Electrolyte and water metabolism of rabbit kidney slices; effect of metabolic inhibitors

Noncoupled Mitochondrial Respiration as Therapeutic Approach for the Treatment of Metabolic Diseases: Focus on Transgenic Animal Models

Mitochondrial dysfunction contributes to numerous chronic diseases, and mitochondria are targets for various toxins and xenobiotics. Therefore, the development of drugs or therapeutic strategies targeting mitochondria is an important task in modern medicine. It is well known that the primary, although not the sole, function of mitochondria is ATP generation, which is achieved by coupled respiration. However, a high membrane potential can lead to uncontrolled reactive oxygen species (ROS) production and associated dysfunction. For over 50 years, scientists have been studying various synthetic uncouplers, and for more than 30 years, uncoupling proteins that are responsible for uncoupled respiration in mitochondria. Additionally, the proteins of the mitochondrial alternative respiratory pathway exist in plant mitochondria, allowing noncoupled respiration, in which electron flow is not associated with membrane potential formation. Over the past two decades, advances in genetic engineering have facilitated the creation of various cellular and animal models that simulate the effects of uncoupled and noncoupled respiration in different tissues under various disease conditions. In this review, we summarize and discuss the findings obtained from these transgenic models. We focus on the advantages and limitations of transgenic organisms, the observed physiological and biochemical changes, and the therapeutic potential of uncoupled and noncoupled respiration.

Swelling and membrane potential dynamics of glial Müller cells

Presently a detailed biophysical model describing reversible and irreversible swelling dynamics of Müller cells (MC) is reported. The model includes a biophysical block of ionic and neutral species transport via MC membrane, water transport induced by osmotic pressure and pressure generated by membrane deformations, MC membrane potential and membrane mechanical properties. The model describes reversible and irreversible MC swelling (MCS) using the same set of parameters. The model was used in fitting available experimental data, and produced numerical values of previously unknown model parameters, including those describing mechanical properties of Müller cell membrane (MCM) with respect to bending and stretching. Numerical experiments simulating MC swelling showed complex oscillation dynamics of the relevant parameters in physiological initial conditions. In particular, MC membrane potential (ΔΨ_MC) demonstrated complex oscillation dynamics, which may be described by a superposition of several oscillations with their periods in the milliseconds, 100-ms and seconds time ranges. Dynamics of reversible and irreversible MCS, and the transition criteria from reversible to irreversible MCS modes were determined in model simulations.

N-myc downstream regulated gene 1 (ndrg1) functions as a molecular switch for cellular adaptation to hypoxia

Lack of oxygen (hypoxia and anoxia) is detrimental to cell function and survival and underlies many disease conditions. Hence, metazoans have evolved mechanisms to adapt to low oxygen. One such mechanism, metabolic suppression, decreases the cellular demand for oxygen by downregulating ATP-demanding processes. However, the molecular mechanisms underlying this adaptation are poorly understood. Here, we report on the role of ndrg1a in hypoxia adaptation of the anoxia-tolerant zebrafish embryo. ndrg1a is expressed in the kidney and ionocytes, cell types that use large amounts of ATP to maintain ion homeostasis. ndrg1a mutants are viable and develop normally when raised under normal oxygen. However, their survival and kidney function is reduced relative to WT embryos following exposure to prolonged anoxia. We further demonstrate that Ndrg1a binds to the energy-demanding sodium-potassium ATPase (NKA) pump under anoxia and is required for its degradation, which may preserve ATP in the kidney and ionocytes and contribute to energy homeostasis. Lastly, we show that sodium azide treatment, which increases lactate levels under normoxia, is sufficient to trigger NKA degradation in an Ndrg1a-dependent manner. These findings support a model whereby Ndrg1a is essential for hypoxia adaptation and functions downstream of lactate signaling to induce NKA degradation, a process known to conserve cellular energy.

