Renal Na-K-ATPase activity during saline infusion in the rabbit.

During saline infusion, sodium reabsorption (RNa) in the diluting segment (thick ascending limb of Henle's loop) increases acutely. The mechanism for this higher pumping rate of outer medullary Na-K-ATPase is unknown. Following left-sided nephrectomy, immediate i.v. infusion of hypertonic saline increased RNa in the remaining whole right kidney by 28 +/- 14% (p less than 0.05). Na-K-ATPase activity in outer medulla was raised by (delta) 23 +/- 4% above the left kidney (p less than 0.05), whereas cortical activity was unchanged. The mechanism for this increase in Na-K-ATPase activity was explored. The catalytic rate per enzyme did not differ in the two kidneys and equalled 5 340 min-1. The increase was therefore due to higher tissue concentration of active enzyme. The response was fully developed during continuous infusion within 20 min, and of equal magnitude whether protein synthesis had been inhibited by cycloheximide (delta = 23 +/- 7%) or stimulated by unilateral nephrectomy 6 days earlier combined with saline infusion for 2 h (delta = 34 +/- 10%). Thus, during hypertonic saline infusion, the increased RNa in the outer medulla was partly accounted for by the activation of latent Na-K-ATPase. High delivery of sodium to the diluting segment for more than 20 min during hypertrophy caused no further activity change.     

Inhibition of transcellular NaCI reabsorption in dog kidneys during hypercalcemia

Reduced concentrating and diluting capacity of the kidney in acute and chronic hypercalcemia may partly be due to inhibition of transcellular sodium reabsorption (R_Na) in the thick ascending limb of Henle's loop. To examine this hypothesis, local heat production and R_Na were measured during normo-and hypercalcemia at comparable glomerular filtration rate (GFR) in volume expanded, anesthetized dogs. Changes in proximal R_Na which might occur during CaCl₂ infusion, were minimized by infusing acetazolamide (75 mg/kg body wt iv). When ultrafiltrable calcium was increased from 1.12±0.09 to 2.95±0.10 mmol/1, cortical heat production was unchanged, whereas outer medullary heat production fell by 32±4%. R_Na was reduced by 32±6%. Bicarbonate reabsorption did not change but calcium reabsorption and potassium excretion increased significantly. The potassium content of cortex and outer medulla increased during hypercalcemia, whereas ouabain, an inhibitor of Na⁺ K⁺-ATPase reduces the potassium content. We conclude that hypercalcemia does not inhibit transcellular R_Na in the diluting segment by a direct effect on the Na⁺ K⁺-ATPase or the mitochondria, but by interfering with the coupled NaCI transport across the luminal cell membrane.     

Role of medullary Na-K-ATPase in renal potassium adaption.

Since recent studies have shown that chronic potassium loading stimulates the specific activity of Na-K-ATPase in renal tissue, experiments were performed to determine whether increased enzyme acitivity correlated with renal adaptation for accelerated potassium excretion. The Na-K-ATPase activity in different renal zones was correlated with the maximum rate of potassium excretion during the intravenous infusion of KCl in animals with normal and reduced renal function, animals on a varied potassium diet and animals treated with methylprednisolone or deoxycorticosterone acetate. The enhanced ability to excrete a potassium load was associated with increased enzyme activity in the outer or red medulla, whether the change in Na-K-ATPase was caused by chronic potassium loading, methylprednisolone treatment, or partial nephrectomy. There was no evidence that a rise in enzyme activity in the cortex influenced the rate of potassium secretion. Moreover, stimulation of Na-K-ATPase in the inner medulla-papilla did not augment the rate of potassium excretion above that found in animals with an increase in enzyme in the outer medulla alone. These experiments provide evidence that links Na-K-ATPase to the mechanism of renal potassium adaptation and suggest that the major increment in potassium secretion by the adapted kidney occurs in the outer medulla.     

