Attenuation by magnesium of the electrophysiologic effects of hyperkalemia on human and canine heart cells

Because magnesium (Mg⁺⁺) has been shown to promote maintenance of a negative resting potential it might oppose the depolarizing effect of potassium (K⁺) in cardiac cells. To test this hypothesis the electrocar diographic changes that occur during hyperkalemia were prospectively studied in 11 patients, 4 of whom had hypermagnesemia. Action potential studies were carried out in single atrial and ventricular cells isolated from 11 canine hearts using similar extracellular concentrations of Mg⁺⁺ _° and K⁺ _° to elucidate further the relative effects of these cations. Hyperkalemia was associated with a marked reduction in P wave amplitude and marked prolongation of the QRS complex. However, normal P waves and normal QRS durations were recorded in hyperkalemic patients with excess Mg⁺⁺ (2.5 mEq/liter or more). Mg⁺⁺ also antagonized some effects of K⁺ in the isolated atrial and ventricular tissues. With elevated levels of [Mg⁺⁺] the K⁺-induced depolarization of the resting potential was less than half as much as when [Mg⁺⁺]was normal (9 versus 21 mV in ventricular cells and 18 versus 40 mV in atrial cells). Furthermore, the fall in linear conduction velocity that accompanied elevated [K⁺]levels in ventricular cells failed to occur when the level of [Mg⁺⁺]was high. Mg⁺⁺-K⁺ antagonism helps to explain the preservation of a normal P wave because the onset of K⁺ effects in isolated atrial cells was delayed when [Mg⁺⁺]was high and action potential amplitude was improved. It is concluded that the heart cells of patients with high serum levels of [Mg⁺⁺]were less sensitive to an increase in [K⁺]than were those of patients with lower [Mg⁺⁺]and, accordingly, that Mg⁺⁺ attenuated the electrophysiologic response to elevated [K⁺].     

Potassium-competitive acid blockers - are they the next generation of proton pump inhibitors?

The modern lifestyle caters to an increase in the incidence of peptic ulcer disease, gastroesophageal reflux disease and several other acid-related conditions of the gut. The drugs to prevent these conditions work either through H2 receptor blockade or inhibition of the H⁺, K⁺ ATPase enzyme. Although proton pump inhibitors have been proven to be efficacious, they have a slow onset of action with limited resolution of symptoms in most patients. Potassium-competitive acid blockers (P-CABs) are novel drugs that bind reversibly to K⁺ ions and block the H⁺, K⁺ ATPase enzyme, thus preventing acid production. P-CABs have a fast onset of action and have dose-dependent effects on acid production. Animal studies exist that differentiate the better results of P-CABs from proton pump inhibitors; further human trials will give a comprehensive picture of the results and will help to elucidate the therapeutic benefits of this new group of drugs.     

Vitamin D and intestinal calcium absorption

The principal function of vitamin D in calcium homeostasis is to increase calcium absorption from the intestine. Calcium is absorbed by both an active transcellular pathway, which is energy dependent, and by a passive paracellular pathway through tight junctions. 1,25Dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) the hormonally active form of vitamin D, through its genomic actions, is the major stimulator of active intestinal calcium absorption which involves calcium influx, translocation of calcium through the interior of the enterocyte and basolateral extrusion of calcium by the intestinal plasma membrane pump. This article reviews recent studies that have challenged the traditional model of vitamin D mediated transcellular calcium absorption and the crucial role of specific calcium transport proteins in intestinal calcium absorption. There is also increasing evidence that 1,25(OH)(2)D(3) can enhance paracellular calcium diffusion. The influence of estrogen, prolactin, glucocorticoids and aging on intestinal calcium absorption and the role of the distal intestine in vitamin D mediated intestinal calcium absorption are also discussed.     

