bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrophysiology of plasma membrane vesicles
Authors: Wright E. M.
Published: December 2017

In both renal and gastrointestinal physiology, it has become popular to study epithelial transport phenomena using vesicles isolated from the apical and basolateral cell membranes. Transport in vesicle preparations is usually monitored with radioactive tracers, but more recently attention has been directed to electrophysiological methods. As it is impossible to measure the electrical properties of membranes in small vesicles (less than 500 nm diam) with classical electrophysiological techniques, indirect methods have to be employed. In this review I focus on the application of voltage-sensitive optical probes to measure membrane potentials in brush border membrane vesicles. Optical signals are calibrated with diffusion potentials generated with known ion gradients in the presence of ionophores, e.g., EKS with K gradients in the presence of valinomycin. Membrane potential measurements can be used 1) to illustrate the specificity and kinetics of sugar-, amino acid-, and carboxylic acid-Na cotransport systems in brush border membranes, and 2) to determine the ion permeability of brush border membranes. All organic solutes known to be transported by Na cotransport across brush border membranes depolarize the membrane in a Na-dependent, saturable manner. The results agree, both qualitatively and quantitatively, with electrophysiological data obtained in the intact renal tubule and with tracer uptake in vesicles. Bi-ionic potential measurements demonstrate that brush border membranes are permselective to anions and cations, but there are indications that the permeabilities are somewhat dependent on the method of vesicle preparation and the experimental conditions. However, electrical potential measurements provide insight into the mechanisms of ion transport in vesicle preparations, and the application of patch-clamp techniques should provide further gains in the future.
Cortical tubular and glomerular dopamine receptors in the rat kidney
Authors: Felder R. A. , Blecher M. , Eisner G. M. , Jose P. A.
Published: December 2017

Dopamine receptors in glomeruli and renal cortical tubules were characterized using radioligand binding and adenylate cyclase studies. The binding of [3H]haloperidol to glomeruli and tubules was rapid, saturable with time and ligand concentration, reversible, of high affinity, and demonstrated stereoselectivity and antagonist and agonist rank potency for binding to dopamine receptors. Analysis of kinetic data and Rosenthal plots in glomeruli revealed a single class of [3H]haloperidol binding sites with an apparent dissociation constant (Kd) of 6 nM and maximum receptor density (Bmax) of 0.42 pmol/mg protein. In tubules, at least two binding sites were noted, one with an apparent Kd of 38 nM and Bmax of 1.90 pmol/mg protein and another with an apparent Kd of 183 nM and Bmax of 3.50 pmol/mg protein. Dopamine and apomorphine increased adenylate cyclase in tubular membranes while no increases were noted in glomeruli. These studies suggest that glomeruli have D2 dopamine receptors, while renal cortical tubules contain the D1 dopamine receptor.
Quantitative ultrastructure and functional correlates in proximal tubule of Ambystoma and Necturus
Authors: Maunsbach A. B. , Boulpaep E. L.
Published: December 2017

The functional properties of the proximal tubule in the salamander Ambystoma tigrinum have been well characterized but its ultrastructure has not been examined. We therefore analyzed the qualitative and quantitative ultrastructure of the proximal tubule in this species as a basis for structure-function correlations. In addition, a comparative study between species was performed between Ambystoma and Necturus. In Ambystoma the basal cell membrane but not the lateral cell membrane has a highly elaborate organization and is greatly amplified at the basal cell surface. Therefore, the bulk of the basolateral membrane does not face the lateral intercellular space but faces a basal extracellular labyrinth immediately adjacent to the peritubular space. We suggest that this intraepithelial compartment may serve as a site for solute-solvent interactions. The morphometric comparative analysis provides quantitative estimates of tubule dimensions, volume of cells and extracellular channels, areas of luminal, lateral, and basal cell membranes as well as averaged dimensions of the lateral intercellular spaces. Structure-function correlations show that when certain functional parameters are normalized on the basis of ultrastructural rather than epithelial dimensions the interspecies variability decreases.
Anoxic cell swelling dissociated from excess permeability by poorly penetrating solutes
Authors: Shay J. , Hein A.
Published: December 2017

Increased plasma membrane permeability, cell swelling, and cell death are consequences of metabolic energy deprivation. Rabbit retinas were incubated in an oxygenated artificial cerebrospinal fluid containing glucose. The incubating medium was modified by causing anoxia and glucose deprivation with one of the following treatments: addition of 97 mM mannitol, equimolar substitution of choline+ for Na+, or substitution of isethionate- for Cl-. Some retinas were resupplied with oxygen and glucose to determine the consequences of solute manipulation. Water compartments and membrane permeability were assayed using [3H]inulin and [14C]mannitol. Abnormal nuclei were counted on blind-coded slides. Both treatments prevented doubling of inulin-free water of untreated retinas after 70 min of deprivation. Neither treatment preserved morphology or prevented massive swelling after restoration of oxygen and glucose and gradual removal of the treatment. Mannitol leaked into deprived cells only, even when swelling was prevented. We conclude that prophylaxis of cell swelling during metabolic energy deprivation prevents neither cell leakiness nor cell death.
Metabolism of pure human erythropoietin in the rat
Authors: Emmanouel D. S. , Goldwasser E. , Katz A. I.
Published: December 2017

