Two modes of Na extrusion in cells from guinea pig kidney cortex slices

Observations on the regulation of cell volume and metabolic control in vitro; changes in the composition and ultrastructure of liver slices under conditions of varying metabolic and transporting activity

Liver slices incubated at 1 degree C underwent swelling of both cellular and intercellular compartments, as judged by electronmicroscopy. The ultrastructure showed marked changes, including disorganization of the cytocavitary network and plasma membrane and alterations of mitochondria. Restoration of metabolically favorable conditions (oxygenated medium at 38 degrees C) caused a nearly complete recovery of ultrastructure closely associated with extrusion of water; measurements of inulin space and electronmicroscopy both indicate a recovery of cell volume, with intercellular spaces remaining somewhat expended. The fluid lost was a roughly isotonic solution of Na+ and Cl-, while K+ was reaccumulated in exchange for Na+. Cyanide prevented recovery. Ouabain and oligomycin each partially prevented fluid extrusion, but had little effect on ultrastructural recovery except to induce intracellular vesicles containing particles of thorium dioxide derived from sinusoidal spaces. The vesicles were, however, markedly different in form with each inhibitor. There are, thus ouabain-sensitive and insensitive components of volume regulation; the former appears to depend on the coupled transport of Na+ and K+ and the latter, we suggest, on a secretion of Na+ and Cl- into vesicles which release their contents into the bile canaliculi by an oligomycin-sensitive mechanism. Mitochondria showed conformational changes between orthodox and condensed forms, but these could not be directly related to tissue energy states; the numbers of mitochondrial dense granules bore a closer relation to tissue ATP.

Trans-proximal tubular steady-state concentration differences studied by micro-puncture and tissue content of sodium and chloride at varying intraluminal sodium concentrations in vitro in rat kidney cortex slices: evidence for a multisite sodium transport system

1. With the aid of micropuncture techniques, proximal tubular transepithelial concentration differences for Na (deltaC Na) and chloride (deltaC Cl) were measured in kidney cortex slices at bathing fluid Na concentrations from 10 to 400 m-mole. kg-1. Tissue content of water, Na and K was also measured in such slices. Under steady-state conditions of zero net flux of NaCl and water, deltaC Na represents the sum of active Na transport, factored by the tubular permeability coefficient added to a component of flux due to electrical forces. 2. The relation between bathing fluid Na concentraton and deltaC Na appeared sigmoid in form suggesting an allosteric mechanism for the transport step. 3. Transtubular potential difference, calculated from transepithelial Cl distribution ratios, did not appear constant at the various bathing fluid Na concentrations. Correcting for the effect of these potential differences on the value of each deltaC Na did not convert the sigmoid transport curve to a hyperbolic one, confirming the suggested allosteric nature of the active Na transport step. 4. Intracellular Na content varied linearly with bathing fluid Na concentrations implying free entry of this cation into the cell. This also suggests that the sigmoid transport curve is related to the properties of the active Na transport pump.

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.

Prostaglandins lack a direct inhibitory action on electrolyte and water transport in the kidney and the erythrocyte

The possibility of a direct effect of prostaglandins of the E, A, and F series upon renal electrolyte and water transport was assessed using in vitro preparations of rabbit cortical and medullary tubular suspensions as well as cortical renal slices from rat and guinea pig and medullary renal slices from rabbit. Net fluxes of Na, K, C1 and H2O between the intracellular compartment and the extracellular fluid were measured in the presence of PGE1, PGE2, PGA1, PGA2 and PGF2alpha in concentrations ranging from 1 X 10(-5) to 1 X 10(-10)M. No inhibitory action was observed with any of these prostaglandins and in fact a slight stimulation of Na transport was seen under some circumstances. We conclude that the natriuresis which follows in vivo administration of some prostaglandins is not the result of a direct inhibition of Na reabsorption at the contraluminal pump site and is most likely secondary to renal vasodilation. We also studied net and isotopic Na fluxes in human erythrocytes. Na transport was not affected by prostaglandins of the E, A or F series using both normal and high sodium erythrocytes. Our results emphasize the need for caution in extrapolating the effects of prostaglandins upon Na transport from one tissue to another since their actions appear to be tissue-specific.

