bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermodynamic analysis of active sodium and potassium transport in the frog corneal epithelium
Authors: Candia O. A. , Reinach P. S.
Published: December 2017

The formalism of linear nonequilibrium thermodynamics for a three-flow system was applied to the isolated frog corneal epithelium to study the coupling between metabolism and the Na-K transport system across this layer. There is little or no net ion transport across the isolated frog corneal epithelium bathed in Na2SO4 Ringer. Addition of amphotericin B to the tear side solution increases apical membrane permeability, which results in a net Na transport (from tear to stroma) and a net K transport in the opposite direction. Corneas were mounted in a modified Ussing chamber that permitted the simultaneous measurements of electrical parameters and O2 consumption by means of Clark-type oxygen electrodes. The overall degree of coupling, q, of the Na-K transport system to metabolism was calculated from measuring the suprabasal O2 consumption rate at "static head" and "level flow" conditions and by a second independent technique. Measurements of electrical conductance used in conjunction with other previously measured parameters allowed the calculation of the affinity, A, of the metabolic reaction driving transport, all phenomenological coefficients, and the electromotive forces of sodium (ENa) and potassium transport (EK). Values of q determined by the two techniques agreed (q = 0.80 and 0.84, respectively). This indicates incomplete coupling and a variable stoichiometric relationship among O2 consumption rate, net Na transport, and net K transport. The value calculated for A was 70.5 kcal.mol-1, for ENa 142.5 mV, and for EK -34.9 mV.
Proximal cell K+ activity: technical problems and dependence on plasma K+ concentration
Authors: Teulon J. , Anagnostopoulos T.
Published: December 2017

K+-selective liquid ion-exchanger double-barreled microelectrodes were used to measure intracellular K+ activity (alpha Ki) of proximal tubular cells in Necturus kidney. SEveral methodological problems inherent in the construction and in vivo application of such microelectrodes were considered, in particular the identification of leaky impalements and the correct assessment of alpha Ki during reversible perfusion of peritubular capillaries from control to a test solution. Peritubular potassium concentration (CpK) could be altered by means of double-barreled micropipettes containing a physiologic and a high or low K solution. The control alpha Ki value averaged 57.9 +/- 8.5 mM (mean +/- SD, n = 38) and the basolateral membrane potential was -70.4 +/- 5.8 mV. Thus, the K+ equilibrium potential across the basolateral membrane (EK) was -81.1 +/- 3.4 mV. Increasing CpK from 3.0 to 30.0 mM raised alpha Ki by 7.0 +/- 1.5 mM, and lowering CpK to 0.3 mM decreased alpha Ki by 9.2 +/- 2.9 mM. Conclusions: 1) the steady-state K+ distribution across the basolateral membrane indicates that potassium is actively pumped into the cell. 2) The relative stability of alpha Ki in the face of large CpK variations underscores the effectiveness of cell homeostasis; passive mechanisms appear to contribute to this end.
Segmental analysis of sodium reabsorption during renal vein constriction
Authors: Burnett J. C. , Haas J. A. , Knox F. G.
Published: December 2017

Clearance and micropuncture studies were performed in rats to identify the nephron site(s) of altered sodium reabsorption during partial renal vein constriction in the presence and absence of volume expansion. Renal vein constriction increased fractional deliver of sodium to the late proximal tubule from 52 +/- 3 to 61 +/- 4% in euvolemia and from 59 +/- 3 to 65 +/- 3% in volume expansion. In euvolemia, fractional delivery of sodium to the early distal tubule was 13 +/- 3% before and 24 +/- 6% after renal vein constriction. In volume expansion, fractional delivery of sodium to the early distal tubule decreased from 15 +/- 3 to 9 +/- 2% in response to renal vein constriction. We conclude that renal vein constriction decreases sodium reabsorption by the proximal tubule both in euvolemia and in volume expansion but that it increases sodium reabsorption by the superficial loop of Henle only in the presence of volume expansion.
Effect of aging on urinary concentrating mechanism and vasopressin-dependent cAMP in rats
Authors: Beck N. , Yu B. P.
Published: December 2017

The effect of aging on urinary concentrating ability and the pathogenic mechanism involved were investigated in Fischer 344 rats. While the rats had free access to drinking water, 24-mo-old rats were polydipsic and polyuric compared with 6- and 12-mo-old rats. The maximum urinary concentrating ability after 40-58 h of water deprivation was not different between 6- and 12-mo-old rats (Uosmol 2,941 +/- 173 vs. 2,706 +/- 96 (SE) mosmol/kg), but it was significantly decreased in 24-mo-old rats (1,885 +/- 172 mosmol/kg, P less than 0.01). Similarly, although 5 mU/ml vasopressin increased the concentration of cAMP and papillary slices in 12-mo-old rats (delta +2.81 +/- 0.62 pmol/mg tissue, P less than 0.01), the same concentration of vasopressin failed to increase the cAMP concentration in 24-mo-old rats (delta +0.25 +/- 0.21 pmol/mg tissue, P greater than 0.05). In the adenylate cyclase preparation of renal papilla, the response to low concentrations of vasopressin was diminished in 24-mo-old rats. The dose-response curve was shifted to the right and the ED50 concentration of vasopressin was increased in 24-mo-old rats compared with 12-mo-old rats: 1.40 +/- 0.12 mU/ml vasopressin vs. 3.04 +/- 0.22. These results suggest that the decrease in vasopressin-dependent cAMP generation may in part be responsible for the impairment of urinary concentrating ability in 24-mo-old rats.
Effects of acute acid-base disturbances on renal tubule reabsorption of magnesium in the rat
Authors: Roy D. R. , Blouch K. L. , Jamison R. L.
Published: December 2017

