Effect of inhibition of the electrogenic Na+/K+ pump on the mechanical activity in the rat uterus

Summary— The effects of ouabain and K⁺-free solution were studied in estrogen-primed rat uterine strips under resting tone or repeatedly stimulated with KCl, acetylcholine or oxytocin applied for 20 minutes at 60 minute intervals. These effects were compared with those of the K⁺ channel opener cromakalim. In preparations under resting tone, ouabain (0.1 mM and 0.3 mM) induced rhythmic contractions which disappeared after 20–30 minutes whereas at a higher concentration (1 mM) it evoked a rapid, phasic response followed by a small tonic contraction. Exposure of the strip to a K⁺-free solution induced either rhythmic waves, which ceased after 8–10 minutes, or a single phasic contraction which was followed by a small and slow increase in the resting tone (54 ± 10 mg after 180 min exposure). Nifedipine (0.3 μM) abolished the rhythmic or phasic component of these responses but failed to modify the late small tonic contraction induced by ouabain 1 mM or by K⁺-free solution. Ouabain (0.1–1 mM) or K⁺-free-evoked responses disappeared after short (4 min) or prolonged (60 min) exposure to a Ca²⁺-free, 3 mM EGTA-containing solution. Cromakalim (10 nM ?0.1 mM) did not induce any variation in the resting tone either in the presence or in the absence of Ca²⁺ in the medium. In strips repeatedly stimulated with acetylcholine (0.1 mM) or oxytocin (1 μM), ouabain (0.3 mM), K⁺-free-solution and cromakalim (10 μM) reduced the amplitude of the initial, phasic response and progressively decreased the oscillatory component of the response to these agonists. Conversely, the successive responses evoked by KCl 60 mM in similar experimental conditions were not affected by ouabain or cromakalim. Ouabain (0.3 mM), K⁺-free solution and cromakalim (10 μM) decreased the Ca²⁺-independent, maintained contractions induced by acetylcholine or oxytocin after prolonged exposure to a Ca²⁺-free, EGTA-containing medium. These inhibitory effects were partially or completely reversed in the presence of the non-selective potassium channel blocker tetraethylammonium (10 mM) or in a Ca²⁺-free solution containing 60 mM K⁺. In conclusion, these results suggest that the response induced by ouabain or K⁺-free solution in estrogen-primed rat myometrium involves Ca²⁺ influx through potential-operated calcium channels but not Ca²⁺ release from intracellular stores. In addition, our results show that prolonged exposure to ouabain or K⁺-free medium decreases membrane receptor-mediated responses in rat uterus. This inhibitory effect seems to be the result, at least in part, of a decrease in the cytosolic level of K⁺, due to the inhibition of the electrogenic Na⁺ pump.     

Na+‐K+‐ATPase,a potent neuroprotective modulator against Alzheimer disease

Alzheimer disease (AD) is a neurodegenerative disorder clinically characterized by progressive cognitive and memory dysfunction, which is the most common form of dementia. Although the pathogenesis of neuronal injury in AD is not clear, recent evidences suggest that Na⁺‐K⁺‐ATPase plays an important role in AD, and may be a potent neuroprotective modulator against AD. This review aims to provide readers with an in‐depth understanding of Na⁺‐K⁺‐ATPase in AD through these modulations of some factors that are as follows, which leads to the change of learning and memory in the process of AD.

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The lymphocyte Na+/H+ antiport: activation in primary hypertension and during chronic NaCl-loading

