Ouabain-insensitive Sodium Efflux Research Articles

Influence of pentachlorophenol on light emission from single barnacle muscle fibers preloaded with aequorin.

Experiments show that the resting ouabain-insensitive sodium efflux in giant fibers from the barnacle Balanus nubilus is stimulated by external application of pentachlorophenol (PCP). This work has now been extended to include a study of muscle fibers preloaded with the Ca2+ indicator aequorin to determine whether PCP is able to increase light emission; and whether its potency depends on the number of chlorine atoms and external pH. The results obtained are as follows: 1) PCP causes a dose-dependent, multiphasic rise in light emission; the threshold concentration in fibers not poisoned with ouabain was in the low micromolar range. 2) The efficacy of PCP is considerably greater than that of less-chlorinated phenols and phenol. 3) The response to PCP is a sigmoidal function of external pH both in unpoisoned and ouabain-poisoned fibers. Reducing external pH potentiates its efficacy. 4) The response to PCP depends on the external Ca2+ concentration, and the requirement for Ca2+ is usually absolute.

Abolition with chloramine-T of inactivation in barnacle muscle fibers results in stimulation of the ouabain-insensitive sodium efflux

The hypothesis that chloramine-T stimulates the basal Na + efflux in barnacle fibers as the results of the entry of trigger Ca 2+ into the myoplasm from the bathing medium was examined in this study. Two reasons for doing so can be given. One is that the oxidant is known to abolish inactivation in sodium and potassium channels. The other is that L-type Ca 2+ channels are present in barnacle fibers, and an increase in internal free Ca 2+ in these fibers is known to stimulate the Na + efflux, particularly in ouabain-poisoned fibers. The results of the experiments are as follows: (i) Chloramine-T exerts a biphasic effect on the Na + efflux: inhibition is followed by stimulation, the threshold concentration being 10 −5 M. This is also found to be the threshold concentration for shortening of these fibers. (ii) The kinetics of the inhibitory effect resemble those of ouabain. (iii) Ouabain is without effect on the stimulatory phase caused by chloramine-Y. (iv) Application of chloramine-T after the full effect of 10 −4 M-ouabain is reached elicits solely a stimulatory response. (v) The dose-response curves for the stimulatory action of chloramine-T in unpoisoned and ouabain-poisoned fibers are alike except that the threshold concentration is less than 10 −5 M in poisoned fibers. (vi) Basal light emission from unpoisoned and ouabain-poisoned fibers loaded with the photoprotein, aequorin, some 60 min beforehand increased as soon as they are exposed to 10 −4 M chloramine-T. The response recorded in unpoisoned fibers is monophasic and usually transitory, whereas it is multiphasic and usually sustained in ouabain-poisoned fibers. (vii) The dose-response curve for chloramine-T shows a shift to the left in poisoned fibers. (viii) The magnitude of the rise in light emission depends on the external Ca 2+ concentration. A rise fails to take place in the nominal absence of external Ca 2+. Taken together, these results support the above hypothesis that chloramine-T causes the entry of trigger Ca 2+ into the myoplasm from the outside and provide evidence that stimulation of the Na + efflux is associated not only with this event but also with a reduced Na + gradient resulting from inhibition of the membrane Na +/K +-ATPase system by the oxidant. Thus, the suggestion put forward is that this oxidant promotes reverse Na +/Ca 2+ exchange and is able to exert multiple effects on membrane transport.

