Quantitative changes in potassium,sodium, and calcium in the submaxillary salivary gland and blood serum of rats exposed to 2880-MHz microwave radiation

Na⁺, K⁺, and Ca²⁺ concentrations in the blood serum and submaxillary salivary gland (SSG) were investigated in adult, male rats exposed to 2880-MHz microwaves modulated with 1.5-μs pulses at a pulse repetition rate of 1000 Hz or in a hyperthermal environment. Rats were exposed, one at a time, for 30 min to microwaves producing a specific absorption rate (SAR) of: 4.2, 6.3,6.8,8.4, 10.8, or 12.6 W/kg, or were sham exposed under similar environmental conditions. In a second series, one group of rats was exposed singly for 15, 30, or 60 min to microwaves producing an SAR of 9.5 W/kg and other rats were exposed for similar periods at 40 °C; and 10 rats were sham exposed. Flame photometric analysis indicated that the thresholds of microwave radiation required to induce a change in Na⁺, K⁺, and Ca²⁺ concentrations in the salivary glands are 6.8, 6.8, and 6.3 W/kg, respectively. The directions of Na⁺, K⁺, and Ca²⁺ ion shifts in exposed rats' salivary glands are similar, whether affected by microwaves or hyperthermia. Greater changes in Na⁺ and K⁺ concentrations in SSG of rats exposed to microwaves for 15 and 30 min were found than in those exposed at 40 °C. On the other hand, exposure to hyperthermia at 40 °C or to microwaves for 1 h caused Na⁺ concentration to be increased by 68.7 and 59.5% and K⁺ concentration to be decreased by 29.6 and 21.7%, respectively.     

Sulfatide role in the sodium pump

Summary Sodium efflux was studied in²²Na-loaded red blood cells in the presence of arylsulfatase, an enzyme that specifically hydrolyzes sulfatide. Sodium efflux was inhibited in proportion to the amount of arylsulfatase present. Maximum inhibition was almost as high as the efflux obtained in medium with K⁺ absent. At maximum inhibition 83.2% of the sulfatide content of the fragmented red blood cell membranes was hydrolyzed and ouabain-sensitive (Na⁺+K⁺)-ATPase activity was inhibited by 100%. Sodium efflux, sulfatide content, and (Na⁺+K⁺)-ATPase activity were unaffected with arylsulfatase in the presence of a high concentration of sulfatide. These results indicate that sulfatide plays a specific role in sodium and potassium ion transport. They also suggest that most sulfatide is localized externally in the red blood cell membrane.     

Effects of lead chloride on human erythrocyte membranes and on kinetic anion sulphate and glutathione concentrations

Our study concerns the effects of exposure to lead chloride on the morphology, K⁺ efflux, SO₄ ^? influx and GSH levels of the human erythrocyte. Blood was collected in heparinized tubes and washed three times. The cells were suspended at 3% hematocrit and incubated for 1 h at 25°C in a medium containing increasing concentrations of lead chloride (0, 0.3, 0.5 and 1 ??M). After incubation, the suspensions were centrifuged and the erythrocyte pellets were divided into three aliquots for testing. The results show: an increase in the permeability of erythrocytes treated with lead chloride with consequent damage and cellular death, especially in the presence of high concentrations; an increase in potassium ion efflux; alterations in the morphology and membrane structure of the red blood cells; and a decrease in sulphate uptake, due either to the oxidative effect of this compound on the band 3 protein, which loses its biological valence as a carrier of sulphate ions, or to a decrease in the ATP erythrocyte concentration. In conclusion, the exposure of erythrocytes to Pb²⁺ ions leads to a reduction in the average lifetime of the erythrocytes and the subsequent development of anemia. These data are discussed in terms of the possible effect of lead on the reduction-oxidation systems of the cell. Oxidant agents, such as lead, are known to cross-link integral membrane proteins, leading to K/Cl-cotransport. The increased K⁺ efflux affects the altered redox state.     