Abstract. Increased activity of the Na⁺/H⁺ antiport may be a major abnormality in essential hypertension. The activity of this transport system was investigated in lymphocytes from 13 patients with untreated essential hypertension (Ht) and 13 normotensive control subjects (Nt) on an ad libitum (130–170 mmol d^-1) NaCl intake. Furthermore, the effects of different states of NaCl balance on lymphocyte Na⁺/H⁺ antiport were evaluated in two groups of Nt volunteers receiving 20 vs. 300 mmol d^-1 (n= 8) and 85 vs. 200 mmol d^-1 (n= 14) of NaCl for 1 week each and in seven Ht patients (20 vs. 300 mmol NaCl d^-1 for 1 week each). Additionally, during the 20 and 300 mmol/d NaCl intake red blood cell membrane transport was studied in eight subjects. For the determination of lymphocyte antiport activity, cells were loaded with the cytosolic pH (pH_i) indicator bis-carboxyethyl carboxyfluorescein (BCECF-AM) and acidified by addition of different amounts of Na⁺-propionate (5–40 mM). Initial pH_i-recovery was taken as the activity of the antiport system and plotted against pH_i-values after acidification. Non-linear regression analysis yielded higher ’apparent’ maximal transport rates in Ht than Nt (Nt: 2·00 pL 0·22; Ht: (3·81 pL 0·59)·10^-3 s^-1; P < 0·025). In contrast, baseline pH_i-values and pH_i-values at half-maximal activity (pK) were identical in Nt and Ht. In normotensive control subjects on an NaCl intake of 20, 85, 200 and 300 mmol d^-1 for 7 d, ’apparent’ maximal transport rates averaged 2.75 0·20, 2·89 0·17, 2·81 ± 0·18 and (3·62 ± 0·25) · 10^-3 s^-1, respectively. Thus, antiport activity was significantly (P < 0·05) stimulated on the 300 mmol d^-1 intake as compared to the three other NaCl intakes. The extreme intakes of NaCl (20 vs. 300 mmol d^-1) in normotensive volunteers did not affect the erythrocyte Na⁺/K⁺ pump, Na⁺/K⁺ cotransport and Na⁺/Li⁺ countertransport. Our study supports the concept that a group of patients with primary hypertension exhibit an activated Na⁺/H⁺ antiport. Furthermore, our data demonstrate that a chronic high intake of NaCl is associated with an increase in lymphocyte antiport activity towards the high values observed in primary hypertension.     

Neuropharmacological effects of lipoic acid and ubiquinone on δ‐aminolevulinic dehydratase,Na+, K+‐ATPase,and Mg2+‐ATPase activities in rat hippocampus after pilocarpine‐induced seizures

In this study, we investigated the effects of lipoic acid (LA) in the hippocampus oxidative stress caused by pilocarpine‐induced seizures in adult rats. Wistar rats were treated with 0.9% saline (i.p., control group), LA (10 mg/kg, i.p., LA group), ubiquinone [20 mg/kg, i.p., ubiquinone (UQ) group], pilocarpine (400 mg/kg, i.p., P400 group), and the association of LA (10 mg/kg, i.p.) plus pilocarpine (400 mg/kg, i.p.) or UQ (20 mg/kg, i.p.) plus pilocarpine (400 mg/kg, i.p.), 30 min before of administration of P400 (LA plus P400 group and UQ plus P400 group, respectively). After the treatments, all groups were observed for 1 h. The enzyme activities (δ‐aminolevulinic dehydratase (δ‐ALA‐D), Mg²⁺‐ATPase, and Na⁺, K⁺‐ATPase) were measured using spectrophotometric methods, and the results compared to values obtained from saline and pilocarpine‐treated animals. Protective effects of LA and UQ were also evaluated on the same parameters. We reported here for the first time that Na⁺, K⁺‐ATPase and δ‐ALA‐D activities inhibition and Mg²⁺‐ATPase stimulation in the pilocarpine model are probably attributed to the oxidative stress caused by seizures in the rat hippocampus. The addition of the antioxidants LA and UQ may reverses the previously mentioned Na⁺, K⁺‐ATPase and δ‐ALA‐D inhibitions and Mg²⁺‐ATPase stimulation. Conclusions: The oxidative stress plays an important signaling role in pilocarpine‐induced seizures, and antioxidant drugs might be considered as therapeutical tools in this pathology.     

