Lesbians and cancer support: clinical issues for cancer patients

Unidirectional, ouabain-insensitive K+ influx rose steeply with warming at temperatures above 37 degreesC in guinea pig erythrocytes incubated in isotonic medium. The only component of ouabain-insensitive K+ influx to show the same steep rise was K-Cl cotransport (Q10 of 10 between 37 and 41 degrees C); Na-K-Cl cotransport remained constant or declined and residual K+ influx in hypertonic medium with ouabain and bumetanide rose only gradually. Similar results were obtained for unidirectional K+ efflux. Thermal activation of K-Cl cotransport-mediated K+ influx was fully dependent on the presence of chloride in the medium; none occurred with nitrate replacing chloride. The increase of K+ influx through K-Cl cotransport from 37 to 41 degrees C was blocked by calyculin A, a phosphatase inhibitor. The Q10 of K-Cl cotransport fully activated by hydroxylamine and hypotonicity was about 2. The time course of K+ entry showed an immediate transition to a higher rate when cells were instantly warmed from 37 to 41 degrees C, but there was a 7-min time lag in returning to a lower rate when cells were cooled from 41 to 37 degrees C. These results indicate that the steepness of the response of K-Cl cotransport to mild warming is due to altered regulation of the transporter. Total unidirectional K+ influx was equal to total unidirectional K+ efflux at 37-45 degrees C, but K+ influx exceeded K+ efflux at 41 degrees C when K-Cl cotransport was inhibited by calyculin or prevented by hypertonic incubation. The net loss of K+ that results from the thermal activation of isosomotic K-Cl cotransport reported here would offset a tendency for cell swelling that could arise with warming through an imbalance of pump and leak for Na+ or for K+.     

Erythrocyte dehydration in pathophysiology and treatment of sickle cell disease

A prominent feature of sickle cell disease is the presence of cells with markedly increased sickle cell hemoglobin concentration, as a consequence of the loss of potassium, chloride, and water from the erythrocyte. Because of the extreme dependency of the kinetic of polymerization on sickle cell hemoglobin concentration, these dehydrated erythrocytes have an increased tendency to polymerize and sickle. Thus blockade of the loss of potassium from the erythrocyte should prevent the increase in sickle cell hemoglobin concentration and reduce sickling. The availability of this potential therapeutic option is based on a detailed knowledge of the mechanisms leading to cell dehydration. Two ion transport pathways, the K-Cl cotransport and the Ca(2+)-activated K+ channel, play a prominent role in the dehydration of sickle erythrocytes. Possible therapeutic strategies include inhibition of K-Cl cotransport by increasing erythrocyte Mg2+ content and inhibition of the Ca(2+)-activated K channel by oral administration of clotrimazole.     

Membrane function and vascular reactivity

The resting potential and monovalent ions in the marginal cells and scala media were measured before and 20 min after the onset of anoxia using ion-sensitive microelectrodes. The resting potential of the marginal cells decreased from 62.7 to -2.4 mV. The K+ activity decreased from 77.7 to 53.2 mEq/l, while the Na+ activity increased from 2.6 to 24.7 mEq/l. The Cl- activity did not change significantly. In the scala media, the endocochlear potential decreased rapidly from 80.9 to -28.0 mV after the onset of anoxia. The K+ activity decreased from 119.0 to 96.5 mEq/l, the Na+ activity increased from 1.3 to 9.5 mEq/l and that of Cl- decreased from 127.0 to 115.1 mEq/l. The electrochemical gradients determined for each ion based on the ionic changes in the scala media and marginal cells, suggested the existence of an Na/K pump and Na-K-2Cl cotransport at the basolateral membrane of the marginal cells, and a rheogenic K pump and Na-K-2Cl transport at the luminal membrane of the marginal cells. The Na+ and K+ must be recycled at the basolateral membrane and luminal membrane of marginal cells, respectively.     

