Control of the erythrocyte free Ca2+ concentration in essential hypertension

Erythrocyte Deformability and Na,K-ATPase Activity in Various Pathophysiological Situations and Their Protection by Selected Nutritional Antioxidants in Humans

The physicochemical and functional properties of erythrocytes are worsened in a variety of diseases. Erythrocyte deformability refers to their ability to adjust their shape according to external forces exerted against them in the circulation. It is influenced by the functionality of the Na,K-ATPase enzyme, which is localized in their membranes. The proposed review is focused on knowledge regarding changes in erythrocyte Na,K-ATPase activity, and their impact on erythrocyte deformability in various pathophysiological situations observed exclusively in human studies, as well as on the potential erytroprotective effects of selected natural nutritional antioxidants. A clear link between the erythrocyte properties and the parameters of oxidative stress was observed. The undesirable consequences of oxidative stress on erythrocyte quality and hemorheology could be at least partially prevented by intake of diverse antioxidants occurring naturally in foodstuffs. Despite intensive research concerning the effect of antioxidants, only a small number of investigations on erythrocyte properties in humans is available in databases. It is worth shifting attention from animal and in vitro experiments and focusing more on antioxidant administration in human studies in order to establish what type of antioxidant, in what concentration, and in which individuals it may provide a beneficial effect on the human organism, by protecting erythrocyte properties.

Calcium/protein kinase C signaling mechanisms in shear-induced mechanical responses of red blood cells

Red blood cell (RBC) deformability has vital importance for microcirculation in the body, as RBCs travel in narrow capillaries under shear stress. Deformability can be defined as a remarkable cell ability to change shape in response to an external force which allows the cell to pass through the narrowest blood capillaries. Previous studies showed that RBC deformability could be regulated by Ca²⁺/protein kinase C (PKC) signaling mechanisms due to the phosphorylative changes in RBC membrane proteins by kinases and phosphatases. We investigated the roles of Ca²⁺/PKC signaling pathway on RBC mechanical responses and impaired RBC deformability under continuous shear stress (SS). A protein kinase C inhibitor Chelerythrine, a tyrosine phosphatase inhibitor Calpeptin, and a calcium channel blocker Verapamil were applied into human blood samples in 1 micromolar concentration. Samples with drugs were treated with or without 3 mM Ca²⁺. A shear stress at 5 Pa level was applied to each sample continuously for 300 s. RBC deformability was measured by a laser-assisted optical rotational cell analyzer (LORRCA) and was calculated as the change in elongation index (EI) of RBC upon a range of shear stress (SS, 0.3-50 Pa). RBC mechanical stress responses were evaluated before and after continuous SS through the parameterization of EI-SS curves. The drug administrations did not produce any significant alterations in RBC mechanical responses when they were applied alone. However, the application of the drugs together with Ca²⁺ substantially increased RBC deformability compared to calcium alone. Verapamil significantly improved Ca²⁺-induced impairments of deformability both before and after 5 Pa SS exposure (p < 0.0001). Calpeptin and Chelerythrine significantly ameliorated impaired deformability only after continuous SS (p < 0.05). Shear-induced improvements of deformability were conserved by the drug administrations although shear-induced deformability was impaired when the drugs were applied with calcium. The blocking of Ca²⁺ channel by Verapamil improved impaired RBC mechanical responses independent of the SS effect. The inhibition of tyrosine phosphatase and protein kinase C by Calpeptin and Chelerythrine, respectively, exhibited ameliorating effects on calcium-impaired deformability with the contribution of shear stress. The modulation of Ca²⁺/PKC signaling pathway could regulate the mechanical stress responses of RBCs when cells are under continuous SS exposure. Shear-induced improvements in the mechanical properties of RBCs by this signaling mechanism could facilitate RBC flow in the microcirculation of pathophysiological disorders, wherein Ca²⁺ homeostasis is disturbed and RBC deformability is reduced.