An assay of optimal cytochrome c oxidase activity in fish gills

Cytochrome c oxidase (COX) catalyzes the terminal oxidation reaction in the electron transport chain (ETC) of aerobic respiratory systems. COX activity is an important indicator for the evaluation of energy production by aerobic respiration in various tissues. On the basis of the respiratory characteristics of muscle, we established an optimal method for the measurement of maximal COX activity. To validate the measurement of cytochrome c absorbance, different ionic buffer concentrations and tissue homogenate protein concentrations were used to investigate COX activity. The results showed that optimal COX activity is achieved when using 50-100 μg fish gill homogenate in conjunction with 75-100 mM potassium phosphate buffer. Furthermore, we compared branchial COX activities among three species of euryhaline teleost (Chanos chanos, Oreochromis mossambicus, and Oryzias dancena) to investigate differences in aerobic respiration of osmoregulatory organs. COX activities in the gills of these three euryhaline species were compared with COX subunit 4 (COX4) protein levels. COX4 protein abundance and COX activity patterns in the three species occurring in environments with various salinities increased when fish encountered salinity challenges. This COX activity assay therefore provides an effective and accurate means of assessing aerobic metabolism in fish.

2,4-dinitrophenol (DNP): a weight loss agent with significant acute toxicity and risk of death

2,4-Dinitrophenol (DNP) is reported to cause rapid loss of weight, but unfortunately is associated with an unacceptably high rate of significant adverse effects. DNP is sold mostly over the internet under a number of different names as a weight loss/slimming aid. It causes uncoupling of oxidative phosphorylation; the classic symptom complex associated with toxicity of phenol-based products such as DNP is a combination of hyperthermia, tachycardia, diaphoresis and tachypnoea, eventually leading to death. Fatalities related to exposure to DNP have been reported since the turn of the twentieth century. To date, there have been 62 published deaths in the medical literature attributed to DNP. In this review, we will describe the pattern and pathophysiology of DNP toxicity and summarise the previous fatalities associated with exposure to DNP.

The potential of water in mammalian tissues

Melting point depression was used as an index of the water potential of rat tissues and serum. Organs removed from anesthetized rats were immediately frozen in liquid nitrogen and ground with mortar and pestle. Aliquots of the resulting frozen powder were suspended in chilled liquid silicone. While the suspension was vigorously stirred and warmed at a constant rate, the temperature of the melting mixture was measured. The melting curves of rat muscle, liver, heart, and brain were not significantly different from those of rat serum. The melting curve depression of whole kidney was greater than that of serum; this was demonstrated to be due to hypertonicity of the renal medullary area alone. It was demonstrated that autolysis will rapidly increase the depression of the melting curve of tissue. It is concluded that within the limits of the method used the melting point depression, and hence the water potential, of intracellular and extracellular fluids is the same.

The freezing point depression of mammalian tissues after sudden heating in boiling distilled water

The calculated freezing point depression of freshly excised boiled mammalian tissue is approximately the same as that of plasma. The boiling procedure was chosen to eliminate the influence of metabolism on the level of the freezing point depression. Problems created by the boiling, such as equilibrium between tissue and diluent, change in activity coefficient by dilution, and loss of CO(2) content, are discussed. A frozen crushed tissue homogenate is hypertonic to plasma. Boiling and dilution of such hypertonic homogenate exposed to room temperature for 5 to 15 minutes did not produce significant or unexplicable decreases in its osmotic activity. Moreover, freezing and crushing of a boiled diluted tissue did not produce any increase of the isoosmotic level of freezing point depression. It is possible to explain these data either with the hypothesis of hypertonic cell fluid or with that of isotonic cell fluid. In the case of an assumed isotonic cell fluid, data can be explained with one assumption, experimentally backed. In the case of an assumed hypertonic theory data can be explained only with the help of at least three ad hoc postulates. The data support the validity of the classical concept which holds that cell fluid is isotonic to extracellular fluid.