Carbon dioxide elimination measures resolution of experimental pulmonary embolus in dogs

The interaction of the red cell membrane with merocyanine 540 or protoporphyrin led to four phenomena, most probably interrelated. (i) The morphology changed from the normal discoid to an echinocytic form. This morphological change persisted when followed over a period of 24 h. (ii) Simultaneously, cell deformability was decreased, as revealed by viscosity measurements and a cell-filtration technique. (iii) Both drugs caused swelling of the erythrocytes in isotonic medium, due to a very-short-term increased permeability of the membrane, also for larger molecules such as lactose. The pathway of this temporary leak seems to be unrelated to the Na+/K+ -ATPase, the K+/Cl- and the Na+/K+/Cl- cotransport systems, the Ca2+-activated Gardos pathway, the oxidation/deformation-activated leak pathway and the so-called residual transport route. Despite the morphological changes, K+-leakage induced by mechanical stress was not increased. (iv) During osmotic swelling, the critical hemolytic volume was found to be increased in the presence of either merocyanine 540 or protoporphyrin. The increase critical volume protected erythrocytes against osmotic hemolysis.     

Discontinuities in the temperature function of transmembrane water transport in Chara: relation to ion transport

The NMR (nuclear magnetic resonance) method of Conlon and Outhred (1972) was used to measure diffusional water permeability of the nodal cells of the green alga Chara gymnophylla. Two local minima at 15 and 30 degreesC of diffusional water permeability (Pd) were observed delimiting a region of low activation energy (Ea around 20 kJ/mol) indicative of an optimal temperature region for membrane transport processes. Above and below this region water transport was of a different type with high Ea (about 70 kJ/mol). The triphasic temperature dependence of the water transport suggested a channel-mediated transport at 15-30 degreesC and lipid matrix-mediated transport beyond this region. The K+ channel inhibitor, tetraethylammonium as well as the Cl- channel inhibitor, ethacrynic acid, diminished Pd in the intermediate temperature region by 54 and 40%, respectively. The sulfhydryl agent p-(chloromercuri-benzensulfonate) the water transport inhibitor in erythrocytes also known to affect K+ transport in Chara, only increased Pd below 15 degreesC. In high external potassium ('K-state') water transport minima were pronounced. The role of K+ channels as sensors of the optimal temperature limits was further emphasized by showing a similar triphasic temperature dependence of the conductance of a single K+ channel also known to cotransport water, which originated from cytoplasmic droplets (putatively tonoplast) of C. gymnophylla. The minimum of K+ single channel conductance at around 15 degreesC, unlike the one at 30 degreesC, was sensitive to changes of growth temperature underlining membrane lipid involvement. The additional role of intracellular (membrane?) water in the generation of discontinuities in the above thermal functions was suggested by an Arrhenius plot of the cellular water relaxation rate which showed breaks at 13 and 29 degreesC.     

Dissociation of changes in metabolic rate and blood pressure with erythrocyte Na-K pump activity in older men after endurance training

We examined whether changes in resting metabolic rate (RMR) and blood pressure in older normotensive men in response to endurance training were associated with alterations in the Na-K pump activity of plasma-bathed erythrocytes. Eleven men performed cycling exercise three times a week for 8 weeks, and six other men served as controls. Measurements included: RMR by indirect calorimetry, supine blood pressure, body composition by underwater weighing, plasma and erythrocyte Na and K parameters using flame photometry and ouabain. Peak VO2 increased 12% (p < .001), RMR increased 10% (p < .01), mean blood pressure decreased 5% (p < .05), erythrocyte K increased 5% (p < .01), plasma K decreased 7% (p < .001), and plasma Na decreased by 4% (p < .001) in response to training. Erythrocyte Na and Na-K pump rate did not change, nor did the individual changes correlate with changes in RMR or mean blood pressure. Exercise training increases RMR and reduces blood pressure in older men, but these changes are dissociated with erythrocyte Na-K pump activity.     