Energy requirement of sodium reabsorption in the thick ascending limb of Henle's loop in the dog kidney: effects of bumetanide and ouabain

To examine whether sodium reabsorption in the thick ascending limb of Henle's loop (TALH) in the dog kidney has a passive component, the ratios between reductions in sodium reabsorption and oxygen consumption (ΔNa/ΔQo ₂ ratio) were measured by inhibiting tubular transport with bumetanide (30 μg kg^-1) and ouabain (120 ng kg^-1 intrarenally). Clearance studies were performed in volume expanded dogs treated with acetazolamide (100 mg kg^-1) or maleate (400 mg kg^-1). In five acetazolamide-treated dogs, bumetanide gave a ΔNa/ΔQo ₂ ratio of 29.9±2.5, whereas the combination of bumetanide and ouabain gave 19.0±0.6. When ouabain was given before bumetanide, ouabain gave a ΔNa/ΔQo ₂ ratio of 19.2±1.1 and the combination gave 19.9±1.2. In the maleate-treated dogs, bumetanide gave a ΔNa/Qo ₂ ratio 30.3±1.7, and the combination of bumetanide and ouabain gave 27.1±1.5. To localize the metabolic effect of bumetanide and ouabain, local heat production was measured at 18 places in four kidneys with copper-constantan thermocouples. Bumetanide reduced metabolic rate in the outer medulla by 51±4%, and in the cortex by 16±6%. Subsequent infusion of ouabain reduced metabolic rate in the outer medulla by only 9±3%, whereas cortical metabolism was reduced by 33±4%. The results show that bumetanide mainly acts in the outer medullar where TALH is located, whereas the additional effect of ouabain is mainly located in cortical segment of the nephron including the proximal tubules. Bumetanide inhibits the reabsorption of 30 mol sodium for each mole oxygen consumed, which show that for each 18 mol sodium that are transported through the cells in the TALH in dog kidneys, 12 mol (40%) are transported along the paracellular route without additional requirement of energy.     

Effect of indomethacin in vivo and PGE2 in vitro on MTAL Na-K-ATPase of the rat kidney

We have previously shown that prostaglandin synthesis inhibition in rats which reduces urinary excretion of PGE₂ and sodium, is associated with increased Na-K-ATPase activity in renal medulla. To further characterize this interaction studies were performed in isolated segments of medullary thick ascending limb of Henle's loop (MTAL) in rats. The effect of pretreatment with indomethacin in vivo and incubation with PGE₂ in vitro on MTAL Na-K-ATPase activity was studied. Pretreatment of rats with indomethacin increased Na-K-ATPase of the MTAL from 37.2±2.0×10⁻¹¹ mol/mm/min in controls to 62.7±2.2 (p<0.001) while Mg-ATPase was only slightly decreased. Incubation of MTAL Na-K-ATPase from indomethacin pretreated rats with increasing concentration of PGE₂ in vitro dose dependently inhibited MTAL Na-K-ATPase activity with no effect on Mg-ATPase. Baseline Na-K-ATPase was 62.7±2.2 in MTAL from indomethacin pretreated rats and decreased to 36.9±1.4 (p<0.001) with 1 uM of PGE₂, to 26.5±2.3 (p<0.001) with 10 uM PGS₂ and to 22.0±1.0 (p<0.001) with 100 uM PGE₂. 100 uM PGE₂ in the incubation medium inhibited MTAL Na-K-ATPase of intact rats from 37.2±2 to 21.3±1.2 (p<0.001) and completely abolished the indomethacin induced increase in MTAL Na-K-ATPase. The results of this study show stimulation of MTAL Na-K-ATPase by pretreatment with indomethacin in vivo and, direct inhibition of MTAL Na-K-ATPase by PGE₂ in vitro. These findings suggest that the increase in MTAL Na-K-ATPase induced by pretreatment with indomethacin may stem directly from PGE₂ depletion. These observations are consistent with direct inhibitory effect of PGE₂ on Na reabsorption in the MTAL.     