Measurements of electrical potential differences on single nephrons of the perfused Necturus kidney

Stable electrical potential differences can be measured by means of conventional glass microelectrodes across the cell membrane of renal tubule cells and across the epithelial wall of single tubules in the doubly perfused kidney of Necturus. These measurements have been carried out with amphibian Ringer's solution, and with solutions of altered ionic composition. The proximal tubule cell has been found to be electrically asymmetrical inasmuch as a smaller potential difference is maintained across the luminal cell membrane than across the peritubular cell boundary. The tubule lumen is always electrically negative with respect to the peritubular extracellular medium. Observations on the effectiveness of potassium ions in depolarizing single tubule cells indicate that the transmembrane potential is essentially an inverse function of the logarithm of the external potassium concentration. The behavior of the peritubular transmembrane potential resembles more closely an ideal potassium electrode than that of the luminal transmembrane potential. From these results, and the effects of various ionic substitutions on the electrical profile of the renal tubular epithelium, a thesis concerning the origin of the observed potential differences is presented. A sodium extrusion mechanism is considered to be located at the peritubular cell boundary, and reasons are given for the hypothesis that the electrical asymmetry across the proximal renal tubule cell could arise as a consequence of differences in the relative sodium and potassium permeability at the luminal and peritubular cell boundaries.

Measurements of electrical potentials and ion fluxes on single renal tubules

Experimental technics are described which permit the measurements of stable electrical potential differences across the cell membrane of single renal tubule cells and across single tubules. The inside of the tubule lumen is normally found to be electrically negative to the outside, while the cell interior is found to be negative to both the peritubular fluid and the tubule lumen. Such electrical measurements, in conjunction with known concentration gradients and flux measurements of various ions across single renal tubules, permit some deductions to be made on the driving forces involved in the movement of various ion species across the luminal and peritubular cell membrane of renal tubule cells.

SODIUM EXTRUSION AND POTASSIUM UPTAKE IN GUINEA PIG KIDNEY CORTEX SLICES

Slices from the cortex corticis of the guinea pig kidney were immersed in a chilled solution without K and then reimmersed in warmer solutions. The Na and K concentrations and the membrane potential V_m were then studied as a function of the Na and K concentrations of the reimmersion fluid. It was found that Na is extruded from the cells against a large electrochemical potential gradient. Q₁₀ for net Na outflux was ∼2.5. At bath K concentrations larger than 8 mM the behavior of K was largely passive. At the outset of reimmersion (V_m > E_K) K influx seemed secondary to Na extrusion. Na extrusion would promote K entrance, being limited and requiring the presence of K in the bathing fluid. At bath K concentrations below 8 mM, K influx was up an electrochemical potential gradient. Thus a parallel active K uptake is apparent. Q₁₀ for net K influx was ∼2.0. Dinitrophenol inhibited net Na outflux and net K influx, Q₁₀ became <1.1 for both fluxes. The ratio between these fluxes varied. Thus at the outset of reimmersion the net Na outflux to net K influx ratio was >1. After 8 minutes it was <1.

The effect of mercury on chloride secretion in the shark (Squalus acanthias) rectal gland

1. Mercuric chloride inhibited chloride secretion in a dose dependent way in isolated perfused rectal glands. The effect was readily apparent at a concentration of 10(-6) M and profound and irreversible at 10(-4) M. 2. The dithiol dithiothreitol (DTT) 10(-2) M completely prevented the effect of 10(-6) M mercuric chloride, reduced that at 10(-5) M and 10(-4) M, and made the inhibition at the latter concentration reversible. 3. Two organic mercurials, mersalyl and meralluride, that are effective diuretics in the mammalian kidney, and p-chloromercuribenzoyl sulfonic acid (PCMBS), that has no diuretic activity, had no effect on chloride secretion by the rectal gland. 4. The effect of mersalyl was not modified by lowering the pH of the solution perfusing the glands. 5. These results indicate that inorganic mercury and organic mercurials do not share the same mechanism of action. 6. The absence of an effect of organic mercurials on chloride transport in the rectal gland suggests that its effect on another chloride transporting epithelia, the thick ascending limb of the loop of Henle, is not mediated by inhibition of the chloride cotransporter or Na+, K(+)-ATPase, common to both epithelia.

