The inulin space, solute concentrations, and weight changes in rat renal medullary slices incubated in iso-osmolal media, and their modification during anoxia and hypothermia

The influence of renal papillary urea concentrations and of plasma vasopressin on the urinary prostaglandins E2 and F2 alpha excretion in conscious rats in steady state of urine formation

Urinary excretion rates of PGE2 and PGF2 alpha were measured radioimmunologically in four different groups of unanaesthetized rats: water diuretic rats (I), rats with free access to water (II), water deprived rats (III) and 1.5% saline-loaded rats (IV). The animals were decapitated when steady states of urine formation were ascertained for three to six spontaneously delivered urine portions. Plasma vasopressin was measured radioimmunologically and urea, sodium, potassium concentrations and osmolalities of papillary fluids and of bladder urines were determined. Group means of urinary prostaglandin excretion, papillary urea concentration and logarithmic-transformed plasma vasopressin values vary in parallel for three of the groups (I, II and III) but a dissociation of the effects of papillary urea and vasopressin on the prostaglandin excretion was obtained for group IV. Statistical analyses indicated that the differences in prostaglandin excretion rates between group I and the three other groups are accounted for by the combined effects of vasopressin and papillary urea. The results support the hypothesis that vasopressin stimulates release of arachidonic acid in the papilla and that urea inhibits the trapping of this prostaglandin precursor in cellular lipids. The ratio of urinary PGF2 alpha to PGE2 varied greatly between groups but no consistent dependency on the measured parameters was found.

Characteristics of ionic binding by rat renal tissue in vitro

A study has been made of Na+ and Cl- binding in metabolically inhibited slices of rat renal cortex and outer medulla incubated in modified Krebs phosphate-bicarbonate Ringer solution. At pH 7.35 in control media (cortex, 147 mmol Na+/l, 105 mmol Cl-/l; outer medulla, 187 mmol Na+/l, 145 mmol Cl-/l) cortical slices bound (mean) 171 nmol Na+ and 56.7 nmol Cl-/mg solute-free dry weight; outer medullary slices bound 188 nmol Na+/mg and negligible amounts of Cl-. In both regions, Na+ was exchangeable on a 1:1 basis for K+ or Li+ in media containing equal concentrations of each cation: Na+ was completely displaced by La3+. In cortical slices in media containing equimolar Cl- and other monovalent anions, binding occurred according to the sequence acetate less than or equal to salicylate less than or equal to Cl- less than SCN-; Cl- was completely displaced by PO4(3-). When medium pH was lowered, Na+ binding was markedly reduced in both regions, whereas Cl- binding increased (and became significant in outer medulla). In NaCl solutions, Na+ binding capacity was saturated at control Na+ concentrations. When [Na+] was progressively reduced (iso-osmolality being maintained by addition of urea), bound Na+ in both regions was nearly linearly related to log medium [Na+]. Raising medium osmolality with urea caused decreased Na+ binding and increased Cl- binding in both regions. Na+ binding in both regions was significantly reduced by pre-treatment with chondroitinase ABC. Binding of both ions was independent of temperature within the range 2-37 degrees C. The possibility is raised that renal ionic binding might influence vectorial ion transport by affecting free ion activity in the region of the transporting cells.

Techniques and applications of extracellular space determination in mammalian tissues

This review summarizes the ways in which the extracellular space (ECS) may be estimated in mammalian tissues, and briefly describes some of the uses to which the EC confinement of certain molecules (markers or tracers) may be put in the elucidation of physiological functions. The introductory section is followed by a description of the more commonly used marker molecules and their functional characteristics, and of factors likely to lead to the spurious over- or under-estimation of the ECS. Certain alternative methods are also described, in particular those based on morphological and electrical criteria which seek to demonstrate small, functionally important, changes in the size of specialized regions of the ECS (e.g. lateral cellular interspaces) without necessarily being required to provide a quantitatively precise estimate of their size. Section III describes the results of measurements of ECS in various mammalian tissues (muscle, gastro-intestinal tract, nervous tissue, crystalline lens, placenta, lung and kidney) and some applications of EC markers to investigation of cellular function (e.g. uptake of metabolic substrates and epithelial transport) and, in outline, characterization of capillary permeability. The available literature in this field is very extensive, and in the interests of brevity the reader is, where appropriate, referred to previous reviews covering specialized aspects of ECS determination and related topics.

