Acclimation to humic substances prevents whole body sodium loss and stimulates branchial calcium uptake capacity in cardinal tetras Paracheirodon axelrodi (Schultz) subjected to extremely low pH

Kinetics of sodium (Na⁺) and calcium (Ca²⁺) uptake were studied in cardinal tetras Paracheirodon axelrodi acclimated to humic substances (HS, 35 mg C l^?1) and low pH (pH 3·72), parallel to analysis of whole body Na⁺ and Ca²⁺ content. This species had a high uptake capacity (J_max) for both Na⁺ and Ca²⁺ in soft, ion‐poor water. The affinity constant (K_m) did not vary significantly among treatments for either Na⁺ or Ca²⁺. J_max Na⁺ increased 30% in fish acclimated to HS for 5 weeks. Acclimation to low pH had no effect on J_max Na⁺ but this treatment was associated with a 32% decrease on whole body Na⁺ content, suggesting that fish were unable to compensate for the increased Na⁺ loss induced by extreme acidity. Exposure of fish to HS + low pH, the treatment most closely approximating to the conditions experienced by the species in its native environment, resulted in an increase in whole body Na⁺ by 31% relative to acclimation to low pH alone. J_max Ca²⁺ in cardinal tetras was high relative to that documented in other freshwater species acclimated to soft water (J_max= 30 nmol g^?1 h^?1). Prolonged exposure of fish to pH 3·72 inhibited J_max Ca²⁺ by 53%, although whole body Ca²⁺ content remained unchanged relative to control. Acclimation of fish to HS + low pH resulted in an increase of J_max Ca²⁺ by 166% relative to low pH alone. Collectively, these results suggest that HS protect cardinal tetras acclimated to soft, acidic waters by preventing excessive Na⁺ loss (as indicated by whole body Na⁺ content) and by stimulating Ca²⁺ uptake (as indicated by increased J_max Ca²⁺) to ensure proper homeostasis.     

High sodium intake enhances insulin-stimulated glucose uptake in rat epididymal adipose tissue

Objective: This study investigated the effect of different sodium content diets on rat adipose tissue carbohydrate metabolism and insulin sensitivity. Methods and Procedures: Male Wistar rats were fed on normal‐ (0.5% Na⁺; NS), high‐ (3.12% Na⁺; HS), or low‐sodium (0.06% Na⁺; LS) diets for 3, 6, and 9 weeks after weaning. Blood pressure (BP) was measured using a computerized tail‐cuff system. An intravenous insulin tolerance test (ivITT) was performed in fasted animals. At the end of each period, rats were killed and blood samples were collected for glucose and insulin determinations. The white adipose tissue (WAT) from abdominal and inguinal subcutaneous (SC) and periepididymal (PE) depots were weighed and processed for adipocyte isolation and measurement of in vitro rates of insulin‐stimulated 2‐deoxy‐d ‐[³H]‐glucose uptake (2DGU) and conversion of ‐[U‐¹⁴C]‐glucose into ¹⁴CO₂. Results: After 6 weeks, HS diet significantly increased the BP, SC and PE WAT masses, PE adipocyte size, and plasma insulin concentration. The sodium dietary content did not influence the whole‐body insulin sensitivity. A higher half‐maximal effective insulin concentration (EC₅₀) from the dose‐response curve of 2DGU and an increase in the insulin‐stimulated glucose oxidation rate were observed in the isolated PE adipocytes from HS rats. Discussion: The chronic salt overload enhanced the adipocyte insulin sensitivity for glucose uptake and the insulin‐induced glucose metabolization, contributing to promote adipocyte hypertrophy and increase the mass of several adipose depots, particularly the PE fat pad.     