Alterations in the dog renal tubular epithelium during normothermic ischemia

Dog kidneys were subjected to one, two, or three hours' normothermic ischemia in situ and were then excised for biochemical and histological evaluation. The uptake of para-aminohippurate (PAH) by cortical slices progressively decreased with prolongation of the ischemia, but active transport was never abolished. Glycine uptake and oxygen consumption were only reduced to a modest extent by the ischemia. The intracellular ion levels were drastically altered, with loss of potassium and gain of sodium and chloride, and considerable increases in tissue water were observed. Acid phosphatase was liberated by the whole organ into the venous blood and by the incubated slices into the incubation medium, but both biochemical and histochemical techniques showed that the total quantity of the enzyme in the cells was hardly changed. The histochemical reaction product was localized exclusively in the lysosomes. Morphological damage was slight after one or two hours' ischemia, but more pronounced after three hours, when some cells were seen to be detached from the basement membrane. These relatively minor changes seem insufficient to predict the ultimate fate of the organ after ischemia.

Substrate metabolism and renal function

Glucose metabolism is related to two major renal functions. Glycolysis may be related to an energy requiring function--fine adjustment of renal sodium absorption. Gluconeogenesis may be related to controlling intracellular pH and salvation of energy otherwise wasted in acidosis. Ammoniagenesis is related to gluconeogenesis in the metabolic acidosis, but the individual phenomena are not necessarily dependent on each other.

Multiple pumps for sodium reabsorption by the perfused kidney

Several distinct transport mechanisms responsible for sodium reabsorption by the rat kidney can be identified by studying the function of isolated perfused kidneys. Approximately one-half of the fractional sodium reabsorption by the isolated perfused rat kidney appears to depend on Na-K-adenosine triphosphatase (AT-Pase) and is inhibited by ouabain. About 10 to 20% is associated with the reabsorption of bicarbonate and is blocked by acetazolamide. This fraction of transported sodium is unaffected by ouabain and therefore does not involve Na-K-ATPase. Neither furosemide nor ethacrynic acid produce further inhibition of sodium reabsorption in a kidney already exposed to ouabain and acetazolamide. Most of the residual transport of sodium is inhibited by cooling the perfused kidney, suggesting that it is powered by metabolic rather than physical sources of energy.

Studies on renin release from isolated superfused glomeruli: effects of temperature, urea, ouabain and ethacrynic acid

1. The effects of different energy substrates, of low temperature, of urea, and of ouabain and ethacrynic acid were studied on the rate of renin release from viable juxtaglomerular cells during superfusion of isolated rat glomeruli. 2. Neither lactate nor glutamate altered renin release rate from that observed using glucose as the sole energy substrate. Succinate 10 mM elevated release transiently but did not influence the release caused by reductions in osmolality through lowering sucrose concentration. 3. Peak renin release was more prolonged and returned more slowly to control following reductions in osmolality in phosphate-Ringer than in bicarbonate-Ringer. 4. At 37 degrees C, the peak of renin released induced by hypo-osmolality was smaller and delayed, and returned earlier to control than at 30 degrees C. Reduction in temperature from 30 to 4 degrees C resulted in a 32-fold increase in basal release rate. At 4 degrees C a 20 m-osmole/kg reduction in tonicity caused an additional 2-5-fold increase in release rate. 6. Increasing superfusate osmolality with urea did not affect basal renin release but 100 mM urea suppressed the releasing effect of a 15 mM reduction in NaCl concentration. 7. Ouabain (10(-4) M) caused a small (33 +/- 9%, P less than 0-025) transient increase in renin release. Ethacrynic acid (10(-3) M) provoked a progressive increase in release reaching 100 +/- 15% above control within 50 min. In the presence of both inhibitors the release provoked by hyposmolality was prolonged. 8. It is concluded that renin release in vitro is a function of actively regulated cell volume and it is proposed that a similar mechanism could underline both barorecptor and macula densa controls of renin secretion in vivo.

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.