The effects of acute metabolic and respiratory acidosis and acute metabolic alkalosis on magnesium excretion and on fractional magnesium delivery to the end-accessible proximal tubule of the superficial nephron and the end-descending limb of the juxtamedullary nephron were examined by micropuncture in anesthetized thyroparathyroid-intact rats. Compared with normal control rats, acute metabolic acidosis (HCl infusion) did not produce any significant change. Acute respiratory acidosis (15% CO2 in inspired air) significantly increased the absolute but not the fractional excretion of magnesium and did not alter fractional delivery of magnesium to the end-accessible superficial proximal tubule or juxtamedullary end-descending limb. Acute metabolic alkalosis (NaHCO3 infusion) significantly reduced absolute and fractional magnesium excretion and fractional magnesium delivery to the end-descending limb of the juxtamedullary nephron but did not affect fractional magnesium delivery to the end-accessible proximal tubule of the superficial nephron. Tubule fluid-to-ultrafilterable magnesium ratio was a function of tubule fluid-to-plasma inulin ratio in the end-descending limb when all groups were combined. These results suggest that although acute metabolic or respiratory acidosis has no significant effect, acute metabolic alkalosis enhances magnesium reabsorption in the juxtamedullary proximal nephron--possibly in the pars recta.
Sodium transport in the rabbit connecting tubule
Authors: Almeida A. J. , Burg M. B.
Published: December 2017

Connecting tubules were dissected from rabbit kidneys and perfused in vitro with a solution identical to that in the bath. Transepithelial sodium fluxes were measured with 22Na. The mean lumen-to-bath flux was 33.7 +/- 3.4 peq . cm-1 . s-1 and the mean bath-to-lumen flux was 13.4 +/- 3.4 peq . cm-1 . s-1. Thus, the net sodium transport was 20.3 peq . cm-1 . s-1, which is approximately 3--4 times higher than the one previously measured in cortical collecting ducts under similar conditions. The sodium permeability calculated from the bath-to-lumen measurements corrected for mean voltage was 1.22 x 10(-5) cm .s-1. The mean transepithelial electrical resistance was 31 omega . cm2. This sodium permeability is much higher and the electrical resistance much lower than those in cortical collecting ducts. Spontaneous transepithelial voltage was oriented negative in the lumen and ranged up to -42 mV at low perfusion pressures. When the perfusion pressure was increased, the voltage decreased to approximately -5 mV without any measurable change in the electrical resistance or the lumen-to-bath sodium flux.
Requirement of Na+ and K+ for the action of antidiuretic hormone on water permeability
Authors: Hardy M. A.
Published: December 2017

Previous reports have shown that in the toad bladder the absence of serosal Na+ or K+ inhibits the action of antidiuretic hormone (ADH) on the osmotic permeability (Pf) but not on diffusional permeability (PDW) to water. This dissociation could be due to unstirred layers with low PDW, precluding detection of changes in the PDW of the cells. When serosal Na+ was replaced by choline, Pf (micrometer/s) was inhibited from 201 to 65. In the same conditions, if appropriate corrections were made to allow for the PDW of unstirred layers in the bulk phase and stroma, the PDW (micrometers/s) of the cellular pathway decreased from 19.8 to 15.9. The Pf/PDW ration then became 10 in the presence of serosal Na+ and 11 in its absence. When serosal K+ was deleted Pf decreased from 197 to 127 and PDW (corrected for unstirred layers) from 19.8 to 13.1 The Pf/PDW ratio was 10, both in the presence and absence of serosal K+. In conclusion, it is impossible to estimate the effect of any given experimental manipulation on the ADH-induced increase in PDW and compare it with the effect of Pf unless attention is paid to the restrictions upon measurements of diffusion imposed by unstirred layers. The deletion of Na+ or K+ from the serosa inhibits the effect of ADH on Pf and PDW to the same extent. Therefore, their presence in the serosa is essential for a full effect of ADH on the permeability to water of the apical membrane.
Interpretation and use of electrical equivalent circuits in studies of epithelial tissues
Authors: Helman S. I. , Thompson S. M.
Published: December 2017

Whereas transepithelial and intracellular voltages continue to be measured in renal and other epithelial tissues, the origins of these voltages, especially in renal epithelia, remain obscure. Because epithelial tissues have multiple transcellular and extracellular routes of ion transport, it is convenient to model them with electrical equivalent circuits and, in this way, attempt to understand the relative importance of and relationships between the parallel-series arrangements of the membranes and barriers involved. The interpretation of the equivalent electromotive forces and resistances can be complicated, however, by virtue of nonlinear current-voltage relationships of ionic channels. Thus, for ion transport pathways displaying nonlinear I-V relationships, it is important to distinguish between chord and slope formalisms in the use and interpretation of electrophysiological data. For ions like Na that are generally not at electrochemical equilibrium, the Thevenin electromotive force (emf) of the slope formalism is not synonymous with the Nernst equilibrium potential of the chord formalism nor are the slope and chord conductances equal or constant at all voltages. Thus, it is mandatory that the empirical data be calculated and interpreted in a way consistent with the formalism adopted. The existence of nonlinear behavior, characterized by either Goldman or other types of rectification, exacerbates determination of relative ionic permeabilities, fractional resistances, transference numbers, and other electrophysiological parameters for simple membranes and especially for epithelia. It is argued that the use and interpretation of electrical equivalent circuits of epithelia are not arbitrary but must take into account nonlinearities of the ionic current-voltage relationships and concentration and voltage dependencies of the emfs and conductances.
Effect of sodium chloride on longevity in mice
Authors: Rosenthal S. M.
Published: December 2017