Acute saline infusion induces extracellular acidification and activation of the Na+/H+ exchanger in man

The effect of acute expansion of the extracellular fluid volume (ECV) with isotonic (0.9%) saline on the activity of the lymphocyte Na⁺/H⁺ antiport (NHE) was studied in a total of 18 healthy volunteers. Saline was infused at a constant rate so that 4 mmol kg^?1 b.w. was administered over 2 h. NHE activity was measured by quantifying cytosolic pH (pH_i) recovery following acidification of the cells with propionic acid and by pH clamping at various pH_i values between 7.2 and 5.8 using nigericin. Both methods demonstrate NHE activation associated with intravenous saline infusion, the kinetic difference being a marked decrease in the Hill coefficient n from 3.28 ± 0.21 (SEM) to 2.22 ± 0.11 in the absence of changes in baseline pH_i (7.14 ± 0.02 vs. 7.08 ± 0.02; P = 0.15), V_max (42.8 ± 2.7 vs. 48.1 ± 2.8 mmol L^?1 min^?1; P = 0.08) and pK (6.32 ± 0.04 vs. 6.35 ± 0.02). NHE activation was associated with significant decreases in serum chloride (P = 0.016), calcium (P = 0.008), total cholesterol (P = 0.008), low-density lipoproteins (P = 0.016) and high-density lipoproteins (P = 0.008). Moreover, saline infusion induced extracellular acidification with a decrease in pH from 7.39 ± 0.01 to 7.37 ± 0.01 (P = 0.016), HCO₃^? from 23.3 ± 0.43 mmol L^?1 to 21.3 ± 0.25 mmol L^?1 (P = 0.008) and base excess from ?1.03 ± 0.38 mmol L^?1 to ?3.00 ± 0.31 mmol L^?1 (P = 0.008). Our results show for the first time that acute ECV expansion with isotonic saline is followed by an activation of the lymphocyte NHE. The underlying mechanism(s) remain to be investigated. However, the demonstration in our study of marked changes in acid–base balance induced by acute saline points to a possible inter-relationship of antiporter activation and extracellular acidification.     

Na+/H+ antiporter activity in peripheral blood lymphocytes of obese and type 2 diabetic patients is increased only in the presence of arterial hypertension

Abstract. The aim of this work is to evaluate whether type 2 diabetes mellitus, obesity and arterial hypertension, three conditions characterized by the presence of insulin resistance, share some common genetic markers. A potential candidate is the Na⁺/H⁺ anti-porter, the increased activity of which is considered a marker of essential hypertension. This ion exchanger seems to be related to the Na⁺/Li⁺ countertransport, that is considered a marker of insulin resistance in essential hypertension and in type 1 diabetes mellitus. In this study we wished to clarify whether the activity of the Na⁺/H⁺ antiporter is increased not only in hypertensive subjects, but also in obese and type 2 diabetic patients, both in the presence and in the absence of arterial hypertension. The activity of the ion exchanger was measured in peripheral blood lymphocytes (PBL) by clamping intracellular pH (pH_i) at 5·8–6·2 and then detecting the rate of the proton efflux after sodium addition. In the absence of arterial hypertension, no significant difference in this parameter was observed in obese and type 2 diabetic patients in comparison with normal subjects. In the presence of arterial hypertension, there was a significant increase in the Na⁺-induced H⁺ efflux at the internal pH (pHi) values of 5·8 and 6·2 both in hypertensive controls and in hypertensive obese and type 2 diabetic patients (P= 0·05–0·0001 vs. normotensive subjects and patients). In particular, H⁺ efflux at pH 5·8 (mmol l^-1 min^-1) was 35·36 ± 2·48 in normotensive and 42·77 ± 1·63 in hypertensive control subjects (P= 0·045), 33·06 ± 1·88 in normotensive and 50·40 ± 5·21 in hypertensive obese patients (P= 0·009), 31·16 ± 1·84 in normotensive and 55·54 ± 5·83 in hypertensive type 2 diabetic patients (P= 0·0001). H⁺ efflux showed a significant correlation with both systolic (at pHi 5·8, r = 0·473, P= 0·001; at pHi 6·2, r = 0·357, P= 0·016) and diastolic blood pressure (at pHi 5·8, r = 0·600, P= 0·0001; at pHi 6·2, r = 0·555, P= 0·0001). Therefore, our study demonstrates that the hyperactivity of the Na⁺/H⁺ exchanger in peripheral blood lymphocytes is also a marker of arterial hypertension in obesity and in type 2 diabetes mellitus, and that the exchanger activity is not increased in these two conditions in the absence of arterial hypertension.     