39K nuclear magnetic resonance and a mathematical model of K+ transport in human erythrocytes

³⁹K nuclear magnetic resonance was used to measure the efflux of K⁺ from suspensions of human erythrocytes [red blood cells (RBCs)], that occurred in response to the calcium ionophore, A23187 and calcium ions; the latter activate the Gárdos channel. Signals from the intra- and extracellular populations of ³⁹K⁺ were selected on the basis of their longitudinal relaxation times, T ₁, by using an inversion- recovery pulse sequence with the mixing time, τ₁, chosen to null one or other of the signals. Changes in RBC volume consequent upon efflux of the ions also changed the T ₁ values so a new theory was implemented to obviate a potential artefact in the data analysis. The velocity of the K⁺ efflux mediated by the Gárdos channel was 1.19±0.40 mmol (L RBC)⁻¹ min⁻¹ at 37°C.     

Transbilayer movement of 24Na in sonicated phosphatidylcholine vesicles exposed to frequency-modulated microwave radiation

Sonicated egg phosphatidylcholine vesicles loaded with ²⁴Na⁺ were exposed at 20mW to a frequency-modulated (3 Hz) microwave field in the range of 2350 to 2550 MHz, or at 80 mW to a 2450-MHz CW (continuous wave) field, in a waveguide. The vesicle suspension absorbed microwaves at about 1 mW/ml and 25 mW/ml (CW experiment). The average temperature change of the irradiated suspension was < 0.1 °C from ambient. Leakage of ²⁴Na⁺ from the vesicles for up to 19 hours was measured. No difference was noted in the movement of ²⁴Na⁺ from the vesicles in the irradiated and control dispersions.     

Effects of exposure to electromagnetic field from 915 MHz radiofrequency identification system on circulating blood cells in the healthy adult rat

We investigated whether exposure to the 915 MHz radiofrequency identification (RFID) signal affected circulating blood cells in rats. Sprague–Dawley rats were exposed to RFID at a whole‐body specific absorption rate of 2 W/kg for 8 h per day, 5 days per week, for 2 weeks. Complete blood counts were performed after RFID exposure, and the CD4⁺/CD8⁺ ratio was determined by flow cytometry. The number of red blood cells (RBCs) and the values of hemoglobin, hematocrit, and RBC indices were increased in the RFID‐exposed group compared with those in the cage‐control and sham‐exposed groups (P < 0.05). However, the RBCs and platelet numbers were within normal physiologic response ranges. The number of white blood cells, including lymphocytes, was decreased in RFID‐exposed rats. However, there was no statistically significant difference between the sham‐exposed and RFID‐exposed groups in terms of T‐cell counts or CD4⁺/CD8⁺ ratio (P > 0.05). Although the number of circulating blood cells was significantly altered by RFID exposure at a whole‐body specific absorption rate of 2 W/kg for 2 weeks, these changes do not necessarily indicate that RFID exposure is harmful, as they were within the normal physiological response range. Bioelectromagnetics. 39:68–76, 2018. © 2017 Wiley Periodicals, Inc.     

Lipophilic impurity of phenol red is a potent cation transport modulator

Previously, we described substantial alterations in the Na⁺ and K⁺ homeostasis of human skin fibroblasts following removal of fetal bovine serum (FBS). Herein, we report that FBS removal per se does not cause any cellular ionic changes unless a lipophilic impurity of commercial phenol red preparations is present. This substance accelerates ⁸⁶Rb⁺ efflux four to seven times, causes a four to eight time increase in cellular Na⁺, and a 40–70% reduction in cellular K⁺ contents. FBS (10%) or albumin (0.8%) appears to bind the impurity thus inhibiting its action. The increased cellular Na⁺ and decreased K⁺ contents do not return to baseline within 4 hours following the removal of the phenol red extract. However, albumin completely reverses the cellular cationic changes that develop during a 2 hour exposure of the cells to the free substance. The reversibility of its action by albumin suggests that the substance exerts its effect on or within the cell membrane and not intracellularly. Among seven different cell lines tested the ⁸⁶Rb⁺ efflux from, and the Na⁺-K⁺ contents of, COS-7 and Hs68 cells also responded to unpurified phenol red in a way similar to human fibroblasts. The amount of the phenol red contaminant is manufacturer dependent. As little as 0.5 μM phenol red, from one vendor, was sufficient to elicit response in the ⁸⁶Rb⁺ efflux. Given that the impurity is unlikely to be more than a small fraction of phenol red, it seems to be a potent ionic transport modulator. Based on these results, the presence of commercial phenol red in serum-free growth or test media, including the increasing variety of chemically defined culture media, should be considered as a potential confounding factor in measurements that depend on intracellular Na⁺-K⁺ homeostasis. The findings of such earlier studies may need to be reconsidered if the cells were exposed to unbound phenol red. We recommend that, until the manufacturers further refine their product, phenol red be purified by ether extraction before its use. The evaluation of the potential physiologic or pharmacologic relevance of this potent cation transport modulator awaits its isolation. © 1993 Wiley-Liss, Inc.     