The metabolism of pure human erythropoietin (EPO) labeled with 125I was studied in the rat. Concentrations of the labeled hormone (125I-EPO) in plasma and urine were measured by both trichloroacetic acid precipitation and gel filtration. During steady-state conditions the metabolic clearance rate of 125I-EPO was slow, averaging 256 +/- 7 microliter. min-1 X kg-1 of which only 19 +/- 2 microliter X min-1 X kg-1 (or 7.4 +/- 0.8% of the metabolic clearance rate) could be accounted for by excretion of the labeled hormone in the urine. Urinary clearance of 125I-EPO amounted to less than 0.3% of the glomerular filtration rate, and there was no detectable arteriovenous concentration difference of 125I-EPO across the kidney. After both pulse injection and constant infusion to equilibrium, disappearance of 125I-EPO from the circulation could be approximated by a single exponential function: plasma half-life was 3.5 +/- 0.2 h in normal rats and was prolonged to 4.4 +/- 0.3 h (P less than 0.05) in animals with ligated renal pedicles. Although kidney homogenates degraded 125I-EPO in vitro (optimum pH 4.5), the hormone did not accumulate in the kidney when injected intravenously. We conclude that EPO metabolism is extremely sluggish compared with that of other polypeptide hormones. Whereas kidney tissue is capable of degrading EPO in vitro, the physicochemical characteristics of this glycoprotein (molecular size, shape, and charge) probably impede its access to degrading sites and therefore account for the limited contribution of renal extraction and excretion to the metabolic clearance of the hormone.
Mechanism of effect of diphenylhydantoin on renal renin release
Authors: Cadnapaphornchai P. , Pontes C. , McDonald F. D.
Published: December 2017

This study was undertaken to delineate the mechanism of the effect of diphenylhydantoin (DPH) on renal renin release. DPH at a dose of 0.18 mg X kg-1 X min-1 was infused for 30 min into the renal artery of anesthetized dogs with acute unilateral renal denervation. In the innervated kidney, DPH infusion increased renin secretion rate (RSR) from 189 +/- 54 to 939 +/- 279 ng ANG I X h-1 X min-1. In the contralateral denervated kidneys, RSR did not change. An identical study was done in a second group of dogs in which unilateral renal denervation was done 24 h prior to DPH infusion. In this group, DPH infusion increased RSR from 63 +/- 57 to 643 +/- 180 ng ANG I X h-1 X min-1 in the innervated kidneys. In the contralateral denervated kidneys, RSR did not change. In a separate group of indomethacin-treated nondenervated dogs, intrarenal infusion of DPH increased RSR from 131 +/- 32 to 452 +/- 88 ng ANG I X h-1 X min-1. The percent increase in RSR in the indomethacin-treated dogs was not significantly different from the non-indomethacin-treated dogs. These data suggest that the stimulatory effect of DPH on renin release is mediated by or requires the presence of renal nerves. The step(s) after the renal nerves is (are) not mediated by prostaglandins.
Renal handling of phosphate during acute respiratory acidosis and alkalosis in the rat
Authors: Haramati A. , Nienhuis D.
Published: December 2017

Clearance experiments were performed in acutely thyroparathyroidectomized rats to evaluate the renal handling of phosphate during respiratory acidosis (R ACID) and alkalosis (R ALK) in rats fed either a normal (0.7%) or low (0.07%) phosphate diet for 4 days. Different acid-base states were achieved by varying the mixture of carbon dioxide in the inspired air. Each group received graded infusions of phosphate to control for differences in plasma phosphate (PPi) and to determine the maximum transport capacity of phosphate reabsorption (TmPi/GFR). In rats fed a normal phosphate diet, PPi and the fractional excretion of phosphate (FEPi) were significantly greater in R ACID than in R ALK. However, there were no differences between R ACID and R ALK when FEPi was evaluated as a function of the PPi, and values for TmPi/GFR during R ACID were not different from those during R ALK. In rats fed low phosphate diet, PPi during R ACID was significantly greater than during R ALK, yet FEPi was less than 1% in all groups due to an adaptive increase in TmPi/GFR. Further, the TmPi/GFR was similar irrespective of the acid-base state. We conclude that acute respiratory acid-base changes do not alter the intrinsic capacity of the kidney to reabsorb phosphate.
Time course of adaptation to altered K intake in rats and sheep
Authors: Rabinowitz L. , Sarason R. L. , Yamauchi H. , Yamanaka K. K. , Tzendzalian P. A.
Published: December 2017

The early time course of adaptation to large step increases in K intake was examined in sheep and rats. Fifteen 3-day experiments were performed on four mature ewes. They received on each day a single meal (730-930 meq K/day) and on days 2 and 3 a rumen KCl supplement (600 mM/day). Adaptation to the changed intake occurred within 47 h and was defined by the ratio of urinary K/K intake approximating normal preloading ratios. K excretion did not correlate significantly with plasma K or with Na excretion. Three groups of four rats, body wt 210 g, were studied over 19 days. Four rats fed a basal diet excreted 1.96 +/- 0.04 (n = 19) meq/day K. For four rats, the basal diet was supplemented with KCl on days 5-15, during which time K excretion was 9.34 +/- 0.36 (n = 11) meq/day; four rats with a higher KCl supplement on days 5-15 excreted 15.37 +/- 0.69 (n = 11) meq/day K. For rats, adaptation to increased and decreased intake was rapid, occurring on the first day of changed intake when urinary K excretion approximated intake. The rapid K adaptation was contrary to the generally accepted, but experimentally unverified, view that adaptation is a chronic process requiring 1 or more weeks to develop.
Viewing the kidney through microelectrodes
Authors: Fromter E.
Published: December 2017