High dietary sodium intake increases white adipose tissue mass and plasma leptin in rats

Objective: Salt restriction has been reported to increase white adipose tissue (WAT) mass in rodents. The objective of this study was to investigate the effect of different sodium content diets on the lipogenic and lipolytic activities of WAT. Research Methods and Procedures: Male Wistar rats were fed on normal‐sodium (NS; 0.5% Na⁺), high‐sodium (HS; 3.12% Na⁺), or low‐sodium (LS; 0.06% Na⁺) diets for 3, 6, and 9 weeks after weaning. Blood pressure (BP) was measured using a computerized tail‐cuff system. At the end of each period, rats were killed and blood samples were collected for leptin determinations. The WAT from abdominal and inguinal subcutaneous (SC), periepididymal (PE) and retroperitoneal (RP) depots was weighed and processed for adipocyte isolation, rate measurement of lipolysis and d ‐[U‐¹⁴C]‐glucose incorporation into lipids, glucose‐6‐phosphate dehydrogenase (G6PDH) and malic enzyme activity evaluation, and determination of G6PDH and leptin mRNA expression. Results: After 6 weeks, HS diet significantly increased BP; SC, PE, and RP WAT masses; PE adipocyte size; plasma leptin concentration; G6PDH activity in SC WAT; and PE depots and malic activity only in SC WAT. The leptin levels correlated positively with WAT masses and adipocyte size. An increase in the basal and isoproterenol‐stimulated lipolysis and in the ability to incorporate glucose into lipids was observed in isolated adipocytes from HS rats. Discussion: HS diet induced higher adiposity characterized by high plasma leptin concentration and adipocyte hypertrophy, probably due to an increased lipogenic capacity of WAT.     

Development of Na+ transport in the chicken colon

To evaluate the developmental changes in colonic Na⁺ transport, Na, K-ATPase activity and the sensitivity of the short-circuit current to amiloride were investigated. The amiloride-sensitive short-circuit current which represents the electrogenic, amiloride-sensitive Na⁺ transport through Na⁺ channels, was not present in chicken embryos but rose significantly after hatching in chicks which were kept on a low-salt diet. Amiloride-sensitive short-circuit current increased gradually but the plateau was not reached during the first 15 days of life. Drinking of 0.9% NaCl totally inhibited the induction of amiloride-sensitive Na⁺ transport. Na⁺, K⁺-ATPase activity increased during development but was not influenced by changes in salt intake. Na⁺ transport in chicken colon therefore undergoes profound developmental changes. The increase of Na⁺ transport refleets not only the adaptation of colonocytes to low salt intake but also the maturation of Na⁺ absorption in colon. The possible role of aldosterone in the adaptation to low-salt intake is discussed.Abbreviations LS low-salt - HS high-salt - I _sc short-circuit current     

Effects of caecal ligation and saline acclimation on plasma concentration and organ mass in male and female Pekin ducks,Anas platyrhynchos

Summary The intestinal caeca reabsorb urinary sodium chloride (NaCl) and water (Rice and Skadhauge 1982). Free water may be generated if the reabsorbed NaCl is secreted via salt gland secretion (Schmidt-Nielsen et al. 1958). Therefore ceacal ligation should (a) reduce hingut NaCl and water reabsorption, (b) enhance the increase in plasma osmolality during saline acclimation, and (c) affect drakes more than ducks. Twelve Pekin drakes and 13 Pekin ducks, Anas platyrhynchos, were caecally ligated or sham operated before acclimation to 450 mmol · 1 NaCl. Body mass, hematocrit, plasma osmolality, and inonic concentrations of plasma, cloacal fluid, and salt gland secretion were measured after each increase in drinking water salinity. Osmoregulatory organ masses were determined. Caecal ligation did not effect plasma osmolality or ion concentrations of plasma, cloacal fluid, or salt gland secretion, but reduced salt gland size in ducks. Drakes and ducks drinking fresh water had the same hematocrit, plasma osmolality, and plasma concentrations of Na⁺ and Cl^–. In both sexes exposure to 75 mmol · 1^-1 NaCl significantly decreased plasma [Na⁺] and doubled cloacal fluid [Na⁺]. Exposure to 450 mmol · 1^-1 NaCl decreased body mass and increased hematocrit, plasma [Na⁺], [Cl^–], and plasma osmolality (more in drakes than in ducks); cloacal fluid osmolality nearly doubled compared to freshwater-adapted ducks, due mainly to osmolytes other than Na⁺ and Cl^–. The [Cl^–] in salt gland secretion only slightly exceeded drinking water [Cl^–].Abbreviations AVT antiduretic hormone - CF cloacal fluid - ECFV extraoellular fluid volume - FW freshwater acclimated - Hct hematocrit - MDWE mean daily water flux - [Na ⁺]_cf cloacal fluid sodium concentration - [Na ⁺]_pl plasma sodium concentration - Osm _cf cloacal fluid osmolality - Osm _pl plasma osmolality - SGS salt gland secretion - TBW total body water     