Calcium and lipoprotein lipase synergistically enhance the binding and uptake of native and oxidized LDL in mouse peritoneal macrophages

The influence of Ca²⁺ and Mg²⁺, together with lipoprotein lipase (LPL), on the binding and uptake of Eu³⁺-labeled native and oxidized low density lipoprotein (LDL) to mouse peritoneal macrophages (MPM), and on the deposition of esterified cholesterol in these macrophages, were studied. We found that both LPL and Ca²⁺ (but not Mg²⁺) increased the binding and uptake of native and mildly or moderately oxidized LDL, and the subsequent deposition of cholesterol esters in MPM. When added together, LPL and Ca²⁺ synergistically increased the binding and uptake of native and oxidized LDL, and the deposition of esterified cholesterol derived from native and mildly or moderately oxidized LDL, in MPM. Since both calcium and LPL are found in the atherosclerotic lesions, our results suggest that Ca²⁺ and LPL may synergistically promote foam cell formation and atherogenesis. Furthermore, future research in the metabolism of lipoproteins should take into account the calcium levels in the experimental conditions.     

Acetaldehyde-Induced Increase in Paracellular Permeability in Caco-2 Cell Monolayer

Evidence indicates that endotoxin-mediated liver injury plays an important role in the pathogenesis of alcoholic liver disease. Elevated plasma endotoxin level in alcoholics is suggested to be caused by enteric bacterial overgrowth and/or increased intestinal permeability to endotoxin. In this study, the effect of ethanol and acetaldehyde on the paracellular permeability was evaluated in Caco-2 cell monolayers. Ethanol was administered into the incubation medium, whereas acetaldehyde was administered by exposing cell monolayers to vapor phase acetaldehyde, or by direct administration of an acetaldehyde generating system (AGS), ethanol + NAD⁺+ alcohol dehydrogenase. Paracellular permeability was assessed by measuring transepithelial electrical resistance (TER), sodium chloride dilution potential, and unidirectional flux of d -[2-³H]mannitol. Administration of ethanol up to 900 mM produced no significant effect on paracellular permeability. Vapor phase acetaldehyde, generated from 5 to 167 mM acetaldehyde solutions in neighboring wells, resulted in a time- and dose-dependent increase in acetaldehyde concentration (99 to 760 μM) in the buffer bathing cell monolayer. Acetaldehyde induced a reduction of TER and dilution potential, and an elevation of mannitol flux in a time and concentration-related manner, without affecting the ability of cells to exclude trypan blue. Removal of acetaldehyde after 1, 2, or 4 hr treatment and subsequent incubation in the absence of acetaldehyde resulted in a time-dependent reversal of TER to baseline values. Administration of AGS also reduced TER and dilution potential, associated with an increase in mannitol flux. This effect of AGS was prevented by 4-methylpyrazole, an alcohol dehydrogenase inhibitor. These results show that acetaldehyde, but not ethanol, reversibly increases the paracellular permeability of Caco-2 cell monolayer.     

Regulatory T Cells in children with intestinal parasite infection

Chronic intestinal parasite infection can induce both persistent immune activation and defective responsiveness of T cells. This study aimed to assess the number and function of T regulatory (Treg) cells in children with intestinal parasite infection. We have studied the peripheral blood from 93 children, 53 of them parasitized with protozoa, helminths, or both; the remainder were non parasitized, healthy controls. The number and function of CD4⁺ CD25^high and CD4⁺ Foxp3⁺ cells were similar in parasitized and control children. In contrast, there was a significant increase in the levels of CD3⁺ CD69⁺, CD4⁺ CTLA-4⁺, and CD8⁺ CD28⁻ T cells in helminth infected children. Moreover, some of these patients showed a diminished response to CD3/CD28 stimulation in comparison with the control children. Our data strongly suggest that whilst Treg cells are not affected by intestinal parasite infection, CD3⁺ CD69⁺, CD4⁺ CTLA-4⁺ and CD8⁺ CD28⁻ lymphocytes may play an important, but as yet undetermined role in the diminished immune competence observed in parasitized children.     