Effect of anesthesia on renal R2* measured by blood oxygen level‐dependent MRI

Blood oxygen level‐dependent (BOLD) MRI is increasingly being used to assess renal tissue oxygenation during disease based on the transverse relaxation rate (R₂*). In preclinical small animal models, the requisite use of anesthesia during imaging may lead to functional changes which influence R₂* and confound results. The purpose of this study was to evaluate the effects of four common anesthetic compounds on renal R₂* in healthy mice. Five female ICR mice were imaged with BOLD MRI approximately 25 min after induction with isoflurane (Iso; 1% or 1.5%, delivered in 100% O₂), ketamine/xylazine (KX), sodium pentobarbital (PB) or 2,2,2‐tribromoethanol (TBE). A significant effect of anesthetic agent on R₂* was observed in all tissue layers of the kidney, including the cortex, outer stripe of the outer medulla (OSOM), inner stripe of the outer medulla (ISOM) and inner medulla (IM). Pairwise significant differences in R₂* between specific agents were found in the cortex, OSOM and ISOM, with the largest difference observed in the ISOM between 1.5% Iso (26.6 ± 1.7 s^–1) and KX (66.0 ± 7.1 s^–1). The difference between 1% Iso and KX in the ISOM was not abolished when KX was administered with supplemental 100% O₂ or when 1% Iso was delivered in 21% O₂, indicating that the fraction of inspired oxygen did not account for the observed differences. Our results indicate that the choice of anesthesia has a large influence on the observed R₂* in mouse kidney, and anesthetic effects must be considered in the design and interpretation of renal BOLD MRI studies. Copyright © 2015 John Wiley & Sons, Ltd.     

Renal Control of Salt and Fluid Homeostasis during i. v. Saline Infusion

The renal effect of infusion of hypo-, iso- and hypertonic saline has been studied in dogs. The infusion rate was comparatively low, 1 % of the b.wt./45 min. The kidneys responded almost instantaneously to the infusion with diuresis and natriuresis. The response was due primarily to an adaptive inhibition of tubular reabsorption. Increases in filtered load of Na⁺ occurred only as a function of increased serum Na⁺ concentration, i.e. only when the hypertonic saline solution were used. The inhibition of tubular reabsorption was mainly signalled by the fall in serum protein concentration. Changes in Na⁺ balance and serum Na⁺ concentration did not contribute to the adaptive inhibition of tubular reabsorption. The effect of the diuretic and natriuretic response on fluid and Na⁺ balance depended primarily on the tonicity of the infused fluid. When the 75 and 150 mEq solutions were used, fluid balance became positive, but did not increase much when more than 2 % of the b.wt. had been given. When the hypertonic saline solutions were used total fluid balance became increasingly negative. The Na⁺ balance was best controlled with the hypotonic saline solution. Vhen hypertonic saline waq given Na⁺ balance increased almost at the same rate as Na⁺ was given.     

Isotonic and hypertonic sodium loading in supine humans

The hypothesis that hypertonic saline infusion induces a greater natriuresis than infusion of the same amount of sodium as isotonic saline was tested in 8 supine subjects on fixed sodium intake of 150 mmol NaCl day^–1. Sodium loads equivalent to the amount of sodium contained in 10% of measured extracellular volume were administered intravenously over 90 min either as isotonic saline or as hypertonic saline (850 mmol L^–1). A third series without saline infusion served as time control. Experiments lasted 8 h. Water balance and sodium loads were maintained by replacing the excreted amounts every hour. Plasma sodium concentrations only increased following hypertonic saline infusion (by 2.7 ± 0.3 mmol L^–1). Oncotic pressure decreased significantly more with isotonic saline (4.1 ± 0.3 mmHg) than with hypertonic saline (3.2 ± 0.2 mmHg), indicating that isotonic saline induced a stronger volumetric stimulus. Renal sodium excretion increased more than a factor of four with isotonic and hypertonic saline but also increased during time control (factor of three). Cumulated sodium excretions following isotonic (131 ± 13 mmol) and hypertonic saline (123 ± 10 mmol) were statistically identical exceeding that of time control (81 ± 9 mmol). Plasma angiotensin II decreased in all series but plasma ANP concentrations and urinary excretion rates of endothelin-1 remained unchanged. In conclusion, hypertonic saline did not produce excess natriuresis. However, as the two loading procedures induced similar natriureses during different volumetric stimuli, part of the natriuresis elicited by hypertonic saline could be mediated by stimulation of osmoreceptors involved in renal sodium excretion. The supine position does not provide stable time control conditions with regard to renal excretory function.     