Potassium fluxes across the blood brain barrier of the cockroach, Periplaneta americana

Potassium fluxes across the blood-brain barrier of the cockroach Periplaneta americana were measured using the scanning ion-selective microelectrode technique. In salines containing 15 mM or 25 mM K⁺, an efflux of K⁺ from the ganglia of isolated nerve cords was counterbalanced by an influx across the connectives. Metabolic inhibition with CN⁻ resulted in an increase in K⁺ efflux across both the ganglia and the connectives. Depletion of K⁺ by chilling the nerve cords in K⁺-free saline was associated with subsequent K⁺ influx across the connectives in K⁺-replete saline at room temperature. There were dramatic increases in K⁺ efflux across both ganglia and connectives when the nerve cords were exposed to the pore-forming antibiotic amphotericin B. K⁺ fluxes across the ventral nerve cord were also altered when paracellular leakage was augmented by transient exposure to 3 M urea. K⁺ efflux was reduced by the K⁺ channel blockers Ba²⁺ and tetraethylammonium or by exposure to Ca²⁺-free saline and K⁺ efflux from the ganglia was increased by addition of ouabain to the bathing saline. The results provide direct support for a model proposing that K⁺ is cycled through a current loop between the ganglia and the connectives and that both the Na⁺/K⁺-ATPase and K⁺ channels are implicated in extracellular K⁺ homeostasis within the central nervous system.     

Effects of haemoglobin O2 saturation on volume regulation in adrenergically stimulated red blood cells from the trout, Oncorhynchus mykiss

Adrenergic stimulation of trout red blood cells activates a Na⁺/H⁺-exchange. If unopposed, the ensuing increase in cell Na⁺ leads to an isosmotic cell swelling. In this study the effect of the level of haemoglobin O₂ saturation on volume regulation has been investigated in adrenergically stimulated red blood cells from trout: at full haemoglobin O₂ saturation, net influx of Na⁺ through the Na⁺/H⁺-exchanger was balanced by net efflux of K⁺ and no increases in cell volume took place. In contrast, at low O₂ saturation (8–14%) adrenergic stimulation led to a substantial increase in cell Na⁺, K⁺ and volume. Moreover, cell volume recovery after adrenergic swelling was incomplete at low O₂ saturation, whereas cells at high O₂ saturation exhibited a fast and complete cell volume recovery. In cells exposed to alternating high and low O₂ saturation, volume regulation was similar to the regulation found in cells maintained at high O₂ saturation. In cells at high O₂ saturation, extrusion of cellular Na⁺ by the Na⁺/K⁺-pump significantly contributed to the volume decrease. It is concluded that trout red blood cells at high or alternating O₂ saturations possess a powerful regulatory volume decrease response that is shut off at low O₂ saturation. The physiological implications of this regulation is discussed. Accepted: 30 September 1996     

Transient Activation of Plasmalemma K Efflux and H Influx in Tobacco by a Pectate Lyase Isozyme from Erwinia chrysanthemi