Osmoregulation in Corophium curvispinum (Crustacea: Amphipoda), a recent coloniser of freshwater

Summary Sodium efflux in three populations of the freshwater amphipod Corophium curvispinum were measured seasonally over a 6-year period and compared to rates recorded in 1980. While continuing to show relatively high Na⁺ loss rates, compared to other freshwater amphipod species, sodium permeability (P_Na) has decreased significantly in the medium term (post 1983). P_Na also shows seasonal fluctuations in all populations. Changes in body sodium content (B^Na) and blood [Na⁺] were found during this period and some alteration of the kinetic characteristics, K _m and V _max, of the sodium uptake system has occurred. Acclimation to different [Na⁺] media, and to low and high temperatures produced significant changes in Na⁺ efflux. The importance of acclimation (acclimatization) and selection in reducing passive Na⁺ loss and effecting changes in Na⁺ regulation of this colonizing species are assessed in relation to environmental changes.     

Pericryptal Myofibroblast Growth in Rat Descending Colon Induced by Low-Sodium Diets Is Mediated by Aldosterone and not by Angiotensin II

Pericryptal myofibroblast growth in descending colonic crypts correlates with the activation of the renin-angiotensin-aldosterone system. Earlier work showed that during the transition from a high-Na⁺ (HS) to low-Na⁺ (LS) diet there are changes in the colonic crypt wall and pericryptal sheath. As LS diet increases both aldosterone and angiotensin II, the aim here was to determine their individual contributions to the trophic changes in colonic crypts. Experiments were conducted on control and adrenalectomized Sprague-Dawley rats fed an HS diet and then switched to LS diet for 3 days and supplemented with aldosterone or angiotensin II. The actions of the angiotensin-converting enzyme inhibitor captopril, the angiotensin receptor antagonist losartan and the aldosterone antagonist spironolactone on extracellular matrix proteins, claudin 4 and E-cadherin myofibroblast proteins, α-smooth muscle actin (α-SMA) and OB-cadherin (cadherin 11), angiotensin type 1 and TGFβr1 membrane receptors were determined by immunolocalization in fixed distal colonic mucosa. The LS diet or aldosterone supplementation following ADX in HS or LS increased extracellular matrix, membrane receptors and myofibroblast proteins, but angiotensin alone had no trophic effect on α-SMA. These results show that aldosterone stimulates myofibroblast growth in the distal colon independently of dietary Na⁺ intake and of angiotensin levels. This stimulus could be a genomic response or secondary to stretch of the pericryptal sheath myofibroblasts accompanying enhanced rates of crypt fluid absorption.     

Voltage dependence of the rheogenic Na+/K+ ATPase in the membrane of oocytes ofXenopus laevis

Summary Electrophysiological experiments were performed to analyze the Na⁺/K⁺-ATPase in full-grown prophase-arrested oocytes ofXenopus laevis. If the Na⁺/K⁺-ATPase is inhibited by dihydroouabain (DHO), the resting potential of the membrane of Na⁺-loaded oocytes may depolarize by nearly 50 mV. This hyperpolarizing contribution to the resting potential depends on the degree of activation of the Na⁺/K⁺-ATPase and varies with intra-cellular Na⁺ activity (a _Na ⁱ ), and extracellular K⁺ (K ₀ ⁺ ) It is concluded that variations ofa _Na ⁱ among different oocytes are primarily responsible for the variations of resting potentials measured in oocytes ofX. laevis. Under voltage-clamp conditions, the DHO-sensitive current also exhibits dependence ona _Na ⁱ that may be described by a Hill equation with a coefficient of 2. This current will be shown to be identical with the electrogenic current generated by the 3Na⁺/2K⁺ pump. The voltage dependence of the pump current was investigated at saturating values ofa _Na ⁱ (33 mmol/liter) and of K ₀ ⁺ (3 mmol/liter) in the range from –200 to +100 mV. The current was found to exhibit a characteristic maximum at about +20 mV. This is taken as evidence that in the physiological range at least two steps within the cycle of the pump are voltage dependent and are oppositely affected by the membrane potential.     

