Cellular Sodium Research Articles

Long-term effects of captopril on passive sodium permeability and contractility in vascular smooth muscles of spontaneously hypertensive rats

Long-term effects of captopril on passive sodium permeability and cellular sodium concentration in the aorta of spontaneously hypertensive rats were examined in terms of contractile properties of the muscle. In cold lithium solution, cellular sodium in the aorta isolated from spontaneously hypertensive rats leaked more rapidly than did that isolated from Wistar Kyoto rats (WKY), suggesting an increased sodium permeability in the aorta of spontaneously hypertensive rats. Six weeks of treatment with captopril reduced the increased sodium permeability after hydralazine had failed. Inhibition of the sodium pump by incubating the aorta in potassium-free solution produced a slowly developing contraction which was associated with accumulation of cellular sodium. Both the magnitude of contraction and the accumulation of sodium during exposure to potassium-free solution for 1 hour were significantly less in the aorta isolated from spontaneously hypertensive rats treated with captopril compared with those from control spontaneously hypertensive rats. These data suggest that after prolonged administration, captopril alters the abnormal sodium permeability of vascular smooth muscle in spontaneously hypertensive rats and that the restoration of normal permeability reduces vascular tone.

Stimulatory (insulin-mimetic) and inhibitory (ouabain-like) action of vanadate on potassium uptake and cellular sodium and potassium in heart cells in culture

(1) The influence of vanadate (Na 3VO 4) on sodium and potassium uptake as well as on cellular ion contents of sodium and potassium has been studied in heart muscle and non-muscle cells obtained from various species. An ouabain-like inhibition of potassium uptake (up to 50%), combined with a decrease of cellular potassium (up to 20%) has been observed by vanadate (10 −4−10 −3 M) in heart non-muscle cells obtained from neonatal guinea pigs and chick embryos. In heart muscle and non-muscle cells prepared from neonatal rats, as well as in Girardi human heart cells, a vanadate-induced stimulation of potassium uptake (up to 100%), combined with a rise in cellular potassium (up to 20%) and without significant alteration of cellular sodium, has been found. A slight increase of 22Na + influx can be measured in rat heart muscle cells and in Girardi human heart cells in the presence of vanadate (10 −4−10 −3 M). (2) In beating rat heart muscle cells in culture, detrimental effects of serum deprivation—concerning beating properties, potassium uptake and cellular potassium—can at least in part be overcome by addition of vanadate. Furthermore, this compound prevents ouabain-induced signs of toxicity (contractures) in these cells. (3) The stimulatory effects of vanadate on potassium can be mimicked by insulin (1–10 mU/ml). Furthermore, vanadate produces an insulin-like stimulation of 2-deoxy- d-glucose uptake in rat heart muscle and non-muscle cells as well as in Girardi human heart cells. (4) The experimental data demonstrate an ouabain-like inhibition as well as an insulin-mimetic stimulation of potassium-uptake in various heart cells. The reason for this antagonistic mode of action may be due to the different capabilities of the heart cell types to reduce vanadium in the V-valence state to vanadium in the IV-valence state, thereby favouring either ouabain-like inhibition (vanadium V) or insulin-mimetic stimulation (vanadium IV) of potassium transport.

Minimum nutritional requirements for cellular growth and extracellular slime polysaccharide production by the human dental plaque bacterial mutant Actinomyces viscosus T14Av

The requirements were examined in chemically-defined media. Magnesium sulphate, potassium phosphate and adenine were essential for cellular growth and sodium bicarbonate and inositol further stimulated growth. The addition of sodium phosphate to this medium stimulated both cellular growth and slime production. In contrast, ammonium sulphate inhibited slime production. Biotin and thiamine stimulated cellular growth and nicotinic acid was essential for slime production. Glutamine, alanine and cystine were essential for cellular growth. A minimal medium which supported both good cellular growth and slime production for strain T14Av contained adenine, sodium bicarbonate, MgSO 4, inositol, glucose, KH 2PO 4, Na 2HPO 4, biotin, thiamine, nicotinic acid, arginine, glutamine, alanine and cystine.