A purified pectate lyase isozyme derived from Erwinia chrysanthemi induced rapid net K⁺ efflux and H⁺ influx in suspension-cultured tobacco cells. Comparable fluxes of other ions (Na⁺, Cl⁻) were not observed. The K⁺ efflux/H⁺ influx response began within 15 minutes after addition of enzyme to cell suspensions and continued for approximately 1 hour after which cells resumed the net H⁺ efflux exhibited prior to enzyme treatment. The response was not prolonged by a second enzyme dose 1 hour after the first. The K⁺/H⁺ response was characterized by saturation at low enzymic activity (2 × 10⁻³ units per milliliter), and inhibition by the protonophore, carbonyl cyanide m-chlorophenylhydrazone, and was not associated with membrane leakiness caused by structural cell wall damage. The total K⁺ loss and H⁺ uptake induced by enzyme was one-fourth to one-third that induced by Pseudomonas syringae pv. pisi and did not reduce cell viability. These results indicate that pectate lyase induces a K⁺ efflux/H⁺ influx response in tobacco similar to but of shorter duration than that induced by P. syringae pv. pisi during the hypersensitive response. Pectate lyase or other cell wall degrading enzymes may therefore influence the induction of hypersensitivity.     

Alkaline pH and Internal Calcium Increase Na+ and K+ Effluxes in LK Sheep Red Blood Cells in Cl−-free Solutions

We examined the effects of pH, internal ionized Ca (Ca²⁺ _i ), cellular ATP, external divalent cations and quinine on Cl-independent ouabain-resistant K⁺ efflux in volume-clamped sheep red blood cells (SRBCs) of normal high (HK) and low (LK) intracellular K⁺ phenotypes. In LK SRBCs the K⁺ efflux was higher at pH 9.0 (350%) than at pHs 7.4 and 6.5, and was inhibited by external divalent cations, quinine, and cellular ATP depletion. The above findings suggest that the increased K⁺ efflux at alkaline pH is due to the opening of ion channels or specific transporters in the cell membrane. In addition, K⁺ efflux was activated (100%) when Ca²⁺ _i was increased (+A23187, +Ca²⁺ _o ) into the μm range. However, in comparison to human red blood cells, the Ca²⁺ _i -induced increase in K⁺ efflux in LK SRBCs was fourfold smaller and insensitive to quinine and charybdotoxin. The Na⁺ efflux was also higher at pH 9.0 than at pH 7.4, and activated (about 40%) by increasing Ca²⁺ _i . In contrast, in HK SRBCs the K⁺ efflux at pH 9.0 was neither inhibited by quinine nor activated by Ca²⁺ _i . These studies suggest the presence in LK SRBCs, of at least two pathways for Cl⁻-independent K⁺ and Na⁺ transport, of which one is unmasked by alkalinization, and the other by a rise in Ca²⁺ _i . Received: 23 May 1996/Revised: 6 December 1996     

Effect of hexachlorophene on monovalent cation transport in human erythrocytes a mechanism for hexachlorophene-induced hemolysis

Hexachlorophene-induced hemolysis, as studied by phase contrast microscopy, appeared to be a result of osmotic swelling. Both swelling and subsequent hemolysis were markedly delayed by addition of the non-penetrating solute sucrose to the incubation mixture. Binding studies indicated that hexachlorophene is associated primarily with the erythrocyte membrane, the remainder being found in the cytoplasm. Hexachlorophane induced a dose-dependent, first-order efflux of Na⁺ and K⁺ from red cells. The rates of hemolysis and K⁺ efflux induced by hexachlorophene were much greater than would be expected if this compound were acting simply as a metabolic inhibitor and/or an inhibitor of (Na⁺-K⁺-Mg²⁺)-ATPase. It is suggested that hexachlorophene induces the efflux of Na⁺ and K⁺ from red cells by directly altering the permeability of the cellular membrane. Further, hexachlorophene-induced hemolysis is probably a secondary event resulting from osmotic swelling subsequent to increased membrane permeability.     

Peculiarities of osmoregulation of circulating red blood cells in steno-and euryhaline marine fish species under hypoosmotic conditions

The peculiarities of osmoregulation of circulating red blood cells of the stenohaline giant gobyGobius cobitis and the euryhaline toad gobyGobius batrachocephalus have been studied under experimental conditions. In the giant goby, volume of the red blood cells increased steadily by 10.6–18.1% (p < 0.05) after reduction of the medium salinity from 15–17 to 6.0–6.8‰ and this volume increase remained during the entire experimental period (40–45 days). Lysis of red blood cells was noticed in some cases, which was indicated by a decrease of the number of red blood cells and an increase of concentration of free hemoglobin in the blood plasma. No similar reactions were observed in the euryhaline toad goby; the mean cell volume did not change statistically significantly. The volume regulation resulted in K⁺ efflux from red blood cells. The blood red cells of the toad goby had a high resistance to osmotic stress. The Na⁺,K⁺-ATPase activity in the red blood cell membranes of the toad goby was higher by 18.8% (p < 0.001) than in the giant goby.     