Relationship of red blood cell ion transport alterations and serum lipid abnormalities in Lyon genetically hypertensive rats

Alterations of Na+ and K+ transport in erythrocytes of hypertensive humans or animals are often associated with abnormal lipid metabolism. The aim of the present study was to investigate red blood cell ion transport in Lyon inbred strains selected from Sprague-Dawley rats for different blood pressure levels. Lyon strains are characterized by important metabolic changes, including plasma lipid abnormalities. Serum triglycerides, cholesterol, and uric acid as well as red blood cell Na+ and K+ (Rb+) transport mediated by Na(+)-K+ pump or Na(+)-K+ cotransport and cation leaks were studied in hypertensive (LH), normotensive (LN), and low blood pressure (LL) Lyon rats aged 12 weeks. Increased erythrocyte Na+ content (Nai+) and higher levels of serum triglycerides, cholesterol, and uric acid were demonstrated in LH rats compared with LN animals. Nevertheless, at this age serum triglycerides and erythrocyte Nai+ of LL rats were even higher than those of LH animals. There were no significant differences between Lyon strains in either Na(+)-K+ pump activity or bumetanide-resistant (BR) cation leaks. The activity of bumetanide-sensitive (BS) Na(+)-K+ cotransport mediating inward Na+ movement was highest in LL rats and lowest in LH animals. In Lyon rats, Nai+ was positively related to serum triglycerides, whereas blood pressure correlated positively with BR Na+ leak and negatively with BS net Na+ uptake. A similar association of erythrocyte Nai+ with serum triglycerides was also observed in Prague hereditary hypertriglyceridemic rats (HTG) that were selected from Wistar rats for high plasma triglycerides. The major difference of the two forms of genetic hypertension associated with abnormal lipid metabolism was in BS net Na+ uptake, which was enhanced in HTG but reduced in LH rats. This was probably due to differences in plasma cholesterol, which was elevated in LH but not in HTG animals. Our study in Lyon rats confirmed the positive association of blood pressure with Na+ leak as a characteristic feature of genetic hypertension.     

Out-of-hospital cardiac arrests in Amsterdam and its surrounding areas: results from the Amsterdam resuscitation study (ARREST) in ''Utstein'' style

K-Cl cotransport (COT) is the coupled movement of K and Cl, present in most cells, associated with regulatory volume decrease, susceptible to oxidation and functionally overexpressed in sickle cell anemia. The aim of this study was to characterize the effect of the oxidant nitrite (NO2-) on K-Cl COT. NO2- is a stable metabolic end product of the short-lived highly reactive free radical nitric oxide (NO), an oxidant and modulator of ion channels, and a vasodilator. In some systems, the response to NO2- is identical to that of NO. We hypothesized that NO2- activates K-Cl COT. Low potassium (LK) sheep red blood cells (SRBCs) were used as a model. The effect of various concentrations (10(-6) to 10(-1) m) of NaNO2 was studied on K efflux in hypotonic Cl and NO3 media, Cl-dependent K efflux (K-Cl COT), glutathione (GSH), and methemoglobin (MetHb) formation. In support of our hypothesis, K efflux and K-Cl COT were stimulated by increasing concentrations of NaNO2. Stimulation of K efflux was dependent upon external Cl and exhibited a lag phase, consistent with activation of K-Cl COT through a regulatory mechanism. Exposure of LK SRBCs to NaNO2 decreased GSH, an effect characteristic of a thiol-oxidizing agent, and induced MetHb formation. K-Cl COT activity was positively correlated with Methb formation. N-ethyl-maleimide (NEM), a potent activator of K-Cl COT, was used to assess the mechanism of NO2- action. The results suggest that NEM and NO2- utilize at least one common pathway for K-Cl COT activation. Since NaNO2 is also a well known vasodilator, the present findings suggest a role of K-Cl COT in vasodilation.     

Relations among transepithelial sodium transport, potassium exchange, and cell volume in rabbit ileum

The relation between active transepithelial Na transport across rabbit ileum and 42K exchange from the serosal solution across the basolateral membranes has been explored. Although 42K influx across the basolateral membranes is inhibited by ouabain and by complete depletion of cell Na, it is not affected when transepithelial Na transport is abolished (i.e. in the presence of an Na-free mucosal solution) or stimulated (i.e. when glucose or alanine is added to the mucosal solution). We are unable to detect any relation between the ouabain-sensitive Na-K exchange mechanism responsible for the maintenance of intracellular Na and K concentrations and active transcellular Na transport. In addition, the maintenance of cell volume (water content) does not appear to be dependent upon transepithelial Na transport or the ouabain-sensitive Na-K exchange pump. Although the results of these studies cannot be considered conclusive, they raise serious questions regarding the role of the Na-K exchange pump, located at the basolateral membranes, in active transepithelial Na transport and the maintenance of cell volume.     