Role of Na+-H+ Exchange on Reperfusion Related Myocardial Injury and Arrhythmias in an Open-Chest Swine Model

The inhibition of Na⁺-H⁺ exchange (NHE) with amiloride analogues in vitro has been shown to prevent reperfusion arrhythmias and additional cell necrosis. Inhibition of intracellular Ca²⁺ overload via NHE inhibition has been suggested as a mechanism of these protective effects. The aim of this study was to examine whether treatment with amiloride analogues reduces the incidence of reperfusion arrhythmias and limits infarct size in vivo. Open-chest swine were exposed to a 30-minute left anterior descending artery (LAD) occlusion and 180 minutes of reperfusion during atrial pacing at 150 ppm. Intravenous 5-(N,N-dimethyI)-amiloride (AML, 5 μg/kg per min) was administered in the treatment group (n = 7) and intravenous saline in the control group (n = 7), starting 10 minutes before coronary occlusion. The infusion was continued during ischemia and reperfusion. The area at risk was defined by monastral blue dye and infarct size by triphenyltetrazolium chloride staining. Limb leads ECG and monophasic action potentials (MAPs) from the epicardium in the ischemic area were recorded. There was no significant difference in the size of the area at risk and hemodynamic parameters between the groups. However, the infarcted area was 0.4%± 1.0% of the area at risk in the treatment group, whereas it was 62%± 29% in the control group (P < 0.05). Pathological examination (Hematoxylin-eosin and mallory s phosphotungstic acid-hematoxylin staining) revealed that all of the infarcted area consisted of contraction band necrosis. MAP duration in both groups was significantly shortened during ischemia. After reperfusion, MAP duration in the treatment group recovered earlier than that of control group. However, there was no significant difference in the incidence of ventricular tachyarrhythmia between the groups. Inhibition of NHE with AML prevented reperfusion related cell necrosis in the in vivo swine model, but did not reduce the incidence of ventricular tachyarrhythmia.     

Local and systemic effects of Na+/K+ ATPase inhibition

The positive inotropic and electrophysiological effects of cardiac glycosides on cardiac muscle are mediated through inhibition of Na⁺/K⁺ ATPase by binding to a specific extracytoplasmic site of the a-subunit of this enzyme. The inhibition of Na⁺/K⁺ ATPase affects ionic flux and produces direct local effects on cardiac contractility, electrical excitability and conduction, but also profound systemic effects mainly as a result of haemodynamic changes. These effects are responsible for beneficial therapeutic as well as toxic effects.
Inhibition of Na⁺/K⁺ ATPase results in potentiation of K⁺ loss from cells and Na⁺ entry into cells, so consequently affects action potential generation and propagation. This also underlines the potentiation of certain effects of cardiac glycosides by hypokalemia and hypomagnesaemia, and the effects of changes in calcium homeostasis on the cardiac glycoside pharmacodynamics. Furthermore, inhibition of Na⁺/Ca⁺⁺ exchange enhances Ca⁺⁺ mobilization and promotes contractility. These effects (locally and systemically) differ greatly, depending on the haemodynamic status and myocardial oxygen supply.
Cardiac glycosides have less affinity for Na⁺/K⁺ ATPases at other sites (e.g. skeletal muscle), but some extracardiac effects (vascular effects, effects on colour vision, CNS and autonomic effects, renal effects) may be related to Na⁺/K⁺ ATPase inhibition.     

