Cellular Sodium Content Research Articles

Dematin and Adducin Tether Sodium-Hydrogen Exchanger, NHE1, to Erythrocyte Membrane Cytoskeleton

Dematin is a critical component of the membrane junctional complex in red blood cells. It tethers the spectrin cytoskeleton proteins to the membrane and its genetic deletion in mice causes dissociation of the spectrin, actin and β-adducin from the membrane resulting in the collapse of the red blood cells (RBCs). As dematin lacks a transmembrane domain, it is still unclear how this critical component of the junctional complex is anchored to the RBC membrane. Our previous studies have shown that the multi-transmembrane glucose transporter-1 (GLUT1) interacts with dematin and β-adducin in human RBCs, suggesting a potential role for GLUT1 in recruiting dematin to the membrane. However, as mouse RBCs do not express a GLUT1 homologue, an equivalent membrane receptor for dematin and/or adducin in mice remains to be determined. Using multiple in vitro and in vivo biochemical assays, here we demonstrate that the ubiquitously expressed plasma membrane Na+/H+ exchanger, NHE1 (Slc9a1), is one of the receptors for dematin and β-adducin in mature mouse red blood cells. NHE1 directly interacts with the core domain of dematin. Moreover, the dematin headpiece domain mutant S381E, which binds to the core domain with a higher affinity than the wild type, abolished the biochemical interaction between dematin and NHE1. This observation suggests that NHE1 and dematin headpiece domain compete for the same binding site(s) on the core domain. Furthermore, this finding highlights a molecular mechanism whereby an intermolecular switch of dematin regulates its interaction with NHE1 by phosphorylation. Dematin and β-adducin directly interact with NHE1 at its membrane-proximal cytoplasmic domain, which in turn regulates NHE1 activity in response to growth factor stimuli and intracellular pH alterations. Accordingly,we observed an increased cellular sodium content in erythrocytes of dematin headpiece and adducin double knockout mice (DAKO), suggesting a higher NHE1 activity in DAKO erythrocytes. Unlike GLUT1, NHE1 is expressed in both mouse and human RBCs. Thus, our results provide a novel mechanism for linking NHE1 to membrane skeleton and multiple cell signaling pathways through dematin and adducin (Figure 1). Since NHE1 is one of the major regulators of intracellular pH and hypertonic stress, our findings raise the possibility that the dematin-adducin-NHE1 complex may modulate these functions in RBCs as well as in other cell types with broad impact on the regulation of the actin cytoskeleton and cell migration. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

A kinetic model for sodium transport via a non‐gastric H+(Na+)/K+ ATPase

Experimental results have suggested that macula densa (MD) cells have a unique way of regulating cellular sodium concentration via an apical H+(Na+)/K+‐ATPase. We developed a kinetic model to represent the sodium transport via this transporter. The model assumes a 2:2 stoichiometry for both the hydrogen and sodium cycles. Rate constant values for the hydrogen cycle were obtained from a renal H+/K+‐ATPase model (A.M. Weinstein, Am J Physiol Renal Physiol 274:F856‐F867, 1998) which were, in turn, based on values obtained from a gastric H+/K+‐ATPase model (P. Brzezinski et al., Biochim. Biophys. Acta 942:215–219, 1988). Rate constants for the sodium cycle are assumed to be equal to those in the hydrogen cycle. Results showed that sodium extrusion is very sensitive to changes in luminal potassium concentration from 0 to 20 mM. In addition, sodium extrusion as a function of internal sodium concentration saturates at ~70 mM. This ATPase pump model is essential in the development of larger scale models of ion transport by the MD cells.Research supported by MBRS‐RISE grant 2R25GM061151‐09 and by NIH‐NIGMS grant SC1GM084744.

Analysis of models for crustacean stretch receptors.