An investigation of the sensitivity of the ouabain-insensitive sodium efflux in single barnacle muscle fibers to pentachlorophenol

The aim of the present work was to explore the possibility that pentachlorophenol (PCP) influences the behavior of the resting Na efflux in single muscle fibers from the barnacle, Balanus nubilus. It is shown here that PCP causes a transitory rise in the Na efflux in both unpoisoned and ouabain-poisoned fibers and that the response is dose-dependent, the minimal effective concentration in ouabain treated fibers being less than 10 −6 m. The efficacy of PCP is significantly greater than that of 2,3,4-trichlorophenol. 2,3-Dichlorophenol is ineffective. This is also the case with phenol. The magnitude of the response to PCP is a function of external pH. Lowering pHe increases the response. The response has an absolute requirement for external Ca 2+ and is a sigmoidal function of external Ca 2+ concentration. Since treatment of these fibers with PCP in high concentration leads to prompt contraction, experiments were designed to determine whether the observed rise in ouabain-insensitive Na efflux is due to a fall in myoplasmic pCa and whether trigger Ca 2+ originates from the bathing medium. The results obtained show that prior injection of ethylene glycol bis(β-aminoethyl ether) N,N′-tetraacetic acid (EGTA) or 1,2-bis(2-aminophenoxyethane- N,N,N′,N′-tetraacetic acid (BAPTA) leads to a drastic reduction in the response to PCP. They also show that prior external application of verapamil or devapamil stops the response to PCP from occurring. Both Cd 2+ and Co 2+ are also effective but only temporarily. Last, the effects of ryanodine and 8-( N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) were tested, since the former is known to block the sarcoplasmic reticulum Ca 2+ release channel, and the latter to impair the action of agents known to release Ca 2+ from internal depots. Both ryanodine and TMB-8 are found to reduce the response to PCP. Taken together, these observations support the hypothesis that PCP stimulates the ouabain-insensitive Na efflux by increasing the internal free Ca 2+ and that the increase in internal Ca 2+ is due to the entry of trigger Ca 2+ from the outside via Ca 2+ channels, as well as release of Ca 2+ is due to the entry of trigger via its channel. They also indicate that the efficacy of PCP depends on the 5 Cl atoms present in its aromatic ring and pH e.

The behavior of the ouabain-insensitive sodium efflux in single barnacle muscle fibers toward the microinjection of aluminum

Recent work with single muscle fibers from the barnacle Balanus nubilus has shown that the injection of Al into these fibers leads to inhibition of the resting Na efflux and that this involves both the ouabain-sensitive and the ouabain-insensitive components of the efflux. This work also showed that the injection of Al into ouabain-poisoned fibers oftern leads to a rise in the remaining Na efflux. This observation suggested the possibility that Al is able to stimulate the ouabain-insensitive Na by increasing myoplasmic free Ca 2+ and that trigger Ca 2+ reaches the myoplasm via voltage-dependent Ca 2+ channels. The results obtained are as follows: (i) The injection of AlCl 3 into fibers poisoned with ouabain produces a biphasic or monophasic effect on the remaining Na efflux. That is, stimulation is followed by inhibition, or there is only stimulation. (ii) This response is dose-dependent and is seen to take place following the injection of Al in a concentration as low as 0.01 m. (iii) Both Ga 3+ and Sc 3+ are able to mimick the effect of Al. (iv) Injection of EGTA following peak stimulation of the ouabain-insensitive Na efflux by injected AlCl 3 leads to reversal of this response. If, however, EGTA is injected long after the onset of peak stimulation and after ouabain reaches its maximum effect, it is found to be ineffective. (v) The magnitude of the stimulatory response of the ouabain-insensitive Na efflux is a sigmoidal function of external Ca 2+ and is almost completely abolished by verapamil, devapamil, and Cd 2+ but is unaffected by injecting Mg 2+ before or after AlCl 3. (vi) Whereas preinjection of Al reduces the response to ryanodine, external preapplication of ryanodine fails to alter the response to Al. The preinjection of deferoxamine (a potent chelator of Al) fails to stop the stimulatory response to Al injection from occurring. Taken together, these findings support the hypothesis that the stimulatory response elicited by Al injection is due to a fall in myoplasmic pCa resulting from activation of voltage-dependent Ca 2+ channels and that it involves the operation of the Na +Ca 2+ exchanger in the reverse mode.