The role of red blood cell deformability and Na,K-ATPase function in selected risk factors of cardiovascular diseases in humans: focus on hypertension, diabetes mellitus and hypercholesterolemia

Deformability of red blood cells (RBC) is the ability of RBC to change their shape in order to pass through narrow capillaries in circulation. Deterioration in deformability of RBC contributes to alterations in microcirculatory blood flow and delivery of oxygen to tissues. Several factors are responsible for maintenance of RBC deformability. One of them is the Na,K-ATPase known as crucial enzyme in maintenance of intracellular ionic homeostasis affecting thus regulation of cellular volume and consequently RBC deformability. Decreased deformability of RBC has been found to be the marker of adverse outcomes in cardiovascular diseases (CVD) and the presence of cardiovascular risk factors influences rheological properties of the blood. This review summarizes knowledge concerning the RBC deformability in connection with selected risk factors of CVD, including hypertension, hyperlipidemia, and diabetes mellitus, based exclusively on papers from human studies. We attempted to provide an update on important issues regarding the role of Na,K-ATPase in RBC deformability. In patients suffering from hypertension as well as diabetes mellitus the Na,K-ATPase appears to be responsible for the changes leading to alterations in RBC deformability. The triggering factor for changes of RBC deformability during hypercholesterolemia seems to be the increased content of cholesterol in erythrocyte membranes.

Calcium and Magnesium ATPase Activities in Women with Varying BMIs

OBJECTIVE

Intracellular calcium (Ca) is increased in obese humans, and magnesium (Mg)-ATPase activity is increased in monosodium glutamate-induced obese rats. The aims of this study were to test the hypotheses that Ca-ATPase activity is negatively correlated with BMI, and that Mg-ATPase activity is positively correlated with BMI and Ca-ATPase activity in obese women.

RESEARCH METHODS AND PROCEDURES

Thirty healthy adult women, with BMIs of 20 to 40, donated a single sample of whole blood and were interviewed as to medical history and family history of obesity. Erythrocyte membranes were isolated and assayed for Ca-ATPase and Mg-ATPase. Weight and height were self-reported. Regression analysis was used to determine relationship between BMI and enzyme activity. Family history of obesity served as a covariant.

RESULTS

Ca-ATPase was negatively correlated with increasing BMI (r = - 0.38, p = 0.02). The relationship between BMI and Ca-ATPase remained valid after controlling for family history of obesity (r = -0.36, p = 0.03). There was a positive correlation between Mg-ATPase activity and Ca-ATPase (r = 0.42, p = 0.024), and this relationship remained valid after controlling for BMI and family history of obesity (r = 0.41, p = 0.03).

DISCUSSION

Ca-ATPase activity decreases as BMI increases. Decreased ATPase activity may contribute to increased intracellular calcium, previously reported in obese persons. Further studies are needed to determine whether a drop in Ca-ATPase activity can serve as a marker for the development of obesity.

The effects of exercise conditioning in normal and overweight pregnant women on blood pressure and heart rate variability

Pre-pregnancy obesity is a risk factor for preeclampsia, gestational diabetes, and hypertension. Regular exercise during pregnancy has been shown to decrease the risk of these obstetrical complications. The purpose of this prospective study was to measure the effects of an exercise program in normal-weight and overweight/obese pregnant women on blood pressure (BP) and cardiac autonomic function, determined by heart rate variability (HRV) and baroreflex sensitivity (BRS). Twenty-two sedentary pregnant women, recruited at 20 weeks gestational age (GA), were grouped as normal weight or overweight/obese. They were systematically assigned to an exercise (walking) group or control (nonwalking) group after the first participants were randomly assigned. Women in the walking groups participated in a 16-week, low-intensity walking program. BP, HRV, and BRS were measured at rest and during exercise at the beginning (20 weeks GA) and end (36 weeks GA) of the walking program. Results indicated that women in the control groups (especially overweight women) showed changes in BP, HRV, and BRS over pregnancy that were not seen in the walking group. Overweight women in the control group increased resting systolic BP by 10 mmHg and diastolic BP by 7 mmHg. HRV declined in the control group but not in the walking group. A reduction in BRS and R-R interval at rest was found in all groups except the walking normal-weight group. The results suggest that an exercise program could attenuate the increase in BP and the loss of parasympathetic tone associated with pregnancy, especially in overweight women.

Impaired erythrocyte filterability of spontaneously hypertensive rats: investigation by nickel filtration technique

BACKGROUND

Deformability of erythrocytes plays a key role in the impairment of the microcirculation in hypertension. However, erythrocyte deformability in spontaneously hypertensive rats (SHR) during development of hypertension has not been fully investigated so far.