Electrical measurements with microelectrodes have proven of great value in the investigation of renal ion transport mechanisms. By virtue of their fine tips (less than 1 micron in diameter) and because of the ease of recording electrical transients, they provide measurements with unparallelled space and time resolution. Early electrophysiological work was done largely in amphibians, because of their larger cell size, whereas studies in mammals were restricted to transepithelial electrical parameters, which provided no insight into individual membrane mechanisms. However, recently techniques have been developed to impale individual tubular cells of mammalian kidneys successfully, both in vivo and in vitro. Such experiments allow us to identify ion transport properties of individual cell membranes from the response of the electrical potential to fast pertubations of the luminal and/or peritubular fluid composition or to applied currents. The power of this approach was greatly increased by the development of ion-selective microelectrodes, allowing us to measure intracellular concentrations of Na+, K+, Cl-, Ca2+, and HCO3- or pH directly and to follow quantitatively their changes in response to different experimental maneuvers. In the present paper our knowledge of ion transport mechanisms of mammalian proximal tubular cell membranes is summarized, with emphasis on the transport of Na+, K+, HCO3-, and Cl-. With the exception of transcellular transport of Cl-, which is quantitatively less important, the major transport mechanisms of all other ions have been identified in the brush border and in the peritubular cell membrane. Emphasis is given to the description of HCO3- exit across the peritubular cell membrane, which has not thus far been studied with other than electrophysiological techniques. Microelectrode techniques will probably continue to provide new insight when regulatory phenomena are studied on the cellular level and individual conductance channels in renal cell membranes are identified with the newly developed patch-clamp technique.
PGE2, forskolin, and cholera toxin interactions in modulating NaCl transport in mouse mTALH
Authors: Culpepper R. M. , Andreoli T. E.
Published: December 2017

Prostaglandin E2 (PGE2) inhibits the ADH-stimulated components of the lumen-positive transepithelial voltage (Ve) and of net chloride absorption (JnetCl) in the isolated microperfused mouse medullary thick ascending limb of Henle (mTALH), presumably by interfering with the ADH-dependent intracellular accumulation of cAMP. These experiments examined the interactions of PGE2 with two nonhormonal stimulators of adenylate cyclase--cholera toxin and forskolin--in an attempt to evaluate the means by which PGE2 inhibits ADH-stimulated transport in these mTALH segments. Forskolin (FSK) stimulated Ve in the mTALH with half-maximal stimulation at 1.4 X 10(-7) M FSK. PGE2 had no effect on FSK stimulation of Ve; 10(-6) M FSK reversed completely the PGE2 inhibition of ADH-stimulated Ve. A low concentration of cholera toxin, 5 X 10(-13) M, stimulated Ve and JnetCl in the mTALH; 10(-6) M PGE2 inhibited the stimulation by cholera toxin; and 10(-6) M FSK reversed the PGE2 inhibition of both Ve and JnetCl in cholera toxin-stimulated mTALH. A higher concentration of cholera toxin, 10(-10) M, stimulated Ve and JnetCl to values identical to those seen with maximal concentrations of ADH, but PGE2 did not inhibit the increments in either Ve or JnetCl produced by 10(-10) M cholera toxin. PGE2 appears to inhibit ADH stimulation of NaCl transport in mTALH by an action distal to hormone-receptor interactions yet proximal to the catalytic subunit of adenylate cyclase.
Angiotensin II in adrenergic-induced alterations in glomerular hemodynamics
Authors: Pelayo J. C. , Ziegler M. G. , Blantz R. C.
Published: December 2017

Micropuncture analysis of glomerular ultrafiltration (SNGFR) was conducted in Munich-Wistar rats to assess the functional responses to moderate-frequency (3-Hz) renal nerve stimulation. Angiotensin II inhibition (ANG II-inhib) was produced by the intravenous administration of [Sar1, Ala8] angiotensin II or MK 421 to investigate whether it modulates the effects of renal nerve stimulation. Micropuncture measurements were obtained before and during renal nerve stimulation. Renal nerve stimulation decreased SNGFR approximately 25% (from 49.9 +/- 2.3 to 38.0 +/- 1.4 nl X min-1 X g kidney wt-1), the result of decreased glomerular capillary hydrostatic pressure gradient and nephron plasma flow. These decreases were due to increased afferent (approximately 43%) and efferent (approximately 30%) arteriolar resistances, since the glomerular ultrafiltration coefficient remained unaffected. The effects of renal nerve stimulation during ANG II-inhib were less in magnitude than in renal nerve stimulation alone: SNGFR decreased from 48.0 +/- 1.5 to 44.8 +/- 2.0 nl X min-1 X g kidney wt-1 after renal nerve stimulation. The net renal production of norepinephrine was augmented by renal nerve stimulation but it was not influenced by ANG II-inhib. In conclusion: renal nerve stimulation can regulate glomerular ultrafiltration by altering vascular resistances, and angiotensin II appears to be a critical factor for the full functional expression of renal nerve stimulation at the glomerulus.
Quantitative characterization of the tubuloglomerular feedback response: effect of growth
Authors: Briggs J. P. , Schubert G. , Schnermann J.
Published: December 2017

Studies were performed to characterize quantitatively the effect of changing loop of Henle flow rate on single nephron glomerular filtration rate (SNGFR) in male Sprague-Dawley rats of varying body weight. Rats weighing 100, 220, and 350 g were studied using standard renal micropuncture techniques. The relationship between loop of Henle flow rate (VLP) and SNGFR was characterized for individual nephrons by multiple determinations of SNGFR during loop perfusion. An inverse sigmoidal relationship was observed that could be described as delta SNGFR = a/(1 + ek(b-VLP], where delta SNGFR is the change in SNGFR from the value measured at zero loop flow, a is delta SNGFRmax, the maximum change, b is V1/2, the flow rate at which the response is half maximum, and k is [4f' (V1/2)]/a with f' (V1/2) the slope at V1/2. delta SNGFRmax increased with increasing body size (7.9 +/- 1.16, 18.9 +/- 0.90, and 25.2 +/- 2.73 nl/min, respectively, in the three groups), and the curve shifted to the right (V1/2 = 10.3 +/- 0.8, 15.4 +/- 0.83, and 22.3 +/- 1.22 nl/min). The maximum slope increased (f' (V1/2) = 0.9 +/- 0.19, 1.7 +/- 0.16, and 3.2 +/- 0.70), but the exponential constant k was uninfluenced by growth. Independent of rat size, a 10% increase in loop flow at the midpoint produced at 5-10% decrease in SNGFR. Free-flow values of SNGFR and VLP were found to lie in the most sensitive range of the feedback curve.
Response of renal NH3 production to chronic respiratory acidosis
Authors: Rodriguez-Nichols F. , Laughrey E. , Tannen R. L.
Published: December 2017