The mechanisms underlying the diverse responses to step current stimuli of models [Edman et al. (1987) J Physiol (Lond) 384: 649-669] of lobster slowly adapting stretch receptor organs (SAO) and fast-adapting stretch receptor organs (FAO) are analyzed. In response to a step current, the models display three distinct types of firing reflecting the level of adaptation to the stimulation. Low-amplitude currents evoke transient firing containing one to several action potentials before the system stabilizes to a resting state. Conversely, high-amplitude stimulations induce a high frequency transient burst that can last several seconds before the model returns to its quiescent state. In the SAO model, the transition between the two regimes is characterized by a sustained pacemaker firing at an intermediate stimulation amplitude. The FAO model does not exhibit such a maintained firing; rather, the duration of the transient firing increases at first with the stimulus intensity, goes through a maximum and then decreases at larger intensities. Both models comprise seven variables representing the membrane potential, the sodium fast activation, fast inactivation, slow inactivation, the potassium fast activation, slow inactivation gating variables, and the intra cellular sodium concentration. To elucidate the mechanisms of the firing adaptations, the seven-variable model for the lobster stretch receptor neuron is first reduced to a three-dimensional system by regrouping variables with similar time scales. More precisely, we substituted the membrane potential V for the sodium fast activation equivalent potential Vm, the potassium fast inactivation Vn for the sodium fast inactivation Vh, and the sodium slow inactivation Vl for the potassium slow inactivation Vr. Comparison of the responses of the reduced models to those of the original models revealed that the main behaviors of the system were preserved in the reduction process. We classified the different types of responses of the reduced SAO and FAO models to constant current stimulation. We analyzed the transient and stationary responses of the reduced models by constructing bifurcation diagrams representing the qualitatively distinct dynamics of the models and the transitions between them. These revealed that (1) the transient firings prior to reaching the stationary state can be accounted for by the sodium slow inactivation evolving more slowly than the other two variables, so that the changes during the transient firings reflect the bifurcations that the two-dimensional system undergoes when the sodium slow inactivation, considered as a parameter, is varied; and (2) the stationary behaviors of the models are captured by the standard bifurcations of a two-dimensional system formed by the membrane potential and the potassium fast inactivation. We found that each type of firing and the transitions between them is due to the interplay between essentially three variables: two fast ones accounting for the action potential generation and the post-discharge refractoriness, and a third slow one representing the adaptation.

A role for sodium in hypoxic but not in hypothermic injury to hepatocytes and LLC-PK1 cells.

Hypothermia is considered to be responsible for sodium influx during cold hypoxic incubation. However, we have previously shown that hypothermia alone leads to a pronounced decrease in cellular sodium content when liver endothelial cells or hepatocytes are incubated under such conditions. In the research described here, we therefore studied the effects of hypothermia and hypoxia, alone or combined, on cellular sodium homeostasis and assessed the role sodium plays in the pathogenesis of hypoxic and hypothermic injury to cultured liver and kidney cells. Isolated hepatocytes and LLC-PK1 cells were incubated in Krebs-Henseleit buffer or a sodium-free modification thereof under normoxic and hypoxic conditions at 4 degrees C as well as at 37 degrees C. Cytosolic sodium concentration was determined in isolated hepatocytes under both warm and cold conditions using digital fluorescence microscopy and the Na+-sensitive dye sodium-binding benzofuran isophthalate. When hepatocytes were incubated under cold normoxic conditions the cellular sodium concentration decreased. However, it increased strongly under hypoxic conditions at 4 degrees C and at 37 degrees C. When either hepatocytes or LLC-PK1 cells were incubated under hypoxic conditions at 4 degrees C or 37 degrees C, sodium-free medium provided protection. In contrast, sodium-free medium did not alleviate the hypothermic injury observed when cells were incubated under cold normoxia. The sodium influx observed during cold hypoxia is triggered by hypoxia and not by hypothermia. Sodium plays a prominent role in hypoxic injury to cultured liver and kidney cells, although hypothermic injury of these cells is independent of sodium homeostasis.