METHODS AND RESULTS

Erythrocyte filterability (whole cell deformability) was investigated in relation to blood pressure measured by the tail-cuff method in SHR and age-matched Wistar-Kyoto rats (WKY), using a highly sensitive and reproducible nickel mesh filtration technique. Impaired erythrocyte filterability was marked (37.0+/-17.5%) in prehypertensive young SHR (7 weeks of age) and sustained (51.6+/-13.3%) in hypertensive mature SHR (18 weeks of age), when compared with that of age-matched WKY (62.1+/-7.2% in 7 weeks of age, P<0.005, and 71.1+/-3.9% in 18 weeks of age, P<0.005, respectively). This impairment in SHR could not be explained by the mean corpuscular volume or mean corpuscular hemoglobin concentration of erythrocytes, but the erythrocyte count was significantly (P<0.005) greater in SHR than in the age-matched WKY.

CONCLUSIONS

Although the precise mechanisms remain to be elucidated, markedly impaired erythrocyte filterability in SHR is considered to contribute to the development and maintenance of genetic hypertension. (Circ J 2010; 74: 129 - 136).

Small Artery Remodeling and Erythrocyte Deformability in L-NAME-Induced Hypertension: Role of Transglutaminases

BACKGROUND

Hypertension is associated with inward remodeling of small arteries and decreased erythrocyte deformability, both impairing proper tissue perfusion. We hypothesized that these alterations depend on transglutaminases, cross-linking enzymes present in the vascular wall, monocytes/macrophages and erythrocytes.

METHODS AND RESULTS

Wild-type (WT) mice and tissue-type transglutaminase (tTG) knockout (KO) mice received the nitric oxide inhibitor Nomega-nitro-L-arginine methyl ester hydrochloride (L-NAME) to induce hypertension. After 1 week, mesenteric arteries from hypertensive WT mice showed a smaller lumen diameter (-6.9 +/- 2.0%, p = 0.024) and a larger wall-to-lumen ratio (11.8 +/- 3.5%, p = 0.012) than controls, whereas inward remodeling was absent in hypertensive tTG KO mice. After 3 weeks, the wall-to-lumen ratio was increased in WT (20.8 +/- 4.8%, p = 0.005) but less so in tTG KO mice (11.7 +/- 4.6%, p = 0.026), and wall stress was normalized in WT but not in tTG KO mice. L-NAME did not influence expression of tTG or an alternative transglutaminase, coagulation factor XIII (FXIII). Suppression of FXIII by macrophage depletion was associated with increased tTG in the presence of L-NAME. L-NAME treatment decreased erythrocyte deformability in the WT mice (-15.3% at 30 dynes/cm(2), p = 0.014) but not in the tTG KO mice.

CONCLUSION

Transglutaminases are involved in small artery inward remodeling and erythrocyte stiffening associated with nitric oxide inhibition-related hypertension.

Electrolytes and pH changes in pre-eclamptic rats

BACKGROUND

Intracellular free calcium [Ca2+]i and magnesium [Mg2+]i ions play major roles in the mechanism of vascular smooth muscle (VSM) contraction. Although essential hypertension and abnormal intracellular homeostasis of these ions have long been recognized as major icons in the pathogenesis of pre-eclampsia, the underlying mechanism(s) remain poorly understood.

METHODS

Alterations of vascular smooth muscle and platelet intracellular cations [Ca2+]i, [Mg2+]i and [H+]i relative to plasma concentrations of these ions in nitric oxide synthase (NOS) blockade-induced models of pre-eclampsia have been evaluated in the present study.

RESULTS

Pregnant rats injected with the NOS inhibitor, NG-nitro-L-arginine methyl ester (L-NAME) developed a significantly elevated arterial blood pressure, proteinuria and other clinical parameters characteristic of pre-eclampsia compared to age-matched pregnant and non-pregnant rat controls that received the L-NAME vehicle only. Plasma total calcium concentration was significantly lower in pre-eclamptic rat models compared to normal pregnant rats (10.29+/-0.08 vs 10.67+/-0.18 mg/dl, p<0.05). A significant increase in plasma calcium was observed in pregnant controls compared to non-pregnant rats (10.67+/-0.18 vs 10.14+/-0.09 mg/dl, p<0.01). Plasma Ca2+ levels in pre-eclamptic rats were consistently lower than those of pregnant controls (5.69+/-0.09 vs 5.98+/-0.06 mg/dl, p<0.05). Resting levels of [Ca2+]i was significantly higher in pre-eclamptic rats than in pregnant controls. (351+/-45.2 vs 196+/-23.2 nmol/l, p<0.01). Blood pH was significantly increased in pre-eclamptic rats as compared to pregnant controls (7.16+/-0.02 vs 7.05+/-0.03, p<0.05). There was no significant difference in plasma and intracellular magnesium concentrations between the three rat groups.