Stimulation of HIT-T15 insulinoma cells by glyceraldehyde does not require its metabolism

The addition of the triose D-glyceraldehyde (5-20 mM) to HIT-T15 hamster insulinoma cells caused a rapid, marked depolarisation of the plasma membrane accompanied by a pronounced intracellular acidification, an increase in the cytosolic free calcium concentration [Ca2+]i and enhanced secretion of insulin. D-glyceraldehyde did not reduce the rate of efflux of 86Rb+ from loaded perifused cells. All of the above effects of D-glyceraldehyde were also observed in response to L-glyceraldehyde. The changes in membrane potential and intracellular pH (pHi) caused by D-glyceraldehyde were unaffected by the glycolytic inhibitor iodoacetate, by K(+)-channel blockers (tolbutamide and tetraethylammonium), or by inhibitors of the transport of lactate (alpha-fluorocinnamate), alanine (methylaminoisobutyrate) or glucose (phloretin, phlorrizin). The glyceraldehyde-induced depolarisation and acidification were also observed in the absence of extracellular Ca2+ or Na+. The increase in [Ca2+]i evoked by D-glyceraldehyde was reversed by removal of Ca2+ from the medium. The formation of lactate by HIT-T15 cells was not significantly increased by addition of 10 mM D-glyceraldehyde or L-glyceraldehyde. In contrast, 10 mM glucose caused an approximately fourfold rise in lactate production. The oxidation of D-glyceraldehyde by HIT-T15 cells was also extremely modest compared to glucose oxidation by these cells. These results suggest that the stimulation of HIT-T15 cells by either D-glyceraldehyde of L-glyceraldehyde does not require metabolism of the triose within the cell and may not involve closure of nucleotide-sensitive K+ channels. We propose that the electrogenic transport of glyceraldehyde across the plasma membrane, possibly via H+ cotransport, might lead to depolarisation and hence to Ca2+ entry into the cell.     

Bile acid uptake via the human apical sodium-bile acid cotransporter is electrogenic

Intestinal absorption of bile acids depends on a sodium-bile acid cotransport protein in the apical membrane of the ileal epithelial cell. Transport is Na+-dependent, but the Na+-bile acid stoichiometry and electrogenicity of transport are not known. Studies in whole intestine, isolated cells, and ileal membrane vesicles have been unable to resolve this issue because transport currents are small and can be obscured by other ionic conductances and transport proteins present in these membranes. In this study, the human apical sodium-bile acid transporter was expressed in stably transfected Chinese hamster ovary cells that lack other bile acid transporters. The Na+-dependent transport of a fluorescent bile acid analog, chenodeoxycholyl-Nepsilon-nitrobenzoxadiazol-lysine, was monitored by fluorescence microscopy in single, voltage-clamped cells. Bile acid movement was bidirectional and voltage-dependent with negative intracellular voltage-stimulating influx. A 3-fold reduction in extracellular Na+ produced a negative 52 mV shift of the flux-voltage relationship, consistent with a 2:1 Na+:bile acid coupling stoichiometry. No Na+- or voltage-dependent uptake was observed in nontransfected Chinese hamster ovary cells. These results indicate that the cotransport of bile acids and Na+ by human apical sodium-bile acid transporter is electrogenic and bidirectional and is best explained by a 2:1 Na+:bile acid coupling stoichiometry. These results suggest that membrane potential may regulate bile acid transport rates under physiological and pathophysiological conditions.     