Cellular swelling in slices of rat renal outer medulla incubated in the presence of bovine serum albumin

1. Cells in slices of rat renal outer medulla incubated for up to 100 min in modified phosphate-bicarbonate Ringer undergo reversible, concentration-dependent swelling (increase in water content) in the presence of bovine serum albumin (b.s.a). 2. Swelling also takes place in the presence of dextran sulphate, but neutral dextran or polyvinylpyrrolidone are without effect. 3. Swelling due to b.s.a. is pH-dependent, decreasing (relative to cell volume in the absence of b.s.a.) as pH is reduced. 4. Swelling due to b.s.a. is associated with the net cellular gain of Na+, the magnitude of which increases at pH is raised. 5. There is an accompanying pH-independent net loss of cellular K+; at pH greater than about 6.20 this loss is smaller than the uptake of Na+, and cells thus show net gain of monovalent cation. 6. The relationships between pH and percentage increase in cell water content and between pH and percentage increase in cell osmotic content due to net gain of cation in the presence of 8% b.s.a. are coincident within the range pH 6.15--7.60. 7. Studies on the volume of distribution of [125I]b.s.a. within slices suggests that more may bind to cells at low pH than at high pH.

The action of ouabain upon chloride secretion in cultured MDCK epithelium

Net Na+ loss from confluent monolayers of cultured epithelial cells grown on plastic petri dishes into choline chloride is consistent with loss from two separate pools (t 1/2 2.4 and 43.7 min). Tissue K+ is lost with a single time constant (t 1/2 76.9 min). Since tissue equilibration of [14C]inulin is also rapid (t 1/2 approx. 1 min), it is inferred that the fast component of Na+ loss comprises loss from extracellular pools, whereas the slow component comprises intracellular loss. By washing extracellular cations from cell monolayers and directly measuring cell numbers and volumes by Coulter Counter, intracellular Na+ and K+ concentrations were estimated to be 16 +/- 2 (S.E.) and 151 +/- 2 (S.E.) mM. Ouabain at high concentrations (1 x 10(-5) to 1 x 10(-3) M) raised intracellular Na+, and lowered intracellular K+. The t 1/2 for cation equilibration with the external medium was approx. 70 min (+ ouabain). Ouabain inhibited ATP-stimulated Cl- secretion by epithelial MDCK monolayers mounted in Ussing chambers. The inhibition was time-dependent and consistent with dissipation of intracellular cation gradients. The ATP-dependent increase in monolayer conductance, observed in control tissues, was largely unaffected by ouabain.

pH and temperature dependence of glutamine uptake, carbon dioxide and ammonia production in kidney slices from acidotic rats

1. The effects of medium pH and temperature on glutamine uptake, NH3 production and CO2 production were examined using kidney cortex slices from normal and acidotic rats. 2. Uptake of glutamine by kidney slices from normal rats shows a pH optimum of 7.5 at 25 degrees C and 7.3 at 37 degrees C. Uptake is optimal, however, at a constant OH-/H+ ratio of 10. 3. In slices from acidotic rats greatest uptake was at pH 6.8 at 25 degrees C and 6.6 at 37 degrees C. Optimal OH-/H+ ratio was 0.4 and constant at both temperatures. 4. CO2 production from glutamine was greatest at pH 7.0 at 37 degrees C in slices from control rats. No pH optimum was detected at 25 degrees C. With slices from acidotic animals, optimal pH for CO2 production became identical with that for uptake. 5. Both basal and glutamine-stimulated NH3 production showed no optimal pH but were significantly higher in slices from acidotic rats compared with those from controls. 6. Dependence of glutamine penetration on optimal OH-/H+ ratio is considered to reflect a general membrane phenomenon which is produced by either an increase in carrier-substrate complexes or an increase in the number of carriers at this ratio. 7. Cellular penetration of glutamine does not appear to be a limiting factor in production of NH3 in vitro.