Effects of angiotensin II on fluid transport, transmural potential difference and blood flow by rat jejunum in vivo

A method has been described for the measurement of fluid transport by rat jejunum in vivo over two consecutive 30 min periods. 2. Subpressor infusion rates of angiotensin (0-59 ng/kg per minute) stimulate fluid transport, while high (pressor) infusion rates (590 ng/kg per minute) inhibit fluid absorption. 3. Both the inhibitory and stimulatory effects of angiotensin on fluid transport are not accompanied by any change in the transmural p.d., total blood flow to the jejunum or distribution of blood flow within the wall of the jejunum. 4. These results are discussed in relation to the mechanism of action of angiotensin on fluid transport and its role in sodium and water homoeostasis.

Cell electrical potentials during enhanced sodium extrusion in guinea-pig kidney cortex slices

1. Experiments were performed on outermost slices of the guinea-pig kidney which are mainly made up of proximal tubular cells. 2. Kidney cells loaded with Na+ by chilling at 0.6 degrees C for 2.5 hr, when subsequently rewarmed to 25 degrees C in a medium containing 16 mM-K+ extrude Na+ at enhanced speed for about 10 min. This Na+ movement is accompanied by efflux of Cl and influx of K+. 3. Measurements of cell potential during enhanced Na+ extrusion show that cells hyperpolarize to values about 30 mV more negative than the K+ equilibrium potential. 4. This hyperpolarization is only partly inhibited by 1 mM ouabain or by 2 mM ethacrynic acid but both agents added together suppress it completely. 5. With 16 mM-Rb instead of 16 mM-K the hyperpolarization is smaller. 6. A diminished extracellular K+ concentration outside of the cells, within the slice, can account for only a small part of the hyperpolarization. 7. The hyperpolarization is proportional to the rate of Na+ pumping. 8. Cl- seems to shunt the hyperpolarization to a greater extent than K+. 9. It is concluded that Na+ extrusion is capable of transferring electric charge across the membrane.

Ionic fluxes in isolated epithelial cells of the abdominal skin of the frog Leptodactylus ocellatus

Unidirectional ion fluxes are measured in cells isolated by a trypsination-dissection method from the epithelium of the frog Leptodactylus ocellatus. Potassium seems to be contained in a single cellular compartment. The influx of potassium is 0.0068 mumole min-1 mg-1 of dry weight and is carried by a ouabain-sensitive pump. Sodium seems to be contained in two cellular compartments, one of which does not exchange its Na within the experimental period. The possibility that these compartments reflect the existence of different types of cells is not discarded. 49% of the rate constant for the Na efflux is ouabain-sensitive and 23% is ethacrynic-sensitive. Under control conditions the permeability to potassium (PK), sodium (PNa) and chloride (PC1) are 7.6 X 10(-5), 2.6 X 10(-5) and 2.8 X 10(-5) liters/min mg, respectively. The value of PNa is much higher than predicted by current electrical models of the epithelium. The discrepancy might offer some insight into the nature of the "inner facing barrier" of the skin.

Ouabain-insensitive Na+ stimulation of an Mg-2+ -dependent ATPase in kidney tissue

1. Freshly prepared microsomal fractions of the outermost cortex of guinea pig kidney show an Mg-2+-dependent ATPase activity which is partially inhibited by 100 mM NaCl, LiCl, KCl, RbCl, CsCl, NH4Cl or choline chloride. 2. If the microsomal preparation is aged by storage at 4 degrees C for 10-15 days, the Mg-2+-dependent activity shows stimulation by Na-+ and Li-+ but not by K-+, Rb-+, Cs-+, NH4-+ or choline. 3. Stimulation is similar with sodium salts of Cl-minus, HCO3-minus, CH3COO-minus, BR-minus, SO4-2-minus or methylsulphonate. 4. Stimulation is insensitive to 1 mM and 10 mM ouabain. 5. Stimulation is unaltered by the presence of 0.5 mM ethyleneglycol-bis-(beta-aminoethyl ether)N,N'-tetracetic acid. 6. Stimulation is 100% inhibited by 2 mM ethacrynic acid, a concentration which inhibits only 30% of the Mg-2+-dependent ATPase and 50% of the (Na-++K-+)-stimulated ATPase. 7. Some of these characteristics coincide with those of an ouabain-resistant, K-+-independent, ethacrynic acid-sensitive mode of Na-+ extrusion out of guinea pig kidney cortex cells.