Selected aspects of cell volume control in renal cortical and medullary tissue

Under normal physiological conditions, demands placed on mammalian renal cortical cells are quite different from those in the medulla. Cortical proximal tubule cells exist in an isotonic environment, but must resorb vast amounts of filtered fluid and solute, and also adjust to solute generated from cellular metabolism. In addition, cortical cells must also adjust to occasional pathological derangements in blood osmolality. By contrast, human medullary cells have a smaller solute resorptive load, but exist in a milieu where osmolality varies from 40 to more than 1200 mosmol/kg H2O, depending on water intake. Remarkably, the cells maintain a near normal size despite these stresses. Under isosmotic conditions, the primary regulator of cell volume is Na-K ATPase. In its absence, factors such as external protein, extracellular matrix and basement membrane, cytoskeleton, and perhaps formation of cytoplasmic vesicular-like structures help prevent cells from swelling massively. Under anisosmotic conditions, a variety of transport processes operating across basolateral and apical membranes either remove solute from or add solute (and water) to cells to minimize changes in their size. Medullary cells have the additional ability to accumulate organic, non-toxic, osmolytes that offset external hypertonicity and allow cells to maintain normal size without increasing cellular inorganic ion concentrations.

Colloid osmotic pressure of cat brain homogenate separated from autogenous CSF by a copper ferrocyanide membrane

The colloid osmotic pressure (oncotic pressure) of cat brain homogenate against cerebrospinal fluid (CSF) was determined using an electronic osmometer with a rigid selectively permeable copper ferrocyanide membrane. First, the basic characteristics of the membrane were examined. The relative value of the reflexion coefficient (sigma) for polyethylene glycol (PEG) became rather stable above a molecular weight of 6000 Da, below which sigma declined. The osmometer showed a linear response to sucrose concentration, whereas it revealed a non-idealistic change with respect to concentration of high molecules (PEG). The temperature effect on sigma for albumin solution was found to be large. The membrane could thus be used for measuring the relative value of the colloid osmotic pressure of protein solutions without dilution and at the same temperature as the calibrating solution. Samples of CSF and brain cortex were freshly obtained from 5 cats. The cortex was immediately homogenized and the colloid osmotic pressure of the homogenate against the CSF was measured at room temperature within 3 min after cortex removal. The mean value was 213 +/- 11 (S.D.) mm Hg with the osmometer calibrated with respect to the colloid osmotic pressure of autogenous plasma.

Morphological and physiological studies of rat kidney cortex slices undergoing isosmotic swelling and its reversal: a possible mechanism for ouabain-resistant control of cell volume

Slices of rat kidney cortex were induced to swell by preincubation at 1 degree C in an isotonic Ringer's solution, and their capacity to reverse swelling, by net extrusion of cellular water, was studied during subsequent incubation at 25 degrees C. The recovery from swelling was prevented by the respiratory inhibitor, antimycin A. On the other hand, extrusion of water was little affected by ouabain. The extrusion of water continuing in the presence of ouabain (but not that in its absence) was significantly reduced when furosemide was added or when medium Cl- was replaced by NO-3 or I-. There was substantial variability in the morphological appearance of cells within the cortical slices. Different segments of the nephron showed different structural changes during swelling and its reversal, the proximal tubules being most markedly affected. Proximal tubular cells of swollen slices showed disorganization of brush borders and expansion of their apical surfaces, and contained vesicles in their apical cytoplasm. Upon recovery at 25 degrees C, the apical portions of these cells showed reversal of the expansion, but some apical vesicles remained. These vesicles were much more numerous after recovery in the presence of ouabain, but they were much reduced in numbers, or totally absent, when recovery took place in the presence of furosemide or absence of Cl-, with or without ouabain. The vesicles seen in the presence of ouabain alone appeared to fuse with each other and with infoldings of the basolateral plasma membrane. Rather similar results were obtained with distal tubular cells in the slices. We suggest that volume regulation in the proximal and distal tubular cells proceeds by way of two mechanisms. The first consists of extrusion of water coupled to the ouabain-sensitive transport of Na+ and K+. The other proceeds by way of an ouabain-resistant entry of water into apical cytoplasmic vesicles, following furosemide-sensitive movements of Cl- and Na+; the vesicles then expel their contents by exocytosis at the basolateral cell borders.