CONCLUSIONS

These findings suggest that a significantly decreased plasma level of Ca2+ coupled with a concomitant increase in VSM [Ca2+]i concentrations and an altered blood pH are associated with pre-eclampsia in the pregnant rat. Routine monitoring of serum pH, Ca2+ and Mg2+ especially in the late third trimester, may have potential in the early detection of patients at risk for pre-eclampsia, and monitoring the progress of diverse therapeutic regimens during clinical management.

Calcium imaging of individual erythrocytes: Problems and approaches

Although in erythrocytes calcium is thought to be important in homeostasis, measurements of this ion concentration are generally seen as rather problematic because of the auto-fluorescence or absorption properties of the intracellular milieu. Here, we describe experiments to assess the usability of popular calcium indicators such as Fura-2, Indo-1 and Fluo-4. In our experiments, Fluo-4 turned out to be the preferable indicator because (i) its excitation and emission properties were least influenced by haemoglobin and (ii) it was the only dye for which excitation light did not lead to significant auto-fluorescence of the erythrocytes. From these results, we conclude that the use of indicators such as Fura-2 together with red blood cells has to be revisited critically. We thus utilized Fluo-4 in erythrocytes to demonstrate a robust but heterogeneous calcium increase in these cells upon stimulation by prostaglandin E(2) and lysophosphatidic acid. For the latter stimulus, we recorded emission spectra of individual erythrocytes to confirm largely unaltered Fluo-4 emission. Our results emphasize that in erythrocytes measurements of intracellular calcium are reliably possible with Fluo-4 and that other indicators, especially those requiring UV-excitation, appear less favourable.

Prognostic impact of low-shear whole blood viscosity in hypertensive men

BACKGROUND

The role of blood viscosity as a marker for discriminating cardiovascular risk in essential hypertension remains uncertain. The aim of this study was to assess whether whole blood viscosity (WBV) could be useful in assessing cardiovascular risk in men with a first diagnosis of hypertension.

DESIGN

A total of 331 middle-aged men with newly diagnosed essential hypertension (age at entry 40-64 years, average blood pressure 151/95 mmHg) underwent low-shear-rate (0.94 s(-1)) and high-shear-rate (94.5 s(-1)) WBV determination and were then followed for a mean of 4.8 +/- 3 years (range 0-12 years).

RESULTS

Cardiovascular event rates in the bottom, middle and top tertiles of the distribution of low-shear WBV were 1.10, 2.13 and 4.43 per 100 patient-years, respectively (log-rank test, P < 0.001). After taking into account several established cardiovascular risk factors in a Cox survival analysis, a raised low-shear WBV conferred an increased risk for cardiovascular events (top vs. bottom tertile hazard ratio = 3.42, 95% confidence interval = 1.4-8.4, P = 0.006; middle vs. bottom tertile hazard ratio = 2.25, 95% confidence interval = 0.9-5.6, P = 0.09). The independent association between high-shear-rate WBV and cardiovascular events bordered statistical significance (P = 0.07). Inclusion in the survival model of low-shear-rate resulted in a significantly greater chi(2) improvement (P < 0.05) than inclusion of high-shear-rate WBV.

CONCLUSIONS

In hypertensive men, an increased WBV at low shear rate is a predictor of cardiovascular events independently from the effect of several traditional risk factors. Low-shear WBV is a better discriminator of cardiovascular risk than high-shear WBV.

Chronological changes of alpha-adrenoceptor-mediated vascular constriction in Otsuka-Long-Evans-Tokushima fatty rats

In recent years, it has been suggested that many factors are involved in the development of hypertension accompanying insulin resistance. Because changes in vascular reactivity could be one of these factors, we here investigated chronological changes of alpha-adrenoceptor (AR)-mediated peripheral arteriolar vasoconstriction in a rat model of type II diabetes. Otsuka-Long-Evans-Tokushima fatty (OLETF) rats that naturally develop insulin resistance at the age of 16 weeks and type II diabetes at the age of 30 weeks (DM group) and control rats (N group) were used. Arterioles with a diameter of approximately 100 microm were removed from the cremaster muscle of 8-, 16- and 40-week-old rats and their diameters were measured in a tissue bath. The concentration-response curve (CRC) was determined for phenylephrine and UK14,304 both with and without N(G)-monomethyl-L-arginine (LNMMA). Although there were no significant differences in the CRC for phenylephrine between the 8-week-old DM group and N group, a leftward shift was seen for the 16- and 40-week-old DM groups. There were no significant differences in the CRC for UK14,304 between the two groups at any age, but in the presence of LNMMA, a leftward shift was seen in the 8- and 16-week-old but not in the 40-week-old DM groups. One possible explanation for these results is that impaired endothelium-dependent dilatation may have offset the reduction in arteriolar smooth muscle contraction. In conclusion, in the OLETF rats, the sensitivity of alpha-AR-mediated arteriolar vasoconstriction increased after the onset of insulin resistance. The sensitivity of alpha2-AR-mediated arteriolar smooth muscle contraction and endothelium-dependent vascular relaxation were both presumed to be impaired after the onset of type II diabetes.