Relationship between L-alanine and sodium ion transport in isolated renal tubules

1. Rat renal tubules were isolated by incubation with collagenase. The Na+ concentration in the tubules at 37 degrees C was increased by additions of g-strophantin and L-alanine. The increase of Na+ in the presence of both g-strophantin and L-alanine was stronger than with either alone. 2. Radioactive sodium (22-Na), which was taken up by the tubules at 0 degrees C in K+-free medium, was more slowly washed out in the buffer with added g-strophantin than in the control buffer, but L-alanine had no effect. 3. At 0 degrees C incubation without K+, g-strophantin did not affect the 22-Na transport of the tubules. But under the same conditions, L-alanine increased Na+ uptake significantly, and in conjunction with it, L-alanine uptake was also increased. 4. The relationship between L-alanine uptake and intra- extracellular Na+ concentration gradients was linear. The ration of L-alanine to Na+ uptake at 0 degrees C was about 1:2. 5. In the incubation without K+ at 0 degrees C, L-alanine could be accumulated in tubules against the chemical concentration gradient (about 1.5-fold). 6. In the incubation without K+ at 37 degrees C, the L-alanine concentration in tubules after 5 min was already steady (Ci/Ce = 2.2), but with K+ it was not stabilized after 10 min. The ration Ci/Ce with K+ WAS HIGHER THAN WITHOUT K+. 7. G-Strophantin, p-hydroxymercuribenzoate, amiloride, and 2,4-dinitrophenol inhibited L-alanine uptake in the tubules and at the same time increased Na+ concentration. The relationship between the L-alanine uptakes inhibited by g-strophantin, amiloride and dinitrophenol, and the respective intra- extracellular Na+ concentration gradients was strikingly linear. But in the case of p-hydroxymercuribenzoate there was no correlation. 8. The results indicate that L-alanine transport into the renal tubules might be regulated mainly by the intra- extracellular Na+ concentration gradient and that inhibitors such as g-strophantin, amiloride, and dinitrophenol could have a secondary effect on the L-alanine transport which follows the change of Na+ concentration in cells. p-Hydroxymercuribenzoate might have an inhibiting effect on the binding of carrier with Na+ and/or L-alanine.

Some aspects of proximal tubular sodium chloride reabsorption in Necturus kidney

Some aspects of proximal tubular sodium chloride reabsorption in Necturus kidney. Renal tubular reabsorption of fluid and sodium was measured by clearance methods in the doubly perfused Necturus kidney in which the bicarbonate concentration was varied between 0 and 60 mEq/liter. The effects of Damox (2.2 times 10-3M), ocubain (10-5M) and ethacrynic acid (10-4M) and of acidosis were also investigated. In addition to clearance experiments, stationary microperfusion experiments were carried out on promimal tubules to measure volume flow and steady-state sodium and chloride concentration differences across the tubular epithelium. In some experiments, the transepithelial electrical potential difference was also measured using an axial electrode system. The following results were obtained: 1) Bicarbonate is not essential to the operation of renal tubular fluid and sodium transport. 2) Total renal and proximal tubular fluid and sodium transport are partially inhibited by Diamox, ouabian and ethacrynic acid. 3) The proximal tubule maintains a significant transepithelial sodium and chloride concentration difference and a significant electrical potential difference (lumen-negative) in the presence of a poorly permeant nonelectrolyte. The direction and magnitude of the electrical polarization fully accounts for the observed chloride concentration difference. The data support the thesis that sodium chloride transport accross the proximal tubular epithelium takes place by active sodium transport and electically coupled passive chloride reabsorption. Important species differences with respect to mammalian transport mechanisms are discussed.