Mg-dependent ecto-ATPase activity in Leishmania tropica

Variation in the level of fetal hemoglobin (HbF) accounts for much of the clinical heterogeneity observed in patients with sickle cell disease (SCD). The HbF level has emerged as an important prognostic factor in both sickle cell pain and mortality, and a % HbF of 10-20% has been suggested as a threshold level for diminished clinical severity. The number of erythrocytes that contain HbF (termed F cells) may also be critically important, as F cells resist intravascular sickling and have preferential in vivo survival. Since F cells can be enumerated with high accuracy using flow cytometry methods, we prospectively studied a cohort of 242 children with SCD. Children with HbS and hereditary persistence of fetal hemoglobin (S/HPFH) had essentially 100% F cells. In contrast, children with homozygous sickle cell anemia (HbSS), HbS/beta0 thalassemia, or HbS/beta+ thalassemia had significantly lower mean % F cell values (55.9, 61.6, and 51.3%, respectively; P < 0.001), and children with HbSC had even fewer F cells (27.0%; P < 0.001). There was a highly significant correlation between the % F cells and the log (% HbF), which was observed for the total population of children (r = 0.95, P < 0.001), as well as for each of the individual subgroups of children with HbSS (r = 0.94, P < 0.001), HbSC (r = 0.89, P < 0.001), or HbS/beta0 thalassemia and HbS/beta+ thalassemia (r = 0.95, P <0.001). This logarithmic correlation between % F cells and % HbF has not been previously described and has important implications for the pharmacologic manipulation of HbF in patients with SCD.     

Analysis of leak current properties in the lobster stretch receptor neurone

Experiments were performed to characterize the so-called leak current of the slowly adapting stretch receptor neurone of the European lobster with respect to its ionic basis, its kinetics and its pharmacology. Estimates of the leak current were obtained by subtraction of a Na-K pump current and of an unspecific impalement current from a non-dynamic ('instantaneous') current, recorded in a voltage range from approximately -120 to approximately -30 mV, after blockage of spike-generating currents and a hyperpolarization-activated inwardly rectifying current (Q-current). The leak current, estimated in this way, was seen to reverse direction at the cell's K+ equilibrium voltage, thus indicating that it is carried by K+ passing through channels which, also, proved to be permeable to Rb+ and NH4+, but not permeable to Na+ or Cl- to any significant extent. Kinetically, the leak current was found to be characterized by being enhanced by increases in extracellular K+ and by being subject to outward rectification, most distinctly at elevated extracellular [K+]. In quantitative terms, these kinetic properties could be accounted for by a mathematical model comprising (1) a one-site two-barrier Eyring formulation describing ion permeation through membrane channels and (2) an ordinary dose-response relationship describing the channel-opening effect of K+ at an extracellular regulatory site. Pharmacologically, the leak current proved to be distinguished by being reversibly blockable, in a non-voltage dependent manner, by CO2+ (Kd = 0.9 mM, Hill coefficient 1.1) and procaine, but not by Ba2+, Gd3+, bupivacaine (a local anesthetic), or other K+ channel blockers such as TEA, 4-AP and Cs+. It is concluded that, in native unimpaled cells, the K+ carried leak current (1) is setting the resting voltage together with the (mainly) Na(+)-carried Q-current and the Na-K pump current, (2) is determining the cell's firing threshold, together with the spike generating currents, and (3) is also stabilizing the cell's membrane excitability in conditions of varying extracellular [K+], by virtue of its K+ sensitivity.     

Axonal contact regulates expression of alpha2 and beta2 isoforms of Na+, K+-ATPase in Schwann cells: adhesion molecules and nerve regeneration

Three isoforms of catalytic alpha subunits and two isoforms of beta subunits of Na+,K+-ATPase were detected in rat sciatic nerves by western blotting. Unlike the enzyme in brain, sciatic nerve Na+,K+-ATPase was highly resistant to ouabain. The ouabain-resistant alpha1 isoform was demonstrated to be the predominant form in rat intact sciatic nerve by quantitative densitometric analysis and is mainly responsible for sciatic nerve Na+,K+-ATPase activity. After sciatic nerve injury, the alpha3 and beta1 isoforms completely disappeared from the distal segment owing to Wallerian degeneration. In contrast, alpha2 and beta2 isoform expression and Na+,K+-ATPase activity sensitive to pyrithiamine (a specific inhibitor of the alpha2 isoform) were markedly increased in Schwann cells in the distal segment of the injured sciatic nerve. These latter levels returned to baseline with nerve regeneration. Our results suggest that alpha3 and beta1 isoforms are exclusive for the axon and alpha2 and beta2 isoforms are exclusive for the Schwann cell, although axonal contact regulates alpha2 and beta2 isoform expressions. Because the beta2 isoform of Na+,K+-ATPase is known as an adhesion molecule on glia (AMOG), increased expression of AMOG/beta2 on Schwann cells in the segment distal to sciatic nerve injury suggests that AMOG/beta2 may act as an adhesion molecule in peripheral nerve regeneration.     