Inhibition of transcellular NaCl reabsorption in dog kidneys during hypercalcemia

Reduced concentrating and diluting capacity of the kidney in acute and chronic hypercalcemia may partly be due to inhibition of transcellular sodium reabsorption (RNa) in the thick ascending limb of Henle's loop. To examine this hypothesis, local heat production and RNa were measured during normo- and hypercalcemia at comparable glomerular filtration rate (GFR) in volume expanded, anesthetized dogs. Changes in proximal RNa which might occur during CaCl2 infusion, were minimized by infusing acetazolamide (75 mg/kg body wt iv). When ultrafiltrable calcium was increased from 1.12 +/- 0.09 to 2.95 +/- 0.10 mmol/l, cortical heat production was unchanged, whereas outer medullary heat production fell by 32 +/- 4%. RNa was reduced by 32 +/- 6%. Bicarbonate reabsorption did not change but calcium reabsorption and potassium excretion increased significantly. The potassium content of cortex and outer medulla increased during hypercalcemia, whereas ouabain, an inhibitor of Na+, K+-ATPase reduces the potassium content. We conclude that hypercalcemia does not inhibit transcellular RNa in the diluting segment by a direct effect on the Na+, K+-ATPase or the mitochondria, but by interfering with the coupled NaCl transport across the luminal cell membrane.     

Effects of experimental pain on jaw muscle activity during goal-directed jaw movements in humans

To study the effects of masseter muscle pain on jaw muscle electromyographic (EMG) activity during goal-directed tasks. Mandibular movement was tracked and EMG activity was recorded from bilateral masseter, and right posterior temporalis, anterior digastric, and inferior head of lateral pterygoid muscles in 22 asymptomatic subjects at postural jaw position, and during three tasks: (a) protrusion, (b) contralateral (left), (c) open jaw movement. Tasks were performed during three conditions: control (no infusion), test 1 [continuous infusion into right masseter of 4.5% hypertonic saline to achieve 30–60 mm pain intensity on 100-mm visual analog scale (VAS)], and test 2 (isotonic saline infusion; in 16 subjects only); the sequence of hypertonic and isotonic saline was randomized. The average EMG root-mean-square values at 0.5 mm increments of mid-incisor-point displacement were analysed using linear mixed effects model statistics (significance: P < 0.05). Right masseter hypertonic saline infusion resulted in significantly (P < 0.0005) more pain (mean ± SD VAS 47.3 ± 14.3 mm) than isotonic infusion (12.2 ± 17.3 mm). Although there was evidence of inter-subject variation, the principal EMG findings were that the significant effects of hypertonic saline-induced pain on EMG activity varied with the task in which the muscle participated irrespective of whether the muscle was an agonist or an antagonist in the tasks. The direction of the hypertonic saline-induced pain effect on EMG activity (i.e., whether the hypertonic saline-induced EMG activity was less than or greater than control EMG activity) could change with the magnitude of jaw displacement. Hypertonic saline infusion had no significant effect on postural EMG activity in any of the recorded jaw muscles. The data suggest that under constrained goal-directed tasks, the pattern of pain-induced changes in jaw muscle EMG activity is not clear cut, but can vary with the task performed, jaw displacement magnitude, and the subject being studied.     

Tubular Sodium Reabsorption and the Regulation of Renal Hemodynamics. The Effect of Hypertonic Saline Infusion on Renal Vascular Resistance

The hemodynamic response following saline loading was found to differ from that induced by the saluretic agent, chlorothiazide, which causes vasoconstriction. When hypertonic NaCl was infused into the renal artery until a profuse sodium diuresis was obtained, and the infusion then interrupted, C_Na/C_In remained elevated for 60–80 min. During this period the renal vascular resistance did not change significantly and the glomerular filtration rate tended to rise as compared with the control periods. This is contrary to what has previouly been found during chlorothiazide administration, where renal vascular resistance was significantly correlated with C_Na/C_In. A hypertonic saline load blocks Na reabsorption in the proximal tubules, chlorothiazide mainly in the distal tubules. It was therefore concluded that it is a reduction of movement of Na into the distal tubule cells, specifically the macula densa, rather than the increased Na concentration of the distal tubular fluid that is responsible for the vasoconstrictive effect of chlorothiazide.     