Abnormal Na+-K+ ATPase kinetics in a subset of essential hypertensive patients

We have performed a kinetic analysis of the interaction of Na+-K+ ATPase with internal Na+ in erythrocytes of 30 normotensive controls and 72 essential hypertensive patients. Neither the maximal rate of ouabain-sensitive sodium efflux (Vmax) nor the internal Na+ content required for half-maximal stimulation (K50%) were significantly different between normotensive and hypertensive patients. Nevertheless, using the 95% confidence limits of the K50% in the normotensive group as a cut-off point, 13 (18.06%) essential hypertensive patients exhibited increased values of this parameter (29.16 +/- 4.31 mmol l-1 cells) revealing decreased affinity of Na+-K+ ATPase for internal Na+ (Pump-hypertensives). The Vmax was also higher in the Pump '-' subset (14.08 +/- 4.85 mmol (1 cells h)-1 vs. 6.92 +/- 1.80; P = 0.0002) and 10 of these 13 hypertensives exhibited a Vmax above the upper end limit of 10.5 mmol (1 cells h)-1, suggesting a compensatory effect. No differences were observed between the Pump '-' subset and the remaining 59 hypertensives without Na+-K+ pump abnormality when basal erythrocyte Na+ content and clinical parameters of hypertension were examined. Decreased apparent affinity of Na+-K+ pump for internal Na+ present in 9-27% of essential hypertensives may be implicated in pathogenetic mechanisms of hypertension.     

Capillary Endothelial Na+, K+, ATPase Transporter Homeostasis and a New Theory for Migraine Pathophysiology

(Headache 2010;50:459‐478) Background.— Cerebrospinal fluid sodium concentration ([Na⁺]_csf) increases during migraine, but the cause of the increase is not known. Objective.— Analyze biochemical pathways that influence [Na⁺]_csf to identify mechanisms that are consistent with migraine. Method.— We reviewed sodium physiology and biochemistry publications for links to migraine and pain. Results.— Increased capillary endothelial cell (CEC) Na⁺, K⁺, ‐ATPase transporter (NKAT) activity is probably the primary cause of increased [Na⁺]_csf. Physiological fluctuations of all NKAT regulators in blood, many known to be involved in migraine, are monitored by receptors on the luminal wall of brain CECs; signals are then transduced to their abluminal NKATs that alter brain extracellular sodium ([Na⁺]_e) and potassium ([K⁺]_e). Conclusions.— We propose a theoretical mechanism for aura and migraine when NKAT activity shifts outside normal limits: (1) CEC NKAT activity below a lower limit increases [K⁺]_e, facilitates cortical spreading depression, and causes aura; (2) CEC NKAT activity above an upper limit elevates [Na⁺]_e, increases neuronal excitability, and causes migraine; (3) migraine‐without‐aura may arise from CEC NKAT over‐activity without requiring a prior decrease in activity and its consequent spreading depression; (4) migraine triggers disturb, and treatments improve, CEC NKAT homeostasis; (5) CEC NKAT‐induced regulation of neural and vasomotor excitability coordinates vascular and neuronal activities, and includes occasional pathology from CEC NKAT‐induced apoptosis or cerebral infarction.     