Effects of inorganic lead in vitro on ion exchanges and respiratory metabolism of rat kidney cortex

The effects of Pb2+ added in vitro to tissue slices, isolated tubules and isolated mitochondria of rat kidney cortex have been studied. Slices were depleted of K+ and loaded with Na+, Cl- and water by pre-incubation at 1 degree C, and reversal of these changes was then induced by incubation under metabolically favourable conditions. The net reaccumulation of K+ was reduced by a maximum of 30% when Pb2+ was present in the medium, the maximal effect being caused by 200 microM Pb2+. Lead also caused a reduction of Na+ extrusion which was approximately equimolar with its effect on K+, but it did not affect the extrusion of Cl- and water. The initial rates of the net, active movements of K+ and Na+ were not altered by Pb2+, divergence from control values only being noted after 15-30 min incubation. The O2 consumption and the ATP content were 25-30% lower in slices incubated with 200 microM Pb2+ than in control slices; the effect on ATP content was not observed until incubation had continued for 30 min. In tubules isolated from the renal cortex, the rate of respiration (50%) and ATP content (30%) were also partly reduced by 200 microM Pb2+. The consumption of O2 by mitochondria isolated from the cortex was much more sensitive to Pb2+ added in vitro than the respiration of intact cells; the rate of respiration in state 3 (presence of phosphate acceptor) and the respiratory control ratio were drastically reduced, with half-maximal inhibition at 30 and 20 microM Pb2+ respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of Pb2+ added in vitro on Ca2+ movements in isolated mitochondria and slices of rat kidney cortex

We have studied the effects of Pb2+ added in vitro on the movements of Ca2+ in renal cortical mitochondria and tissue slices. The isolated mitochondria rapidly accumulated 45Ca2+ at 25 degrees by a mechanism that was dependent on respiration and inhibited 96% by ruthenium red. A concentration of 10 microM Pb2+ inhibited the Ca2+ accumulation at least as effectively as did ruthenium red. About 20% of the Ca2+ accumulation persisted at 1 degrees with a similar sensitivity to inhibitors, including 60% inhibition by Pb2+. Similar results were obtained when the accumulation of Ca2+ at 25 degrees was measured by means of a calcium-sensitive electrode, Pb2+ inhibiting by 80%. Calcium that had been accumulated by mitochondria at 25 degrees was released completely by the ionophore A23187 or by 10 microM Pb2+. The release induced by Pb2+ was greatly inhibited by ruthenium red. The Ca2+ content of tissue slices of renal cortex increased 4-fold during incubation at 1 degree while the Ca2+ content of mitochondria within the slices more than doubled, the latter being determined by isolation of mitochondria from the slices after incubation. The presence of Pb2+ (200 microM) in the incubation medium of the slices substantially reduced the entry of Ca2+ into the whole slices and into mitochondria within the slices. When the slices preincubated at 1 degree were warmed to 25 degrees in oxygenated medium, they brought about a net extrusion of Ca2+, some of which was derived from the mitochondria; Pb2+ did not alter the final level of Ca2+ then attained in the slices, but it caused a significant decrease in the quantity retained in the mitochondria. We conclude that Pb2+ both inhibits the uptake of Ca2+ by renal cortical mitochondria and displaces Ca2+ from them, these effects occurring whether the mitochondria are isolated or in situ.

Effects of medium acetate on cellular volume in rabbit renal cortical slices

Slices of rabbit renal cortex were incubated at 25 degrees C in media in which acetate replaced chloride. There was gross cellular swelling in isosmotic 132 mM-acetate medium, and this swelling was unique in that, with a normal medium potassium concentration, it was accompanied by a substantial increase in cellular potassium content. This accumulation of potassium, but not the cellular swelling, was dependent upon metabolism and inhibited by ouabain. This accumulation of potassium was not dependent upon the cellular swelling. It also occurred in a hyperosmotic acetate medium in which swelling was minimized. In isosmotic media, the cellular swelling was proportional to medium acetate concentration and was also affected markedly by medium pH, being greatest at an initial medium pH of 7.1 and least at pH 7.7. The swelling was reversed and cellular composition restored when tissue was re-incubated in NaCl medium. Ouabain (10(-3)M) largely prevented this recovery in volume. The results are consistent with plasma-membrane-based theories, on the assumption that membranes are much more permeable to undissociated acetic acid than they are to the acetate ion. They are inconsistent with the expectations of an alternative hypothesis (the association--induction hypothesis) which ascribes the maintenance of cellular composition to properties of cellular proteins and cellular water rather than to those of the plasma membrane. The results do not favour the suggestion that cellular swelling itself results in irreversible cellular damage. The results are consistent with the hypothesis that the ouabain-inhibitable Na-K-ATPase plays a major role in the regulation of cellular volume. No alternative metabolically dependent volume regulating mechanism need be postulated to explain them.