Sodium Content and Sodium Efflux of Mononuclear Leucocytes From Young Subjects at Increased Risk of Developing Essential Hypertension

Mononuclear leucocytes were used as a cellular model for the in vitro measurements of volume, sodium and potassium content, sodium efflux rate constants and absolute sodium efflux in order to assess any cellular changes in young men at increased risk of developing essential hypertension, and to analyze whether any such changes were associated with borderline hypertension and/or heredity. Four groups of subjects were evaluated: 28 normotensive (NTO) and 20 borderline hypertensive (BHO) offspring of hypertensives, 12 borderline hypertensives with normotensive parents (BH) and 28 normotensive subjects with normotensive parents (NT). The cellular sodium/potassium contents of the four groups were not discernibly different. Ouabain insensitive sodium efflux rate constant and corresponding absolute efflux were significantly increased in offspring of hypertensives. Ouabain sensitive absolute sodium efflux was significantly increased in borderline hypertensives (BHO + BH) compared to normotensives (NT + NTO). These results indicate that leucocytes from subjects predisposed to hypertension possess an increased ouabain insensitive sodium transport mechanism and in subjects with borderline hypertension the sodium-potassium pump seems activated.

Influence of race, sex, and blood pressure on erythrocyte sodium transport in humans.

Sodium transport of erythrocytes from normotensive and essential hypertensive subjects was evaluated by determining ouabain-sensitive and ouabain-insensitive sodium efflux rates, Na+-Li+ countertransport rates, Li+-K+ cotransport rate constants (lithium replacing sodium), intracellular sodium concentrations, and the number of Na+,K+-adenosine triphosphatase (ATPase) sites per erythrocyte. Subjects included men and women, blacks and whites. Hypertensive subjects had significantly higher sodium transport than did normotensive subjects for ouabain-sensitive sodium efflux (p less than 0.025) and Na+-Li+ countertransport (p less than 0.001). Sexual differences were noted for ouabain-sensitive (p less than 0.001) and ouabain-insensitive (p less than 0.001) sodium efflux, for intracellular sodium concentration (p less than 0.025), and for the Li+-K+ cotransport rate constant (p less than 0.005), all with higher values for men than for women. Racial differences were noted for ouabain-insensitive sodium efflux (p less than 0.005), Na+-Li+ countertransport (p less than 0.001), and the Li+-K+ cotransport rate constant (p less than 0.001); values were higher in whites than blacks for all three measurements. The number of [3H]ouabain binding sites was lower for blacks (p less than 0.001) and the intracellular sodium concentration was higher for blacks (p less than 0.001). Among all subjects, significant (p less than 0.001) correlations were found between intracellular sodium concentration and the number of Na+,K+-ATPase sites per erythrocyte (r = -0.78) and between the ouabain-sensitive sodium efflux per site and intracellular sodium concentration (r = 0.85, p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Sodium transport parameters in erythrocytes of patients with primary aldosteronism.

Primary aldosteronism is an uncommon cause of hypertension but one of particular interest because of its distinctive pathophysiological mechanism of blood pressure elevation. Aldosterone has been associated with increased Na+,K+-adenosine triphosphatase (ATPase) activity, but there is controversy over which sodium transport parameters are responsible for this increase. We measured intracellular sodium, ouabain-sensitive and ouabain-insensitive sodium efflux, and the number of Na+,K+-ATPase sites of washed erythrocytes, as well as Na+-Li+ countertransport and the Li+-K+ cotransport rate constant of lithium-loaded red blood cells (RBCs) in six patients with primary aldosteronism and in 50 normal subjects. Ouabain-sensitive sodium efflux was significantly (p less than 0.001) higher for the primary aldosteronism patients than for normal subjects (1.85 +/- 0.29 vs 1.51 +/- 0.21 mmol/L RBC/hr) even though the intracellular sodium concentration (7.2 +/- 1.5 vs 6.7 +/- 1.9 mM) and the number of the Na+,K+-ATPase sites per RBC (331 +/- 52 vs 385 +/- 97) were not increased. The elevated sodium efflux appeared to be due to a significant (p less than 0.001) increase in the rate constant (1.60 +/- 0.12 x 10(-15) vs 1.28 +/- 0.15 x 10(-15) mmol/site/hr) of the ouabain-sensitive sodium efflux. The rate constant decreased significantly (p less than 0.01) after treatment.