NO3- nutrition and salt tolerance in the cyanobacterium Anabaena sp. PCC 7120 and mutant strains.

Growth of the cyanobacterium Anabaena sp. PCC 7120 and its nitrate assimilation-defective mutants was inversely proportional to the NaCl concentration in the medium. Presence of nitrate in the saline medium protected the growth of the parent but not of the mutant strains from salt toxicity. On the other hand, ammonium nitrogen protected the growth of all the strains from salt toxicity. However, the effect was less than that of nitrate. An altered sodium transport system was evident in the mutant strains and was most marked in mutant SP9. The cellular sodium concentration in parent and mutant strains also varied. Although mutant SP9 exhibited the lowest level of cellular sodium, it was as sensitive to salt toxicity as other strains. It is assumed that merely the presence of a toxic level of NaCl in the ambient environment is sufficient to damage the structural and functional components of the plasma membrane.

Rapid decrease in cellular sodium and chloride content during cold incubation of cultured liver endothelial cells and hepatocytes.

Hypothermia, as used for organ preservation in transplantation medicine, is generally supposed to lead to an intracellular accumulation of sodium, and subsequently of chloride, via inhibition of the Na+/K+-ATPase. However, on studying the cellular sodium concentration of cultured liver endothelial cells using fluorescence microscopy, we found a 55% decrease in the cellular sodium concentration after 30 min of cold incubation in University of Wisconsin (UW) solution. To confirm this surprising result, we set up a capillary electrophoresis method that allowed us to determine the cellular contents of inorganic cations and of inorganic anions. Using this method we measured a decrease in the cellular sodium content from 104+/-11 to 55+/-4 nmol/mg of protein, accompanied by a decrease in the chloride content from 71+/-9 to 25+/-5 nmol/mg of protein, after 30 min of cold incubation in UW solution. When the endothelial cells were incubated in cold Krebs-Henseleit buffer or in cold cell culture medium instead of UW solution, similar early decreases in cellular sodium and chloride contents were observed, thus excluding the possibility of the decreases being dependent on the preservation solution used. Furthermore, experiments with cultured rat hepatocytes yielded a similar decrease in sodium content during initiation of cold incubation in UW solution, so the decrease does not appear to be cell-specific either. These results suggest that, contrary to current opinion, sodium efflux predominates over sodium influx during the early phase of cold incubation of cells.

Corneocytes Undergo Systematic Changes in Element Concentrations Across the Human Inner Stratum Corneum

Using analytical electron microscopy of freeze-dried cryosections, physiologic elements were visualized within individual cells across the human inner stratum corneum. Human corneocytes undergo systematic changes in element composition as they advance through this region. Phosphorus is largely excluded from the stratum corneum, undergoing a precipitous drop in concentration at the granular/stratum corneum interface. The cellular potassium concentration has a profile similar to that of phosphorus but with a slower decline, thus migrating further into the stratum corneum. In contrast, the cellular chloride concentration increases in the innermost corneocyte layer, increases further in the subsequent layer or two (as potassium declines), and then decreases to values comparable to those in the innermost corneocyte. The cellular sodium concentration (per unit volume of tissue) is relatively unaltered in transit across the inner stratum corneum. The initial potassium and chloride movements are oppositely directed and have the appearance of creating an electrical charge imbalance. The position-dependent alterations in corneocyte elemental composition may reflect sequential stages of chemical maturation occurring intracellularly during stratum corneum transit, an example of which is the breakdown of filaggrin that occurs over this same region of the inner stratum corneum.

Cyclosporine A enhances total cell calcium independent of Na-K-ATPase in vascular smooth muscle cells.