The effects of dietary sodium chloride on the longevity, body weight, and food consumption in a normotensive strain (A/J) of mice was studied. Four groups of 50 mice each were fed diets containing 0.5 (control group), 1.5, 2.5, and 4.5% sodium chloride. The mean life span was 115.2 wk in the control group, and 115.5, 110,5, and 116.1 wk for groups 2, 3, and 4, with no significant differences from the control group. No differences were present in food consumption, but a graded weight loss was present after the 20th wk, which persisted throughout the experiment. No significant effect of salt loading was demonstrable on the extravascular fluid movement in either acute experiments or in the long-term dietary sodium chloride groups.
Vasopressin stimulates prostaglandin and thromboxane synthesis in toad bladder epithelial cells
Authors: Burch R. M. , Halushka P. V.
Published: December 2017

The effects of arginine vasopressin (AVP) and its nonpressor analogue desamino-8-arginine vasopressin (dDAVP) on immunoreactive prostaglandin E and thromboxane B2 synthesis from endogenous arachidonic acid by epithelial cells isolated from toad urinary bladders were investigated. In epithelial cell suspensions prepared using a collagenase treatment, AVP (5 mU/ml) stimulated prostaglandin E synthesis from 0.27 +/- 0.05 to 0.53 +/- 0.09 pmol . min-1 . mg protein-1 (P less than 0.01, n = 6) and stimulated thromboxane A2 synthesis, as assessed by measurement of its stable metabolite thromboxane B2, from 0.032 +/- 0.004 to 0.054 +/- 0.009 pmol . min-1 . mg protein-1 (P less than 0.02, n = 6). dDAVP (130 nM) also stimulated immunoreactive prostaglandin E and thromboxane B2 synthesis (P less than 0.05, n = 6). In cells prepared by EDTA treatment or scraping, aVP did not alter prostaglandin or thromboxane synthesis. This study demonstrates that AVP and dDAVP stimulate both prostaglandin and thromboxane synthesis in epithelial cells from the toad urinary bladder and suggests that the antidiuretic activity of these peptides is associated with this effect. The results are consistent with previous observations that the synthesis of prostaglandin E and thromboxane by epithelial cells results in a negative and positive modulation, respectively, of the action of AVP on water transport.
Polycystic kidney disease: a predominance of giant nephrons
Authors: Grantham J. J.
Published: December 2017

Polycystic kidney disease is a bilateral disorder that affects approximately 200,000-400,000 persons in the United States. The most common form of the disease is inherited as an autosomal dominant trait (ADPKD). It typically causes renal insufficiency by the fifth or sixth decade of life. The disease is characterized by the progressive enlargement of a portion of renal tubule segments (proximal, distal, loop of Henle, collecting duct). The tubules enlarge from a normal diameter of 40 microns to several centimeters in diameter, causing marked gross and microscopic anatomic distortion. The cause of the cystic change in the tubules is unknown, but current possibilities include obstruction of tubule fluid flow by hyperplastic tubule cells, increased compliance of the tubule basement membranes, and/or increased radial growth of cells in specific portions of the renal tubule. Several studies show that the epithelia of the cysts continue to transport Na+, K+, Cl-, H+, and organic cations and anions in a qualitative fashion similar to that of the tubule segment from which they were derived. ADPKD, then, is a disease in which some gigantic renal tubules, over a period of several decades, impair the function of nonaffected nephrons and thereby lead to renal failure.
Intracellular microelectrode characterization of the rabbit cortical collecting duct
Authors: Koeppen B. M. , Biagi B. A. , Giebisch G. H.
Published: December 2017

Cortical collecting ducts of the rabbit were perfused in vitro and the intracellular potential (Vbl) was measured with KCl-filled microelectrodes. The ratio of apical to basolateral membrane resistance (Ra/Rbl) was estimated from the voltage divider ratio using cable analysis. In control tubules Vbl averaged--84.0 +/- 2.5 mV and Ra/Rbl was 0.83 +/- 0.11. Pretreatment of the rabbits with mineralocorticoid caused Vbl to hyperpolarize to--105.8 +/- 3.1 mV and Ra/Rbl to decrease slightly to 0.62 +/- 0.10. A 10-fold increase of the luminal [K+] caused a 40.6 +/- 3.1 mV depolarization of Vbl in control tubules and a 33.0 +/- 4.2 mV depolarization in tubules from DOCA-pretreated rabbits. Concurrently, Ra/Rbl decreased in both groups, consistent with the existence of a conductive K+ channel at the apical cell membrane. This apical K+ channel was not sensitive to amiloride but was blocked by Ba2+. Conductive movement of Na+ across the apical membrane was also apparent in that Ra/Rbl increased with amiloride from 0.61 +/- 0.10 to 1.45 +/- 0.28. A 10-fold increase in the bath [K+] caused a 28.6 +/- 3.8 and a 49.4 +/- 4.4 mV depolarization of Vbl in tubules obtained from control and DOCA-pretreated rabbits, respectively. In both groups Ra/Rbl increased, suggesting that the basolateral cell membrane also contains a conductive K+ channel. Taken together the results support a model in which the transepithelial reabsorption of Na+ and the transepithelial secretion of K+ are driven by the Na+-K+-ATPase located in the basolateral cell membrane, with passive movement of these ions occurring through separate conductive pathways in the apical cell membrane.
Hypertaurinuria in the C57BL/6J mouse: altered transport at the renal basolateral membrane
Authors: Rozen R. , Scriver C. R. , Mohyuddin F.
Published: December 2017