Effect of increased distal sodium delivery on organic osmolytes and cell electrolytes in the renal outer medulla

Sodium absorption in distal tubule segments was stimulated by increasing the distal delivery via infusion of hypertonic saline. In these animals, and in control rats, electrolyte concentrations in thick ascending limb cells, light and dark cells of the collecting duct in the outer and inner stripe of the outer medulla and in cells of the proximal straight tubule (outer stripe only) were studied. The measurements were performed by electron microprobe analysis of freeze-dried cryosections of the outer medulla. In addition, organic osmolytes (glycerophosphorylcholine, betaine and myo-inositol) were measured by high performance liquid chromatography in cortex and outer medulla. Augmented delivery of sodium chloride to the distal tubule was associated with increased sodium concentrations of thick ascending limb cells both in the outer and inner stripe and of medullary collecting duct light and dark cells in the outer stripe. While the sum of organic osmolyte concentrations was 28% higher in the outer medulla of the salt-loaded animals compared with controls, this value was unchanged in the renal cortex. These findings indicate that the primary event underlying stimulation of sodium absorption along the thick ascending limb during increased distal sodium delivery is enhanced entry of sodium across the apical cell membrane. This would be expected to lead to higher cell sodium concentrations and stimulation of basolateral active Na-K-exchange. The enhanced transport activity of outer medullary tubules may be associated with increased interstitial tonicities and intracellular retention of organic osmolytes.     

Effect of hypertonic saline on rat hypothalamic paraventricular nucleus parvocellular neurons in vitro

The effects of hypertonic saline on hypothalamic paraventricular nucleus (PVN) parvocellular neurons were examined using whole-cell patch-clamp technique. Under current-clamp, 50% (41/82) of parvocellular neurons were depolarized than the predicted values by hypertonic saline, and associated with increasing action potential frequency. Under voltage-clamp, unless hypertonic saline induced a shift of reverse potential to more positive values, neither mannitol nor hypertonic saline obviously increased the conductance in parvocellular neurons. Moreover, spontaneous excitatory postsynaptic currents (sEPSCs) were increased by isotonic increases in [Na⁺]_o in the parvocellular neurons. Bath application AMPA receptor antagonist CNQX or non-selective glutamate antagonist kynurenic acid almost completely blocked the sEPSCs. Extracellular application of gadolinium (Gd³⁺) blocked the hypertonic saline-induced response. These results suggested that subpopulation of PVN parvocellular neurons are selectively sensitive to NaCl. Hypertonic saline excited the PVN parvocellular neurons through Na⁺-detection and the excitatory glutamatergic synaptic input.     

Hypertonic saline infusion induces activation of the lymphocyte Na+/H+ antiport and cytosolic alkalinization in healthy human subjects

The Na⁺/H⁺ antiport is a membrane transport protein that extrudes intracellular protons in exchange for extracellular sodium. Some details of its physiological and pathophysiological role remain poorly defined. Experimental evidence suggests that the antiporter is involved in the regulation of cell volume. In the present study, we therefore investigated the activity of the lymphocyte Na⁺/H⁺ antiport in nine healthy volunteers following acute hypertonic (2.5%) saline infusion (4 mmol NaCl/kg over 120 min). Antiport activity was measured after acidifying the cells with Na⁺ propionate (5–40 mM) using the fluorescent dye bis-carboxyethyl carboxyfluorescein. Hypertonic saline induced significant increases in plasma osmolality (308.4±2.3 vs. 293.5±2.7 mOsm/kg; P<0.01), serum Na⁺ (150.8±3.7 vs. 138.9±0.5 mmol/kg; P<0.01), and Cl^– concentrations (118.0±3.9 vs. 101.1±1.0 mmol/kg; P<0.01). Extracellular hypertonicity was followed by a stimulated activity of the lymphocyte Na⁺/H⁺ antiport with an increase in the apparent V _max values from 2.44^±0.16 to 3.27^±0.34 10^–3 s^–1 (P<0.01) and a slight rise in pK from 6.81±0.03 to 6.87±0.03 (P<0.05) after hypertonic saline. In addition to antiport activation, cytosolic alkalinization was observed with cytosolic pH values averaging 6.90±0.02 before and 6.99±0.02 (P<0.01) after hypertonic saline. Our results show for the first time that acute extracellular hypertonicity in man due to hypertonic NaCl loading is associated with a stimulated lymphocyte Na⁺/H⁺ antiport activity and cytosolic alkalinization.Abbreviations BCECF-AM bis-carboxyethyl carboxyfluorescein, acetoxymethyl ester - HEPES 4-(2-hydroxyethyl)-1-piperazine ethane sulfonic acid     