The effect of cyclosporine A in enhancing vasconstrictor-induced calcium (Ca2+) mobilization in vascular smooth muscle cells may contribute to important side effects in cyclosporine therapy such as hypertension and nephrotoxicity. As we have previously shown, cyclosporine A stimulates transmembrane Ca2+ influx. Since Ca2+ efflux was not affected by cyclosporine A, we concluded that cyclosporine augments angiotensin II induced Ca2+ mobilization in vascular smooth muscle cells by an increased amount of Ca2+ in angiotensin II sensitive intracellular Ca2+ stores. The present study was therefore designed to examine the effect of cyclosporine A on cellular calcium content and on membrane calcium transport mechanisms. An important mechanism of Ca2+ extrusion from the cell is the Na-Ca exchanger. Its activity is closely related with that of the Na-K-ATPase. By increasing cellular sodium concentration the blockade of Na-K-ATPase would in turn activate cellular calcium uptake bx the Na-Ca exchanger. Therefore, we hypothesized that cyclosporine A might exert its effects in the same manner as a circulating Na-K-ATPase inhibitor. Total cell calcium was measured by atomic absorption and activity of Na-K-ATPase was estimated by an assay measuring phosphate production. Preincubation of the cells with cyclosporine (10 micrograms/ml) for 15 min increased total cell calcium from 31.4 +/- 5.0 to 46.5 +/- 5.3 nmol/mg protein (P < 0.05). Activity of Na-K-ATPase was not affected by cyclosporine A (3.9 +/- 0.2 vs. 4.3 +/- 0.2 mumol Pi h-1 mg-1 protein). Therefore, cyclosporine A induced Ca2+ influx is not mediated by an inhibition of the Na-K-ATPase.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of loop diuretics on organic osmolytes and cell electrolytes in the renal outer medulla

Electron microprobe analysis on freeze-dried cryosections was used to determine the effect of the loop diuretics torasemide and furosemide on intracellular electrolyte concentrations in individual cells of the outer and inner stripe of the outer medulla and on cell rubidium uptake, the latter a measure of basolateral Na-K-ATPase activity. In addition, the organic osmolytes glycerophosphorylcholine (GPC), betaine, inositol and sorbitol in cortex, outer medulla and inner medulla were measured using HPLC. Both loop diuretics significantly reduced sodium and chloride concentrations and rubidium uptake in thick ascending limb cells, but did not affect sodium concentration or rubidium uptake in the proximal straight tubule (PST) cells or in the light or dark cells of the outer medullary collecting duct (OMCD). Chloride concentrations in these cells (that is, PST cells, OMCD light and dark cells) were lowered by loop diuretics, albeit less than in thick ascending limb cells. Administration of both loop diuretics for only 20 minutes was sufficient to significantly depress tissue concentrations of GPC, betaine, and myo-inositol in the outer medulla and of GPC, betaine and sorbitol at the papillary tip. These results indicate that loop diuretics, presumably by blocking apical sodium entry, decrease thick ascending limb cellular sodium concentration and, as a consequence, reduce Na-K-ATPase activity as assessed by cell rubidium uptake. Although this has been shown previously in in vitro preparations, the present study confirms this for the first time in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)

Increases in cellular sodium concentration by arginine vasopressin and endothelin in cultured rat glomerular mesangial cells