The C57BL/6J mouse is an inbred strain with selective hypertaurinuria. C3H/HeJ mice (control) and C57BL/6J mice have comparable values for plasma taurine and renal creatinine clearance but significantly different fractional taurine excretion: C3H mice, 0.15 +/- 0.03; C57BL mice, 0.44 +/- 0.08 (P less than 0.01). C57BL mice fed control diet have significantly higher renal cortex taurine (11.5 +/- 0.4 mumol/g wet wt, mean +/- SE) relative to C3H mice (10.5 +/- 0.5 mumol/g, P less than 0.05); the difference is magnified when mice are fed low protein or low sulfur amino acid diet and experience renal adaptation with enhanced taurine transport at the luminal membrane (P less than 0.01). Taurine transport by purified brush border membrane vesicles is similar in the two strains fed control diet. On the other hand, renal cortex slices show the following differences: 1) net uptake of taurine at 0.11 mM is lower in C57BL slices at initial rates and at steady state; 2) the difference in uptake between strains is magnified in the presence of phlorizin, an inhibitor of taurine efflux; 3) efflux of taurine from preloaded slices is less per unit time in C57BL mice; and 4) uptake differences are specific for taurine. These findings are not accountable to differences in taurine oxidation, slice weight, or water spaces. They indicate that hypertaurinuria in the C57BL/6J strain is a function of decreased basolateral membrane permeability to taurine at physiologic concentrations.
Renal response to AVP and DDAVP after angiotensin II blockade in the rat
Authors: Fejes-Toth G. , Zahajszky T. , Filep J.
Published: December 2017

Inhibition of the renin-angiotensin system with saralasin or with SQ 20,881 was used to examine a possible interaction between endogenous angiotensin II and antidiuretic hormone in renal water excretion. In sodium-depleted anesthetized rats undergoing water diuresis, neither saralasin nor SQ 20,881 had any significant effect on water excretion. Both drugs, however, markedly potentiated the antidiuretic response to arginine vasopressin. A similarly enhanced antidiuresis was also observed when the renal response to 1-desamino-8-D-arginine vasopressin was investigated in the presence or absence of saralasin. There were no significant changes in sodium or potassium excretion or in glomerular filtration rate in any of the groups studied. Neither was there any interaction of the drugs with relation to blood pressure. These results seem to indicate that endogenous angiotensin II is capable of antagonizing the hydroosmotic effect of antidiuretic hormone.
Support of kidney function by long-chain fatty acids derived from renal tissue
Authors: Fonteles M. C. , Cohen J. J. , Black A. J. , Wertheim S. J.
Published: December 2017

To determine whether the oxidation of long-chain fatty acids (LCFA) derived from renal tissue lipids can support renal function, we perfused isolated rat kidneys with a substrate-free Krebs-Ringer bicarbonate solution containing 6 g/100 ml substrate-free (defatted) albumin. We measured GFR, TNa+, and Qo2 at 7-min intervals from 15 to 99 min after cannulation of the renal artery. Two groups (A and B) of 12 perfusions each were done. During substrate-free perfusion mean %TNa+ was low (A = 45 +/- 2%, B = 62 +/- 5%). When 10(-4) M 2-tetradecylglycidic acid (2-TDGA), a specific and irreversible inhibitor of long-chain acylcarnitine transferase-I, was added to the substrate-free perfusate, significant decreases in %TNa+ (A to approximately 25%; B to approximately 35%) and in Qo2 (delta = -25%) occurred. During perfusion with either 5 mM lactate or 5 mM alpha-ketoglutarate (alpha-KG) %TNa+ increased to approximately 80%. When 2-TDGA was added in the presence of lactate or of alpha-KG no decrease in %TNa+ or Qo2 occurred. Thus, 2-TDGA does not inhibit net renal Na+ transport or O2 uptake in the presence of high concentrations of lactate or alpha-KG, substrates not requiring long-chain acylcarnitine transferase for their utilization. We conclude that oxidation of LCFA released from renal tissue lipids can support a significant portion of Na+ reabsorption.
Autoradiographic determination of dexamethasone binding sites along the rabbit nephron
Authors: Farman N. , Vandewalle A. , Bonvalet J. P.
Published: December 2017

Specific binding sites of tritiated dexamethasone ([3H]dex) along the tubule of rabbit kidney were investigated using an autoradiographic method (dry film) on isolated tubular segments. After in vitro incubation of kidney pyramids with [3H]dex (0.15-53 nM) in the presence or absence of an excess (X200) of unlabeled dexamethasone, tubular segments were microdissected and processed for autoradiography. A quantitative analysis of specific labeling over cytoplasm and nuclei was performed. Specific nuclear binding was observed in all tubular segments beyond the pars recta. This binding was dose dependent and reached much higher values than those reported for aldosterone. In the proximal tubule, the specific labeling was also high but remained mostly cytoplasmic. The meaning of these drastically different intracellular localizations is still open to interpretation. Autoradiography was performed after in vivo injection of [3H]dex and [3H]aldosterone. The results were not different from those described here for dexamethasone and from those previously reported for aldosterone after in vitro incubation. We conclude that specific nuclear binding sites for dexamethasone range over the nephron except for proximal tubule, with no great difference among segments, in contrast to specific sites for aldosterone, which are restricted to distal and cortical collecting tubules. The exact significance of the proximal cytoplasmic specific binding of [3H]dex remains to be determined.
Renal excretion of ascorbic acid in the rat: a micropuncture study
Authors: Martin M. , Ferrier B. , Roch-Ramel F.
Published: December 2017