Hormonal and pharmacological modification of plasma potassium homeostasis

Human skeletal muscles contain the largest single pool of K⁺ in the body (2600 mmol, 46 times the total K⁺ content of the extracellular space). Intense exercise may double arterial plasma K⁺ in one min. This is because of excitation‐induced release of K⁺ from the working muscle cells via K⁺ channels. This hyperkalemia is rapidly corrected by reaccumulation of K⁺ into the muscle cells via Na⁺,K⁺ pumps, often leading to hypokalemia. Hyperkalemia may also arise from muscle cell damage, excessive oral or intravenous administration of K⁺, acidosis, renal failure, depolarization of muscle cells with succinyl choline, activation of K⁺ channels by fluoride poisoning, hyperkalemic periodic paralysis, malignant hyperthermia, inhibition of the Na⁺,K⁺ pumps by digitalis glycosides or treatment with nonselective beta blockers. Hyperkalemia may cause arrhythmia and can be treated with beta₂ agonists, insulin or hemodialysis. Hypokalemia may be induced by the stimulation of the Na⁺,K⁺ pumps in skeletal muscles seen postexercise, or by catecholamines, beta₂ agonists, pheochromocytoma, theophylline, caffeine or insulin, by sepsis, myocardial infarction, trauma, burns and heart failure. Rare causes are hypokalemic periodic paralysis, inhibition of K⁺ channels by barium, chloroquine or barbiturates. Hypokalemia often reflects dietary K⁺ deficiency, alkalosis, renal or gastrointestinal loss of K⁺. Hypokalemia is more likely to cause arrhythmia than hyperkalemia and can be treated by oral or intravenous administration of K⁺ under frequent control of electrocardiogram and plasma K⁺. Because of their size and high contents of K⁺, Na⁺,K⁺ pumps and K⁺ channels, the skeletal muscles play a central role in the acute, from min‐to‐min ongoing regulation of plasma K⁺. This is decisive for the maintenance of muscle contractility and heart function.     

A novel mechanism of cytokine release in phagocytes induced by aggretin,a snake venom C‐type lectin protein,through CLEC‐2 ligation

Summary Background: Macrophages are major immune cells and play an important role in modulating homeostasis and the immune defense mechanism. In inflammatory responses to the infection of pathogens, macrophages are activated, producing various inflammatory mediators. Snake venom C‐type lectin proteins (snaclecs) have diverse targets, including platelet GPVI, GPIb, integrin α2β1 or CLEC‐2 expressed in platelets, endothelial cells or myeloid cells. Methods: In this study, murine macrophages (RAW 264.7 cells) and human monocytes (THP‐1) were treated with different snaclecs, including aggretin, gramicetin, trowaglerix and convulxin, in the absence or presence of LPS for 24 h. Results: The production of cytokines, such as tumor necrosis factor‐α (TNF‐α) and interleukin‐6 (IL‐6), in supernatants was measured by ELISA. Aggretin increased the production of TNF‐α and IL‐6 in both RAW264.7 and THP‐1 cells; however, the other snaclecs did not. Aggretin induced extracellular signal‐regulated kinase 1/2 (ERK1/2) and c‐Jun N‐terminal kinase (JNK) tyrosine phosphorylation of RAW264.7 cells. Pretreatments with inhibitor of ERK, JNK, p38 or NF‐κB abolished cytokine release caused by aggretin. Aggretin bound to THP‐1 cells in a concentration‐dependent manner and it displaced the CLEC‐2 mAb binding to THP‐1 cells and the immobilized aggretin selectively bound to CLEC‐2 of both platelets and THP‐1 cell lysates. Furthermore, aggretin elevated the plasma level of IL‐6 in ICR mice as it was administered intramuscularly. Conclusion: These results indicate that aggretin may induce cytokine TNF‐α/IL‐6 release via interacting with CLEC‐2 receptor and the subsequent MAPK and NF‐κB activation in monocytes/macrophages.     

Erythrocyte Na+–H+ exchanger kinetics and Na+–Li+ countertransport activity in essential hypertensive patients

The authors measured Na⁺–H⁺ exchanger kinetics together with Na⁺–Li⁺ countertransport V _max in the erythrocytes of 21 subjects with essential hypertension and 16 normotensive control subjects. Na⁺–H⁺ exchanger V _max appeared to be increased in patients with essential hypertension, while the Na⁺–H⁺ exchanger affinity for intracellular proton sites ( K _50%) proved to be unchanged and the index of cooperativity among intracellular proton binding sites as measured by Hill's coefficient (Hill's n ) decreased as compared with normotensive control subjects. Na⁺–Li⁺ countertransport V _max appeared to be higher in patients with essential hypertension than in control subjects. The authors were unable to find any correlations between Na⁺–H⁺ exchanger kinetic parameters and metabolic variables such as parameters of insulin resistance and plasma lipids. On the basis of the data obtained, erythrocyte Na⁺–H⁺ exchanger activity was found to be abnormal in two kinetic variables in essential hypertensive patients and showed no simple linear correlations with the main variables of glucose metabolism, plasma lipids, renin or aldosterone.     