The present study was undertaken to determine whether arginine vasopressin (AVP), angiotensin-II, and endothelin (ET) increase the cellular sodium concentration ([Na+]i) in cultured rat glomerular mesangial cells. [Na+]i was measured using the fluorescence indicator dye sodium-binding benzofuran isophthalate. These three vasoconstrictor hormones increased cellular free calcium ([Ca2+]i) and [Na+]i in a dose-dependent manner ([Na+]i: basal, 11.5; 10(-7) M AVP, 20.5; 10(-7) M angiotensin-II, 13.8; and 10(-7) M ET, 21.2 mM). The mobilization of [Ca2+]i was faster than that of [Na+]i. The AVP-induced increase in [Na+]i was completely blunted by the potent V1 antagonist d(CH2)5Tyr(Me)AVP. Vasoconstrictor hormones produced a biphasic cellular pH (pHi) change, characterized by a transient acidification, followed by a sustained alkalinization. The Ca(2+)-free condition markedly reduced AVP- and ET-induced increases in [Ca2+]i and [Na+]i and biphasic changes in pHi. In the Na(+)-free state, the hormonally mobilized [Ca2+]i was significantly enhanced. Basal [Na+]i decreased to below 3 mM, and there was little increase in [Na+]i after the addition of vasoconstrictor hormones, suggesting that the source of [Na+]i is extracellular space. Only early acidification was obtained in the absence of a sustained alkalinization. The [Na+]i mobilization was closely related to the biphasic change in pHi. These results indicate that AVP, ET, and angiotensin-II increase [Na+]i in glomerular mesangial cells, and that the early mobilization of [Na+]i depends on Na+/Ca2+ exchange, and the sustained phase depends on Na+/H+ exchange. The hormonally mobilized [Ca2+]i is essential for the activation of Na+/H+ exchange, and an increase in [Na+]i is suggested to play an important role in cellular alkalinization.

Augmentation of vasopressin-induced cAMP production by high potassium in rat renal papillary collecting tubule cells in culture

The effect of high potassium, 60 mM KCl, on the cellular action of arginine vasopressin (AVP) was studied in rat renal papillary collecting tubule cells in culture. In the presence of 0.5 mM 3-isobutyl-1-methylxanthine AVP-induced cAMP production was enhanced by pretreatment of the cells with 60 mM KCl. Such an enhancement was not found in cells pretreated with Ca2+-free medium containing 1 mM EGTA or in Na+-free medium, which rather reduced AVP-induced cAMP production. Similar results were obtained with the blockers of cellular Ca2+ uptake, 1 × 10−4 M verapamil and 1 × 10−5 M nifedipine. The 60 mM KCl elevated the cellular sodium concentration ([Na+]i) from 15.1 to 18.8 mM, cellular pH (pHi) from 7.18 to 7.32, and basal cellular free calcium concentration ([Ca2+]i). These results indicate that high potassium promptly augments AVP-induced cAMP production in renal papillary collecting tubule cells. This effect is based on the alkalinized pHi and the increased [Ca2+]i.

Leukocyte isotopically exchangeable intracellular sodium fractions in lean and overweight hypertensives

Leukocyte intracellular sodium, as measured by flame photometry, is increased in essential hypertension, especially when associated with a body mass index greater than 27 kg · m −2. A triple isotope method for measuring the isotopically exchangeable pool of intracellular sodium was used to assess if this pool was increased in hypertension. No significant differences in the isotopically exchangeable intracellular sodium concentration were found between lean and overweight hypertensives compared with normotensive controls. Lean hypertensives with systolic blood pressures below the median had significantly lower exchangeable intracellular sodium concentrations than lean normotensives, whereas those with systolic blood pressures above the median had raised exchangeable intracellular sodium concentrations. The obese hypertensives did not show this trend. The exchangeable intracellular sodium concentration was correlated to systolic ( r = .53, P < .001) and diastolic ( r = 0.39, P < .01) blood pressure in hypertensives. We conclude that the increase in total cellular sodium content (as measured by flame photometry) in hypertensives described in previous studies is not associated with any increase in the isotopically exchangeable pool of intracellular Na +, except in those lean hypertensives with systolic blood pressures above the median. By implication, there may be an increased slowly exchangeable pool of intracellular Na + in leukocytes from most hypertensives.