Aldosterone Reduces Crypt Colon Permeability during Low-Sodium Adaptation

Fluid and electrolyte absorption by colonic crypts depends on the transport properties of crypt cellular and paracellular routes and of the pericryptal sheath. As a low-Na⁺ diet increases aldosterone and angiotensin II secretion, either hormone could affect absorption. Control and adrenalectomized (ADX) Sprague-Dawley rats were kept at a high-NaCl (HS) diet and then switched to low-NaCl (LS) diet for 3 days. Aldosterone or angiotensin II plasma concentrations were maintained using implanted osmotic mini-pumps. The extracellular Na⁺ concentration in isolated rat distal colonic mucosa was determined by confocal microscopy using a low-affinity Na⁺-sensitive fluorescent dye (Sodium red, and Na⁺-insensitive BODIPY) bound to polystyrene beads. Crypt permeability to FITC-labelled dextran (10 kDa) was monitored by its rate of escape from the crypt lumen into the pericryptal space. Mucosal ion permeability was estimated by transepithelial electrical resistance (TER) and amiloride-sensitive short-circuit current (SCC). The epithelial Na⁺ channel, ENaC, was determined by immunolocalization. LS diet decreased crypt wall permeability to dextran by 10-fold and doubled TER. Following ADX, aldosterone decreased crypt wall dextran permeability, increased TER, increased Na⁺ accumulation in the pericryptal sheath and ENaC expression even in HS. Infusion of angiotensin II to ADX rats did not reverse the effects of aldosterone deprivation. These findings indicate that aldosterone alone is responsible for both the increase in Na⁺ absorption and the decreased paracellular and pericryptal sheath permeability.     

Changes in Sodium or Glucose Filtration Rate Modulate Expression of Glucose Transporters in Renal Proximal Tubular Cells of Rat

Renal glucose reabsorption is mediated by luminal sodium-glucose cotransporters (SGLTs) and basolateral facilitative glucose transporters (GLUTs). The modulators of these transporters are not known, and their substrates glucose and Na⁺ are potential candidates. In this study we examined the role of glucose and Na⁺ filtration rate on gene expression of glucose transporters in renal proximal tubule. SGLT1, SGLT2, GLUT1 and GLUT2 mRNAs were assessed by Northern blotting; and GLUT1 and GLUT2 proteins were assessed by Western blotting. Renal cortex and medulla samples from control rats (C), diabetic rats (D) with glycosuria, and insulin-resistant 15-month old rats (I) without glycosuria; and from normal (NS), low (LS), and high (HS) Na⁺-diet fed rats were studied. Compared to C and I rats, D rats increased (P < 0.05) gene expression of SGLT2 by ∼36%, SGLT1 by ∼20%, and GLUT2 by ∼100%, and reduced (P < 0.05) gene expression of GLUT1 by more than 50%. Compared to NS rats, HS rats increased (P < 0.05) SGLT2, GLUT2, and GLUT1 expression by ∼100%, with no change in SGLT1 mRNA expression, and LS rats increased (P < 0.05) GLUT1 gene expression by ∼150%, with no changes in other transporters. In summary, the results showed that changes in glucose or Na⁺ filtrated rate modulate the glucose transporters gene expression in epithelial cells of the renal proximal tubule. Received: 14 July 2000/Revised: 8 March 2001     