Evidence for chloride dependent potassium and water transport induced by hyposmotic stress in erythrocytes of the marine teleost,Opsanus tau

Red blood cells of the marine teleost,Opsanus tau (oyster toadfish), were characterized as to their normal hemoglobin, ion and water contents. Cells were exposed to ouabain containing, hyposmotic salt solutions (osmolarity reduced to 2/3 of normal) in which the cation or anion composition was varied. It was found that the initial cell volume expansion due to water influx was independent of the anion present. However, a secondary volume reduction was dependent on the presence of chloride or bromide anions. During volume reduction, cellular potassium and chloride ion contents fell by about equal amounts. Potassium loss was commensurate to the total amount of potassium ions detected extracellularly about 1.5h after the initial osmotic shock. No major changes were seen in the cellular sodium ion contents. When chloride ions within the cells and in the suspending medium were replaced by nitrate, iodide or thiocyanate, the cells failed to return to volumes close to those of isosmotically suspended controls, and the cellular potassium content also remained constant. In hypotonic potassium chloride the cells failed to extrude potassium chloride and water, and hence retained their expanded volume. Neither potassium loss nor volume decrease occurred in cells swollen in hypotonic sodium chloride media containing furosemide or 4,4′ diisothiocyano-2,2′-stilbene-disulfonic acid (DIDS). These two compounds are known inhibitors of monovalent cation cotransport and anion self exchange, respectively, in mammalian red cells. Hence toadfish red cells respond to osmotic swelling primarily by activation of an ouabain-insensitive, chloride dependent potassium transport system which is sensitive to inhibition by furosemide and DIDS.

Effect of intracellular sodium on calcium uptake in isolated guinea-pig diaphragm and atria

(1) Effects of cellular sodium on the 45Ca uptake of isolated guinea-pig diaphragm and atria were studied. (2) Cellular sodium and calcium contents were higher in diaphragm compared to atria after incubating the tissues in normal Krebs-Henseleit solution. (3) Cellular sodium content in atria and diaphragm were reduced signficantly by incubating the tissues in high potassium Krebs-Henseleit solution ( K + = 34.7 mM ), while it was increased by incubating the tissues in the ice-cold low potassium and low calcium Krebs-Henseleit solution ( K + = 0.65 mM , Ca 2+ = 0.2 mM ). Cellular potassium content was changed inversely to the sodium content. (4) In atria, cellular content of calcium was not altered significantly by the above conditions. But in diaphragm, the cellular content of calcium was decreased slightly but significantly after incubation in the ice-cold low potassium and low calcium Krebs-Henseleit solution. (5) At normal cellular sodium levels, the 45Ca uptake of both tissues was similar. (6) The reduction of the cellular sodium content caused a significant decrease in the 45Ca uptake into both tissues. (7) When the cellular sodium content was increased in atrial preparations, a marked increase in the 45Ca uptake was observed. On the other hand, in diaphragm preparations, only a slight increase was observed, even when cellular sodium content was much higher than the normal level. (8) These results indicate that even when the intracellular sodium is increased by some physiological of pharmacological events, calcium influx through Na +/Ca 2+ exchange mechanism is very slight and slow in diaphragm.

Inhibition by somatostatin of bovine growth hormone secretion following sodium channel activation.