In vitro and in vivo lipogenesis of the rat renal papillae from glucose

The rate of [14C]glucose incorportion into rat renal papillary glycerolipids has been studied. Glucose is incorported mainly into the glycerol moiety of these lipids. 74 and 93% of the activity incorporated into triacylglycerols in vitro and in vivo, respectively, was present in the glycerol backbone. In phospholipids it was 82 and 96%, respectively. The fatty acid synthesis from [14C]glucose was similar to that from [14C]acetate. In accordance with previous experiments with [14C]acetate the papillary tissue was found to have a high capacity for chain elongation of preexisting fatty acids with the major product being cis-7,10,13,16-docosatetraenoic acid (chain elongated arachidonic acid). The in vitro and in vivo turnover rates of papillary glycerolipids can be calculated. A half-life of 25 h can be estimated for membrane phospholipids and less than 11 h for lipid droplet triacylglycerols. These appreciably high rates of turnover are discussed in relation to membrane turnover in renal papillae from rats in different physiological states and to variation in number of lipid droplets of papillary interstitial cells reported by others.

The influence of urea on lipogenesis in renal papillae of rats

The osmolality has been determined for the papillary interstitial fluids obtained from the isolated papillae of rats in different states of water balance. Hypertonic buffers for in vitro experiments were prepared by addition of urea to regular Krebs-Ringer phosphate buffers (340 mosmol/kg H2O) since urea is the most changeable solute of the renal papillary tissue in response to external influences. The effect of such hypertonic buffers on papillary lipogenesis was very pronounced. The fatty acid synthesis from acetate decreased by a factorr of 7-9 in response to increased osmolality from 340 to 1370 mosmol/kg H2O. In the physiological range of osmolalities (500-1800 mosmol/kg H2O), the de novo synthesis of papillary glycerolipids from glucose decreased by a factor of ca. 5. A possible specific inhibitory effect of hypertonic buffers on the pentose phosphate cycle was studied with a negative result. It is concluded that the addition of urea causes a decrease of total energy metabolism in the tissue.

Calcium-dependent action of osmolality on adenosine 3',5'-monophosphate accumulation in rat renal inner medulla: evidence for a relationship to calcium-responsive arachidonate release and prostaglandin synthesis

When urea and NaCl are employed as the major solutes of high osmolality buffers, the cyclic AMP (cAMP) content of oxygenated slices of rat renal inner medulla increases three- to fivefold as osmolality is decreased from 1,650 to 305 mosM. Incubation of slices in Ca2+-free media containing 2 mM EGTA largely abolished this action of osmolality on cAMP, whereas exclusion of Mg2+ or 5+ from the incubation media was without effect. Addition of Ca2+ to Ca2+-deprived inner medulla incubated at 750 mosM (175 mM Na+, 380 mM urea) significantly increased tissue cAMP and media prostaglandin (PG)E accumulation. Ca2+ also stimulated the release of 14C-fatty acid from Ca2+-deprived slices prelabeled with [14C]arachidonate, but not from those labeled with [14C]palmitate. The divalent cation ionophore A23187 enhanced the actions of Ca2+ to increase tissue cAMP, media PGE accumulation, and the release of [14C]-arachidonate from prelabeled inner medulla. By contrast, when slices were incubated at 1,650 mosM (365 mM Na+, 900 mM urea) in the presence or absence of A23187, all of these actions of Ca2+ were markedly suppressed or abolished. Addition of exogenous arachidonate increased tissue cAMP and media PGE at both 750 and 1,650 mosM, whereas palmitate and stearate had no effect on cAMP at either osmolality. The actions of Ca2+ and arachidonate to increase cAMP and PGE accumulation were abolished by the cyclo-oxygenase inhibitors, indomethacin and meclofenamate. They were also abolished by exclusion of molecular O2, which serves as cosubstrate with arachidonate in prostaglandin synthesis. At maximally effective concentrations, exogenous PGE2 and arachidonate produced similar increases in inner medullary cAMP. The maximal effects of the two agents on cAMP were not additive, but were expressed in the absence of Ca2+ at both 750 and 1,650 mosM. However, in marked contrast to the O2-dependent action of arachidonate, PGE2 increased cAMP in the presence or absence of O2. Comparison of the separate actions of urea and NaCl indicated that suppression of Ca2+-responsive [14C]arachidonate release, PGE, and cAMP accumulation at 1,650 mosM reflected primarily an effect of urea, whereas hypertonic NaCl, mannitol, and sucrose alone stimulated inner medullary cAMP and PGE accumulation by a pathway which did not require extracellular Ca2+. Analogous to the actions of hypertonic urea, tetracaine and mepacrine inhibited the actions of Ca2+ plus A23187 to stimulate [14C]-arachidonate release, PGE, and cAMP accumulation. Inhibition of PGE and cAMP accumulation by tetracaine and mepacrine was also overcome by arachidonate. The results suggest that high osmolaity media with urea as a major solute reduces inner medullary cAMP content, at least in part, through effects on Ca2+-dependent prostaglandin synthesis. Inhibition of PGE synthesis, in turn, may be the result of osmotic suppression of Ca2+-dependent release of arachidonate, the availability of which is often rate limiting to prostaglandin generation.