Cholesterol enrichment inhibits Na/K pump in endothelial cells

We have previously shown that cholesterol enrichment reduces ³H-ouabain binding in cultured vascular endothelial cells. The present study aimed to determine the effect of cholesterol enrichment on ouabain-sensitive ⁸⁶Rb (as a substitute for K⁺) influx, i.e. K+ transport via the pump, and to examine whether cellular K+ content was affected in human umbilical vein endothelial cells. ⁸⁶Rb influx was inhibited by both ouabain and bumetanide in a dose-dependent manner. Consistent with an earlier report [1], inhibition achieved was greater for ouabain ( 70% at mM range) than for bumetanide ( 55% at 0.1 mM), indicating that K⁺ influx via Na⁺/K⁺ pump was greater than that via Na⁺---K⁺---Cl⁻ cotransport in these cells. After incubation of 18 h or more with cholesterol-enriched liposomes (2:1 cholesterol to phospholipid ratio), a significant reduction (>20%) of the ouabain-sensitive K⁺ influx and an increase in cellular cholesterol content were observed. The inhibitory effect was observed only at liposome concentrations above 2 mg/ml. Following 18 h incubation with 2 mg/ml cholesterol-enriched liposomes, cellular K⁺ content was significantly decreased. The phospholipid liposome treatment did not alter K⁺ content, suggesting that the inhibitory effect on Na⁺/K⁺ pump and the cellular K⁺ content reduction was not due to liposome fusion alone or to the phospholipid present. These findings indicate that cholesterol enrichment inhibits Na⁺/K⁺ pump and thus reduces cellular K⁺ content in endothelial cells, and may play a role in the widely observed abnormal endothelium-dependent vascular response induced by hypercholesterolemia.     

Molecular aspects of intestinal calcium absorption

Intestinal Ca2+ absorption is a crucial physiological process for maintaining bone mineralization and Ca2+ homeostasis. It occurs through the transcellular and paracellular pathways. The first route comprises 3steps: the entrance of Ca2+ across the brush border membranes(BBM) of enterocytes through epithelial Ca2+ channels TRPV6, TRPV5, and Cav1.3; Ca2+ movement from the BBM to the basolateral membranes by binding proteins with high Ca2+ affinity(such as CB9k); and Ca2+ extrusion into the blood. Plasma membrane Ca2+ ATPase(PMCA1b) and sodium calcium exchanger(NCX1) are mainly involved in the exit of Ca2+ from enterocytes. A novel molecule, the 4.1R protein, seems to be a partner of PMCA1 b, since both molecules colocalize and interact. The paracellular pathway consists of Ca2+ transport through transmembrane proteins of tight junction structures, such as claudins 2, 12, and 15. There is evidence of crosstalk between the transcellular and paracellular pathways in intestinal Ca2+ transport. When intestinal oxidative stress is triggered, there is a decrease in the expression of several molecules of both pathways that inhibit intestinal Ca2+ absorption. Normalization of redox status in the intestine with drugs such as quercetin, ursodeoxycholic acid, or melatonin return intestinal Ca2+ transport to control values. Calcitriol [1,25(OH)2D3] is the major controlling hormone of intestinal Ca2+ transport. It increases the gene and protein expression of most of the molecules involved in both pathways. PTH, thyroid hormones, estrogens, p ro l a c t i n, g ro w t h h o r m o n e, a n d g l u c o c o r t i c o i d s apparently also regulate Ca2+ transport by direct action, indirect mechanism mediated by the increase of renal 1,25(OH)2D3 production, or both. Different physiological conditions, such as growth, pregnancy, lactation, and aging, adjust intestinal Ca2+ absorption according to Ca2+ demands. Better knowledge of the molecular details of intestinal Ca2+ absorption could lead to the development of nutritional and medical strategies for optimizing the efficiency of intestinal Ca2+ absorption and preventing osteoporosis and other pathologies related to Ca2+ metabolism.     

An association between activity of the Na/K-pump and resistance of Schistosoma mansoni towards complement-mediated killing

The Na/K-pump or Na⁺/K⁺-ATPase (EC 3.6.1.37), couples the hydrolysis of ATP to the active transport of Na⁺ and K⁺ ions across the plasma membrane of virtually all animal cells. The relationship between activity of the Na⁺/K⁺-ATPase and the sensitivity of Schistosoma mansoni to immunological attack has been investigated. It has been observed that ouabain, the specific inhibitor of the pump, via a synergistic effect with specific antibody and complement, affects the average membrane potential causing depolarization and death of complement resistant parasites. Thus, apparently, there is association between the inhibition of the Na/K-pump and the lysis and death of the complement-resistant parasite.     