1. Growth hormone secretion, exchangeable cellular sodium and calcium concentrations measured by 22Na and 45Ca incorporation, and efflux of 45Ca were studied in dispersed bovine anterior pituitary cells. 2. Addition of veratridine (100 microM), an activator of sodium channels, increased exchangeable sodium and calcium concentrations in the cells, the efflux of 45Ca from prelabelled cells, and caused a biphasic stimulation of the rate of growth hormone secretion. Secretion of growth hormone was not stimulated when the extracellular calcium was decreased below 0.1 mM. 3. The increases in growth hormone secretion, exchangeable calcium concentration and 45Ca efflux from prelabelled cells caused by veratridine were abolished by addition of the calcium antagonist verapamil (20 microM). Verapamil also reduced the rise in exchangeable sodium caused by veratridine and increased the resting exchangeable sodium concentrations. 4. The peptide somatostatin (1 micrograms/ml) prevented veratridine-stimulated growth hormone secretion but did not inhibit the increases in exchangeable sodium and calcium caused by veratridine. The peptide itself elicited a transient increase in 45Ca efflux and subsequently partially inhibited veratridine-stimulated 45Ca efflux. 5. The data suggest that anterior pituitary cells possess voltage-sensitive sodium channels. Activation of these channels by veratridine may lead to depolarization and increased entry of calcium via potential-dependent calcium channels, which contributes to a rise in cytoplasmic calcium concentration and the subsequent stimulation of growth hormone secretion. We conclude that the calcium antagonist verapamil may also interact with sodium channels, and that the peptide somatostatin may act on growth-hormone-secreting cells either to prevent the rise in cytoplasmic calcium by hyperpolarizing the cells or to decrease the affinity of a population of calcium binding sites in the cells.

Leucocyte Electrolytes and Sodium Efflux Rate Constants in the Hypertension of Pre-Eclampsia

1. Leucocyte electrolytes were measured in pre-eclampsia and comparison was made with leucocytes from normal primigravidae and from the original pre-eclamptic subjects 6 months after delivery when blood pressure had returned to normal. 2. In pre-eclamptic subjects, leucocyte sodium was elevated and potassium depressed, and the rate constant for sodium efflux was depressed. 3. These changes returned to normal after delivery. 4. An increase in cellular sodium as a result of altered sodium pump activity may be the cause of hypertension in pre-eclampsia.

Erythrocyte 22Na efflux and urinary sodium excretion in essential hypertension.

1. The rate constant for total 22Na efflux from erythrocytes was examined in patients with mild to moderate hypertension and in normotensive controls. No difference in 22Na efflux rate constant was found when the cells from both groups were incubated in artificial medium. When the cells from both groups were incubated in their own plasma, the rate constant for Na efflux was significantly elevated for hypertensive patients compared with controls (0.40 +/- 0.02, 0.36 +/- 0.01 respectively; P < 0.05). 2. In hypertensive patients sodium efflux rate constant varied inversely with 24 h urinary sodium excretion when erythrocytes were incubated in artificial medium (r = -0.34, P < 0.05) or in plasma (r = -0.42, P < 0.05). No association between sodium efflux rate constant and urinary sodium excretion occurred in normotensive subjects. 3. These findings provide further evidence that sodium is an important aetiological factor in hypertension. In 'salt-sensitive' individuals dietary sodium may interact with the regulation of cellular sodium transport via both humoral and cellular mechanisms to elevate blood pressure.

Effect of prolactin on human red cell sodium transport.

Incubation of red cells with higher concentrations of prolactin in vitro enhanced the cellular sodium level and produced a significant reduction in erythrocyte membrane adenosine triphosphatase activity. This effect was dose and time-dependent. It is the result of an inhibition of the active sodium pump similar to that produced by ouabain, suggesting altered red cell function and electrolyte balance in hyperprolactinemic states.

Pathogenesis of the uremic syndrome.

Uremia is the last of four progressive stages of renal disease. Symptoms are referable to major organ systems and appear to be intensified by high intake of crude dietary protein. In many respects uremia resembles systemic poisoning from a toxic substance, and many chemicals are now suspected, but not proved, to be causative agents. The hypometabolism and low body temperature commonly seen in advanced uremia could result from alterations in cellular sodium transport. These changes can be reversed by hemodialysis or renal transplantation.

Modulation of ouabain binding and potassium pump fluxes by cellular sodium and potassium in human and sheep erythrocytes.