Air Displacement Plethysmography: Validation in Overweight and Obese Subjects

Objective: Patients with moderate and severe obesity, because of their physical size, often cannot be evaluated with conventional body composition measurement systems. The BOD POD air displacement plethysmography (ADP) system can accommodate a large body volume and may provide an opportunity for measuring body density (D_b) in obese subjects. D_b can be used in two‐ or three‐compartment body composition models for estimating total body fat in patients with severe obesity. The purpose of this study was to compare D_b measured by ADP to D_b measured by underwater weighing (UWW) in subjects ranging from normal weight to severely obese. Research Methods and Procedures: D_b was measured with UWW and BOD POD in 123 subjects (89 men and 34 women; age, 46.5 ± 16.9 years; BMI, 31.5 ± 7.3 kg/m²); 15, 70, and 10 subjects were overweight (25 ≤ BMI < 30 kg/m²), obese (30 ≤ BMI < 40 kg/m²), and severely obese (BMI ≥ 40 kg/m²), respectively. Results: There was a strong correlation between D_b(kilograms per liter) measured by UWW and ADP (r = 0.94, standard error of the estimate = 0.0073 kg/L, p < 0.001). Similarly, percent fat estimates from UWW and ADP using the two‐compartment Siri equation were highly correlated (r = 0.94, standard error of the estimate = 3.58%, p < 0.001). Bland‐Altman analysis showed no significant bias between D_b measured by UWW and ADP. After controlling for D_b measured by ADP, no additional between‐subject variation in D_b by UWW was accounted for by subject age, sex, or BMI. Discussion: Body density, an important physical property used in human body composition models, can be accurately measured by ADP in overweight and obese subjects.     

Sodium is required for nitrogenase activity in cyanobacteria

The cyanobacteriaAnabaena torulosa andAnabaena L-31 require sodium (Na⁺) for growth on N₂ but not in the presence of NH₄ ⁺. Na⁺-starved cultures show relatively little or no nitrogenase activity although they differentiate normal heterocysts. Nitrogenase activity appears rapidly on addition of Na⁺ to Na⁺-starved cultures. The time course of appearance of activity after addition of Na⁺ suggests that Na⁺ is involved in activation of the existing enzyme rather than in its de novo synthesis.     

Energetics of sulfate transport in Desulfomicrobium baculatum

The freshwater sulfate reducer Desulfomicrobium baculatum accumulated ³⁵S-sulfate up to 120-fold by an energy-dependent transport system, as was concluded from inhibition of transport by tetrachlorosalicylanilide (TCS). Sulfate accumulation was completely reversible and depended on the presence of sodium ions. The sodium ion gradient ([Na⁺]_out/[Na⁺]_in) was eightfold and was built up by electrogenic Na⁺/H⁺ antiport. Together with a membrane potential of-145 m V, the sodium ion motive force was-199 m V, from which a symport stoichiometry of two sodium ions per sulfate was calculated. This is the first report of a freshwater sulfate reducer taking up sulfate electroneutrally in symport with sodium ions and not with protons.Abbreviations ETH 2120 N,N'-Dibenzyl-N,N'-diphenyl-1,2-phenylendioxydiacetamide - TCS Tetrachlorosalicylanilide     

Regulation of Sodium Influx in the NaCl-Resistant (NaClr) Mutant Strain of the Cyanobacterium Anabaena variabilis

A NaCl^r mutant of the diazotrophic cyanobacterium Anabaena variabilis has been isolated by NTG mutagenesis and selection for NaCl resistance. The NaCl^r strain has been characterized with respect to its mechanism of NaCl tolerance and regulation of Na⁺ influx. NaCl^r strain exhibits low Na⁺ influx, accumulated high level of glycine betaine as a compatible solute, and persistent synthesis of SSPs at a higher rate than its wild-type counterpart. DCMU, an inhibitor of PS-II, inhibited Na⁺ influx, suggesting that Na⁺ influx is an energy-dependent process and that the energy is derived from photophosphorylation. This contention is further supported by the inhibition of Na⁺ influx under dark conditions. The inhibition of Na⁺ influx by KCN, DNP, NaN₃ also supports the involvement of oxidative phosphorylation in the regulation of active Na⁺ influx. Thus, it appears that the synthesis of SSPs, accumulation of compatible solutes, and exhibition of low Na⁺ influx in the NaCl^r strain made this organism NaCl tolerant. Received: 6 July 2000 / Accepted: 11 August 2000     