Evidence for Na+ dependent rheogenic HCO 3 − transport in fused cells of frog distal tubules

The mechanism of HCO ₃ ^– transport was studied applying microelectrodes in giant cells fused from single epithelial cells of the diluting segment of frog kidney. A sudeen increase of extracellular HCO ₃ ^– concentration from 10 to 20 mmol/l at constant pH hyperpolarized the cell membrane potential of the fused cell. This cell-voltage response was totally abolished by 10^–3 mol/l SITS and significantly reduced by 10^–4 mol/l acetazolamide or by omission of Na⁺ from the extracellular perfusate. Removal of Na⁺ from the perfusate caused a transient depolarization. Reapplication of Na⁺ induced a transient hyperpolarization. 10^–3 mol/l SITS abolished the cell-voltage response to removal and reapplication of Na⁺. In the intact diluting segment of the isolated perfused frog kidney peritubular perfusion of 10^–4 mol/l acetazolamide reduced the limiting transepithelial electrochemical gradient for H⁺ significantly from 30±4 mV to 14±3 mV. The results suggest: (i) In the diluting segment of the frog kidney a Na⁺-dependent rheogenic HCO ₃ ^– transport system exists across the peritubular cell membrane. (ii) This rheogenic peritubular Na⁺/HCO ₃ ^– cotransporter cooperates with a Na⁺/H⁺ exchanger in the luminal membrane, thus driving HCO ₃ ^– reabsorption. (iii) Reabsorption of HCO ₃ ^– and secretion of H⁺ depend upon the presence of carbonic anhydrase.     

Effects of renal artery infusion of various hypertonic solutions on the renal blood flow and renal handling of PAH in the dog

Summary Effects of renal artery infusion of hypertonic solutions of glucose, mannitol, Na₂SO₄, NaCl and urea on renal blood flow (RBF) and renal handling of PAH were studied in anesthetized dogs. RBF was determined by continuous venous outflow recording and glomerular filtration rate as renal plasma flow times creatinine extraction ratio.Glucose solution increased, mannitol and Na₂SO₄ did not significantly alter while urea and NaCl depressed RBF. Only for NaCl RBF depression became greater with increasing solute loads applied. Spontaneous renal vasoconstriction and ureteral occlusion prevented RBF fall during urea and NaCl infusions. It is proposed that renal vascular reponse to local elevation of plasma osmolality is a resultant of two opposed effects: nonspecific vasodilatation as described for other vascular beds and vasoconstriction characteristic for renal vasculature and demonstrable only in normally functioning kidney.The extraction ratio of PAH (E _PAH) was not altered by hypertonic urea but decreased with the four remaining infusates. The net tubular transport of PAH fell with NaCl infusion but was not changed with glucose, Na₂SO₄, mannitol and urea. It is concluded thatE _PAH depression during NaCl infusion was due to inhibition of cellular PAH transport while that observed with glucose, Na₂SO₄ and mannitol reflected increased fraction of RBF perfusing nonsecretory renal medullary tissue.     

Relation between Na-K-ATPase activity and respiratory rate in the rat kidney.

The relation between Na-k-ATPase activity in homogenates of rat kidney and oxygen consumption in kidney slices was studied by employing different physiological maneuvers known to change the activity of renal Na-K-ATPase. Treatment of euthyroid rats with 3,5,3'-triiodo-1-thyronine increased Na-K-ATPase activity, sodium-dependent oxygen consumption (QO2[t]), and para-aminohippurate (PAH) accumulation by kidney slices without changing glomerular filtration rate or net sodium reabsorption by the intact kidney. Treatment with methylprednisolone also increased Na-K-ATPase, QO2[t], and PAH transport. Chronic potassium loading, on the other hand, increased renal Na-K-ATPase to the same degree as the first two procedures, but QO2[t] and PAH accumulation were unchanged. Partial nephrectomy induced an increase in the activity of Na-K-ATPase in homogenates of the remaining kidney fragment, but QO2[t] did not change significantly and PAH uptake was unaltered. An increase in the activity of Na-K-ATPase in kidney homogenates is therefore not necessarily associated with a parallel change in oxygen consumption by the intact cell.     