Although chronic metabolic acidosis results in an adaptive increase in the renal capacity to produce NH3, the response to a low pH produced by chronic respiratory acidosis is unknown. Rats were placed in a specially constructed chamber with an ambient CO2 of 10% for 3 days, which increased their PCO2 to 76 +/- 4 mmHg. NH3 production was determined in vitro using both isolated kidneys perfused with 0.5 mM glutamine and cortical tubules incubated with 1 mM glutamine. Conscious rats with chronic respiratory and chronic metabolic acidosis had similar arterial pHs (7.29 +/- 0.01 and 7.31 +/- 0.01), which were significantly lower than controls (7.41 +/- 0.04). NH3 production by kidneys from rats with chronic respiratory acidosis perfused at pH 7.4 did not differ significantly from normal controls (1.13 +/- 0.13 vs. 1.07 +/- 0.17 mumol X min-1 X g-1). By contrast, kidneys from rats with chronic metabolic acidosis produced significantly more NH3 than both these groups (2.73 +/- 0.29 mumol X min-1 X g-1). Cortical tubules from rats with chronic respiratory acidosis also showed no evidence of adaptation in both NH3 (8.8 +/- 0.8 vs. 11.6 +/- 0.8 mumol X min-1 X g-1) and glucose (1.38 +/- 0.08 vs. 1.41 +/- 0.13 mumol X min-1 X g-1) production in comparison with controls, whereas chronic metabolic acidosis stimulated both ammoniagenesis and gluconeogenesis twofold or more. Thus a low systemic pH does not account for the adaptation in the capacity of the kidney to produce either ammonia or glucose.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of phosphate depletion on blood pressure and vascular reactivity to norepinephrine and angiotensin II in the rat
Authors: Saglikes Y. , Massry S. G. , Iseki K. , Brautbar N. , Barndt R. , Brunton L. L. , Buxton I. L. , Vlachakis N. , Campese V. M.
Published: December 2017

Phosphate depletion (PD) adversely affects myocardial function but its influence on blood pressure is not well elucidated. In this study we evaluated whether PD influences blood pressure and/or affects its hormonal regulation or the peripheral vascular response to pressor agonists. Mean arterial pressure (MAP) in PD rats was lower than in normal animals, whereas heart rate was not significantly different between the two groups. Cardiac index (CI) in PD rats was lower and systemic vascular resistance (SVR) was higher than in controls. Plasma norepinephrine (NE) in the resting state and during the stress of immobilization was significantly greater in PD rats than in controls. Base-line plasma renin activity was also significantly higher in PD rats and increased similarly in the two groups of rats after administration of isoproterenol. Bolus injections of NE or angiotensin II produced a smaller rise in MAP in PD rats than in controls. Reduced responsiveness to NE was also demonstrated in isolated hind-limb preparation from PD rats. When NE was infused to achieve a rise in MAP of 30 mmHg, the dose required in PD was higher than in controls. Treatment with indomethacin did not affect the response in MAP to NE. The content and affinity of both alpha- and beta-receptors in PD hearts were not different from those of control hearts. The contents of PiATP, and AMP in the mesenteric vessels of PD rats were significantly lower than in control animals. These data show that PD leads to reductions in MAP, arteriolar response to pressor agents, and CI with appropriate compensatory rise in NE but with inadequate compensatory increase in SVR.(ABSTRACT TRUNCATED AT 250 WORDS)
An alternate method for estimating efferent arteriolar plasma colloid osmotic pressure
Authors: Wolfert A. I. , Laveri L. A. , Oken D. E.
Published: December 2017

The colloid osmotic pressure (COP) of efferent arteriolar plasma in glomerular dynamic studies generally is estimated from the measured protein concentration (CE) while the nephron filtration fraction (SNFF) is derived from CE and the systemic plasma protein concentration (CA) according to the equation SNFF = (1 - CA/CE). Estimates of both SNFF and COPE are quite sensitive to small errors in protein measurement, however, with a putative coefficient of variation of +/- 5% in protein measurement at a typical SNFF of 0.33, for example, providing an uncertainty (i.e., +/- SD) of +/- 14% in the SNFF estimate and +/- 2.4 mmHg in the estimated COPE value. In this study, we evaluated in vitro the precision with which the COP of plasma samples can be estimated after ultrafiltration by coupling direct oncometry of native plasma with isotopically measured filtration fractions derived employing nanoliter and microliter volumes and applying a modification of the equation of Ladegaard-Pedersen (Scand. J. Clin. Lab. Invest. 23: 153-158, 1969). The measured and estimated oncotic pressures were then compared. The mean differences between theoretic and measured COP values at filtration fractions of less than 0.1, 0.1-0.2, 0.2-0.3 and greater were: -0.4 +/- 0.8 (SE) (n = 22); 1.8 +/- 1.1; 3.9 +/- 1.0; and 6.0 +/- 1.7%, respectively. It is concluded that the coupling of direct oncometric measurement of arterial plasma colloid osmotic pressure with isotopically determined filtration fractions provides a satisfactory estimate of COPE that is suitable for studies of glomerular dynamics.
Evidence for transcellular osmotic water flow in rat proximal tubules
Authors: Preisig P. A. , Berry C. A.
Published: December 2017