Reversal of cyclic AMP-mediated intestinal secretion by ethacrynic acid

Ethacrynic acid (EA) has been reported to reduce cholera toxin-induced intestinal fluid secretion in the intact animal. We explored the nature of this inhibition in vitro by measuring unidirectional, transmural fluxes of (22)Na and (36)Cl across isolated rabbit ileal mucosa. Under control conditions (short-circuited mucosa bathed in bicarbonate-Ringer), there was net absorption of Na and Cl. Theophylline (10 mM), cyclic AMP (5 mM), and cholera toxin (added in vivo) abolished net Na flux and produced net Cl secretion. In the presence of either theophylline or cAMP, addition of 0.1 mM EA to the serosal bathing solution abolished net Cl secretion and restored net Na absorption. Cholera toxin-treated mucosa was exposed to 0.05 and 1.0 mM EA. The lower concentration restored net Na absorption but did not significantly reduce Cl secretion. The higher concentration abolished net transport of both Na and Cl. Short-circuit current and Na flux measurements in the presence and absence of glucose indicated that 0.1 mM EA does not inhibit glucose-coupled Na transport. Short-circuit current measurements in the presence of 1.0 mM EA suggested that even this concentration of EA does not inhibit glucose-coupled Na transport. Thus EA appears to specifically inhibit Cl (or NaCl) secretion without inhibiting the absorptive Na "pump." The anti-secretory effect of 0.1 mM EA does not appear to result from inhibition of adenylate cyclase since secretion stimulated by addition of 5 mM cAMP was abolished. Furthermore, 0.1 mM EA did not significantly reduce theophylline-augmented and cholera toxin-augmented cAMP levels in ileal mucosa. We conclude that EA interacts specifically with the active Cl (or NaCl) secretory mechanism of the small intestine at a step beyond generation of cAMP.

Spontaneous salivation in the rabbit submandibular gland

1. Salivation has been studied in the submandibular gland of the rabbit. A very slow spontaneous salivation took place when all possibility of nerve influence had been excluded. Salivation was not due to ultrafiltration.2. The ;spontaneous' saliva had a mean K concentration of 148 mM and Na concentration of 46 mM. With increasing salivation rate produced by parasympathetic nerve stimulation, K concentration fell to a plateau level of about 30 mM whilst Na concentration fell rapidly to reach the low value of 3 mM, then began to rise again at the higher flow rates.3. Ligation of the submandibular duct produced a reversal of the ion concentrations in spontaneous saliva. By 4 days K concentration was lower and that of Na higher than control values until by 2 weeks the effect was maximal with mean concentrations of 25 mM for K and 153 mM for Na.4. Ouabain increased the spontaneous salivation rate and ethacrynic acid slowed or prevented it altogether. On the basis of the known sites of action of these drugs it is postulated that two pumps are involved in the regulation of spontaneous salivation. There appears to be basal activity of an acinar mechanism pumping NaCl into the lumen, taking water with it. This pump is activated directly or indirectly by the intracellular Na concentration which itself is controlled by an Na-K exchange pump.5. Excitation of the sympathetic trunk produced a small, though definite, increase in salivation rate. There was evidence that myoepithelial cells might also be involved in the sympathetic response and that they were activated by alpha receptor stimulation. Salivation evoked by sympathetic nerve stimulation would seem to be a response to beta receptor stimulation, but the possibility that activation of both alpha and beta receptors was required could not be excluded entirely.

Relationship between tubular net sodium reabsorption and peritubular potassium uptake in the perfused Necturus kidney

1. K influx from peritubular space into renal tubular cells, varphi(i) (K), was measured in doubly perfused Necturus kidneys by studying tissue uptake of (42)K added exclusively to the portal circulation. Concomitantly, net tubular Na reabsorption, varphi(n) (Na), was measured by clearance techniques. varphi(n) (Na) and varphi(i) (K) were varied widely by replacing solutions of physiological composition (controls) with solutions containing high K, low K, low Na, cyclamate instead of Cl, ouabain (10(-7)-10(-4)M) or ethacrynic acid (10(-5)-10(-4)M).2. The ratio of varphi(n) (Na) to varphi(i) (K) was found to vary with the experimental conditions, the control value of about 2 was maintained over a threefold variation in absolute Na reabsorption. This ratio increased with low K or ouabain to values near 4. With high K, ethacrynic acid, low Na or cyclamate the relationship was one or lower. Thus, net Na reabsorption can be uncoupled from peritubular K influx.3. These results can be best explained if there are two Na pumps working in parallel: pump A transporting Na (with Cl) and pump B, a Na-for-K-exchange pump. The ratio of Na efflux to K influx could approach infinity if only pump A works (if B is inhibited) and could approach one if only B works. It should vary between these limits in controls when both pumps are active, or when neither of the two pumps is completely inhibited.4. Alternatively, the experimental findings could be explained by a Na pump with a coupling ratio that varies within two extreme values, from high Na-K ratios (with Na reabsorption at, or near, control values but with very low K influx values) to low ratios (with normal K influx values but with low Na reabsorption values).