1. Erythrocytes were treated with nystatin to alter internal Na (Nai) and K (Ki) composition. Although the rates of K pumping and [3H]ouabain binding were altered dramatically, the relationship between glycoside binding and K pump inhibition was unaffected. 2. Human cells with high Nai and low Ki exhibited an increased rate of ouabain binding as compared to high Ki, low Nai cells; this paralleled the stimulated K pump activity of high Nai cells. 3. At constant Ki, increasing internal Na stimulated K pump and ouabain binding rates concomitantly. 4. At low Nai, increasing Ki inhibited both K pumping and ouabain binding. However, at high Nai, increasing Ki from 4 to 44 mM stimulated the rate of glycoside binding, parallel to its effect of increasing the rate of active K influx. 5. Anti-L, an isoantibody to low K (LK) sheep red cells, increased the rate of ouabain binding via its stimulation of K pump turnover. Since the latter effect is the result of affinity changes at the internal cation activation site(s) of the pump (Lauf, Rasmusen, Hoffman, Dunham, Cook, Parmelee & Tosteson, 1970), the antibody's effect on ouabain binding reflected the positive correlation between the rates of K pump turnover and glycoside binding. 6. These data provide the first evidence in intact cells for the occurrence of a Nai-induced conformational change in the Na/K pump during its normal operational cycle.

Epithelial cell electrolytes in relation to transepithelial sodium transport across toad urinary bladder.

Aspects of the relationships between cellular composition and transepithelial sodium transport across toad urinary bladder are reviewed. Changes in cellular sodium produced by amiloride, vasopressin, aldosterone, hypoxia, ouabain, and sodium-free media are consistent with a cellular sodium transport pool. Metabolic studies suggest that this pool gains its sodium from the mucosal medium and that there is little recycling of sodium between cell and serosal medium. One-third of the cellular potassium equilibrates readily with serosal potassium. The rate of exchange of potassium is much less than the rate of sodium transport supporting the contention that sodium transport in this tissue is electrogenic. Studies with 36Cl suggest that chloride does not cross the apical cellular membranes, but exchanges with serosal chloride. Possible relationships between transepithelial sodium transport and cellular volume regulation are discussed.

Relationship between cellular electrolytes and the contraction force of isolated guinea-pig atria with special regard to the extracellular space volume

A micromethod is described which allows the quantitative evaluation of the extracellular space volume of isolated guinea-pig atria (> 15 mg tissue wet weight) by means of an enzymatic estimation of inulin. In addition, the acidic tissue extracts are analysed for the potassium, sodium, magnesium, calcium and 45calcium content. Taking into account the individual extracellular space volumes, it is possible to calculate the cellular electrolyte content and relative specific 45calcium activity of each atrium. Our experiments reveal under steady state conditions a significant correlation between the force of contraction and the cellular electrolyte content. Atria with a higher contraction force were found to contain a significantly elevated cellular potassium content and a lower content of cellular sodium and calcium than atria with a smaller contraction force. The decrease of cellular calcium content is exclusively caused by the lowering of the fraction of unexchanged tissue calcium. The significance of the results is discussed with respect to the events leading to contraction and relaxation of the heart muscle.

The sodium transport pool.

The sodium transport pool in epithelial cells represents sodium involved in active transport across the epithelium. There has been much controversy about the size of such a pool and even about its existence. Techniques for estimating the size of this pool are described. By analysis of toad bladder epithelial cells scraped from hemibladders mounted in chambers under a variety of conditions it has proved possible to detect and to quantify a sodium transport pool. Only about 20 percent of non-inulin space sodium measured flame photometrically is contained in this pool. This represents the total sodium entering cells from the mucosal medium, is in good agreement with the cellular sodium measured by the electron microprobe, and averages some 10-16 mmol/kg tissue H2O. Measurements of the pool in other tissues are considered.

Kinetics of Na+ transport in Necturus proximal tubule.