To determine the predominant pathway for transepithelial osmotic water flow, the transepithelial osmotic water permeability [Pf(TE)] and the apparent dimensions of paracellular pores and slits were determined in rat proximal convoluted tubules microperfused in vivo. To measure Pf(TE), tubules were perfused with a hyposmotic, cyanide-containing solution. Pf(TE), calculated from the observed volume flux in response to the measured log mean osmotic gradient, was 0.12-0.15 cm/s, assuming sigmaNaCl equal to 1.0-0.7, respectively. The dimensions of the paracellular pathways were determined using measured sucrose and mannitol permeabilities (nonelectrolytes confined to the extracellular space). These were 0.43 and 0.87 X 10(-5) cm/s, respectively. By using the ratio of these permeabilities, their respective free solution diffusion coefficients and molecular radii, and the Renkin equation, the radius of the nonelectrolyte-permeable pores and the total pore area/cm2 surface area/channel length were calculated to be 1.4 nm and 3.56 cm-1, respectively. Similar calculations for slits yielded a slit half-width of 0.8 nm and a total slit area/cm2 surface area/channel length of 3.16 cm-1. The osmotic water permeability of these nonelectrolyte-permeable pathways was calculated by Poiseuille's law to be 0.0018 cm/s (pores) or 0.0014 cm/s (slits), at most 2% of Pf(TE). We conclude that the nonelectrolyte-permeable pathway in the tight junctions is not the major route of transepithelial osmotic water flow in the rat proximal tubule.
Aldosterone binding in isolated tubules. IV. Autoradiography along the nephron of the spontaneously hypertensive rat
Authors: Farman N. , Bonvalet J. P.
Published: December 2017

The binding of aldosterone was studied in tubular segments isolated by microdissection from kidneys of spontaneously hypertensive (SHR, n = 8), Kyoto normotensive (KWR, n = 8), and normal Wistar (NWR, n = 6) rats with an autoradiographic technique on dry film. All animals had been previously adrenalectomized. Kidney pyramids were incubated in vitro before microdissection with collagenase and 2 X 10(-9) M [3H]aldosterone in the presence or absence of an excess of unlabeled aldosterone. In addition, the displacement of the binding by 10 times excess dexamethasone or aldosterone was examined in the cortical and medullary collecting tubule of SHR and KWR to assess the specificity of binding sites. In the three groups, no specific nuclear labeling was detectable in the proximal tubule. The highest specific nuclear labeling was found in the distal portions of the nephron, and intermediate values were present along the loop of Henle. In the cortical collecting tubule, the most specific mineralocorticoid segment, the specific nuclear binding, expressed in silver grains per unit surface, was significantly elevated in SHR (16.1 +/- 1.5) and KWR (13.7 +/- 1.5) as compared with NWR (10.2 +/- 0.8, P less than 0.001 and less than 0.05, respectively). The difference between SHR and KWR did not reach statistical significance. In the medullary collecting tubule, binding was higher in SHR (14.3 +/- 1.6) than in both KWR (8.7 +/- 1.0, P less than 0.005) and NWR (10.1 +/- 0.9, P less than 0.025).(ABSTRACT TRUNCATED AT 250 WORDS)
Nephron adaptation to renal injury or ablation
Authors: Brenner B. M.
Published: December 2017

In early stages of permanent renal injury or extensive ablation, structural and functional adaptations associated with hypertrophy partially compensate for nephron losses. Glomerulotubular balance is maintained in these conditioned nephrons by intrinsic tubule and peritubular capillary adaptations that parallel single nephron glomerular filtration rate (SNGFR). Studies of Na+-H+ exchange in renal cortical brush border membrane vesicles indicate that tubule functional adaptation is not tied to loss of renal mass per se but rather to factors such as dietary protein content that set the level of SNGFR. Likewise, the structural heterogeneity that follows chronic renal injury or extreme ablation of renal mass is less a consequence of nephron injury than of adaptation linked to dietary protein intake. Indeed, since dietary protein restriction blunts the need for compensatory glomerular hyperfiltration, there is neither a stimulus for nephron hypertrophy nor for enhanced tubule ion and fluid transport. In rats with remnant kidneys, experimentally induced diabetes mellitus, or severe hypertension, increases in glomerular pressures and flows precede proteinuria, glomerular sclerosis, and azotemia. Protein restriction prevents these hemodynamic adaptations as well as the late complications. Similar conclusions appear to be applicable to a wide spectrum of clinical circumstances characterized by reduced nephron number.
Fasting induces denervation natriuresis in the conscious rat
Authors: Szenasi G. , Bencsath P. , Szalay L. , Takacs L.
Published: December 2017

The participation of renal nerves in the regulation of sodium excretion was studied in fed and overnight-fasted rats subjected to acute or chronic left kidney denervation or sham operation. Clearance experiments were performed on conscious restrained animals. Urine flow, glomerular filtration rate (GFR), and urinary sodium excretion were not different in left and right kidneys of sham-operated rats. In fed conscious rats, urine flow, GFR, and urinary sodium excretion of innervated (I) and denervated (D) kidneys were similar. In fasted conscious rats, significant denervation natriuresis was observed after both acute (I, 1.06 +/- 0.27; D, 1.56 +/- 0.40 mumol . min-1 . g-1, P less than 0.05) and chronic (I, 1.55 +/- 0.19; D, 2.20 +/- 0.18 mumol . min-1 . g-1, P less than 0.01) renal sympathectomy, whereas urine flow and GFR in I and D kidneys were not different. Additional experiments revealed that extracellular fluid and plasma volumes of fasted rats were decreased by approximately 10% compared with those of fed animals due to a significant overnight natriuresis and negative water balance. In fed conscious rats, the renal nerves do not seem to participate in the regulation of sodium excretion. The presence of denervation natriuresis in conscious fasted rats suggests that renal nerves are involved in sodium conservation during fasting to maintain extracellular fluid and plasma volume.
Fluorescence identifies an alkaline cell in turtle urinary bladder
Authors: Graber M. L. , Dixon T. E. , Coachman D. , Herring K. , Ruenes A. , Gardner T. , Pastoriza-Munoz E.
Published: December 2017