持续低效血液透析滤过对重症急性胰腺炎患者肠黏膜屏障功能及免疫功能的影响

目的 评价持续低效血液透析滤过（SLEDF）对重症急性胰腺炎（SAP）患者肠黏膜屏障功能及免疫功能的影响。方法 将51例SAP患者随机分为持续静脉静脉血液滤过（CVVH）组25例和SLEDF组26例,在常规治疗基础上分别接受CVVH和SLEDF治疗。比较两组患者预后、血、尿淀粉酶恢复正常时间、治疗前和治疗第2、4、8、14d血D-乳酸、内毒素（ET）、二胺氧化酶(DAO)、CD3⁺、CD4⁺、CD8⁺T淋巴细胞水平、CD4⁺/CD8⁺T淋巴细胞比值及血液净化相关并发症发生情况。结果 两组患者死亡率、血、尿淀粉酶恢复正常时间比较差异均无统计学意义,血D-乳酸、ET、DAO、CD3⁺、CD4⁺、CD8⁺T淋巴细胞水平和CD4⁺/CD8⁺T淋巴细胞比值在治疗前和治疗第2、4、8、14d比较差异均无统计学意义（P>0.05）。两组患者治疗第4、8、14d D 乳酸、ET和DAO水平均较同组治疗前降低,第8、14d均较同组治疗第4d降低（P＜0.05）。两组患者治疗第4、8、14d的CD3⁺、CD4⁺、CD8⁺T淋巴细胞水平和CD4⁺/CD8⁺T淋巴细胞比值均较同组治疗前升高,第8、14d均较同组治疗第4d升高（P＜0.05）;两组患者治疗第4、8d的CD8⁺T淋巴细胞水平较同组治疗前降低,第8、14d较第4d降低（P＜0.05）。结论 SLEDF和CVVH改善SAP患者肠道屏障功能障碍和免疫功能异常的作用相似,其中SLEDF操作方便,医疗费用低,值得临床推广。     

Effects of metformin on bile salt transport by monolayers of human intestinal Caco-2 cells

The antidiabetic biguanide metformin has been shown to increase faecal excretion of bile salts in type 2 diabetes. Cultured human intestinal Caco-2 cell monolayers provide a model of human enterocytes. These monolayers are used here to determine the effect of metformin on the secondary-active, sodium-linked transfer of ¹⁴C-glycocholate from the apical (brush border) to the basolateral (serosal) surface. During 24-h incubations, 10⁻² mol/l metformin significantly reduced ¹⁴C-glycocholate transfer. This could not be attributed to alterations of monolayer integrity or Na⁺-K⁺ ATPase pump activity. For example, the secondary-active transport of glucose and proline was not interrupted, and the inhibitory effect of metformin on bile salt transport was additive to the inhibitory effect of ouabain. The results suggest that metformin can act directly on intestinal enterocytes to reduce the active transfer of bile salts by a mechanism that is independent of Na⁺-K⁺ ATPase activity.     

Effects of Ethanol on NMDA Receptors in Brain: Possibilities for Mg2+ -Ethanol Interactions

The major excitatory neurotransmitter in the CNS is L-glutamate, and one of the subtypes of L-glutamate receptors, the N -methyl-D-aspartate (NMDA) subtype, has been found to be quite sensitive to inhibition by low concentrations of ethanol (5–50 mm). The NMDA receptor-ion channels are unique in that they exhibit a voltage-dependent blockade by physiological concentrations of Mg²⁺, a blockade that is relieved as the cell membrane is depolarized. Several lines of evidence also suggest that the activity of this receptor-channel complex may be regulated through a high-affinity Mg²⁺ site, which is distinct from the channel-blocking site and could even be located on the extracellular domain of the protein. This high-affinity Mg²⁺ site has been shown to increase the binding of N -[1-(2-thienyl) cyclohexyl]piperidine within the ion channel, as well as the binding of competitive antagonist such as 3-(±)-carboxypiperazine-4-yl)-[1,2]-propyl-1-phosphonic acid and the receptor coactivator glycine. The relationship between the acute effects of ethanol on receptor activation and the regulatory properties of Mg²⁺ is not yet known, although the hypomagnesemia that occurs in chronic alcoholism could certainly have implications for receptor function. A significant amount of molecular characterization of the multiple isoforms of the NMDA receptor-ion channel will be required before the role of Mg²⁺ can be clarified and any relationship between Mg²⁺ regulation and ethanol inhibition established.     