The dependence of proximal tubular sodium and fluid readsorption on the Na(+) concentration of the luminal and peritubular fluid was studied in the perfused necturus kidney. Fluid droplets, separated by oil from the tubular contents and identical in composition to the vascular perfusate, were introduced into proximal tubules, reaspirated, and analyzed for Na(+) and [(14)C]mannitol. In addition, fluid transport was measured in short-circuited fluid samples by observing the rate of change in length of the split droplets in the tubular lumen. Both reabsorptive fluid and calculated Na fluxes were simple, storable functions of the perfusate Na(+) concentration (K(m) = 35-39 mM/liter, V(max) = 1.37 control value). Intracellular Na(+), determined by tissue analysis, and open-circuit transepithelial electrical potential differences were also saturable functions of extracellular Na(+). In contrast, net reabsorptive fluid and Na(+) fluxes were linearly dependent on intracellular Na(+) and showed no saturation, even at sharply elevated cellular sodium concentrations. These concentrations were achieved by addition of amphotericin B to the luminal perfusate, a maneuver which increased the rate of Na(+) entry into the tubule cells and caused a proportionate rise in net Na(+) flux. It is concluded that active peritubular sodium transport in proximal tubule cells of necturus is normally unsaturated and remains so even after amphotericin-induced enhancement of luminal Na(+) entry. Transepithelial movement of NaCl may be described by a model with a saturable luminal entry step of Na(+) or NaCl into the cell and a second, unsaturated active transport step of Na(+) across the peritubular cell boundary.

The dependence on contraction frequency of the positive inotropic effect of dihydro-ouabain.

1. The positive inotropic effect of dihydroouabain in the isolated guinea-pig papillary muscle was studied in dependence on frequency of contraction and on extracellular calcium concentration. 2. Reduction of contraction frequency from 1 Hz to 1/300 Hz at a calcium concentration of 3.2 mM led to a decrease in inotropic efficiency of the glycoside as evidenced by a marked shift of its concentration-effect curve. A concentration of 5×10−5 M dihydroouabain which was, on the average, maximally effective at 1 Hz contraction frequency was practically ineffective when the muscles contracted only once every 5 min. 3. Reduction of [Ca2+]0 from 3.2 mM to 0.6 mM at a contraction frequency of 1 Hz led only to a shift of the glycoside concentration-effect curve on the vertical axis according to the decrease in control force of contraction. 4. The different parameters of the isometric contraction curve (steepness of the ascending and descending limb, S1 and S2; time to peak force, t1, and relaxation time, t2) were equally affected in relation to peak force of contraction (Fc) by changes in contraction frequency in absence and in presence of different concentrations of dihydro-ouabain. In contrast, the time parameters t1 and t2 were differently influenced by a change in [Ca2+]0. 5. The results are consistent with the hypothesis of the inhibition of the cellular sodium pump by cardioactive steroids as the cause of their positive inotropic effect on the heart.

Relationships between serosal medium potassium concentration and sodium transport in toad urinary bladder. II. Effects of different medium potassium concentrations on epithelial cell composition.

Epithelial cells from hemibladders incubated in potassium-free sodium Ringer's serosal medium lost potassium, both in exchange for serosal sodium and with chloride and water. Cellular sodium of mucosal origin did not change. The loss of cellular potassium, chloride and water closely followed the fall in short-circuit current (SCC). One third as much potassium, chloride and water were lost in 1 mM potassium serosal medium; SCC fell 1/3 as much. Potassium-free choline Ringer's serosal medium abolished the initial increase in SCC and reduced the fall in cellular potassiu, chloride and water and in SCC. Ouabain (10(-2)M) in potassium-free medium prevented the initial increase in SCC and the loss of cellular chloride and water. Ouabain (5 X 10(-4)M) caused loss of cellular potassium in exchange for mucosal and serosal sodium, effects different from those of absence of serosal potassium although SCC was similarly inhibited. Sodium-free mucosal medium abolished SCC and prevented the initial transient of SCC and diminished loss of cellular potassium, chloride and water on removing serosal potassium. When serosal potassium concentration was increased considerably, cells gained potassium, chloride and water, and in 116 mM potassium media, lost sodium of serosal origin. A hypothesis is advanced to explain the transients in SCC on changing serosal potassium concentration. The fall in cellular potassium, not water, probably inhibits sodium transport in media of less than 2 mM potassium.