Intracellular pH (pHi) of turtle bladder mucosal cells was studied by the trapped fluorescent indicator technique. Bladders efficiently accumulated and converted 4-methylumbelliferyl acetate to its pH-sensitive derivative 4-methylumbelliferone (4MU). Excited at the pH-indifferent wavelength 334 nm, bladders fluoresced a uniform blue. Using pH-sensitive 365-nm excitation, 10-20% of the mucosal cells fluoresced distinctly brighter, suggesting a more alkaline pHi. Using the 365/334 ratio to quantitate pHi, this difference averaged 0.1 pH units. Bright cells were more distinct after SITS or acetazolamide but disappeared after digitonin permeabilization, dinitrophenol, or treatment with propionate, DMO, and NH4Cl. Essentially the same population of bright cells was identified by carboxyfluorescein diacetate. The brighter cell corresponded exactly to a population of cells with distinctive acridine orange staining and bright costaining with the potential-sensing probes Di-O-C5, Di-S-C3, and 4-Di-5-Asp. Two extremes of bright cell shape were seen: an elongate cell, prevalent under conditions stimulating H+ secretion, and a more compact cell, when acidification was inhibited. These observations support the hypothesis that acidification represents H+ secretion via the luminal membrane and that a primary role of carbonic anhydrase in this process is to support the exit of base from the cell. The more alkaline cells appear to be the carbonic anhydrase-rich cells. These cells are chemically isolated from the surrounding granular cells and change their morphology in response to changes in acidification. These special properties indicate a unique role for the carbonic anhydrase cell in H+ secretion.
Effects of ouabain, amiloride, monensin, and other agents on ovine parotid secretion
Authors: Wright R. D. , Blair-West J. R. , Nelson J. F.
Published: December 2017

Secretion by the parotid gland of Na-replete and -depleted sheep was investigated by examining the effects of modifiers of ionic transfer on salivary composition and flow rate. These agents were infused into the arterial blood supply of the vascularly isolated gland in anesthetized sheep. Ouabain inhibited Na+-K+ exchange in the ducts caused by Na depletion and restored the [Na+], [K+], and osmolality to close to those of Na-replete saliva. Ouabain also inhibited Cl- -HCO3- exchange in the ducts in Na repletion and depletion. Amiloride partially inhibited Na+-K+ exchange in Na depletion without affecting Cl- -HCO3- exchange. Monensin potentiated Na+-K+ exchange in Na repletion and depletion. Amiloride and monensin gained access to the saliva, but furosemide and ethacrynic acid were almost totally excluded, and, up to 10(-3) M in blood, they did not affect salivary composition or flow rate. Methazolamide gained free access to saliva but was without effect. 4-Acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid at 10(-3) M slightly increased salivary [Na+] and [HPO4(2-)]. The results indicate potent effects of ouabain on basolateral Na+-K+ pumps and of amiloride and monensin on transcellular delivery of Na+ to these pumps, but ouabain had no effect on salivary flow rate until O2 consumption approached zero and secretion failed. The findings do not support a proposal that the salivary secretion depends on a Cl- -dependent furosemide-sensitive system energized by Na+-K+-ATPase-dependent Na pumps.
Body sodium in rats: response to DOCA, adrenalectomy, changes in salt intake, and a salt load
Authors: Simpson F. O. , Ledingham J. M. , Paulin J. M. , Purves R. D.
Published: December 2017

Body Na was studied by an isotope method in rats on Na-free diet plus a choice of H2O and 0.5% or 0.1% NaCl. Two groups (1 on 0.5%, 1 on 0.1% NaCl) had Silastic deoxycorticosterone acetate (DOCA) implants, two similar groups were sham operated, and a fifth group (on 0.5% NaCl) underwent adrenalectomy (ADX). Saline consumption increased in DOCA-treated and ADX rats. Body Na was increased by DOCA and by drinking 0.5% NaCl compared with 0.1% NaCl. Body Na after intraperitoneal NaCl loading (which raised body Na 8-10%) and withdrawal of NaCl drinking fluids was analyzed by use of the model y = Ae-a(t-d) + Be-bt, where y is body Na at time t and d is delay before fast rate constant a is established; d was greater on the lower Na intake. Rate constant a was not reduced by chronic DOCA treatment. Coefficient B of the slow exponential, representing the basal level to which body Na falls on zero Na intake, and equivalent to Hollenberg's "set-point," was higher in DOCA-treated rats. This analysis makes use of Hollenberg's set-point concept, but the findings suggest that the set-point is related to mineralocorticoid activity and is thus presumably variable.
Primary culture of flounder renal tubule cells: transepithelial transport
Authors: Dickman K. G. , Renfro J. L.
Published: December 2017