Adenylate cyclase of catfish hepatocyte membranes: basal properties and sensitivity to catecholamines and glucagon

Some characteristics of adenylate cyclase of catfish (Ictalurus melas) liver membranes were studied, and the effects of catecholamines and of glucagon were tested. The enzyme has an optimum temperature of 40 °C, and a K_m for ATP of 0.16 mM at 30 °C, and requires Mg²⁺ for its activity. The enzyme activity is inhibited with a Ca²⁺ concentration higher than 5 × 10⁻⁵ M, and enhanced with F⁻ higher than 10⁻⁴ M. The response of adenylate cyclase to GTP is biphasic, with a maximum of activity at 10⁻⁵ M GTP. Catecholamines (epinephrine, norepinephrine, isoproterenol, phenylephrine) enhance cyclase activity. Propranolol inhibits the increase in enzyme activity induced by catecholamines, whereas phentolamine is ineffective. This indicates that catecholamines (phenylephrine included) activate adenylate cyclase through a β-adrenergic mechanism. Glucagon (mammalian) has a smaller effect than epinephrine in increasing the enzyme activity of catfish hepatocyte membranes. This fact is the opposite of that observed for the cyclase activity of rat liver membranes.     

In vivo and in vitro effects of the pineal gland and melatonin on [Ca2++ Mg2+]-dependent ATPase in cardiac sarcolemma

Abstract: The possible diurnal variation in cardiac [Ca²⁺+ Mg²⁺]-dependent ATPase (Ca²⁺ pump) activity and the influence of pinealectomy and melatonin on this enzyme in rat heart have been studied. Lowest levels of cardiac sarcolemma] membrane [Ca²⁺+ Mg²⁺]-dependent ATPase activity were measured in late afternoon in rats kept under a 14:10 light:dark cycle. Late in the dark phase the enzyme activity began to increase with the rise continuing until 0900, 3 hr after light onset. These time-dependent changes in [Ca²⁺+ Mg²⁺]-dependent ATPase activity did not occur in either pinealectomized or light-exposed rats suggesting that melatonin, secreted from the pineal gland during the night, induces the change in [Ca²⁺+ Mg²⁺]-dependent ATPase activity. In vitro studies in which cardiac tissue was incubated in the presence of melatonin over a wide range of doses showed that this indole stimulated the Ca²⁺ pump. The half-maximal effect of melatonin was observed at a melatonin concentration of 28 ng/ml. These findings suggest that the daily change in [Ca²⁺+ Mg²⁺]-dependent ATPase activity in the sarcolemma of heart tissue is a result of the circadian rhythm in pineal melatonin production and secretion. These findings may be applicable to normal cardiac physiology.     

Mechanisms of cholecystokinin-induced calcium mobilization in gastric antral interstitial cells of Cajal