Inhibition of Na+, K+-ATPase activates swelling-induced taurine efflux in a human neuroblastoma cell line

The Na⁺ pump (Na⁺, K⁺-ATPase) has been implicated in the regulation of many cellular functions, including cell volume regulation. The effects of inhibiting Na⁺ pump activity on cell volume and taurine efflux were evaluated in the human neuroblastoma cell line CHP-100. Cell volume changes monitored with the Coulter Multisizer technique and confocal microscopy showed that neuroblastoma cells exposed to ouabain swelled by 22 ± 4% (n = 5). The rapid cell swelling was followed by regulatory volume decrease (RVD). In cells treated with ouabain, ¹⁴C-taurine efflux increased by 183 ± 11% compared with controls. However, cells exposed simultaneously to ouabain and hypoosmotic solution resulted in a ¹⁴C-taurine efflux of 207 ± 18%. Western blot and immunofluorescence microscopy with specific monoclonal antibodies for the catalytic α isoforms of Na⁺, K⁺-ATPase demonstrated high levels of the ubiquitously expressed α1 and the neuronal-specific α3. Ouabain-binding data showed that CHP-100 cells express ∼3 × 10⁵ pump units/cell. The present data indicate that efflux of taurine may be involved during volume recovery subsequent to blockade of Na⁺, K⁺-ATPase in CHP-100 cells. J. Cell. Physiol. 174:145–153, 1998. © 1998 Wiley-Liss, Inc.     

Peculiarities of osmoregulation of circulating red blood cells in steno- and euryhaline marine fish species under hypoosmotic conditions

The peculiarities of osmoregulation of circulating red blood cells of the stenohaline giant gobyGobius cobitis and the euryhaline toad gobyGobius batrachocephalus have been studied under experimental conditions. In the giant goby, volume of the red blood cells increased steadily by 10.6–18.1% (p (WENA) 0.05) after reduction of the medium salinity from 15–17 to 6.0–6.8‰ and this volume increase remained during the entire experimental period (40–45 days). Lysis of red blood cells was noticed in some cases, which was indicated by a decrease of the number of red blood cells and an increase of concentration of free hemoglobin in the blood plasma. No similar reactions were observed in the euryhaline toad goby; the mean cell volume did not change statistically significantly. The volume regulation resulted in K⁺ efflux from red blood cells. The blood red cells of the toad goby had a high resistance to osmotic stress. The Na⁺,K⁺-ATPase activity in the red blood cell membranes of the toad goby was higher by 18.8% (p (WENA) 0.001) than in the giant goby.     

Lithium Treatment Aggregates the Adverse Effects on Erythrocytes Subjected to Arsenic Exposure

The present study was designed to investigate the effects of lithium treatment on red blood cells which were given arsenic exposure. Long-term lithium therapy is being extensively used for the treatment of bipolar disorders. Arsenic is a group I carcinogen and a major toxic pollutant in drinking water that affects millions of people worldwide. Male SD rats were segregated into four groups, viz. normal control, lithium treated, arsenic treated, and lithium + arsenic treated. Lithium was supplemented as lithium carbonate at a dose level of 1.1 g/kg diet for a period of 8 weeks. Arsenic was given in the form of sodium arsenite at a dose level of 100 ppm in drinking water, ad libitum, for the same period. Lysates of red blood cells were used to investigate the effects of lithium and arsenic treatments on anti-oxidant enzymes, reduced glutathione (GSH), and lipid peroxidation (LPO) levels. Various hematological parameters, activities of Na⁺ K⁺ ATPase and delta-aminolevulinic acid dehydratase (δ-ALAD) were also assessed. A significant reduction was observed in the activities of antioxidant enzymes, GSH levels, total erythrocyte counts, Na⁺ K⁺ ATPase, and ALAD enzyme activities in lysates of red blood cells when exposed either to lithium or arsenic. In addition, a significant increase in the levels of malondialdehyde (MDA), lymphocytes, neutrophils, and total leukocytes was also observed following lithium as well as arsenic treatments. However, when arsenic-treated rats were subjected to lithium treatment, a pronounced alteration was noticed in all the above parameters. Therefore, we conclude that lithium supplementation to the arsenic-treated rats enhances the adverse effects on red blood cells and therefore use of lithium may not be medicated to patients who are vulnerable to arsenic exposure through drinking water. It can also be inferred that adverse effects of lithium therapy may get aggravated in patients thriving in the arsenic-contaminated area.