Renal proximal tubule cells from the winter flounder (Pseudopleuronectes americanus) were maintained in a functionally differentiated state for up to 16 days in primary culture on floating collagen gels. The cells were confluent after 7-8 days in culture, contracted the collagen gels, and exhibited ciliary activity. Electron microscopy indicated that the cultures were composed of continuous sheets of columnar epithelial cells that had established structural polarity. When mounted in Ussing chambers, the cultures exhibited a small mucosa-negative potential difference (0.6 +/- 0.10 mV) and a low transepithelial resistance (23 +/- 2.3 omega X cm2). Short-circuit current averaged 24 microA/cm2. The cultured epithelium was four times more permeable to Na than to Cl and actively secreted sulfate and p-aminohippuric acid and reabsorbed hexoses. Glucose reabsorption was rheogenic and occurred via a high-affinity (Km = 0.16 mM), low-capacity (Vmax = 5 microA/cm2), phlorizin-sensitive transport system. We concluded that the cultured cells express many of the differentiated properties of the intact flounder proximal tubule and thus provide a suitable model system for studying renal transport processes.
Prevention of hypercalcemia-induced renal concentrating defect and tissue calcium accumulation
Authors: Harris D. C. , Gabow P. A. , Linas S. L. , Rosendale D. E. , Guggenheim S. P. , Schrier R. W.
Published: December 2017

The mechanism of the concentrating defect of hypercalcemia is explored by examining the effect of concomitant phosphate restriction. Rats were pair fed a normal phosphorus diet, without (group 1) or with dihydrotachysterol (group 2), or a low-phosphorus diet (group 3). Hypercalcemia was comparable in groups 2 (12.1 +/- 0.6 mg/dl) and 3 (11.8 +/- 0.4 mg/dl), but serum phosphate was lower in group 3 than group 2 (3.8 +/- 0.7 vs. 7.1 +/- 1.1 mg/dl, P less than 0.005). Group 2 rats had impaired maximum urinary concentration after 24 h of fluid deprivation (2,441 +/- 450 mosmol/kg H2O, P less than 0.001) compared with group 1 (3,263 +/- 466 mosmol/kg H2O) or group 3 (3,332 +/- 515 mosmol/kg H2O) animals. Polydipsia and polyuria were found in group 2 rats only. Tubular calcium reabsorption was higher in group 2 (83.1 +/- 33.5 mg/24 h, P less than 0.001) than group 1 (47.0 +/- 26.1 mg/24 h) or group 3 (52.8 +/- 19.3 mg/24 h) animals, and medullary calcium concentration was higher in group 2 (7.57 +/- 3.08 nmol/mg dry wt, P less than 0.05) as compared to group 1 (5.04 +/- 1.37 nmol/mg dry wt) or group 3 (5.32 +/- 0.98 nmol/mg dry wt) rats. Total medullary solute concentration was significantly higher in group 3 than group 2 animals. Thus phosphate restriction prevents the defect of urinary concentrating ability of chronic hypercalcemia, probably by decreasing tubular uptake and tissue accumulation of calcium.
Effect of atrial natriuretic factor on renal hemodynamics in the rat
Authors: Pollock D. M. , Arendshorst W. J.
Published: December 2017

Clearance experiments were conducted to determine the effects of atrial natriuretic factor (ANF) on renal hemodynamics and excretory function in anesthetized, euvolemic Munich-Wistar rats. Intra-aortic infusions of synthetic ANF (28 amino acids) at 7.5 and 15 micrograms X kg-1 X h-1 produced dose-related increases in absolute and fractional sodium and water excretion under steady-state conditions; renal blood flow (RBF) was unchanged, whereas mean arterial pressure significantly decreased but remained within the autoregulatory range. An apparent maximal response was elicited by 15 micrograms X kg-1 X h-1 as 30 micrograms X kg-1 X h-1 produced a similar increase in urine flow and sodium excretion. ANF infusion at 30 micrograms X kg-1 X h-1 produced no transient or sustained changes in RBF (electromagnetic flow probe). Renal vascular resistance was significantly decreased in parallel with reductions in arterial pressure; ANF-induced changes in resistance can be explained by autoregulatory adjustments. In another series, intra-aortic vs. intravenous infusion of ANF (7.5 micrograms X kg-1 X h-1) were compared in the same animal; the diuretic and natriuretic response to ANF was similar with the two routes of administration. We observed no consistent changes in glomerular filtration rate (GFR). Our results indicate that the diuretic and natriuretic effects of synthetic ANF in the rat do not require an increase in RBF or GFR.
Cytoplasmic calcium in individual proximal tubular cells in culture
Authors: Goligorsky M. S. , Loftus D. J. , Hruska K. A.
Published: December 2017

The development of high quantal yield Ca2+-sensitive fluorescent indicators has made microspectrofluorometric monitoring of cytoplasmic calcium feasible. The detailed technique to monitor cytoplasmic calcium concentration in individual proximal tubular cells grown on glass cover slips is described. Manipulations of cytoplasmic calcium concentration by means of a Ca2+ ionophore or Ca2+-free medium resulted in corresponding changes of fura-2 fluorescence. Parathyroid hormone elicited a fivefold increase in cytoplasmic calcium concentration, with the subsequent complete recovery of this parameter in 3 min. This effect of parathyroid hormone was abolished by perfusion of the cells with Ca2+-free medium. Repeated pulses of parathyroid hormone spaced at an interval of 20 min, caused refractoriness of adenosine 3',5'-cyclic monophosphate response, whereas cytoplasmic calcium transients remained unaltered. When the frequency of the sequential pulses with parathyroid hormone was increased (5 min intervals), the amplitude of calcium transients was diminished, and the recovery of basal level of cytoplasmic calcium was incomplete and protracted. These observations may have application to disordered renal cell calcium metabolism in hyperparathyroid states.
Surgical thyroparathyroidectomy of the rabbit
Authors: Tan S. Q. , Thomas D. , Jao W. , Bourdeau J. E. , Lau K.
Published: December 2017