Phorbol ester stimulates a protein kinase C-mediated agatoxin-TK-sensitive calcium permeability pathway in human red blood cells

Calcium entry into mature erythrocytes (red blood cells; RBCs) is associated with multiple changes in cell properties. At low intracellular Ca(2+), efflux of potassium and water predominates, leading to changes in erythrocyte rheology. At higher Ca(2+) content, activation of kinases and phosphatases, rupture of membrane-to-skeleton bridges, stimulation of a phospholipid scramblase and phospholipase C, and induction of transglutaminase-mediated protein cross-linking are also observed. Because the physiologic relevance of these latter responses depends partially on whether Ca(2+) entry involves a regulated channel or nonspecific leak, we explored mechanisms that initiate controlled Ca(2+) influx. Protein kinase C (PKC) was considered a prime candidate for the pathway regulator, and phorbol-12 myristate-13 acetate (PMA), a stimulator of PKC, was examined for its influence on erythrocyte Ca(2+). PMA was found to stimulate a rapid, dose-dependent influx of calcium, as demonstrated by the increased fluorescence of an entrapped Ca(2+)-sensitive dye, Fluo-3/AM. The PMA-induced entry was inhibited by staurosporine and the PKC-selective inhibitor chelerythrine chloride, but was activated by the phosphatase inhibitors okadaic acid and calyculin A. The PMA-promoted calcium influx was also inhibited by omega-agatoxin-TK, a calcium channel blocker specific for Ca(v)2.1 channels. To confirm that a Ca(v)2.1-like calcium channel exists in the mature erythrocyte membrane, RBC membrane preparations were immunoblotted with antiserum against the alpha(1A) subunit of the channel. A polypeptide of the expected molecular weight (190 kDa) was visualized. These studies indicate that an omega-agatoxin-TK-sensitive, Ca(v)2.1-like calcium permeability pathway is present in the RBC membrane and that it may function under the control of kinases and phosphatases.

Optimizing blood pressure control in the obese patient

Obesity is a major public health issue, and hypertension is one of the most common associated comorbidities. Current guidelines for optimal blood pressure levels in obese patients or for the treatment of obesity-hypertension do not provide specific recommendations that go beyond the rather general recommendation to lose weight. Based on the strong ties between obesity, hypertension, and type 2 diabetes, and the similarity of complications that occur in obesity-related hypertension and in hypertension associated with type 2 diabetes, it seems appropriate to explore the optimal blood pressure levels for obese hypertensive patients. Recently published studies underline the importance of weight reduction to reach this goal. Several lines of reasoning support the use of angiotensin converting enzyme inhibitors or angiotensin receptor blockers as the appropriate first-line therapy in obese patients with uncomplicated hypertension. Nondihydropyridine calcium channel blockers, a-blockers, or low-dose diuretics may be added when necessary. Clearly, further studies are needed to define target blood pressure levels in obese patients and to clarify the value of established and newer drugs, like angiotensin receptor blockers, for the treatment of obese hypertensive patients. The role of antiobesity drugs in the management of the obese hypertensive patient also remains to be defined.

Normal erythrocyte calpain I activity on membrane proteins under near-physiological conditions in patients with essential hypertension

CONTEXT

It has been reported that the equilibrium between the erythrocyte protease calpain I and its physiological inhibitor calpastatin is disrupted in patients with essential hypertension.

OBJECTIVE

To investigate the activity of non-purified calpain I in hemolysates against the erythrocytic membrane proteins, rather than against other substrates.

DESIGN

Evaluation of calpain I red cell activity upon its own physiological substrates in hypertensive patients, in a near-physiological environment.

SETTING

LIM-23 and LIM-40 of Hospital das Clinicas of the Faculty of Medicine of USP.