Ouabain-uninhibited sodium transport in human erythrocytes. Evidence against a second pump

Others have concluded that a second Na "pump" (active Na outflux) exists in human erythrocytes. This second pump was said to be ouabain-insensitive, unlike the classic ouabain-sensitive Na-K pump. An alternative explanation is that "pump II" is Na exchange diffusion. These hypotheses were examined in the present experiments, utilizing (22)Na influx and outflux measurements, net Na fluxes, and ATPase determinations. Ouabain-uninhibited Na outflux was reduced 0.58+/-0.05 mmol/liter cells per h when extracellular Na (Na(o)) was replaced by Mg. Ethacrynic acid or furosemide produced similar decrements of outflux (0.50 mmol) in the presence of ouabain and Na(o). However, these diuretics had minimal inhibitory effects on outflux in the absence of Na(o) suggesting that they inhibited principally the Na(o)-dependent outflux. Whereas this ouabain-uninhibited portion of outflux was dependent on Na(o), it was independent of K(o). Contrary to expectations, Na influx did not change when intracellular Na was altered. No uphill, net Na transport (ouabain-uninhibited) could be demonstrated under a variety of circumstances. Furosemide at high concentrations inhibited ATPase, reducing both ouabain-sensitive and ouabain-insensitive enzyme at 1.0 mM concentration while showing no effect on ATPase at 0.05-0.1 mM concentration. The effects of furosemide on ATPase and on Na flux were dissociable on a dose-response curve. Energy depletion for 22 h practically eliminated the Na(o)-dependent, diuretic-inhibited Na outflux. Activation energies and temperature coefficients for the diuretic-inhibited outflux were one-half the values for the classic ouabain-inhibited pump. These data are interpreted as evidence against a second Na pump. Exchange diffusion accounts adequately for most of these observations; however, the ouabain-insensitive fluxes may be complex and composed of several processes.

Renal sodium-potassium-activated adenosine triphosphatase and sodium reabsorption

The role of renal Na(+),K(+)-ATPase in sodium reabsorption was further examined in dogs in which digoxin, a specific inhibitor of the enzyme system, was infused into one renal artery in doses ranging from 0.4 to 0.9 mug/kg/min (low dose) and from 1.0 to 4.0 mug/kg/min (high dose). A significant natriuresis occurred with both dose ranges which was accompanied by inhibition of Na(+),K(+)-ATPase of cortex and medulla in the infused kidney. Despite over 90% enzyme inhibition in many experiments, at least 80% of the filtered sodium continued to be reabsorbed. The per cent change in enzyme activity correlated with the rate of digoxin administration and the total dose administered but not with changes in sodium excretion. Changes in medullary Na(+),K(+)-ATPase activity, however, bore a direct relationship to alterations in fractional solute free water reabsorption (T(c) (H2O)). Inhibition of cortical enzyme activity alone was not associated with natriuresis, suggesting that medullary enzyme activity must be depressed for increased sodium excretion to occur during digoxin infusion. In high-dose experiments, significant inhibition of cortical and medullary enzyme in the contralateral control kidney was also observed, but natriuresis did not occur. In these experiments the rate at which digoxin reached the control kidney rose progressively but never equaled the rates in the directly infused kidney with either dose. Nevertheless, it is clear that under certain circumstances enzyme inhibition of either cortex or medulla need not be accompanied by natriuresis. We conclude that the major role of renal Na(+),K(+)-ATPase is in sodium reabsorption in the medulla (ascending limb of Henle's loop) and that it has a relatively small role in proximal sodium reabsorption. The kidney can rely on other sodium reabsorptive mechanisms depending on the rate of enzyme inhibition, so that natriuresis may not occur at all if depression in activity occurs "slowly." The nature of these mechanisms is not clear.