Previous studies in the rabbit suggest resistance to parathyroid hormone (PTH) despite the reported presence of PTH-sensitive adenylate cyclase activity in renal cortical slices and tubules. The lack of response may reflect difficulties with complete parathyroidectomy in this species, which has been reported to possess 32 accessory glands. Aided by systematic histology of tissues extirpated during exploration, we tested the hypothesis that the rabbit possesses only four functional parathyroid glands and that the rabbit kidney is sensitive to the expected physiological actions of endogenous PTH. In all rabbits studied, only four glands could be identified histologically, two within the thyroids and two located in the fascial plane between the sternohyoid and sternothyroid muscles and the carotid artery. Surgical thyroparathyroidectomy markedly reduced serum Ca (6.3 vs. 10.6 mg/dl in sham-operated controls), increased the clearance (C) (3.51 vs. 0.78 ml/min) and fractional excretion (FE) of Ca (44.5 vs. 8.3%) while decreasing CP (1.14 vs. 2.40 ml/min), FEP (14.8 vs. 29.9%) and adenosine 3',5'-cyclic monophosphate (cAMP) excretion (341 vs. 760 pmol/min). These findings demonstrate the feasibility of using the described techniques for complete parathyroidectomy in the rabbit. Furthermore, they document the presence of only four functioning parathyroid glands and the renal sensitivity to endogenous PTH in this species.
Angiotensin receptor subtypes of the kidney cortex
Authors: Douglas J. G.
Published: December 2017

Angiotensin II (ANG II) binds with high affinity to specific renal receptors and exerts major influences on hemodynamics and tubular transport. Glomerular and tubular epithelial receptors are well characterized in contrast to pre- and postglomerular and medullary vasculature. Therefore, the scope of this review is limited to an indepth comparison of ANG II receptor kinetics, analogue specificity, and mechanisms of receptor regulation and signal transduction in glomeruli and epithelial cells. Despite the fact that these receptors are in close proximity anatomically, there is evidence from a number of laboratories that permits classification into two distinct receptor subtypes. The receptor of the glomerular mesangium, classified herein as “type A,” is characterized by high affinity for ANG II and the heptapeptide, des-Asp1-Ang II (ANG III), “downregulation” with high ambient concentrations of ANG II and signal transduction mediated by phospholipase C-induced Ca2+ transients. The tubular epithelial ANG II receptor, “type B,” is of lower affinity for ANG II and ANG III, “upregulated” by high levels of ANG II and mediates inhibition of adenylate cyclase following coupling to an inhibitory GTP binding protein. Both receptors possess secondary mechanisms of signal transduction that may also participate in regulation of cellular function(s). These findings support the hypothesis that at least two distinct classes of ANG II receptors are present in the kidney cortex.
Video measurement of basolateral NaCl reflection coefficient in proximal tubule
Authors: Welling L. W. , Welling D. J. , Ochs T. J.
Published: December 2017

Isolated, lumen-collapsed, proximal and distally occluded segments of rabbit S1 and S2 proximal tubule were equilibrated in isotonic NaCl or isosmotic raffinose medium and then exposed acutely to hypotonic or hypertonic raffinose or NaCl solution. The result was a water flux per millimeter tubule length, JVo, across the basolateral cell membranes and a consequent cell swelling or shrinkage that could be measured by a video technique in the initial 0.1 s or less after a change from steady state. The cell volume change was proportional to the applied osmolality difference, delta pi, and differed consistently with the solute employed. From the equation JVo/delta pi = sigma LpA, where sigma is the basolateral membrane reflection coefficient for the osmotic solute used and LpA is the membrane hydraulic conductivity per millimeter tubule length, and from the assumption that sigma raffinose = 1, sigma NaCl was obtained by dividing the JVo/delta pi values from the NaCl studies by those from the raffinose studies. For both S1 and S2 segments, sigma NaCl was found to be approximately 0.5. A similar value was obtained from the rate of cell shrinkage immediately after isosmolar exchange of raffinose for NaCl medium.
Glomerular size selectivity in nephrotic rats exposed to diets with different protein content
Authors: Remuzzi A. , Battaglia C. , Rossi L. , Zoja C. , Remuzzi G.
Published: December 2017

Glomerular size-selective properties in animals made nephrotic by adriamycin (ADR) injection and fed standard (20% protein) or high-protein (35% protein) diets were investigated using dextran fractional clearances. To interpret filtration and dextran-sieving data, a theoretical approach previously developed for analysis of experimental data in healthy and nephrotic humans was used. Four types of hypothetical pore-radius distributions were compared in order to establish the best tool for describing membrane pore structure in normal and nephrotic rats. This analysis revealed that a spread distribution of pores, the lognormal probability distribution, is the most adequate in representing membrane intrinsic characteristics. ADR animals on standard diet developed massive proteinuria and a lower glomerular filtration rate (GFR) than control animals. High-protein feeding in ADR rats induced a further increase in urinary protein excretion and in GFR. Dextran fractional clearance was more elevated for larger dextran fractions (greater than 46 A) in ADR animals on the standard diet than in control rats. No differences were observed in dextran-sieving curves between ADR rats on the standard and high-protein diet. Theoretical analysis of filtration and fractional clearance data revealed comparable changes in the intrinsic parameters of glomerular size selectivity in the two groups of nephrotic animals. These observations indicate that increased traffic of plasma proteins through the glomerular capillary wall does not imply, in our experimental condition, a further loss of glomerular size-selective properties. The greater urinary protein excretion of ADR animals on high-protein diet than ADR animals on a standard diet cannot be explained by further impairment of glomerular size selectivity but more likely reflects hemodynamic changes.