Concerning stimulation by high external potassium and calcium injection of the ouabain-insensitive sodium efflux in barnacle muscle fibers

1. 1. The behavior of the ouabain-insensitive Na efflux in barnacle muscle fibers toward external high K and injection of Ca 2+ has been further investigated. 2. 2. Raising Ke to 100 mM after the injection of 0.25 M or 0.1 M GTPNa 2 results in a biphasic stimulatory response: the initial response is prompt in onset and small but transitory, whereas the delayed response is large and sustained. This second stimulatory phase is reduced markedly by injecting EGTA but not by PKI. 3. 3. Raising Ke to 100 mM in the presence of the 2 xanthine derivatives, viz. PMX and IAX, leads to a sustained stimulatory response of the ouabain-insensitive Na efflux which is halved by injecting PKI but unaffected by injecting EGTA. 4. 4. Injection of 0.1 M or 0.5 M CaCl 2 in the presence of PMX and IAX leads to a sustained stimulatory response, which is almost completely abolished by injecting PKI but unaffected by injecting EGTA. 5. 5. These results confirm the earlier finding that the response of the ouabain-insensitive Na efflux to high Ke in fibers preinjected with GTPNa 2 is biphasic and that the delayed second stimulatory phase is sustained rather than transitory. The ability of injected EGTA to only partially reverse the delayed response suggests that a fall in myoplasmic pCa is not the sole factor governing the kinetic picture. The experiments with PMX and IAX strongly suggest that cAMP is involved in the termination of the Ca 2+ message.

Blood pressure in essential hypertension correlates with the concentration of a circulating inhibitor of the sodium pump.

The influence of serum from patients with essential hypertension on the sodium efflux rate constants of human lymphocytes and on the activity of isolated (Na+ + K+)-ATPase was investigated. The ouabain-sensitive sodium efflux rate constant was significantly decreased (p less than 0.001) in the sera of 19 hypertensives (1.92 +/- 0.11 h-1) compared with the sera of 30 normotensives (2.44 +/- 0.07 h-1). The ouabain-insensitive sodium efflux was unaffected. These results corresponded with a significant difference (p less than 0.005) of (Na+ + K+)-ATPase activity (1.03 +/- 0.04 mU/ml and 0.079 +/- 0.06 mU/ml), when an isolated (Na+ + K+)-ATPase was incubated with the sera of 22 normotensives or 18 hypertensives. Both the rate constant of ouabain-sensitive sodium efflux and the (Na+ + K+)-ATPase activity correlated significantly with the diastolic and systolic blood pressure (p less than 0.001). These data, therefore, demonstrated the close relationship between essential hypertension and the concentration of a circulating inhibitor of the sodium pump.

Leukaemic promyelocytes and normal bone marrow cells release a passive sodium transport modifier (inhibitin).

Previous studies have shown that leukaemic immature cells, specifically promyelocytes but not mature leucocytes, contain and release an inhibitor of ouabain-insensitive sodium transport (inhibitin). In the present study, medium from cultured leukaemic promyelocytes significantly reduced the ouabain-insensitive sodium efflux from erythrocytes, whereas medium from the same cell line which had been made to differentiate did not have this effect. Culture medium from normal bone marrow cells (containing promyelocytes) also significantly (P less than 0.001) reduced ouabain-insensitive sodium efflux. These data suggest that inhibitin is secreted by primitive but not by mature leukaemic cells and normal bone marrow cells.