     

K+-dependent net Na+ efflux in roots of barley plants

Summary The influence of K⁺ ions on the net Na⁺ fluxes in cells of excised barley roots (Hordeum distichon L.) and roots of whole barley plants was investigated. The fluxes were determined by flame photometry in the external solution. In both cases a transient net Na⁺ efflux against the external Na⁺ concentration was observed upon addition of K⁺. The results stress the effectiveness of the K⁺-dependent Na⁺ efflux mechanism residing at the plasmalemma, and its involvement in K–Na-selectivity in whole barley plants.     

Volume-stimulated,Cl−-dependent K+ efflux is highly expressed in young human red cells containing normal hemoglobin or HbS

Summary We report here that a Cl^–-dependent K^– (KCl) efflux, which is stimulated by N-ethylmaleimide, (NEM) and by increased red cell volume, exists in young red cells of individuals with normal hemoglobin A (AA) and in those homozygous for hemoglobin S (SS). We have investigated this KCl efflux in several density-defined red cell fractions obtained from Percoll-Stractan continuous density gradients. We found high activity of the NEM-stimulated KCl transport in reticulocytes and young red cells from nine sickle cell (SS) patients (43±27 mean±sd mmol K⁺/liter of cells/hr=flux units (FU)) and in the young cell fraction of three AA individuals with high reticulocytosis recuperating from nutritional anemias (41.7±10 FU). In addition, we observed significant interindividual variation of this KCl efflux in the discocyte fraction of SS blood. Cell swelling markedly stimulated the KCl efflux, in SS whole blood (9.8±7.4 FU, in SS young cells (13±13 FU), and in AA young cells (21.4±11 FU). The activity of the Na–K–Cl cotransport, as estimated by the bumetanide sensitive K⁺ efflux was not found to be cell-age dependent in either AA or SS cells.Measurements of red cell density by isopycnic gradients indicated that 27% of the young cells reduce their volume by a Cl^–-dependent process in hypotonic or low pH-induced swelling.The large volume-stimulated KCl efflux in AA young cells raises the possibility that these fluxes may be involved in the maturation of erythropoietic precursors. The high activity in the red cells of sickle cell anemia patients and its interindividual variation may have pathophysiological consequences since it reverses the decrease in the intracellular concentration of hemoglobin which occurs in response to low pH or osmolarity, an unwelcome pro-sickling event.     