Effects of cholera toxin on cellular and paracellular sodium fluxes in rabbit ileum

The diarrhea observed in patients which cholera is known to be related to secretion of water and electrolytes into the intestinal lumen. However, the exact mechanisms involved in these secretory processes have remained unclear. Although it is clear that purified toxin acts on epithelial cell metabolism, its activity on Na + transport across intestinal mucosa is equivocal: reported either to prevent net Na + absorption or to cause net secretion of Na + from serosa to mucosa. Since total transmural Na + fluxes across “leaky” epithelia involve very significant movement via a paracellular shunt pathway, we studied the effects of cholera toxin on the cellular and paracellular pathways of Na + movement. Unidirectional Na + fluxes were examined as functions of applied potential in control tissues and in tissues from the same animal treated with purified cholera toxin. Treatment of rabbit ileum in vitro with toxin stimulated the cellular component of serosa-to-mucosa Na + flux (from 2.41 ± 0.49 μ equiv./h per cm 2 under control conditions to 4.71 ± 0.43 μ equiv./h per cm 2 after treatment with toxin, P < 0.01). The effect of cholera toxin on Na + movement through the cells from mucosa to serosa appeared to be insignificant. Finally, a marked decrease in the Na + permeability ( P < 0.01) and no detectable significant changes in transference number for Na + of the paracellular shunt pathway were observed following treatment with cholera toxin. These results provide direct evidence for the hypothesis that purified cholera toxin stimulates active sodium secretion but has minimal effect on sodium absorption.

The sodium transport pool in toad urinary bladder epithelial cells.

The sodium which equilibrates with 24-Na in epithelial cells of toad urinary bladders has been determined. With sodium Ringer's bathing both mucosal and serosal surfaces, 24-Na in the mucosal medium equilibrated with about 35 mmoles cellular sodium/kg cellular dry weight, representing about 20% of the total cellular sodium determined flame photometrically; 24-Na in the serosal medium equilibrated with 120 mmoles cellular sodium/kg cellular dry weight, about 80% of the total cellular sodium. With 24-Na in both media all cellular sodium was labeled within 30 min. In the absence of serosal sodium, total cellular sodium and that sodium which equilibrated with mucosal 24-Na in sodium Ringer's were both similar to the cellular sodium of mucosal origin which had been determined in epithelial cells exposed on both surfaces to sodium Ringer's. Sodium-free mucosal medium, and sodium Ringer's containing amiloride 10-4 or 10-3 M in the mucosal medium, both virtually completely inhibited transepithelial sodium transport. But, whereas the cellular sodium of mucosal origin fell to only 2 mmoles/kg cellular dry weight with sodium-free mucosal medium, an appreciable labeling of cellular sodium was found whether amiloride was present before, or only after, exposure of tissue to mucosal 24-Na. Rapid washing of the mucosal surface of hemibladders just before removal of epithelial cells for analysis removed most of this sodium labeled in the presence of amiloride, suggesting that the cellular sodium of mucosal origin consists of at least two fractions with only about two-thirds truly intracellular. The sodium transport pool measured directly in these experiments is appreciably smaller than any previous estimates of pool size all of which have been obtained by indirect techniques involving use of whole hemibladders rather than epithelial cells alone.

Role of calcium in volume regulation by dog red blood cells.

Dog red blood cells (RBC) are shown to regulate their volume in anisosmotic media. Extrusion of water from osmotically swollen cells requires external calcium and is associated with net outward sodium movement. Accumulation of water by osmotically shrunken cells is not calcium dependent and is associated with net sodium uptake. Net movements of calcium are influenced by several variables including cell volume, pH, medium sodium concentration, and cellular sodium concentration. Osmotic swelling of cells increases calcium permeability, and this effect is diminished at acid pH. Net calcium flux in either direction between cells and medium is facilitated when the sodium concentrations is low in the compartment from which calcium moves and/or high in the compartment to which calcium moves. The hypothesis is advanced that energy for active sodium extrusion in dog RBC comes from passive, inward flow of calcium through a countertransport mechanism.