High‐Sensitivity C‐Reactive Protein in Japanese Patients with Type 2 Diabetes

Objective: To assess the relationship between high‐sensitivity (HS) C‐reactive protein (CRP) and metabolic syndrome (MetS) or atherosclerosis and to assess effects of strict metabolic control on the degree of inflammation and MetS in patients with type 2 diabetes. Research Methods and Procedures: Four hundred thirteen patients with diabetes were enrolled in the cross‐sectional study. Of these 413 patients, 161 patients were further admitted for 2.4 ± 0.4 weeks (mean ± SD) to investigate the change in HS‐CRP or other parameters under strict metabolic control. Results: Log‐transformed HS‐CRP value (log HS‐CRP) was strongly correlated with BMI (r = 0.448, p < 0.01). Log HS‐CRP was also correlated with the presence of MetS or each component of MetS. Furthermore, a positive significant trend in HS‐CRP levels was shown with an increasing number of MetS components (p < 0.05). Log HS‐CRP showed a significant positive correlation with carotid artery intima‐media thickness (IMT) (r = 0.152, p < 0.01). In multiple step‐wise regression analysis, BMI, hemoglobin A_1c, right IMT, duration of diabetes, and triglyceride were selected as explanatory variables for log HS‐CRP (R² = 0.412). Under strict metabolic control, HS‐CRP was significantly (p < 0.01) lower, together with lower levels of other markers for MetS. The change in HS‐CRP was significantly correlated with the change in BMI (r = 0.161, p = 0.04). Discussion: In subjects with type 2 diabetes, HS‐CRP levels are related to MetS and subclinical atherosclerosis. Strict weight management and metabolic control were associated with a reduction in HS‐CRP levels, and changes in HS‐CRP were related to changes in weight, supporting the hypothesis that lifestyle modification reduces inflammation and the risk of CHD.     

Ion Secretion and Isotonic Transport in Frog Skin Glands

The aim of this study was to clarify the mechanism of isotonic fluid transport in frog skin glands. Stationary ion secretion by the glands was studied by measuring unidirectional fluxes of ²⁴Na⁺, ⁴²K⁺, and carrier-free ¹³⁴Cs⁺ in paired frog skins bathed on both sides with Ringer's solution, and with 10⁻⁵ m noradrenaline on the inside and 10⁻⁴ m amiloride on the outside. At transepithelial thermodynamic equilibrium conditions, the ¹³⁴Cs⁺ flux ratio, J ^out _Cs/J ⁱⁿ _Cs, varied in seven pairs of preparations from 6 to 36. Since carrier-free ¹³⁴Cs⁺ entering the cells is irreversibly trapped in the cellular compartment (Ussing & Lind, 1996), the transepithelial net flux of ¹³⁴Cs⁺ indicates that a paracellular flow of water is dragging ¹³⁴Cs⁺ in the direction from the serosal- to outside solution. From the measured flux ratios it was calculated that the force driving the secretory flux of Cs⁺ varied from 30 to 61 mV among preparations. In the same experiments unidirectional Na⁺ fluxes were measured as well, and it was found that also Na⁺ was subjected to secretion. The ratio of unidirectional Na⁺ fluxes, however, was significantly smaller than would be predicted if the two ions were both flowing along the paracellular route dragged by the flow of water. This result indicates that Na⁺ and Cs⁺ do not take the same pathway through the glands. The flux ratio of unidirectional K⁺ fluxes indicated active secretion of K⁺. The time it takes for steady-state K⁺ fluxes to be established was significantly longer than that of the simultaneously measured Cs⁺ fluxes. These results allow the conclusion that — in addition to being transported between cells — K⁺ is submitted to active transport along a cellular pathway.Based on the recirculation theory, we propose a new model which accounts for stationary Na⁺, K⁺, Cl⁻ and water secretion under thermodynamic equilibrium conditions. The new features of the model, as compared to the classical Silva-model for the shark-rectal gland, are: (i) the sodium pumps in the activated gland transport Na⁺ into the lateral intercellular space only. (ii) A barrier at the level of the basement membrane prevents the major fraction of Na⁺ entering the lateral space from returning to the serosal bath. Thus, Na⁺ is secreted into the outside bath. It has to be assumed then that the Na⁺ permeability of the basement membrane barrier (P ^BM _Na) is smaller than the Na⁺ permeability of the junctional membrane (P ^JM _Na), i.e., P ^JM _Na/P ^BM _Na > 1. The secretory paracellular flow of water further requires that the Na⁺ reflection coefficients (σ_Na) of the two barriers are governed by the conditions, σ^BM _Na > 0, and σ^BM _Na > σ^JM _Na. (iii) Na⁺ channels are located in the apical membrane of the activated gland cells, so that a fraction of the Na⁺ outflux appearing downstream the lateral intercellular space is recirculated by the gland cells. Based on measured unidirectional fluxes, a set of equations is developed from which we estimate the ion fluxes flowing through major pathways during stationary secretion. It is shown that 80% of the sodium ions flowing downstream the lateral intercellular space is recycled by the gland cells. Our calculations also indicate that under the conditions prevailing in the present experiments 1.8 ATP molecule would be hydrolyzed for every Na⁺ secreted to the outside bath. Received: 30 January 1996/Revised: 12 March 1996     