Intracellular electrolyte composition following renal ischemia

The technique of electron microprobe analysis was used to determine the intracellular electrolyte concentrations in proximal or distal tubular cells of the rat kidney during ischemia. When the exposed kidney was maintained in air during ischemia, the composition of the surface cells differed little from control, and the electrolyte disturbances were confined to the deeper lying cells. When maintained in nitrogen, all cells underwent changes in cellular electrolyte concentrations that were uniform, indicating that the surface cells can preserve their composition during ischemia by utilizing oxygen from the air. In the proximal tubular cells, after 20 or 60 min of ischemia in nitrogen, sodium increased from 20 to 93 or 112, chloride rose from 21 to 53 or 66, potassium fell from 141 to 65 or 42, phosphate decreased from 145 to 110 or 95 mmoles.kg-1 of wet wt, and the dry wt dropped from 22.6 to 20.3 or 17.5% of wet wt, respectively. In the distal tubular cells, 20 min of ischemia in nitrogen produced little effect on cellular composition, but after 60 min, sodium increased from 11 to 77, chloride rose from 15 to 48, potassium fell from 134 to 89, phosphate decreased from 168 to 145 mmoles.kg-1 of wet wt, and the dry wt dropped from 20.8 to 18.4% of wet wt. The disturbances in sodium and potassium are caused primarily by an inhibition of the sodium/potassium pump, whereas the changes in chloride, phosphate, and dry weight content result mainly from an influx of extracellular fluid. When blood flow was reintroducing, the electrolyte disturbances were rapidly reversed in all cells, restoration being virtually complete within 60 min, but returned in some proximal cells by 18 hr of reperfusion. Thus, the disturbance in electrolyte composition increases with the duration of ischemia, is less pronounced in the distal than proximal cells and, although initially completely reversible when blood flow is restored, reappeared in the proximal cells 1 days after the initial injury.

Anion exchange and volume regulation during metabolic blockade of renal cortical slices

1. The development of swelling of rat and guinea-pig renal cortical slices was studied after metabolic blockade (hypoxia plus glycolytic blockade with iodo-acetic acid) and/or exposure to 'isotonic' high potassium, no sodium solution. 2. Swelling was greater after exposure to oxygenated high potassium solution than after metabolic blockade in physiologic Krebs-Henseleit solution. Swelling was reduced after metabolic blockade in high potassium solution compared to incubation in oxygenated high potassium solution. Increasing periods of transient metabolic blockade in Krebs-Henseleit solution progressively blunted swelling when slices were subsequently incubated in oxygenated high potassium solution. 3. Metabolic blockade in Krebs-Henseleit solution resulted in marked reductions in potassium and increases in sodium. Incubation in high potassium solution resulted in marked increases in potassium and similar low levels of sodium regardless of associated interventions. Metabolic blockade in both media resulted in significantly greater increases in renal cortical chloride than in monovalent cations (potassium plus sodium). Incubation in oxygenated high potassium solution was associated with similar increases in renal cortical chloride and total monovalent cations. 4. Renal cortical losses of solids and protein and increases in renal cortical inulin space were greater after metabolic blockade than after incubation under oxygenated conditions regardless of the incubation media. 5. These data support the conclusion that during metabolic blockade there is a significant replacement of larger intracellular anions by extracellular chloride. The loss of osmotically active intracellular anions limits the increase in renal cortical volume during metabolic inhibition and exposure to high potassium solution.