Sodium and Obesity in the Pathogenesis of Hypertension

In the present work I focus on the pathophysiological mechanisms that may explain the association between high sodium intake, obesity and high blood pressure. Despite epidemiological and etiological controversies on the link between excess sodium in the diet and elevated arterial pressure, the association could be explained on the basis of three different pathophysiological mechanisms: (1) abnormal electrolyte transport across cell membranes, a defect that alters sodium/potassium exchange and also sodium/calcium exchanges, increasing the concentration of intracellular calcium ions that heightens vessel wall tension and the smooth muscle process, (2) increased sympathetic nervous system activity and (3) altered cellular sodium concentration that induces waterlogging in the peripheral arteriolar walls. These mechanisms increase peripheral resistance and enhance arterial pressure. Early epidemiological studies documented a strong association between obesity and hypertension; and a greater incidence of high blood pressure and diabetes was reported in persons with upper body obesity (high waist/hip ratio). Researchers have explained obesity-related hypertension accordingly with various mechanisms. Hyperinsulinemia and vascular resistance may trigger the metabolic and adrenergic changes described in obese hypertensive patients in several ways. Insulin may increase absorption of sodium in the diluting segment of the distal nephron with consequent water retention. Alternatively, insulin might alter sodium/potassium distribution thus causing increased vascular peripheral resistance. The increased sodium stimulates adrenergic activity. The water retention in obese subjects increases absolute volume that is predominantly redistributed in the cardiopulmonary area, leading to augmented venous return and cardiac output. These changes in association with a total peripheral resistance considered inappropriately normal, are the main hemodynamic characteristics of obesity-related hypertension.

The response of the filamentous cyanobacterium Spirulina platensis to salt stress

The responses of the filamentous cyanobacterium Spirulina platensis to increased NaCl concentrations (0.25–1.0 M) in addition to the concentration of sodium in the growth medium were studied. A two stage response to the salt stress was observed. This consisted of a relatively short shock stage, followed by adaptation process. It was shown that upon exposure to high salt concentrations of 0.5 M and above, immediate inhibition of photosynthesis and respiration, and complete cessation of growth occurred. After a time lag, the energy-yielding processes exhibited restored activity. At 0.5 and 1.0M NaCl photosynthesis reached 80% and 50% that of the control, while respiration was enhanced by 140 and 200%, respectively. The time lags were longer when the cells were exposed to higher NaCl concentrations. The resumption of growth and the establishment of new steady state growth rates were found to be correlated to the recovery in respiration. The relationship between the growth rates after adaptation and the increased NaCl concentrations was found to be inversely linear. The cellular sodium content was maintained at a constant low level, regardless of the external NaCl concentration, while potassium content declined linearly vs. the external NaCl concentration. The carbohydrate content of the cells rose exponentially with the increase in NaCl concentration.

Cell membrane handling of sodium in lymphocytes during salt restriction in normotensives

Lymphocyte sodium content and sodium efflux were studied in 9 healthy normotensive males without history of essential hypertension before, during and after 5 weeks of severe sodium depletion. Sodium depletion caused a significant increase in sodium content and a slight but non-significant decrease in potassium content. Total and ouabain-sensitive sodium efflux rate constants decreased significantly during sodium depletion, while absolute sodium efflux, derived from cellular sodium concentration and the corresponding sodium efflux rate constants, remained unchanged. A significant reduction in arterial mean and diastolic blood pressure, measured by ambulatory as well as by home readings, was observed during salt restriction. Prolonged severe sodium depletion of normotensive subjects leads to changes in lymphocytic sodium homeostasis, probably due to a primary inhibition of the sodium pump and a secondary intralymphocytic sodium accumulation. The mechanism underlying these changes remains unclarified.

Effect of chronic treatment with cystic fibrosis fibroblast medium on rat submandibular gland acinar cells

The effect of chronic treatment with cystic fibrosis (CF) fibroblast medium on rat submandibular gland and pancreas was investigated. Rats were injected for 8 days with conditioned medium from normal or CF fibroblasts. The elemental content of the acinar cells was measured by X-ray microanalysis of cryosections. A significant increase in cellular calcium, and a decrease in cellular sodium concentrations were found after treatment with CF medium. The ultrastructure of the submandibular acinar cells was not affected by the conditioned CF fibroblast culture medium. No effect of treatment with CF medium on ultrastructure and elemental content of pancreatic acinar cells could be demonstrated. The response to α-adrenergic, β-adrenergic, cholinergic, and peptidergic stimulation in submandibular gland acinar cells of rats injected with normal or CF medium was investigated in vitro. With regard to changes in elemental composition after stimulation, no significant differences in response between the two groups could be found. Apparently, a factor in conditioned medium from cultured CF fibroblats induces a net increase in calcium content of rat submandibular gland acinar cells. Possibly, this factor acts in a similar way in CF patients and may cause elevated calcium levels in CF cells.