Biological evaluation of two anomeric glucose analogues iodinated in position 6

Two anomeric analogues of glucose labelled with 123 iodine in position 6, proposed as tracers of glucose transport in vivo, have been synthesized: alpha- and beta-methyl-6-deoxy-6-iodo-D-glucopyranoside (alpha MDIG and beta MDIG). The aim of this study was to determine whether these molecules interact with the glucose transporter and whether they could be used as tracers of glucose transport in vivo. The biodistribution of alpha MDIG and beta MDIG was studied in the mouse in vivo. To determine if these two anomers enter the cell via the glucose transporter, their uptake was measured in isolated perfused rat hearts, in human erythrocytes in suspension, and in cardiomyocytes of neonatal rat in culture. Both alpha MDIG and beta MDIG had similar repartitions in the mouse: myocardial uptake averaged 7% of the injected dose/g of organ at 2 min postinjection and alpha MDIG competed with D-glucose to enter the cells. Insulin produced a 123% increase of its uptake in isolated perfused rat hearts and a 100% increase in cardiomyocytes of neonatal rat in culture. alpha MDIG uptake was lowered in the presence of glucose transport inhibitors in each experimental model. An interaction between beta MDIG and glucose transporters was observed only in human erythrocytes in suspension. Only alpha MDIG interacts with the glucose transporter, and thus could be used to estimate glucose transport in vivo.     

Hormonal and osmotic regulation of NaCl transport in renal distal nephron epithelium

One of the most important factors controlling blood pressure is the total body Na+ content, which depends upon Na+ intake and excretion. The kidney influences body Na+ content by regulating the tubular absorption of the Na+ filtered through the glomeruli. Thus, the regulation of Na+ absorption in the tubules of the kidney plays an important role in controlling blood pressure. More than 99% of the Na+ passing through the glomerulus is reabsorbed in the kidney. About 90% of the filtered Na+ through the glomerulus is reabsorbed in the proximal tubule and the ascending limb of the loop of Henle. The remainder of the Na+ absorption occurs in the distal nephron. This process is regulated by hormones such as aldosterone and antidiuretic hormone (ADH), and also by the osmolality of the plasma. These observations suggest that the regulation of Na+ transport in the distal nephron by hormones and osmolality plays an important role in the control of blood pressure. The distal nephron is composed of two different types of epithelial cells: the principal cell and the intercalated cell. The latter is also composed of two types of cells: alpha and beta intercalated cells. In addition to Na+ absorption, the distal-nephron epithelial cells also participate in K+ and H+ secretion. Na+ absorption is mediated through the principal cell, which also contributes to K+ secretion, whereas H+ is secreted through both types of intercalated cells, alpha and beta, in different ways. There are, in general, two steps in the transepithelial ion movement across the epithelium, including the distal-nephron epithelium. For example, in the case of Na+ absorption, one is the entry step of Na+ across the apical membrane and the other is the extrusion step of Na+ across the basolateral membrane. This means that there are two major regulatory sites of transepithelial Na+ absorption: namely, regulation of the entry and extrusion steps of Na+. It is generally thought that the entry step of Na+ across the apical membrane is the rate-limiting step in the transepithelial Na+ transport and that Na+ channels in the apical membrane play an important role as an entry step of Na+ and are regulated by hormones and plasma osmolality. In this review, we describe the regulatory mechanisms of Na+ absorption in renal distal-nephron epithelium by aldosterone, ADH and osmolality. Further, we will review the regulatory mechanisms of Cl- transport, which also plays an important role in Na+ transport as a major counter ion, and discuss other roles of Cl- in the active regulation of Na+ transport.     