Diabetes mellitus and subjects' ageing: a study on the ATP content and ATP-related enzyme activities in human erythrocytes

Na⁺/K⁺- and Ca²⁺-ATPase are the major ATP-dependent membrane-bound enzymes that regulate the cation transmembrane gradient which is altered both in red blood cell (RBC) senescence and in RBCs of diabetic patients. In an attempt to clarify the possible connection between diabetes mellitus and ageing, we investigated the relationship between RBC ATP content, Na⁺/K⁺-ATPase, Ca²⁺-ATPase activities and ageing in healthy, insulin-dependent (IDDM) and non-insulin-dependent (NIDDM) subjects. A significant correlation was found (r = ?0.82; P < 0.001) between RBC ATP content and subject's age only in the control group. A significant reduction in Na⁺/K⁺-ATPase activity was observed in the older group (C₂) of control subjects, in comparison with the younger (C₁) one. In both IDDM and NIDDM subjects, the enzymatic activity was significantly decreased when compared with healthy subjects of similar age (P < 0.001). A significant negative correlation was found between age and enzymatic activity in healthy subjects (r = ?0.60; P < 0.001). No difference was observed in the RBC membrane Ca²⁺-ATPase activity between younger (C₁) and older (C₂) healthy subjects. Ca²⁺-ATPase activity was significantly increased both in IDDM patients compared with C₁ (P < 0.001) and in NIDDM patients compared with C₂ (P < 0.001). The present data indicate that ageing causes a reduction in the erythrocyte ATP content in both healthy and diabetic subjects. In diabetic patients Na⁺/K⁺-ATPase activity decreases independently of age.     

Abnormal Na+K+ cotransport function in a group of patients with essential hypertension

In 50 normotensive controls, the increase in erythrocyte Na+ concentration up to 12.4 +/- 2.0 mmol/l cells (mean +/- SD) ensures half-maximal stimulation of outward Na+,K+ cotransport fluxes. Forty-six out of sixty-five patients with essential hypertension required more than 16 mmol/l cells of internal Na+ concentration to obtain a similar effect, strongly suggesting an abnormal cotransport function. Seven out of fourteen hypertensive patients with normal Na,K cotransport function showed Na+,Li+ countertransport fluxes higher than the normal upper limit of 220 mumol (1 cells h)-1. Conversely, countertransport fluxes were normal in fourteen hypertensives with abnormal cotransport function. The above results indicate that the total population of patients with essential hypertension is heterogeneous and includes one subgroup of subjects with abnormal Na+,K+ cotransport function, and another with increased Na+,Li+ countertransport fluxes.     

Antidiabetic omarigliptin dilates rabbit aorta by activating voltage-dependent K+ channels and the sarco/endoplasmic reticulum Ca2+-ATPase pump