The retino-recipient zone of the feline pulvinar. should it be considered as part of the lateral geniculate complex? [proceedings]

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The influence of chloride ions on renal outer medullary cell volume

1. Slices of rat renal outer medulla have been incubated in media made hyperosmotic (540 and 1055 m-osmole/kg H2O) by the addition of urea, and containing variable concentrations of Cl (90, 144, 189 and 215 mM) and constant concentrations of Na (180 mM) and K (5.9 mM). A small number of incubations have been conducted in the presence of 100 mM-Na. 2. Changes in cell volume during incubation have been calculated on the basis of initial and final slice weight and inulin space. 3. The capacity of cells to shrink in response to extracellular osmotic stress was related principally to the external Cl concentration rather than to osmolality, increases in concentration being associated with enhanced shrinkage. Shrinkage was accompanied by net loss of cellular Cl. The ratio between intra- and extracellular Cl concentration (ca. 0.41) remained constant in all media. 4. In media containing low Cl concentration (90 mM), reduction of media Na concentration to 100 mM enhanced shrinkage. This effect was not observed when medium Cl concentration was greater than 90 mM. 5. Ethacrynic acid-cysteine (1 mM) significantly impaired the shrinkage response to extracellular osmotic stress, and caused cell swelling in media of relatively low Cl concentration and osmolality. It did not abolish the dependency of cell volume upon Cl concentration. There was marked reduction in the net amount of Cl lost from cells. 6. Ethacrynic acid-cysteine caused an increase in cellular Na content only in media containing 540 m-osmole/kg H2O and Cl concentrations less than 215 mM. 7. Ouabain (1 mM) inhibited cell shrinkage to a lesser extent than ethacrynic acid-cysteine in all media except that causing the greatest shrinkage under control conditions (215 mM-Cl/1055 m-osmole/kg H2O). It is suggested that a ouabain-sensitive process may play an increasingly important role in Cl-related cell shrinkage as this becomes more pronounced. 8. The findings are consistent with the view that Cl ions influence cell volume both through their effective external osmotic pressure and by means of Cl-specific process; the latter is associated with net loss of cellular Cl. A dependence of this loss upon Na/k exchange-linked metabolism is inferred, but the present findings do not permit the active or passive nature of the extrusion to be defined.

Effects of osmolality and oxygen availability on soluble cyclic AMP-dependent protein kinase activity of rat renal inner medulla