The dipsogenic effect of intracerebroventricular infusion of hypertonic NaCI in the sheep is mediated mainly by the Na ion

In order to examine the importance of the chloride ion in the dipsogenic effect of intracerebroventricular (ICV) infusion of hypertonic NaCI, the water intake in response to 30-min ICV infusons of hypertonic solutions of different Na salts (0.25 M NaCI, Nal, NaSCN and 0.125 _M Na₂S₂O₃), mannitol (0.5 M) and choline chloride (0.25 M) was studied in the sheep. All solutions of the Na salts caused significant water drinking compared with ICV control infusions of isotonic artificial cerebrospinal fluid (CSF), except Na thiosulphate (Na₂S₂O₃), which was much less effective, even after equilibration of its osmolality with the other sodium solutions by adding mannitol (0.125 M Na₂S₂O₃/o.25 M mannitol). An inconsistent and small intake of water was induced by ICV hypertonic mannitol and choline chloride. It is concluded that the dipsogenic effect of ICV infusion of hypertonic NaCI in the sheep is mainly caused by the increased Na rather than the CI ion concentration or the hyperosmolality in the extracellular fluid of juxtaventricular brain tissue.     

Intracellular pH in diluting segment of frog kidney

Chronic exposure to high potassium (K⁺ adaptation) stimulates H⁺ net secretion in the diluting segment of the frog kidney. In order to investigate the cellular mechanism of the H⁺ secretory process intracellular pH (pH_i) measurements were performed in cells of the diluting segment of the isolated doubly-perfused kidney of K⁺ adaptedRana esculenta. pH_i changes were monitored by pH-sensitive microelectrodes while the tubule lumen was rapidly perfused with various solutions. With control solutions (extracellular pH=7.80) pH_i averaged 7.60±0.05. Luminal application of furosemide (5 · 10^–5 mol/l) or reduction of luminal Cl^– (from 104 mmol/l to 9 mmol/l) hyperpolarized the cell membrane potentials but pH_i was not altered. Reduction of luminal Na⁺ (from 98 mmol/l to 3 mmol/l) depolarized the cell membrane potentials but pH_i remained constant. Complete removal of luminal Na⁺, however, led to a significant decrease of pH_i from 7.61±0.08 to 7.18±0.08. Luminal application of amiloride (1 · 10^–3 mol/l) also decreased pH_i significantly (pH_i=0.15±0.02).The results indicate that an amiloride-sensitive H⁺ extrusion mechanism exists in the luminal cell membrane of the K⁺ adapted frog diluting segment. The data are consistent with Na⁺/H⁺ exchange which maintains a constant pH_i even at extreme experimental conditions.Parts of the data were presented at the 16th Ann. Meeting of the Am. Soc. Nephrol., Washington (1983)     

Canjoint Action of Sodium and Angiotensin on Brain Mechanisms Controlling Water and Salt Balances

Andersson , B. and L. Eriksson , Conjoint action of sodium and angiotensin on brain mechanisms controlling water and salt balances. Acta physiol. scand. 1971. 81. 18–29. The effects on water and salt balances of a simultaneous infusion of angiotensin and hypertonic NaCl into the 3rd brain ventricle were studied in goats in normal water balance and in hydrated animals. For comparison similar infusions of angiotensin alone (solved in slightly hypotonic saline) and of hypertonic NaCl were made. Like the hypertonic NaCl, 30 min infusions of angiotensin alone induced drinking in animals in normal water balance, and an inhibition of the water diuresis in the hydrated goat. The simultaneous infusion of both substances resulted in a marked potentiation of the dipsogenic and the antidiuretic effects. A possible explanation may be that angiotensin facilitates the transport of Na⁺ into brain cells regulating thirst and ADH release, and that the intracellular Na⁺ concentration rather than strictly osmotic factors determines the activity of these cells. In the hydrated goat a central effect of angiotensin strongly enhanced the natriuretic response to intraventricular infusions of hypertonic NaCl, and extreme natriuresis developed as result of the combined infusions in hydrated, salt-supplemented animals. During normal water balance this sodium-angiotensin synergism was less obvious, which suggests that both an expanded fluid volume and an elevated intracellular Na⁺ concentration are needed for optimal activation of a brain mechanism which stimulates renal Na' excretion, The time course of the centrally induced natriuresis indicates that the effect on the kidney may be mediated by a humoral agent.