Sodium transport in filamentous nitrogen fixing cyanobacteria

Two filamentous, nitrogen fixing cyanobacteria were examined for their salt tolerance and sodium (Na⁺) transport.Anabaena torulosa, a saline form, grew efficiently and fixed nitrogen even at 150 mM salt (NaCl) concentration while,Anabaena L-31, a fresh water cyanobacterium, failed to grow beyond 35 mM NaCl.Anabaena torulosa showed a rapidly saturating kinetics of Na⁺ transport with a high affinity for Na⁺ (K _m, 0.3 mM).Anabaena L-31 had a much lower affinity for Na⁺ (K_m, 2.8 mM) thanAnabaena torulosa and the pattern of uptake was somewhat different. BothAnabaena spp. exhibited an active Na⁺ extrusion which seems to be mediated by a Na⁺-K⁺ ATPase and aided by oxidative phosphorylation.Anabaena L-31 was found to retain much more intracellular Na⁺ thanAnabaena torulosa. The results suggest that the saline form tolerates high Na⁺ concentrations by curtailing its influx and also by an efficient Na⁺ extrusion, although these alone may not entirely account for its success in saline environment.     

Intracellular sodium homeostasis in relation to the effective free-energy change of ATP hydrolysis: studies of crayfish muscle fibers

We investigated the impact of reductions in the effective free-energy change of ATP hydrolysis (dG/d_ATP) on intracellular sodium homeostasis in bundles of fibers from the abdominal extensor muscle of the crayfish Procambarus clarkii. ³¹P nuclear magnetic resonance (NMR) spectroscopy was used to monitor high-energy phosphate levels and intracellular pH while interleaved ²³Na-NMR spectra were acquired to monitor changes in sodium. Previous work has shown that the bulk of intracellular Na⁺ is NMR visible (see Ivanics et al. 1994). The ²³Na-NMR spectra were diffusion-weighted which effectively filtered out signal contributions from extracellular sodium. The efficacy of this procedure was validated using a relatively non-toxic chemical shift reagent which allowed resolution of extracellular and intracellular Na⁺ signals. Metabolic inhibition (cyanide/iodoacetate) produced pronounced reductions in dG/d_ATP coincident with dramatic increases in intracellular Na⁺ levels ([Na⁺]_i). However, the increases in [Na⁺]_i occurred at dG/d_ATP values well above the threshold value of −46 kJ · mol⁻¹ required by the existing Na⁺ gradient and the membrane potential. These results suggest that the global dG/d_ATP value may not reflect the dG/d_ATP value in the vicinity of the pump. Alternatively, other factors, including low molecular modulators of Na⁺, K⁺-ATPase activity, may be important in this context. Accepted: 15 May 1997     