The renal inner medulla is ordinarily exposed to osmolalities that are much higher and to O2 tensions that are lower than those in other tissues. The effects of media osmolality and O2 availability on basal and arginine vasopressin(AVP)-responsive soluble cyclic (c)AMP-dependent protein kinase activity were examined in slices of rat inner medulla. Increasing total media osmolality from 305 to 750 or 1,650 mosM by addition of urea plas NaCl to standard Krebs-Ringer bicarbonate buffer significantly reduced basal cAMP content and protein kinase activity ratios. This occurred in the presence or absence of O2. Incubation of slices in high osmolality buffer also blunted increases in inner medullary slice cAMP and protein kinase activity ratios induced by O2. These changes reflected predominantly an action of the urea rather than the NaCl content of high osmolality buffers. In contrast to effects on basal activity, high media osmolality significantly enhanced activation of inner medullary protein kinase by AVP. Conversely, increases in media O2 content suppressed AVP stimulation of enzyme activity. This inhibitory effect of O2 was best expressed at low osmolality. Naproxen and ibuprofen, inhibitors of prostaglandin biosynthesis, reduced basal kinase activity ratios and increased AVP responsiveness in the presence, but not in the absence, of O2. Exogenous prostaglandins (PG) modestly increased (PGE2 and PGE1) or did not change (PGF2alpha) cAMP and protein kinase activity ratios in O2-deprived inner medullary slices. Protein kinase activation by PGE2 was not observed in oxygenated inner medulla with high basal activity ratios. The stimulatory effects of PGE2 and PGE1 on protein kinase activity observed in O2-deprived slices were additive with those of submaximal or maximal AVP. PGE2, PGE1, and PGF2alpha all failed to suppress AVP activation of protein kinase. Thus, enhanced endogenous PGE production may contribute to the higher basal protein kinase activity ratios induced by O2. However, the results do not support a role for PGE2, PGE1, or PGF2alpha in O2-mediated inhibition of AVP responsiveness. The present data indicate that both solute content and O2 availability can alter the expression of AVP action on cAMP-dependent protein kinase activity in inner medulla. AVP activation of protein kinase is best expressed when osmolality is high and O2 availability is low, conditions that pertain in inner medulla during hydropenia.

The determination of extracellular space using hemoglobin

The ECS of guinea-pig atria and frog sartorii can be determined using hemoglobin. For guinea-pig atria an ECS of (32.2 +/- 2.6)% wet wt for frog sartorii an ECS of (12.4 +/- 1.0)% wet wt can be measured.

Factors affecting the distribution of chloride ions in rat renal outer medulla

1. The intracellular Cl- concentration, [Cl-]1, of rat renal outer medullary slices has been studied in iso-osmolal media containing 42, 93, 144, 189 or 225 mM chloride, [Cl-]0. Equilibrium values for [Cl-]1 were attained within 25-50 min from the start of incubation such that [Cl-]1/[Cl-]0 = 0-46. This ratio was independent of [Cl-]0 within the range studied. Intracellular Na+ was unaffected, and only minor variations of cell volume were observed (calculated from slice weight changes and [14C]carboxyl inulin spaces. 2. When [Cl-]0 = 189 mM, [Cl-]1 remained constant at 87 mM for up to 50 min, indicating that these figures may represnet the interstitial [Cl-] and mean intracellular [Cl-] respectively in outer medulla. 3. Omission of bicarbonate from medium containing 189 mM-Cl- caused an increase in [Cl-]1/[Cl-]0 to 0-58, which was not significantly affected by anoxia or by the presence of arsenite (5 X 10(-3) M) or 2,4-dinitrophenol (10(-3) M). Significant further increases were observed in the presence of iodoacetic acid (5 X 10(-3) M) (0-70), acetazolamide (10(-3) M or 5 M 10(-3) M) (0-71) and iodacetic acid plus 2,4-dinitrophenol (0-85). The addition of the diuretic agents ouabain, ethacrynic acid-cysteine and frusemide (all 10(-3) M) to 189 mM-Cl- media containing bicarbonate reduced [Cl-]1/[Cl-]0 to 0-36, 0-37 and 0-42 respectively. 4. The mean 36Cl- space of outer medulla after 50 min incubation in 189 mM Cl- medium was 49-7 +/- 2-1 micronl./100 mg wet wt. The volume of distribution was not significantly affected by ouabain, ethacrynic acid-cysteine or frusemide (10(-3) mM). 5. Net efflux of 36Cl- from slices loaded with isotope into 'cold' 189 mM Cl medium showed three components with rate constants of 69 X 10(-3), 18 X 10(-3) and 9-9 X 10(-5) sec-1 respectively. Efflux was not affected by ouabain, ethacrynic acid-cysteine or frusemide (10(-3) mM). 6. The main conclusions drawn from this study are: (i) the interstitial fluid Cl- concentration of normally hydrated rat outer medulla is approx. 189 mM; (ii) the [Cl-]1/[Cl-]0 ratio 0-46 may represent a chiefly passive distribution maintained by the opposing gradient of a second anion, probably bicarbonate; (iii) the energy required to maintain unequal distribution of Cl- in the absence of external bicarbonate is derived chiefly from glycolysis, with a small aerobic component; (iv) there may be two intracellular chloride pools whose net rates of Cl- exchange differ by a factor of approx. 180.