Ascorbate concentration was measured by high-performance liquid chromatography and amperometry in plasma, tubular fluid, and urine from rats infused with ascorbic acid to steady-state levels. At a low concentration of ascorbate in plasma (Pasc = 0.2 mM) reabsorption occurred along the proximal convoluted tubule (PCT). The fractional delivery (FD) of ascorbate [(TF/P)asc/(TF/P)polyfructosan] to the late proximal convoluted tubule was 0.64 +/- 0.04, and the fractional excretion of ascorbate (FEasc) was 0.56 +/- 0.01. At higher Pasc (0.9 mM) net secretion occurred in the PCT, while the FDasc was 1.5 +/- 0.2 to the early and 1.8 +/- 0.2 to the late PCT. At still higher Pasc the secretory and the reabsorptive transports were saturated and the FDasc and FEasc approached unity, indicating that reabsorptive as well as secretory transport occurs in the proximal tubule. In clearance experiments the reabsorptive transport and secretory transport were inhibited by 2-nitroprobenecid. The drug induced a fall of FEasc when infused at a low rate (0.9 mumol X kg body wt-1 . min-1), which was followed by an increase in FEasc when the rate of infusion of 2-nitroprobenecid was increased to 3 mumol . kg body wt-1 X min-1.
Distribution of immunoreactive kallikrein along the rat nephron
Authors: Proud D. , Knepper M. A. , Pisano J. J.
Published: December 2017

We have used a direct radioimmunoassay to localize kallikrein along the corticomedullary axis of the rat kidney and in microdissected rat cortical nephron segments. As previously seen in rat and dog, kallikrein content was highest in the outer cortex and decreased progressively toward the papillary tip. In microdissected cortical nephron segments, the highest kallikrein content was found in the connecting tubule [176 +/- 16 (SE) pg/mm tubule length (n = 12)]. In addition, a significant amount of kallikrein was found in distal convoluted tubules [53 +/- 4 pg/mm (n = 14)], initial collecting tubules [75 +/- 10 pg/mm (n = 14)], and cortical collecting ducts [37 +/- 4 pg/mm (n = 13)]. Little or no kallikrein was found in glomeruli, proximal convoluted tubules, proximal straight tubules, and cortical thick ascending limbs. These results are compatible with a site of action of the kallikrein-kinin system in the cortical segments of the rat distal nephron.
Alterations in renal cortical phospholipid content induced by gentamicin: time course, specificity, and subcellular localization
Authors: Knauss T. C. , Weinberg J. M. , Humes H. D.
Published: December 2017

Increasing evidence suggests that membrane phospholipids are a major site of interaction between gentamicin and renal tubular cells. To help assess the impact of this interaction on renal tubular cell phospholipid metabolism, renal cortical phospholipid levels were assessed serially during treatment with nephrotoxic doses of gentamicin in the rat. Within 15 h of treatment with a single 100 mg/kg dose of gentamicin, significant increases in phosphatidylinositol and phosphatidic acid occurred, and further increases in these acidic phospholipids were seen 24 h after two and four daily doses. No consistent sustained changes were observed in total phospholipid levels or in levels of other phospholipids. None of these gentamicin treatment regimens was associated with wide-spread tubular cell necrosis in the rat at the intervals studied. In contrast, during models of acute renal failure secondary to HgCl2 and glycerol, increases in phosphatidylinositol and phosphatidic acid were found only after the development of wide-spread tubular cell necrosis. Subcellular fractionation studies showed that the increase in phosphatidylinositol produced by gentamicin involved multiple cell membranes, including mitochondria, brush border membranes, endoplasmic reticulum, and lysosomes, suggesting that the effects of gentamicin on renal cortical acidic phospholipid metabolism are not limited to inhibition of intralysosomal degradative processes but, rather, occur in such fashion as to influence the phospholipid composition of multiple subcellular membranes.
Glomerular ultrafiltration dynamics during increased renal venous pressure
Authors: Dilley J. R. , Corradi A. , Arendshorst W. J.
Published: December 2017

The effects of unilateral partial renal venous ligation on whole kidney and single nephron function were determined in anesthetized euvolemic Munich-Wistar rats using clearance, blood flow, and micropuncture techniques. Increased venous pressure (4-22 mmHg) reduced glomerular filtration rate (GFR) and renal plasma flow (RPF) to 60% of control values; filtration fraction (FF) was constant. Similar responses occurred in the superficial cortex, as evidenced by a 40% fall in SNGFR determined while intratubular pressure was maintained at the elevated precollection level. Fractional reabsorption by the proximal convoluted tubule remained constant, indicating maintenance of glomerulotubular balance. The contralateral kidney exhibit a diuresis and natriuresis while GFR and RPF were stable. In the experimental kidney single nephron glomerular plasma flow decreased by 35% due to increments in preglomerular and efferent arteriolar resistance. The transcapillary hydrostatic pressure gradient was unchanged since there were similar 7- to 8-mmHg increases in glomerular capillary and Bowman's space pressures. Filtration pressure disequilibrium was observed in control and experimental periods. Mean effective ultrafiltration pressure was similar in both periods. Specific values for the ultrafiltration coefficient (Kf) fell from 0.023 to 0.015 nl . s-1. mmHg-1. Accordingly, partial renal venous ligation produces ipsilateral vasoconstriction and a fall in GFR that is primarily due to a proportional decline in Kf.
Citrate uptake by basolateral and luminal membrane vesicles from rabbit kidney cortex
Authors: Jorgensen K. E. , Kragh-Hansen U. , Roigaard-Petersen H. , Sheikh M. I.
Published: December 2017