AIM:To investigate the effect of sulfated cholecystokinin-8(CCK-8S) on calcium mobilization in cultured murine gastric antral interstitial cells of Cajal(ICC) and its possible mechanisms.METHODS:ICC were isolated from the gastric antrum of mice and cultured.Immunofluorescence staining with a monoclonal antibody for c-Kit was used to identify ICC.The responsiveness of ICC to CCK-8S was measured using Fluo-3/AM based digital microfluorimetric measurement of intracellular Ca2+ concentration([Ca2+]i).A confocal laser scanning microscope was used to monitor [Ca2+]i changes.The selective CCK1 receptor antagonist lorglumide,the intracellular Ca2+-ATPase inhibitor thapsigargin,the type Ⅲ inositol 1,4,5-triphosphate(InsP3) receptor blocker xestospongin C and the L-type voltage-operated Ca2+ channel inhibitor nifedipine were used to examine the mecha-nisms of [Ca2+]i elevation caused by CCK-8S.Immunoprecipitation and Western blotting were used to determine the regulatory effect of PKC on phosphorylation of type Ⅲ InsP3 receptor(InsP3R3) in ICC.Protein kinase C(PKC) activator phorbol 12-myristate 13-acetate(PMA) and inhibitor chelerythrine were used to assess the role of PKC in the CCK-8S-evoked [Ca2+]i increment of ICC.RESULTS:ICC were successfully isolated from the gastric antrum of mice and cultured.Cultured ICC were identified by immunofluorescence staining.When given 80 nmol/L or more than 80 nmol/L CCK-8S,the [Ca2+]i in ICC increased and 100 nmol/L CCK-8S significantly increased the mean [Ca2+]i by 59.30% ± 4.85%(P 0.01).Pretreatment of ICC with 5 μmol/L lorglumide inhibited 100 nmol/L CCK-8S-induced [Ca2+]i increment from 59.30% ± 4.85% to 14.97% ± 9.05%(P 0.01),suggesting a CCK1R-mediated event.Emptying of intracellular calcium stores by thapsigargin(5 μmol/L) prevented CCK-8S(100 nmol/L) from inducing a [Ca2+]i increase.Moreover,pretreatment with xestospongin C(1 μmol/L) could also abolish the CCK-8S-induced effect,indicating that Ca2+ release from InsP3R-operated stores appeared to be a major mechanism responsible for CCK-8S-induced calcium mobilization in ICC.On the other hand,by removing extracellular calcium or blocking the L-type voltage-operated calcium channel with nifedipine,a smaller but significant rise in the [Ca2+]i could be still elicited by CCK-8S.These data suggest that the [Ca2+]i release is not stimulated or activated by the influx of extracellular Ca2+ in ICC,but the influx of extracellular Ca2+ can facilitate the [Ca2+]i increase evoked by CCK-8S.CCK-8S increased the phosphorylation of InsP3R3,which could be prevented by chelerythrine.Pretreatment with lorglumide(5 μmol/L) could significantly reduce the CCK-8S intensified phosphorylation of InsP3R3.In the positive control group,treatment of cells with PMA also resulted in an enhanced phosphorylation of InsP3R3.Pretreatment with various concentrations of PMA(10 nmol/L-10 μmol/L) apparently inhibited the effect of CCK-8S and the effect of100 nmol/L PMA was most obvious.Likewise,the effect of CCK-8S was augmented by the pretreatment with chelerythrine(10 nmol/L-10 μmol/L) and 100 nmol/L chelerythrine exhibited the maximum effect.CONCLUSION:CCK-8S increases [Ca2+]i in ICC via the CCK1 receptor.This effect depends on the release of InsP3R-operated Ca2+ stores,which is negatively regulated by PKC-mediated phosphorylation of InsP3R3.     

结核性与恶性胸腔积液中CD4+CD25+调节性T细胞及相关因子的检测

目的检测结核性胸腔积液及恶性胸腔积液中D₄⁺ CD₂₅⁺调节性T细胞的分布与可溶性白介素-2受体(sIL-2R)及转化生长因子β1(TGF-β1)浓度,并探讨良恶性胸腔积液患者的局部免疫机制。方法47例结核性胸腔积液及34例肺癌并恶性胸腔积液患者于第1次抽液时留取胸腔积液,ELISA法检测sIL-2R及TGF-β1的浓度,Ficoll梯度离心分离单个核细胞,抗体标记后应用流式细胞仪分析D₄⁺ CD₂₅⁺调节性T细胞占淋巴细胞的比例。结果47例结核性胸腔积液与34例肺癌并恶性胸腔积液中D₄⁺ CD₂₅⁺调节性T细胞占淋巴细胞的比例分别为(8.7±0.6)%、(21.1±2.3)%,有显著性差异(P<0.05);结核性胸腔积液与恶性胸腔积液中sIL-2R浓度分别为(563.2±92.61)ng/ml,(390.12±101.12)ng/ml,有显著性差异(P<0.05);恶性胸腔积液中TGF-β1的水平(88.4±16.7mg/L),显著高于结核性胸腔积液组(40.3±3.6mg/L),结核性胸腔积液中sIL-2R、TGF-β1浓度与D₄⁺ CD₂₅⁺调节性T细胞占淋巴细胞的比例均无明显相关关系(P>0.05)。结论D₄⁺ CD₂₅⁺调节性T细胞,sIL-2R及TGF-β1可作为判定结核或恶性胸腔积液的辅助诊断指标。     