Stimulation by proctolin of the ouabain-insensitive sodium efflux in single barnacle muscle fibers

1. 1. A study has been made of the action of the neuropeptide proctolin on the radiosodium efflux from single barnacle muscle fibers. 2. 2. Proctolin (10 −8 M) when applied externally causes stimulation of the Na efflux in unpoisoned and ouabain-poisoned fibers. The response is prompt in onset, reaches a peak in 15 min and decays slowly. 3. 3. The response of the ouabain-insensitive Na efflux to external proctolin is dose-dependent, the concentration threshold being less than 10 −10M. 4. 4. The response to proctolin is dependent on external Ca 2+ but not on Na +. 5. 5. (i) The response to proctolin is abolished by high external Mg 2+, as well as by verapamil, Co 2+, Cd 2+ and WB-4101. (ii) The response is also abolished by preinjecting 0.5 M MgCl 2 or 0.1 M EGTA. 6. 6. The calmodulin antagonists trifluoperazine and imipramine are without effect on the response to proctolin. 7. 7. (i) Adenylate cyclase agonists, e.g. forskolin, fail to augment the response to proctolin. (ii) Prior injection of the phosphodiesterase inhibitors 1-propyl-3-methyl-7-(5-hydroxyhexyl)-xanthine (PMX) or 1-isoamyl-3-isobutylxanthine (IAX) fails to augment the response to proctolin. (iii) Prior injection of protein kinase inhibitor is ineffective. 8. 8. The response to proctolin is significantly reduced in the presence of tyramine. 9. 9. Taken together, these results support the view that proctolin stimulates the ouabain-insensitive Na efflux by activating Ca 2+ channels and that the cAMP-protein kinase system is not involved in this response.

Isolation of a sodium transport inhibitory factor, inhibitin, from cultured leukemic promyelocytes.

Previous studies have shown that leukemic blood contains a factor that has an inhibitory effect on bidirectional sodium transport in erythrocytes. This study was designed to isolate this factor from cultured leukemic promyelocytes. An extract from the promyelocytes reduced significantly (P less than 0.001) the ouabain-insensitive sodium efflux rate, from 0.096 +/- 0.009 to 0.056 +/- 0.003 SD. Using the inhibition of ouabain-insensitive sodium transport in erythrocytes as an assay to identify the factor, we ran the crude promyelocyte extract through Sephadex G-25 and G-10, with an intermediate ion-exchange step on DE-32, and finally subjected the active fraction to reverse-phase high-performance liquid chromatography. The specific inhibitory activity of the final fraction was 180-fold higher than that of the crude promyelocyte extract. The inhibitory activity could be destroyed by acid hydrolysis and by enzymatic digestion with several proteases but not by heating at 80 degrees C for 30 min; these characteristics suggest that the active factor, called inhibitin, is a peptide. Inhibitin is released by immature myeloid cells but not by differentiated white cells or by leukemic lymphocytes. It has no effect on potassium influx but inhibits sodium/sodium exchange in erythrocytes.

A circulating inhibitor of leucocyte sodium transport in patients with advanced liver cirrhosis.

Leucocyte sodium efflux was measured in control leucocytes pre-incubated for 90 min with serum from patients with advanced liver cirrhosis. Serum from patients with advanced alcoholic liver cirrhosis was inhibitory to sodium transport in control leucocytes. The degree of inhibition was similar to that seen in the patients' own leucocytes; the defect induced by patient serum was primarily inhibition of ouabain-insensitive sodium efflux, whereas in the patients' own leucocytes, inhibition was seen in both ouabain-sensitive and -insensitive sodium efflux, as shown previously. The results suggest that a circulating factor, present in patients with advanced cirrhosis, is capable of inhibiting sodium transport in leucocytes.

A passive sodium transport inhibitory factor (inhibitin) released from leukaemic promyelocytes in culture.