Effects of thyroid hormone on sodium pump sites, sodium content, and contractile responses to cardiac glycosides in cultured chick ventricular cells.

Sensitivity of cardiac muscle to digitalis glycosides depends on the thyroid state. The mechanism of this interaction was investigated at the cellular level using spontaneously beating monolayers of cultured chick embryo ventricular cells. Cells were grown for 48 h in serum-free medium containing concentrations of triiodothyronine (T3) from zero to 10(-7) M, and the total number of sodium pump sites, sodium content, and contractile amplitude in the presence and absence of various concentrations of ouabain were determined. T3 caused a concentration-dependent increase in the number of specific ouabain binding sites; the maximal increase to 160% of control was observed in response to 10(-8) M T3. T3 lowered steady-state cellular sodium content in a concentration-dependent manner, also. Ouabain (1 microM) exposure elevated cellular sodium content in all cells, but the increase was greatest in cells grown in T3-free medium and least in cells grown in 10(-8) M T3. The positive inotropic and toxic effects of ouabain in cells grown in 10(-8) M T3 were diminished at any given ouabain concentration, and thus, the dose-response curve was shifted to the right. These results indicate that T3 causes induction of additional sodium pump sites that are functional. The increased tolerance of hyperthyroid cells and reduced tolerance of hypothyroid cells to cardiac glycosides can be explained by these changes in the number of sodium pump sites and cellular sodium content, and consequently, calcium influx via sodium-calcium exchange.

Cellular sodium concentration and vasoconstrictor state in hypertension.

The sodium content of peripheral blood leucocytes was estimated in two separate investigations of the relationship between cellular sodium content and the vasoconstrictor state. In the first study various parameters of forearm blood flow were measured in a group of 31 normal subjects. A positive correlation was found between peripheral vascular resistance and leucocyte sodium content (p less than 0.05), and a negative correlation between venous compliance (VV60) and leucocyte sodium content (p less than 0.001). In the second study the leucocyte sodium content of 14 patients with essential hypertension was investigated before and after treatment with the calcium antagonist verapamil. The sodium content was found to be abnormally high, as previously described, and treatment with verapamil was found to reverse the defect. Both studies indicate a link between cell sodium content and the vasoconstrictor state, and the results are discussed in light of current theory.

Ouabain-binding and 86rubidium-uptake in lymphocytes of normal and borderline hypertensive subjects.

In borderline hypertensives cellular sodium concentration seems to be increased, indicating that cellular abnormalities are present in the early course of essential hypertension. In order to study the mechanisms underlying this finding the number of sodium/potassium pump sites and the cation pump activity were studied in lymphocytes of nine borderline hypertensives (27 (20-36) years) and nine controls (28 (20-36) years). Maximum 3H-ouabain binding and 86Rb-uptake were taken as measures of the number of pump sites and cation pump activity, respectively. The median number of sodium/potassium pump sites was 49.6 X 10(3) molecules/cell in the BH group compared to 32.4 X 10(3) in the control group (P less than 0.01). Median 90 min 86Rb-uptakes were 54.0 pmol/10(6) cells in BH subjects and 39.4 in controls (P less than 0.10). The increased number of sodium/potassium pump sites and the tendency to increased cation pump activity in lymphocytes of BH subjects in vitro may be interpreted as an adaptive change possibly induced by a circulating natriuretic substance.

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.