Depressed Cheek Cell Sodium Transport in Human Hypertension

Na⁺ transport activity was measured in cheek cells from untreated hypertensive subjects and age-matched normotensive controls identified from a blood pressure screening program. Cheek cells were isolated by a simple mouth wash procedure and Na⁺ transport activity was measured as the proton-dependent uptake of ²²Na⁺ using a rapid filtration assay. The rate of Na⁺ uptake was about 45% lower in hypertensive subjects and this difference persisted in a follow up study 2 years later involving those subjects who remained untreated for their hypertension. The proton independent Na⁺ uptake was also reduced by about 46% in the hypertensive group. The increase in the rate of cheek cell Na⁺ transport with increasing transcellular proton gradient values was also significantly lower in hypertensive subjects. The reduced cheek cell Na⁺ transport observed in hypertensive subjects may indicate decreased activity of the Na⁺/H⁺ antiporter and/or changes in the ion permeability properties of the cheek cell plasma membrane in the hypertensive state. This novel assay provides a biochemically based method for discriminating between normotensive and hypertensive subjects and makes use of tissue which can be obtained in a relatively non-invasive manner.     

Calcium-mediated mechanisms of eicosapentaenoic acid-induced relaxation in hypertensive rat aorta

We have previously demonstrated the vasorelaxant properties of the omega-3 fatty acid, eicosapentaenoic acid (EPA), in normotensive and spontaneously hypertensive rat (SHR) aorta, although the mechanism(s) of action are not fully understood. Because endothelial dysfunction and increased intracellular free calcium concentration ([Ca²⁺]_i) are seen in hypertensive rat aorta, we investigated the potential role of Ca²⁺ signaling, endothelium and derived factors, and the opening of potassium (K⁺) channels in EPA-induced relaxation. In the presence of extracellular Ca²⁺, EPA induced significant relaxations at > 10 μmol/L (P < .01) in norepinephrine (NE) (10⁻⁶ mol/L)-contracted aortic rings and at 30 μmol/L (P <. 001) in high K⁺ (80 mmol/L)-contracted aortic rings. In the absence of extracellular Ca²⁺, EPA (10 to 30 μmol/L) inhibits the tonic component of NE-induced contraction (P < .0001). The relaxant properties of EPA in SHR aorta appear specific to Ca²⁺ release from an internal storage site associated with NE-induced tonic contraction. Further studies with the use of fura-2 to measure [Ca²⁺]_i in cultured vascular smooth muscle (VSM) cells from SHR aorta indicated that EPA (30 μmol/L)-pretreatment attenuated angiotensin II (50 nmol/L)-induced Ca²⁺ transient by 95%, suggesting that an inhibitory effect on the Ca²⁺ signaling may underlie EPA-induced relaxation of the vessel preparation. In addition, EPA per se induced an increase in [Ca²⁺]_i with a duration of approximately 20 min in VSM cells, and the effect was not altered by removal of extracellular Ca²⁺. There was no increase in the level of inositol-1,4,5-trisphosphate in response to EPA (30 μmol/L). The actions of EPA are independent of endothelium-derived factors, cyclooxygenase metabolites, and activation of K⁺ channels since endothelium removal, N^ω-nitro- -arginine methyl ester hydrochloride, (L-NAME, 100 μmol/L), indomethacin (10 μmol/L), tetraethylammonium (1 mmol/L), and glibenclamide (10 μmol/L) did not affect EPA-induced vasodilation in NE-precontracted aortic rings. These results suggest that EPA directly modulates intracellular Ca²⁺ signaling in VSM cells, and that this may contribute to the vasorelaxant effect and, at least in part, the blood pressure-lowering effect of fish oil.