Active potassium transport in reticulocytes of high-K+ and low-K+ sheep

The kinetics of active K+ transport were studied in immature red blood cells cells from high-K+ and low-K+ sheep particulary with respect to the effects of varying intracellular K+ concentration, [K]i. Comparison was made with active transport, or pump, activity in mature high-K+ and low-K+ red cells. Reticulocytes from both types of sheep had much higher maximal active K+ influxes than did mature cells. In both types of reticulocytes, and in mature high-K+ cells as well, the pump was relatively insensitive to increasing [K]i. In contrast, intracellular K+ markedly inhibited the pump in mature low-K+ cells. Active K+ transport in low-K+ reticulocytes, however, as in mature low-K+ cells, is stimulated by specific isoimmune anti-L serum. Therefore the K+ pumps of high-K+ and low-K+ reticulocytes have similar kinetic properties. Maturation of the red cells, involving inactivation of most of the pump activity in both cell types, results in mature high-K+ and low-K+ cells with K+ pumps of very different kinetic characteristics.     

Altered permeability of the erythrocyte membrane for sodium and potassium ions in spontaneously hypertensive rats

Permeability of the erythrocyte membrane for sodium and potassium ions was studied in 8-10-week old spontaneously hypertensive rats (SHR, Kyoto Wistar strain), normotensive Wistar and Sprague-Dawley rats. The rate constnat of Na/Na exchange was considerably greater in the SHR than in the normotensive Wistar and Sprague-Dawley rats. This difference remained the same in the rats adrenalectomized 7 days prior to the experiment. The maximum difference in the constants was found when the sodium pump was blocked by ouabain. The accumulation of 42K in the erythrocytes of the SHR (the sodium pump being blocked) took place at a considerably slower rate, and the K+ washout into a potassium-free medium was faster than in the normotensive Wistar and Sprague-Dawley rats. These results seem to indicate a higher permeability of the SHR's erythrocyte membrane for Na+ and K+ ions, as compared to normotensive Wistar and Sprague-Dawley strains. It is suggested that the increased permeability of the erythrocyte membrane for Na+ and K+ in the SHR may reflect a more widespread cell membrane defect, which could serve as a general cause for activating the mechanisms maintaing high blood pressure.     

The erythrocyte Na,K,Cl cotransporter and its circulating inhibitor in Dahl salt-sensitive rats

BACKGROUND: Abnormal Na,K,Cl cotransport is thought to be a pathogenic factor in Dahl salt-sensitive rat models, but the only direct evidence for this is an increased cotransport activity found in erythrocytes from salt-loaded Dahl salt-sensitive rats. OBJECTIVE: To re-examine erythrocyte cotransport fluxes and a circulating cotransport inhibitory factor (CIF) in inbred Dahl rats maintained on a low (0.2%) salt diet. Cotransport fluxes were investigated both under basal conditions and after stimulation by cell shrinking. METHODS: Blood was drawn from 12 male Dahl salt-sensitive and 12 Dahl salt-resistant rats of the inbred John Rapp strain. Erythrocyte Na,K,Cl cotransport activity was equated to the bumetanide-sensitive fluxes of sodium, rubidium or lithium. Plasma CIF activity was tested in human erythrocytes. RESULTS: In Dahl salt-sensitive rats: (1) plasma CIF activity (5.7+/-0.4 units/ml) was modestly higher than in Dahl salt-resistant rats (2.97+/-0.12 units/ml, P < 0.0001), but much lower than that previously found in salt-loaded Dahl salt-sensitive rats (16.1 units/ml), and (2) erythrocytes exhibited a similar bumetanide-sensitive sodium efflux (rate constant 0.056+/-0.008 h(-1)) as in Dahl salt-resistant rats (0.047+/-0.007 h(-1)). Following hypertonic shock, the bumetanide-sensitive rubidium influx reacted more to cell shrinkage in Dahl salt-sensitive than in Dahl salt-resistant erythrocytes (cell volume decrease required to stimulate bumetanide-sensitive rubidium influx by 4000 micromol/l cells per h=-4.04+/-0.36 versus -5.89+/-0.44 fl, respectively; P< 0.01). CONCLUSIONS: When fed a low-salt diet, Dahl salt-sensitive rats present slightly increased plasma CIF levels and normal erythrocyte cotransport fluxes under basal conditions, but an increased response to a hypertonic shock. Therefore, if there is any primary cotransport abnormality in Dahl salt-sensitive rats, it appears to be restricted to the renal Na,K,Cl cotransporter BSC1 isoform. Alternatively, any such change may be the consequence of abnormal regulation by osmolarity-dependent mechanisms.