Studies on the mechanism of action of angiotensin on ion transport by kidney cortex slices

1. A study has been made of the effects of cyclic AMP, phosphodiesterase inhibitors and protein synthesis inhibitors on the response of rat kidney cortex slices to physiological doses of angiotensin.2. The additions of cyclic AMP, dibutyryl cyclic AMP and/or phosphodiesterase inhibitors to the incubation medium (conditions which would be expected to increase intracellular cyclic AMP levels) were without effect on sodium or potassium transport by kidney slices.3. Actinomycin D (an inhibitor of the transcription stage of protein synthesis), at concentrations which inhibit RNA synthesis by 75%, has no effect on either control or angiotensin stimulated sodium transport.4. Cycloheximide or puromycin (inhibitors of the translation stage of protein synthesis), at concentrations which inhibit protein synthesis by 70-80%, have no effect on control sodium and potassium transport by kidney slices, but completely block the angiotensin stimulation of these processes.5. These findings are discussed in relation to the possible involvement of cyclic AMP and protein synthesis in the mechanism of action of angiotensin on kidney sodium and potassium transport.

Formation of saliva and potassium transport in the perfused cat submandibular gland

1. In the cat submandibular gland perfused with modified Locke solutions, salivary secretion during acetylcholine (ACh) infusion and K uptake from the perfusion fluid after the ACh-induced K loss were measured.2. Strophanthin G (10(-5)M) abolished K uptake, whereas salivary secretion was unaffected.3. Ethacrynic acid (10(-4)-2 x 10(-4)M) hardly affected K uptake whereas salivary secretion was severely inhibited.4. During perfusion with Ca-free solution K uptake was unaffected, whereas salivary secretion was severely reduced.5. The presence or absence of CO(2)/HCO(3) in the perfusion fluid was of no importance for the secretory process and the K uptake. Acetazolamide (2 x 10(-4)-10(-3)M) did not inhibit these transport processes.6. It is suggested that two kinds of Na transport occur in the acinar cells of the salivary glands: a Na extrusion coupled with K uptake, responsible for the maintenance of the concentration gradients across the cell membrane; and a Na transport coupled with Cl transport into the acinar lumen, responsible for the formation of the primary secretion.

The distribution of sodium-potassium--activated adenosine triphosphatase in medulla and cortex of the kidney

The activity of sodium-potassium-activated adenosine triphosphatase (Na-K-ATPase) is considerably higher in homogenates of outer medulla than in the cortex or papilla of the kidney. The enzyme has similar kinetic characteristics in both cortex and medulla, and binds ouabain in the same proportion. The discrepancy in enzymatic activity is not paralleled by similar change in the activity of adenyl cyclase, 5'nucleotidase, glucose-6-phosphatase, or succinic dehydrogenase. Na-K-ATPase is also higher in distal convoluted tubules (ventral slices) than in the proximal tubules (dorsal slices) of the kidney of Amphiuma. The high concentration of Na-K-ATPase in the red medulla of the kidney is probably related to the presence here of the thick ascending limb of the loop of Henle, and this has important implications with regard to the mechanism of sodium reabsorption by different portions of the nephron.

The effect of angiotensin on cation transport by rat kidney cortex slices

1. A study has been made of the effect of angiotensin (10(-12) g/ml.) on active and passive transport of sodium, potassium and water between rat kidney cortex slices and the incubation medium.2. Angiotensin has no effect on the passive uptake of sodium and loss of potassium by slices incubated under conditions which inhibit active transport.3. Active sodium extrusion by slices incubated under aerobic conditions is stimulated, whereas active potassium uptake is inhibited by angiotensin.4. Sodium pump activity is stimulated by angiotensin in the presence of ouabain or in the absence of potassium in the incubation medium, conditions which block the sodium for potassium exchange pump.5. There is a 2 min latent period following the application of angiotensin before a response is observed.6. These findings are discussed in relation to the mechanism of action of angiotensin on kidney sodium and fluid transport processes.