Metabolic requirements for anaerobic active Cl and Na transport in the bullfrog cornea

In the bullfrog cornea, the relationships between the rates of aerobic and anaerobic glycolysis and active Cl and Na transport were studied. In NaCl Ringer (glucose-free), the short-circuit current (SCC) declined much more slowly under aerobic than under anaerobic conditions. The aerobic lactate effluxes in glucose-free and glucose-rich NaCl Ringer were 0.08 and 0.23 micromol/h.cm2, respectively. The transition to anoxia caused these values to increase significantly and was accompanied by depletion of endogenous glycogen in glucose-free Ringer. In Na2SO4 Ringer, amphotericin B (10(-5) M) stimulation of the aerobic SCC was not dependent on the presence of glucose but under anoxia, SCC stimulation required glucose. In Na2SO4 (glucose-rich) Ringer, amphotericin B stimulated the aerobic lactate efflux from 0.26 to 0.36 mumol/h.cm2 and anoxia increased it to 0.55 micromol/h.cm2. In NaCl Ringer, the addition of either 0.5 mM adenosine or 1 mM ATP with 26 mM glucose restored the anaerobic-inhibited SCC and lactate efflux of glucose-depleted corneas. The results show that the reactions of glycolysis are a sufficient energy source for supporting active Na and Cl transport.

Ouabain and regulation of cellular volume in freshly prepared slices of rabbit renal cortex

1. Changes in the water and ion contents of rabbit renal cortical slices, which had been bathed, immediately after slicing, in air-equilibrated media at room temperature ('freshly prepared slices'), were followed during subsequent incubation at 25 degrees C in oxygenated media of the same composition as the initial bathing medium. 2. In comparison with conventional 'equilibrated' slices (slices incubated at 25 degrees C in oxygenated ordinary medium immediately after slicing) these 'freshly prepared' slices had increased tissue water, sodium and chloride contents and low tissue potassium contents. 3. Control freshly prepared slices incubated at 25 degrees C in oxygenated ordinary medium recovered within 4 min to the tissue water content that is usual for rabbit renal cortical slices incubated in oxygenated ordinary medium at 25 degrees C. Freshly prepared slices incubated at 25 degrees C in oxygenated media containing 1 mM-oubain took 75 min or more to recover to this usual tissue water content. Thus the presence of 1 mM-oubain in both bathing and incubation media produced a marked inhibition of the volume recovery observed when freshly prepared slices are incubated in oxygenated media at 25 degrees C. 4. Reduction of the ouabain concentration reduced the inhibition of cell volume recovery. 5. Replacement of medium glucose by 3-O-methylglucose did not inhibit cell volume recovery in the absence of ouabain. 6. The oxygen consumptions of slices that were bathed and incubated in 1 mM-ouabain media were similar to those of slices initially bathed and incubated in ouabain-free media and then incubated in ouabain media. Thus the effect of ouabain in inhibiting cell volume recovery was unlikely to be secondary to inhibition of cellular energy production. 7. The tissue potassium content of slices incubated aerobically in 1 or 10 mM ouabin fell to an apparently stable value of approximately 100 m-mole/kg dry wt., which corresponds to a calculated concentration ratio of 10:1 across the cellular membrane, suggesting that some residual potassium uptake may still have been occurring. 8. These results indicate that in freshly prepared rabbit renal cortical slices ouabain-sensitive mechanisms play a major role in cell volume recovery. They are not in accord with the postulate that renal cortical cells possess a separate ouabain-insensitive mechanism regulating cell volume.

Tubular chloride transport and the mode of action of some diuretics

The renal diluting segment (thick ascending limb of Henle's loop) reabsorbs sodium chloride in excess of water and is responsible for dilution of the urine as well as reabsorption of a large fraction of the salt present in the glomerular ultrafiltrate. In this segment, there is active reabsorption of chloride which causes the voltage to be positive in the tubule lumen. Most, if not all, of the sodium transport is passive, driven by the voltage. Three major diuretic drugs (mersalyl, furosemide and ethacrynic acid) act in the lumen of the diluting segment to inhibit active chloride transport, not sodium transport as previously believed. This specific action on chloride transport may explain how these drugs are able to inhibit salt transport in the kidney while having so little effect on the electrolyte transport processes elsewhere in the body.