We investigated the vasodilatory effect of omarigliptin, an oral antidiabetic drug in the dipeptidyl peptidase-4 inhibitor class, and its related mechanisms using phenylephrine (Phe)-induced pre-contracted aortic rings. Omarigliptin dilated aortic rings pre-constricted with Phe in a dose-dependent manner. Pretreatment with the voltage-dependent K⁺ channel inhibitor 4-aminopyridine significantly attenuated the vasodilatory effect of omarigliptin, whereas pretreatment with the inwardly rectifying K⁺ channel inhibitor Ba²⁺, ATP-sensitive K⁺ channel inhibitor glibenclamide, and large-conductance Ca²⁺-activated K⁺ channel inhibitor paxilline did not alter its vasodilation. Pretreatment with the sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) pump inhibitors thapsigargin and cyclopiazonic acid significantly reduced the vasodilatory effect of omarigliptin. Neither cAMP/PKA-related signaling pathway inhibitors nor cGMP/PKG-related signaling pathway inhibitors modulated the vasodilatory effect of omarigliptin. Removal of endothelium did not diminish the vasodilatory effect of omarigliptin. Furthermore, pretreatment with the nitric oxide synthase inhibitor L-NAME or small-conductance Ca²⁺-activated K⁺ channel inhibitor apamin, together with the intermediate-conductance Ca²⁺-activated K⁺ channel inhibitor TRAM-34, did not influence the vasodilatory effect of omarigliptin. In conclusion, omarigliptin induced vasodilation in rabbit aortic smooth muscle by activating voltage-dependent K⁺ channels and the SERCA pump independently of other K⁺ channels, cAMP/PKA- and cGMP/PKG-related signaling pathways, and the endothelium.     

Activated protein C protects against myocardial ischemic/reperfusion injury through AMP‐activated protein kinase signaling

Summary. Background: Activated protein C (APC) is a vitamin K‐dependent plasma serine protease that down‐regulates clotting and inflammatory pathways. It is known that APC exerts a cardioprotective effect by decreasing apoptosis of cardiomyocytes and inhibiting expression of inflammatory mediators after myocardial ischemia. Objectives: The objective of this study was to understand the mechanism of the APC‐mediated cardioprotection against ischemic injury. Methods: Cardioprotective activities of wild‐type APC and two derivatives, having either dramatically reduced anticoagulant activity or lacking signaling activity, were monitored in an acute ischemia/reperfusion injury model in which the left anterior descending coronary artery (LAD) was occluded. Results: APC reduced the myocardial infarct size by a mechanism that was largely independent of its anticoagulant activity. Thus, the non‐anticoagulant APC‐2Cys mutant, but not the non‐signaling APC‐E170A mutant, attenuated myocardial infarct size by EPCR and PAR‐1‐dependent mechanisms. Further studies revealed that APC acts directly on cardiomyocytes to stimulate the AMP‐activated protein kinase (AMPK) signaling pathway. The activation of AMPK by APC ameliorated the post‐ischemic cardiac dysfunction in isolated perfused mouse hearts. Moreover, both APC and APC‐2Cys inhibited production of TNFα and IL‐6 in vivo by attenuating the ischemia/reperfusion‐induced JNK and NF‐κB signaling pathways. Conclusions: APC exerts a cardioprotective function in ischemic/reperfusion injury through modulation of AMPK, NF‐κB and JNK signaling pathways.     

A study of erythrocyte membrane cation transport adenosine triphosphatases in pregnancy-induced hypertension and of in vivo effects of diuretic treatment

Plasma and erythrocyte Na⁺ and K⁺ and erythrocyte membrane (EM) Na⁺, K⁺ ATPase, Mg²⁺ ATPase and Ca²⁺, Mg²⁺ ATPase activities were studied in four groups of women — non-pregnant, normal pregnant, with pregnancy edema (PE) and with pregnancy induced hypertension (PIH). The effect of diuretic therapy in PE and PIH was also evaluated. Plasma Na⁺ concentration was higher in PE and PIH. There was a significant reduction in (Na⁺ + K⁺ ratio between cell and plasma in these two groups. EM Na⁺, K⁺ ATPase was unaltered in PE and PIH. The Mg⁺ ATPase was elevated by 44% in PE and by 100% in PIH subjects. There was a 50% reduction in Ca²⁺, Mg²⁺ ATPase activity in PE. Diuretic therapy had no effect either on electrolyte levels or on any of the EM ATPases.From these results it may be concluded that Na, K, ATPase — which in kidney is a site of action for furosemide, a potent diuretic — is unaffected in PE and PIH and, hence, treatment with diuretics in such patients may be ineffective.