Previous studies have shown that myeloid leukaemic blast cells contain a heat stable factor which inhibits bidirectional sodium transport in normal erythrocytes. This study was undertaken to establish whether leukaemic promyelocytes in culture secrete this factor. Two cell-lines of leukaemic promyelocytes (HL-60 and JR) were grown and culture media from both reduced significantly the ouabain-insensitive sodium efflux rate constant, whereas conditioned culture medium (incubated like the cells in culture) had no inhibitory effect. Promyelocyte extract reduced significantly (P less than 0.01) the total sodium efflux rate constant from 0.393 +/- 0.030 (SD) to 0.311 +/- 0.060, and ouabain-insensitive efflux rate constant from 0.131 +/- 0.008 to 0.079 +/- 0.009 (P less than 0.001). The inhibitory factor was heat stable (80 degrees C for 30 min) and it inhibited sodium efflux through a pathway which was not inhibited by ouabain or frusemide. These studies suggest that leukaemic promyelocytes secrete the previously identified passive sodium transport inhibitory factor.

Erythrocyte membrane sodium transport in patients with treated and untreated essential hypertension.

Various parameters of erythrocyte membrane sodium transport were measured in patients with untreated essential hypertension, in the normotensive offspring of parents with hypertension, and in patients whose hypertension had been controlled by medication. Net sodium efflux, measured by an isotopic tracer technique, was 2.12 +/- 0.17 mM Na+/1 of red blood cells (RBCs)/hr in patients with untreated essential hypertension, compared with 1.55 +/- 0.12 mM Na/1 of RBCs/hr in a group of normotensive controls (p less than .025). Partitioning sodium efflux into ouabain-sensitive and ouabain-insensitive components revealed a significant elevation of both components of membrane sodium transport in the patients with untreated essential hypertension. Ouabain-sensitive sodium efflux was 1.38 +/- 0.09 mM Na/1 RBCs/hr in the patients, compared with 1.04 +/- 0.07 mM Na/1 RBCs/hr in the controls. Ouabain-insensitive sodium efflux was also increased from 0.51 +/- 0.05 mM Na/1 RBCs/hr in the controls to 0.74 +/- 0.09 mM Na/1 RBCs/hr in those with untreated hypertension. Despite these changes in sodium efflux, Na,K-ATPase activity in the erythrocyte membrane, measured at maximum velocity (Vmax), was normal, suggesting that the observed abnormalities in membrane sodium transport in patients with untreated essential hypertension resulted from a change in pump control mechanisms rather than a change in enzyme activity. With the techniques used in this study we were unable to identify changes in erythrocyte membrane transport in the normotensive offspring of hypertensive parents. Membrane sodium transport was also examined in hypertensive patients whose blood pressure had been controlled by medication. In this group it was found that erythrocyte sodium transport did not differ from that in our control group, which suggests that treatment of hypertension can modify fundamental pathophysiologic changes at the level of the cell membrane.

Studies of Sodium Transport in Thymocytes of Rats with DOC/Salt Hypertension

1. Sodium transport and intracellular sodium content were studied in thymocytes of rats made hypertensive by treatment for 4 or 8 weeks with deoxycorticosterone (DOC) and salt (DOC/salt). 2. The systolic blood pressure in the DOC/salt animals was 152 ± sem 3 and 189 ± 3 mmHg after 4 and 8 weeks' treatment respectively. This was significantly higher than pressures in their respective controls (124 ± 4 and 126 ± 5 mmHg), which had been given 1% sodium chloride solution (171 mmol/l) only. 3. The total sodium efflux rate constant in the DOC/salt rats was lower than that in the control group after 8 weeks of treatment (5.56 ± sem 0.21 vs 6.12 ± 0.11 h−1; P < 0.05) but not after 4 weeks of treatment (5.93 ± 0.13 vs 6.32 ± 0.13 h−1;0.1 > P > 0.05). 4. Intracellular sodium content in the DOC/salt rats was significantly higher than that of the control animals after 8 weeks' treatment (49.6 ± 2.5 vs 42.1 ± 1.0 mmol/kg dry weight; P < 0.05). 5. No significant changes were observed in intracellular potassium content, sodium influx or ouabain-insensitive sodium efflux rate constant.

Abnormal sodium efflux in erythrocytes of patients with essential hypertension.