The mechanisms of tubular transport of citrate in renal basolateral and luminal membrane vesicles were studied under various experimental conditions. Both membrane preparations take up citrate by a Na+-dependent transport system, although with different characteristics. The uptake of citrate by basolateral membrane vesicles was insensitive to changes in membrane potential, which is indicative of electroneutral transport of the anion. The Na+-dependent uptake of citrate by luminal membrane vesicles was influenced by the presence of Na+salt anions of different permeabilities in the order: chloride greater than sulfate greater than gluconate. Furthermore, addition of citrate to membrane vesicle-potential-sensitive dye suspensions resulted in optical changes of the dye, indicative of electrogenic transfer of this compound. The apparent affinity of the citrate transport system located in luminal membrane vesicles, in contrast to basolateral membrane vesicles, was sensitive to changes in medium pH and was higher than that of basolateral membrane vesicles in the pH range studied. On the basis of these results a model for the transport of citrate by rabbit kidney proximal tubule is proposed.
Presence in normal human urine of a hypotensive and platelet-activating phospholipid
Authors: Sanchez-Crespo M. , Inarrea P. , Alvarez V. , Alonso F. , Egido J. , Hernando L.
Published: December 2017

Urine from normotensive volunteers and patients with systemic lupus erythematosus glomerulonephropathy was sequentially concentrated by negative-pressure ultrafiltration, dialyzed against distilled water, and extracted into the chloroform phase of a mixture of organic solvents(chloroform:methanol:water, 1:1:0.9 vol/vol). The lipid fraction was further purified by thin-layer chromatography on silica gel plates using neutral, acidic, and basic mixtures of organic solvents and it was then tested for its ability to induce the release of [3H]serotonin from rabbit platelets. All of the samples contained a platelet-activating moiety similar to a synthetic platelet-activating factor (PAF-acether) on the basis of its chromatographic behavior, resistance to the pretreatment of platelets by 10(-6) M indomethacin, and loss of activity by alkaline methanolysis or treatment by phospholipases A2, C, and D. Cross-densensitization experiments between synthetic PAF-acether and the urine factor showed that both compounds act on platelets through the activation of the same putative receptor. Further, the urine factor induced hypotension when intra-arterially injected in normotensive rats, and this activity was also abrogated by alkaline methanolysis. In summary, these data provide evidence of the presence in normal human urine and, probably, of the release by the kidney of a lipid factor with platelet-activating and hypotensive activity whose general structure seems to be alkyl-acyl-glyceryl-phosphorylcholine and, therefore, is similar to the structure of the inflammatory mediator PAF-acether and the antihypertensive polar renomedullary lipid.
Evidence for bidirectional net movement of creatinine in the rat kidney
Authors: Namnum P. , Insogna K. , Baggish D. , Hayslett J. P.
Published: December 2017

Although the clearance of endogenous creatinine is used in many physiologic and metabolic studies in the rat as an index of glomerular filtration rate, there is no evidence that creatinine is a reliable test substance. Studies were therefore performed in anesthetized and conscious rats to determine the creatinine-to-inulin clearance ratio (CCr/CIn). In anesthetized animals the CCr/CIn ratio was 0.5 and in conscious rats it was 0.7 at normal basal plasma creatinine levels. After an increase in plasma creatinine to 1.9 mg/dl induced by the intravenous infusion of creatinine, the CCr/CIn ratio was 1.2. Accordingly, these data indicate that net creatinine transport across the renal tubule is bidirectional and that transport is influenced by the plasma creatinine level. At normal plasma levels creatinine is extensively reabsorbed along the nephron, whereas net secretion is associated with elevated plasma creatinine. The results demonstrate that creatinine is not a reliable marker of glomerular filtration rate in the rat.
Phosphate uptake by a kidney cell line (LLC-PK1)
Authors: Rabito C. A.
Published: December 2017

The uptake of inorganic phosphate was studied in an epithelial cell line of renal origin. Phosphate was accumulated through a mechanism with several features of a carrier-mediated process. The influx was accounted for by a saturable Na+-dependent and a nonsaturable Na+-independent process. Kinetic analysis at pH 6.6 and 7.4 suggests that the dibasic form of phosphate is the form transported by the saturable Na+-dependent system. The presence of Na+ in the incubation medium increased Vmax without affecting Km. Arsenate competitively inhibited the Na+-dependent phosphate transport with a Ki of 1.2 mM at 140 mM Na+ and pH 7.4. Other known inhibitors of phosphate reabsorption in the proximal tubule also inhibited phosphate transport by this cell line. Uptake studies from either side of the monolayers indicated that this transport system is preferentially located in the apical membrane of the cultured renal cells. These results show a close similarity between the Na+-dependent phosphate transport system in LLC-PK1 cells and the system present in the apical membrane of the proximal tubular cells.
Effect of pH and amiloride on the intrarenal formation of kinins
Authors: Scicli A. G. , Diaz M. A. , Carretero O. A.
Published: December 2017

Changes in urinary kallikrein excretion are assumed to reflect changes in intrarenal formation of kinins. Yet factors that alter the enzymatic activity of renal kallikrein and kininases may alter the concentration of kinins in the nephron independent of amount of kallikrein excreted. In anesthetized rats, we measured excretion of urinary kallikrein (kininogenase activity) and kinin excretion during altered urinary pH and after amiloride, which reportedly inhibits urinary kallikrein. In rats fed a low sodium diet, urine was acidified by intravenous 0.28 M sodium sulfate. This decreased urinary pH from 6.1 +/- 0.09 to 5.3 +/- 0.17 and urinary kinin excretion from 28.0 +/- 9.0 to 10.5 +/- 5.0 pg/min. Urinary kallikrein excretion doubled from 43.0 +/- 5.0 to 82.5 +/- 13.5 ng/min. The optimum pH of kallikrein is congruent to 8.5, so the decreased excretion of urinary kinins is probably secondary to decreased kininogenase activity at lower urinary pH. Amiloride decreased urinary kinins from 35.5 +/- 7.3 to 18.2 +/- 2.5 pg/min and kallikrein from 18.7 +/- 4.9 to 9.3 +/- 1.8 ng/min, while urinary pH increased from 6.7 +/- 0.07 to 7.3 +/- 0.07. The depressed excretion of kallikrein and kinins with amiloride may not have been due to inhibition of kallikrein, since amiloride (1 mM) did not inhibit the kininogenase activity of rat urinary kallikrein (congruent to 1.2 nM) on dog or rat kininogen in vitro. We conclude that changes in urinary kallikrein may not reflect changes in intrarenal formation of kinins. These data also indicate that kallikrein excretion increases and kinin formation decreases when urine is acidified in the distal nephron and that there may be a link between the kallikrein-kinin system and the renal mechanisms affected by amiloride.
Effect of betamethasone on Na-K-ATPase activity and basal and lateral cell membranes in proximal tubular cells during early development
Authors: Igarashi Y. , Aperia A. , Larsson L. , Zetterstrom R.
Published: December 2017

