lateral and apical cell membranes approximately doubled, but their surface densities remained essentially constant. Therefore the larger cells in the absence of sodium had proportionally enlarged surface areas, so that the volume-to-surface area ratio remained constant. These morphological changes occurred concomitantly with the maintenance of net fluid absorption and might play a permissive role in such maintenance in the absence of sodium.
Superficial and juxtamedullary nephron function during converting enzyme inhibition
Authors: Goransson A. , Sjoquist M. , Ulfendahl H. R.
Published: December 2017

The influence of the renin-angiotensin system on whole-kidney and regional single-nephron function was studied in anesthetized Munich-Wistar rats by use of a converting enzyme inhibitor (CEI), captopril (3 mg . h-1 . kg-1 body wt-1). Single-nephron glomerular filtration rate (SNGFR) was measured in superficial (S) and juxtamedullary (JM) nephrons by a micropuncture technique that blocked tubuloglomerular feedback (TGF) activity. Hydrostatic free-flow pressure (FFP) measurements were conducted in S proximal tubules, in JM loops of Henle, and in papillary vasa recta. Glomerular filtration rate (GFR) and urinary electrolyte excretion were measured in the contralateral kidney. In the control situation SNGFR of S nephrons was 35.4 +/- 2.24 nl . min-1 . g kidney wt-1 and of JM nephrons was 75.0 +/- 9.41 nl . min-1 . g-1 kidney wt-1. Thus it was more than twice as high in JM as in S nephrons when the TGF activity was blocked. In this situation administration of CEI had no additional effect on either S or JM nephrons. However, administration of CEI resulted in a significant increase in whole-kidney GFR by 25% (P less than 0.05) and in urine flow rate by 60% (P less than 0.001) under free-flow conditions. Further, intratubular FFP increased significantly in JM nephrons by an average of 2.9 +/- 0.52 mmHg (P less than 0.001), indicating an increase in tubular urine flow in JM nephrons, whereas S nephrons were unaffected. These results suggest an active preglomerular vasoconstriction in JM nephrons under normal free-flow conditions. This seems to be mediated by TGF and modulated by angiotensin II.
Electrophysiology of salamander proximal tubule. II. Interspace NaCl concentrations and solute-coupled water transport
Authors: Sackin H.
Published: December 2017

The role of the paracellular interspace in solute-coupled water transport was investigated in isolated perfused salamander (Ambystoma) proximal tubules using a null-point technique to estimate interspace NaCl concentrations. Constant composition of luminal fluid was maintained by rapid (200 nl/min) perfusion of tubules 600,micron or less in length. Inhibition of active transport by a decrease in bath temperature from 22 to 0 degrees C in 400 ms produced rapid depolarizations of both the transepithelial (Vte) and basolateral (Vbl) potential, followed by slower changes in potential that occurred at low temperature. During this period, the time course of Vbl was independent of small changes in bath NaCl concentration, whereas the time course of Vte at low temperature varied from a slow depolarization to a slow repolarization depending on whether the concentration of NaCl in the bath equaled or exceeded that in the perfusate. Absence of a slow change in Vte at low temperature indicated a match between the NaCl concentration of the interspace and the test concentration of NaCl in the bath. Using this technique with 12 tubules, the normal interspace NaCl concentration appeared to be approximately 4% above the NaCl concentration of either the lumen or bath, demonstrating that the interspace of the salamander proximal tubule can function as a local hyperosmotic compartment to facilitate fluid transport between solutions of identical composition.
Electrophysiological studies on primary cultures of proximal tubule cells
Authors: Bello-Reuss E. , Weber M. R.
Published: December 2017

Primary confluent monolayers were grown from proximal tubule fragments of rabbit kidneys. The fragments were obtained by gradient centrifugation and seeded on an ad hoc dish whose bottom was a permeable and transparent collagen membrane. The culture medium was a mixture of 50% Ham's F-12 and 50% Dulbecco's modified Eagle's medium supplemented with insulin, transferrin, ethanolamine, sodium selenite, and amino acids. The monolayers were studied at 6-14 days after seeding. Transmission electron microscopy revealed cuboidal cells 8.5-10.5 microns high, with a 1.5 to 2.5-microns apical brush border, abundant mitochondria, vacuoles, lysosomes, and irregular basal interdigitating processes. Cyclic AMP synthesis was stimulated by parathyroid hormone and was insensitive to vasopressin and isoproterenol. Electrophysiological studies performed with the same physiological salt solution on both sides revealed a transepithelial voltage of -2.6 +/- 0.6 mV (n = 10) and a basolateral membrane voltage of -51.0 +/- 4.5 mV (n = 13), both referred to the basal solution. The transepithelial electrical resistance was 7 +/- 2 omega X cm2. The apical membrane depolarized on addition of glucose to the apical side and hyperpolarized on removal of glucose. Changes in apical membrane voltage on addition of varying glucose concentrations (at [Na] = 135 mM, 37 degrees C) demonstrate the presence of a glucose transport system with an apparent Km of 3.54 +/- 0.54 and a Vmax of 7.2 +/- 0.4 mV. Thus this preparation exhibits morphological and electrophysiological characteristics of proximal tubule cells; these studies demonstrate the feasibility of the use of intracellular microelectrode techniques to study the transport properties of cultured epithelia.