Erythrocyte sodium efflux as well as sodium, potassium, and water content were studied in 12 untreated men with uncomplicated essential hypertension and in 18 normotensive control subjects. In the patients with essential hypertension, the rate constant for total sodium efflux was significantly lower than in the normotensives (5.96.10(-3) +/- 0.45.10(-3) min-1 vs 6.69.10(-3) +/- 0.49.10(-3) min-1; p less than 0.005), which was due to a reduced ouabain-sensitive sodium efflux rate constant. Significant differences in total sodium efflux and ouabain-sensitive sodium efflux, however, could not be demonstrated, since intracellular sodium concentrations, although insignificant, were higher in the patients with essential hypertension (6.11 +/- 0.74 mmole/liter vs 5.97 +/- 0.66 mmole/liter. The rate constants for ouabain-insensitive sodium efflux, for ouabain-insensitive furosemide-sensitive sodium efflux, and for passive (ouabain-insensitive furosemide-insensitive) sodium efflux were similar in hypertensives and in normotensives. The cause of the reduced rate constant for ouabain-sensitive sodium efflux is not clear. However, as suggested for other types of altered erythrocyte transport mechanisms described recently, it might be determined genetically.

The effects of alterations in the external sodium concentration on human leucocyte sodium and potassium transport in vitro.

Human leucocytes incubated in tissue culture fluid of low-sodium concentration (2 mM; iso-osmolarity maintained with choline chloride) reached a new equilibrium within 1 hour and lost approximately 25% of intracellular potassium and 70% of intracellular sodium. The rate constant for ouabain-sensitive sodium efflux fell by more than 50% and the ouabain-insensitive rate constant increased nearly threefold in the low-sodium medium. Total sodium efflux fell in proportion to internal sodium whereas ouabain-insensitive sodium efflux remained unchanged. A reduction in external sodium from 140 to 2 mM was associated with a 75% fall in sodium influx. In the low-sodium medium ouabain-sensitive potassium influx exceeded ouabain-sensitive sodium efflux and no ouabain-sensitive potassium efflux could be demonstrated. Ouabain-insensitive potassium influx and that portion of potassium efflux which is dependent on external potassium fell in parallel in low-sodium cells, suggesting reduced activity of a ouabain-insensitive K:K exchange system.

Erythrocyte lipid composition and sodium transport in human liver disease

In patients with liver disease there are usually increases in erythrocyte cholesterol and phosphatidylcholine concentrations. This increase in membrane lipid changes the shape of the erythrocyte and “spur” or “target” cells may be present. Sodium fluxes were measured in erythrocytes from 17 patients with a variety of liver diseases and from 17 normal subjects and the values related to the lipid content of the membrane. Ouabain-insensitive and ouabain-sensitive effluxes were lower in patients than in normal subjects and the reduction in ouabain-insensitive efflux was more marked. Sodium influx was also significantly lower in erythrocytes from patients than controls. Ouabain-sensitive and ouabain-insensitive effluxes and sodium influx did not correlate with the cholesterol content of erythrocytes from patients. Significant negative correlations were noted between ouabain-insensitive sodium efflux ( r = −0.63, P < 0.01), sodium influx ( r = −0.61, P < 0.01) and intracellular sodium concentration ( r = −0.66, P < 0.01) and the cholesterol : phospholipid molar ratio of the cell but there was no significant correlation between this ratio and the ouabain-sensitive sodium efflux ( r = 0.41, P > 0.05). These results support the hypothesis that an altered lipid composition may affect the permeability of the erythrocyte membrane in patients with liver disease.

Effect of zinc on leucocyte sodium transport in vitro.

1. In a preparation of human leucocytes maintained in tissue culture fluid, increasing the extracellular zinc concentration leads to a significant increase in both ouabain-sensitive sodium efflux and in sodium influx. 2. Cell water and sodium content do not alter significantly with increasing extracellular zinc concentration. 3. A small increase in the ouabain-insensitive sodium efflux can be demonstrated when the external zinc concentration is raised from 0.75 mumol/l to 90 mumol/l.