The mechanism by which betamethasone induces Na-K-ATPase activity in developing tissue was studied in homogenates of proximal tubular cells from 10-day-old rats. A significant increase in Na-K-ATPase activity occurred after 5 micrograms . 100 g-1 . 12 h-1 X 2 beta-methasone and a maximal increase after 15-60 micrograms . 100 g-1 . 12 h-1 X 2. Following a single dose of 60 micrograms . 100 g-1 betamethasone Na-K-ATPase activity increased significantly after 16 h and maximally after 24-30 h. The 16-h time lag suggests that betamethasone does not act only directly on Na-K-ATPase synthesis. Betamethasone 60 micrograms . 100 g-1 increases Na-K-ATPase activity significantly in kidneys in which glomerular filtration rate is reduced by ureteral ligation, but the increase is significantly less pronounced than in kidneys with intact ureters, suggesting that the induction is not mediated only by alterations in sodium supply. Twenty-four hours after 10-60 micrograms . 100 g-1 betamethasone there was no significant increase in glucose-6-phosphatase and Mg-ATPase activity in 10-day-old rats or in Na-K-ATPase activity in 40-day-old rats. The basal and lateral cell membranes of the proximal tubular cells were not significantly increased 24 h after 60 micrograms . 100 g-1 betamethasone. Accordingly, structural development is not a prerequisite for enzymatic differentiation.
Secretion of tetraethylammonium by proximal tubules of rabbit kidneys
Authors: Schali C. , Schild L. , Overney J. , Roch-Ramel F.
Published: December 2017

The secretory transport of tetraethylammonium (TEA) was investigated in perfused and nonperfused isolated S1, S2, and S3 segments of proximal tubules from rabbit kidneys. In the perfused tubules the transepithelial net secretory flux and in nonperfused tubules the TEA cellular uptake were saturable (Km = 67 microM, Vmax = 2,480 fmol X min-1 X mm-1 in perfused S2 segments), energy dependent, and inhibited by mepiperphenidol. The net secretory flux of TEA (J b leads to j TEA) at a bath TEA concentration of 40 microM differed for the three segments and decreased in the order S1 greater than S2 greater than S3. The concentration of TEA in the perfusate leaving the tubule was approximately twice as great and the intracellular TEA concentration approximately 40 times as great as that in the bath. In nonperfused segments (40 microM TEA in the incubation medium) the TEA tissue water-to-medium ratio reached 100. In the three segments the ability to accumulate TEA across the peritubular membrane, thus, was similar, but the transepithelial secretory flux differed significantly. The differences in secretory rate between the three segments presumably result from differences in the luminal membrane permeability.
Effects of dopamine blockade on renal sodium excretion
Authors: Pelayo J. C. , Fildes R. D. , Eisner G. M. , Jose P. A.
Published: December 2017

The renal responses to a specific dopamine antagonist (cis-flupentixol) and its stereoisomer (trans-flupentixol), a weak dopamine antagonist, were examined during hydropenia and Ringer loading in anesthetized rats. During hydropenia glomerular filtration (GFR), absolute (UNaV), and fractional (FENa) sodium excretion rates were similar as were single-nephron filtration (SNGFR) and proximal tubular flow rate (VTF). After Ringer loading GFR, UNaV, and FENa increased in all groups, but the increments were less in the cis-flupentixol than in the control or trans-flupentixol group. SNGFR and VTF increased similarly in all groups. In another series of experiments Ringer loading was performed prior to drug administration. Perfusion pressure (PP) was decreased in trans-flupentixol rats by aortic constriction to control for cis-flupentixol-induced reduction in PP. UNAV and FENa were lower in the cis-flupentixol- than trans-flupentixol-treated rats at comparable PP and GFR. In conclusion, dopamine blockade attenuated the natriuresis of Ringer loading; the mechanism is uncertain but may be related to a tubular effect at a site beyond the proximal convoluted tubule and/or in deeper nephrons.
Function of proximal tubule carbonic anhydrase defined by selective inhibition
Authors: Lucci M. S. , Tinker J. P. , Weiner I. M. , DuBose T. D.
Published: December 2017