The effects of ouabain and ethacrynic acid on the intracellular sodium and potassium concentrations in renal medullary slices incubated in cold potassium-free ringer solution and re-incubated at 37 degrees C in the presence of external potassium

1. The cells in slices cut from the renal outer medulla of normally hydrated adult rats were loaded with Na and depleted of K by incubation for up to 100 min in cold iso-osmolal K-free Ringer containing 180 mM-Na. There was a continuous net cellular water loss during this time; an inverse linear relationship existed between water content and intracellular Na concentration. 2. The original intracellular Na and K concentration were restored following 60 min re-incubation in warm Ringer (37 degrees C) containing 5-9 mM-K. Restoration of cellular water content was incomplete after re-incubation for up to 120 min. 3. During incubation in cold K-free Ringer the presence of 1 mM ouabain did not affect cellular Na uptake or K and water loss. Ethacrynic acid, 1 mM, completely blocked cellular Na uptake and water loss, without affecting the intracellular K concentration at 100 min. When ouabain and ethacrynic acid were present together water loss was also prevented but intracellular Na concentration rose slightly by 100 min. 4. During re-incubation in warm K-containing Ringer 1 mM ouabain inhibited Na extrusion completely for up to 60 min while only partially preventing K uptake and further depressing the level of cellular hydration. Ouabain in the presence of 1 mM ethacrynic acid had similar effects on intracellular Na and K concentrations, but raised the level of intracellular water above that of cells in control slices. 5. Ethacrynic acid alone, 1 mM, did not interfere with Na extrusion or K uptake, but also raised intracellular water above control values. 6. The results obtained are discussed in relation to (a) the nature of the preparation used, (b) the possible membrane transport processes occurring and their known or suggested sensitivity to ouabain and ethacrynic acid, (c) the mechanisms which may be responsible for cell volume maintenance in the medulla.

Volume adjustment by renal medullary cells in hypo- and hyperosmolal solutions containing permeant and impermeant solutes

1. The changes in the volumes of cells in slices (thickness 0-3-0-4 mm) of rat renal outer and inner medulla have been investigated during aerobic incubation for 20 min at 37 degrees C in Krebs phosphate-bicarbonate Ringer modified by the addition of urea or sucrose in order to produce a range of media hypo- and hyperosmolal with respect to the calculated tissue fluid osmolalities in these regions. 2. On the assumption that under these conditions the measured inulin space approximates to the true extracellular space (ECS), it was found that osmotic swelling or shrinkage of cells was not accompanied by any significant variation in the absolute size of the ECS. 3. Calculated cell volume changes in both regions were minimal when slices were incubated in urea-containing media iso-osmolal with tissue fluids in that region. In sucrose-containing media minimal cell volume changes occurred when media were hypo-osmolal in relation to tissue fluids by a factor of approximately 0-68. 4. In all except the most hypo-osmolal media studied, calculated cell volume changes (as percentage of initial volume) were linearly related to the reciprocal of the incubation media osmolalities. The points of interception of the regression lines on the cell volume axis were dependent upon both the region studied and the composition of the incubation medium (urea or sucrose). 5. These changes were accompanied by variations in slice solute concentrations. Slice [Na] was greatest, and slice [K] least, following incubation in those media producing the greatest percentage changes in cell volume. 6. The volume of distribution [14-C]sucrose within the inner medulla was 61-7 plus or minus 2-5 mul./100 mg wet weight of tissue (mean plus or minus S.E., n equals 6) after 10 min incubation. The increase to 70-8 plus or minus 4-2 mul./100 mg (n equals 6) after 100 min was not significant (0-1 greater than P greater than 0-05). The volume of distribution within the outer medulla rose markedly during this period, from 38-1 to 58-2 mul./100 mg.