Effect of Family History of Type 2 Diabetes on White Blood Cell Count in Adult Women

Objective: To evaluate the effect of a first‐degree family history of type 2 diabetes on white blood cell (WBC) count, a risk factor for atherosclerotic vascular disease, in glucose‐tolerant adult women Research Methods and Procedures: WBC count was measured in 174 normal weight, overweight, and obese female offspring of type 2 diabetic patients (FH⁺) and 174 age‐ and BMI‐matched female controls with no family history of type 2 diabetes (FH^?). Other measurements included fat mass (FM), measured by body impedance analysis; central fat accumulation, evaluated by waist circumference; insulin resistance, estimated by homeostatic model assessment for insulin resistance (HOMA_IR); systolic and diastolic blood pressure; and fasting concentrations of glucose, insulin, and lipids. Results: WBC count, waist circumference, systolic blood pressure, and fasting levels of glucose, insulin, and triglycerides were significantly higher in FH⁺ than in FH^? subjects. In FH⁺ individuals, WBC count was positively associated with BMI, FM, waist circumference, HOMA_IR, and triglyceride and insulin concentrations, and negatively correlated with age and high‐density lipoprotein‐cholesterol. In FH^? subjects, WBC count was directly associated with BMI, FM, waist circumference, and triglyceride and insulin concentrations, and inversely correlated with age and high‐density lipoprotein‐cholesterol. After multivariate analyses, WBC count maintained a significant association with age, systolic blood pressure, and HOMA_IR in FH⁺ subjects and with age, BMI, FM, and triglycerides in FH^? individuals. Discussion: This study indicates that WBC count is increased in adult women with genetic predisposition to type 2 diabetes, and its main correlates are insulin resistance in FH⁺ and adiposity in FH^? individuals.     

Role of sodium ions for sulfate transport and energy metabolism in Desulfovibrio salexigens

The sodium ion gradient and the membrane potential were found to be the driving forces of sulfate accumulation in the marine sulfate reducer Desulfovibrio salexigens. The protonmotive force of –158 mV, determined by means of radiolabelled membrane-permeant probes, consisted of a membrane potential of –140 mV and a pH gradient (inside alkaline) of 0.3 at neutral pH_out. The sodium ion gradient, as measured with silicone oil centrifugation and atomic absorption spectroscopy, was eightfold ([Na⁺]_out/[Na⁺]_in) at an external Na⁺ concentration of 320 mM. The resulting sodium ionmotive force was –194 mV and enabled D. salexigens to accumulate sulfate 20000-fold at low external sulfate concentrations (<0.1 M). Under these conditions high sulfate accumulation occurred electrogenically in symport with three sodium ions (assuming equilibrium with the sodium ion-motive force). With increasing external sulfate concentrations sulfate accumulation decreased sharply, and a second, low-accumulating system symported sulfate electroneutrally with two sodium ions. The sodium-ion gradient was built up by electrogenic Na⁺/H⁺ antiport. This was demonstrated by (i) measuring proton translocation upon sodium ion pulses, (ii) studying uptake of sodium salts in the presence or absence of the electrical membrane potential, and (iii) the inhibitory effect of the Na⁺/H⁺ antiport inhibitor propylbenzilylcholin-mustard HCl (PrBCM). With resting cells ATP synthesis was found after proton pulses (changing the pH by three units), but neither after pulses of 500 mM sodium ions, nor in the presence of the uncoupler tetrachorosalicylanilide (TCS). It is concluded that the energy metabolism of the marine strain D. salexigens is based primarily on the protonmotive force and a protontranslocating ATPase.Abbreviations MOPS morpholinopropanesulfonic acid - TCS tetrachlorosalicylanilide - PrBCM propylbenzilylcholin-mustard HCl - Tris tris(hydroxymethyl)aminomethane - TPP⁺ bromide tetraphenylphosphonium bromide