The specific role of luminal carbonic anhydrase in bicarbonate reabsorption by the proximal tubule has not been established because it has been difficult to inhibit selectively the luminal enzyme without simultaneous inhibition of the cytoplasmic enzyme. The present experiments employed in vivo microperfusion, microcalorimetry, and microelectrode techniques to determine the effects of luminal application of a dextran-bound carbonic anhydrase inhibitor (DBI) on bicarbonate reabsorptive rate (JtCO2) and intraluminal pH in the rat proximal convoluted tubule. Tubules were perfused at 20 nl/min with an artificial ultrafiltrate. Aminoethyl dextran (AED) with no enzyme-inhibitor activity was added to the control perfusate, and the effects of the parent inhibitor STZ not bound to dextran were also determined. Both DBI and STZ significantly reduced JtCO2 from 138 ⁺/⁻ 10 pmol X mm-1 X min-1 (control) to 30 ⁺/⁻ 4 and 30 ⁺/⁻ 9, respectively. In contrast to the indistinguishable effects on JtCO2, intraluminal pH measured close to the site of perfusion was 6.80 ⁺/ 0.02 during DBI perfusion, whereas with STZ perfusion the pH was 7.24 ⁺/⁻ 0.04 (P less than 0.001). Using the collected perfusate total CO2 concentration and a renal cortical PCO2 of 60 mmHg, the calculated equilibrium pH for this solution was 7.27. DBI inhibited only luminal carbonic anhydrase, therefore. We conclude that luminal carbonic anhydrase is in functional contact with proximal tubule fluid and is necessary for at least 80% of bicarbonate reabsorption by this segment.(ABSTRACT TRUNCATED AT 250 WORDS)
Effects of calcitonin on the renal concentrating mechanism
Authors: de Rouffignac C. , Elalouf J. M.
Published: December 2017

The effects of salmon calcitonin on the renal concentrating mechanism were investigated in homozygous DI Brattleboro rats. The levels of peptide hormones believed to produce the same physiological responses as antidiuretic hormone on the thick ascending limb (glucagon, parathyroid hormone, and calcitonin) and the cortical collecting ducts (calcitonin) were reduced by acute thyroparathyroidectomy and somatostatin administration. In these hormone-deprived animals, the corticomedullary concentration gradient was almost abolished; the (F/P)osmol at the tip of the juxtamedullary nephrons was 1.19 +/- 0.05. Calcitonin administration restored the gradient [(F/P)osmol = 1.85 +/- 0.14] and simultaneously absolute and fractional water excretion fell significantly despite the concomitant rise in the glomerular filtration rate. It is concluded that 1) in the hormone-deprived animal, calcitonin administration consistently enhances the corticomedullary concentration gradient, and 2) the effects of hormone deprivation and calcitonin administration on the urinary concentrating mechanism are compatible with direct stimulation by calcitonin of electrolyte reabsorption along the thick ascending limb and/or of the water permeability of the cortical collecting ducts.
Effector loci for renal nerve control of cortical microcirculation
Authors: Kon V. , Ichikawa I.
Published: December 2017

To determine the effector loci for renal neural vasomotor control, we performed micropuncture measurements before or after renal nerve stimulation and during low- (0.5-1.5 Hz) (LFS) or high- (3-5 Hz) (HFS) frequency nerve stimulation in Munich-Wistar rats. In response to HFS, single nephron glomerular filtration rate decreased on average from 24.1 +/- 4.1 to 10.4 +/- 2.3 nl/min. Although mean glomerular transcapillary hydraulic pressure difference remained essentially constant, HFS led to a marked fall in glomerular plasma flow rate (71.3 +/- 0.9 to 44.1 +/- 10.4 nl/min). The latter was associated with significant increase in both afferent (RA) and efferent (RE) arteriolar resistance, on average by more than twofold. Because of this profound arteriolar constriction, early peritubular capillary hydraulic pressure (PEA) fell markedly during HFS (mean: 19.1 +/- 1.4 vs. 13.2 +/- 1.4 mmHg). The ultrafiltration coefficient (Kf) also decreased significantly, on average from 0.055 +/- 0.014 to 0.015 +/- 0.002 nl/(s . mmHg) with HFS. By contrast, LFS affected these indices to a much lesser and more variable degree although the marked decline in PEA was again demonstrated. Despite this decrease in postglomerular capillary hydraulic pressure, absolute proximal tubule fluid reabsorption (APR) failed to change in some animals and decreased slightly in others. Analysis of the Starling forces acting across the peritubular capillaries showed that due largely to a uniform decrease in mean peritubular capillary hydraulic pressure, mean net reabsorption pressure (Pr) rose substantially and significantly, on average by more than 5 mmHg.(ABSTRACT TRUNCATED AT 250 WORDS)
Perturbation analysis of tubuloglomerular feedback in hydropenic and hemorrhaged rats
Authors: Moore L. C. , Mason J.
Published: December 2017

A closed-feedback-loop method was used to investigate regulation of SNGFR and distal fluid delivery by tubuloglomerular feedback (TGF) in hydropenic and hemorrhaged rats. Unblocked nephrons were perturbed by early proximal perfusion of previously collected, inulin-free, tubular fluid at 0, 7.5, and 15 nl/min, thereby increasing nephron fluid load. The resultant changes in SNGFR, tubular reabsorption, proximal intratubular pressure, and early distal flow were measured. During perfusion, SNGFR decreased and distal flow increased; the effect on reabsorption was variable. Analysis of the data indicated that the combined action of TGF and changes in proximal tubule and Henle's loop reabsorption were able to provide a maximum of 56% compensation for the effect of the perturbation on distal delivery in hydropenic rats and 70% compensation in hemorrhaged rats. In one group of hydropenic rats in which a significant fall in reabsorption was found, the total fluid load presented to the nephron, SNGFR plus the perfusion rate, was significantly better regulated than distal delivery. This result is consistent with the behavior of a model used to estimate the contribution of TGF to the observed regulation. The results indicated that TGF alone could provide 56% compensation for the perturbation in hydropenia and a significantly greater 72% compensation following hemorrhage. The conclusions are 1) that the properties of TGF are sufficient to result in significant regulation of distal fluid delivery and SNGFR, 2) that hemorrhage increases the strength of the TGF response, and 3) that TGF regulation of SNGFR and distal delivery is strongly influenced by changes in proximal tubule and loop of Henle reabsorption.