C-peptide,Na+,K+-ATPase,and Diabetes

Na⁺,K⁺-ATPase is an ubiquitous membrane enzyme that allows the extrusion of three sodium ions from the cell and two potassium ions from the extracellular fluid. Its activity is decreased in many tissues of streptozotocin-induced diabetic animals. This impairment could be at least partly responsible for the development of diabetic complications. Na⁺,K⁺-ATPase activity is decreased in the red blood cell membranes of type 1 diabetic individuals, irrespective of the degree of diabetic control. It is less impaired or even normal in those of type 2 diabetic patients. The authors have shown that in the red blood cells of type 2 diabetic patients, Na⁺,K⁺-ATPase activity was strongly related to blood C-peptide levels in non–insulin-treated patients (in whom C-peptide concentration reflects that of insulin) as well as in insulin-treated patients. Furthermore, a gene-environment relationship has been observed. The alpha-1 isoform of the enzyme predominant in red blood cells and nerve tissue is encoded by the ATP1A1 gene.Apolymorphism in the intron 1 of this gene is associated with lower enzyme activity in patients with C-peptide deficiency either with type 1 or type 2 diabetes, but not in normal individuals. There are several lines of evidence for a low C-peptide level being responsible for low Na⁺,K⁺-ATPase activity in the red blood cells. Short-term C-peptide infusion to type 1 diabetic patients restores normal Na⁺,K⁺-ATPase activity. Islet transplantation, which restores endogenous C-peptide secretion, enhances Na⁺,K⁺-ATPase activity proportionally to the rise in C-peptide. This C-peptide effect is not indirect. In fact, incubation of diabetic red blood cells with C-peptide at physiological concentration leads to an increase of Na⁺,K⁺-ATPase activity. In isolated proximal tubules of rats or in the medullary thick ascending limb of the kidney, C-peptide stimulates in a dose-dependent manner Na⁺,K⁺-ATPase activity. This impairment in Na⁺,K⁺-ATPase activity, mainly secondary to the lack of C-peptide, plays probably a role in the development of diabetic complications. Arguments have been developed showing that the diabetesinduced decrease in Na⁺,K⁺-ATPase activity compromises microvascular blood flow by two mechanisms: by affecting microvascular regulation and by decreasing red blood cell deformability, which leads to an increase in blood viscosity. C-peptide infusion restores red blood cell deformability and microvascular blood flow concomitantly with Na⁺,K⁺-ATPase activity. The defect in ATPase is strongly related to diabetic neuropathy. Patients with neuropathy have lower ATPase activity than those without. The diabetes-induced impairment in Na⁺,K⁺-ATPase activity is identical in red blood cells and neural tissue. Red blood cell ATPase activity is related to nerve conduction velocity in the peroneal and the tibial nerve of diabetic patients. C-peptide infusion to diabetic rats increases endoneural ATPase activity in rat. Because the defect in Na⁺,K⁺-ATPase activity is also probably involved in the development of diabetic nephropathy and cardiomyopathy, physiological C-peptide infusion could be beneficial for the prevention of diabetic complications.     

Exposure of colonic epithelial cells to oxidative and endoplasmic reticulum stress causes rapid potassium efflux and calcium influx

Endoplasmic reticulum (ER) stress and oxidative stress have recently been linked to the pathogenesis of inflammatory bowel diseases. Under physiological conditions, intestinal epithelial cells are exposed to ER and oxidative stress affecting the cellular ionic homeostasis. However, these altered ion flux ‘signatures’ during these stress conditions are poorly characterized. We investigated the kinetics of K⁺, Ca²⁺ and H⁺ ion fluxes during ER and oxidative stress in a colonic epithelial cell line LS174T using a non‐invasive microelectrode ion flux estimation technique. ER and oxidative stress were induced by cell exposure to tunicamycin (TM) and copper ascorbate (CuAsc), respectively, from 1 to 24 h. Dramatic K⁺ efflux was observed following acute ER stress with peak K⁺ efflux being ?30·6 and ?138·7 nmolm^?2 s^?1 for 10 and 50 µg ml^?1, respectively (p < 0·01). TM‐dependent Ca²⁺ uptake was more prolonged with peak values of 0·85 and 2·68 nmol m^?2 s^?1 for 10 and 50 µg ml^?1 TM, respectively (p < 0·02). Ion homeostasis was also affected by the duration of ER stress. Increased duration of TM treatment from 0 to 18 h led to increases in both K⁺ efflux and Ca²⁺ uptake. While K⁺ changes were significantly higher at each time point tested, Ca²⁺ uptake was significantly higher only after prolonged treatment (18 h). CuAsc also led to an increased K⁺ efflux and Ca²⁺ uptake. Functional assays to investigate the effect of inhibiting K⁺ efflux with tetraethylammonium resulted in increased cell viability. We conclude that ER/oxidative stress in colonic epithelial cells cause dramatic K⁺, Ca²⁺ and H⁺ ion flux changes, which may predispose this lineage to poor stress recovery reminiscent of that seen in inflammatory bowel diseases. Copyright © 2012 John Wiley & Sons, Ltd.