SAMPLE

Patients with moderate primary hypertension over 21 years of age who were given amlodipine (n:10) and captopril (n:10) for 8 weeks, plus normal controls (n:10).

MAIN MEASUREMENTS

Red cell membrane proteins were incubated with and without protease inhibitors and with and without calcium chloride and underwent polyacrylamide gel electrophoresis.

RESULTS

Digestion of bands 2.1 and 4.1 was observed, indicating calpain I activity. No statistical differences regarding bands 2.1 and 4.1 were observed before treatment, between the controls and the hypertensive patients, either in ghosts prepared without calcium or with increasing concentrations of calcium. Nor were statistical differences observed after treatment, between the controls and the patients treated with amlodipine and captopril, or between the patients before and after treatment with both drugs.

CONCLUSION

The final activity of non-purified calpain I upon its own physiological substrate, which was the approach utilized in this study, may more adequately reflect what happens in red cells. Under such conditions no imbalance favoring calpain I activity increase was observed. The protective factor provided by calpastatin against calpain I activity may diminish under hypertension.

Role of the sympathetic adrenal system in the pathogenesis of the insulin resistance syndrome

The pathophysiology of the various manifestations of Syndrome X has been poorly understood. A possible mechanism involves stimulation of the sympathetic nervous system (SNS). Insulin plays an important role in the relationship between dietary intake and SNS activity. Because insulin-mediated glucose uptake in central hypothalamic neurons regulates SNS activity in response to dietary intake, a hypothesis was developed that links the hyperinsulinemia of obesity to sympathetic stimulation, the latter exerting a prohypertensive effect mediated by the kidney, the heart, and the vasculature. Evidence in support of this hypothesis has been obtained from the Normative Aging Study (NAS) in which a relationship between insulin (and glucose) and the SNS, and between insulin and SNS activity and blood pressure was demonstrated. The characteristic dyslipidemia in NAS subjects, moreover, was related to insulin and epinephrine. As reported in other studies, insulin level was directly associated with low HDL and high triglyceride levels. An independent inverse association was also noted between urinary epinephrine excretion and lipid levels: high epinephrine excretion rates were associated with high HDL and low triglyceride levels and, conversely, low epinephrine excretion was associated with low HDL and high triglycerides. In the NAS, therefore, increased SNS activity contributes to hypertension while diminished adrenal medullary activity contributes to the low HDL and high triglyceride levels commonly seen in association with hypertension.

Combined SSCP and heteroduplex analysis of the human plasma membrane Ca(2+)-ATPase isoform 1 in patients with essential hypertension

In recent theories concerning the pathogenesis of essential hypertension, altered calcium homeostasis plays an important role. Increased intracellular Ca(2+) levels have repeatedly been reported in different cell types of hypertensive subjects. In vascular smooth muscle cells the plasma membrane Ca(2+)-ATPase (PMCA) represents the most important Ca(2+)-ejection system. Modifications of this pump therefore have been assumed to increase contractile tone of small vessels. For this reason, the purpose of this study was to determine if genetic alterations in the hPMCA1 gene might be associated with arterial hypertension. For detection of polymorphisms all 22 PMCA1 exons from 44 patients with essential hypertension (based on rigorous clinical data in addition to a positive family history) and from 40 normotensives without a family history of hypertension were PCR amplified and subsequently subjected to combined single-strand conformation polymorphism (SSCP) and heteroduplex (HTX) analysis. Despite the high sensitivity of almost 100%, differences could not be identified between hypertensives and normotensives within the two groups. These data indicate that at least in this population PMCA1 polymorphisms are presumably not related to common forms of essential hypertension. Furthermore, the high degree of evolutionary conservation of the PMCA1 gene underlines the pivotal role of this ATPase for cell physiology.

Erythrocyte voltage-dependent calcium influx is reduced in hemodialyzed patients

BACKGROUND

Uremia displays increased cytosolic free calcium ([Ca2+]i) in many different cell types, supporting the hypothesis of an altered Ca2+ transport modifying the functional activity of calcium signaling pathway.

METHODS

Thirty-five hemodialyzed patients and 20 age-matched subjects were studied. Erythrocyte resting [Ca2+]i and Ca2+ influx were measured by the fluorescent Ca2+-sensitive dye fura-2.

RESULTS

We found an increase of resting [Ca2+]i in erythrocytes from uremic hemodialyzed patients compared with matched healthy controls (103 +/- 2.5 nM, N = 20, vs. 90 +/- 4, N = 20, P < 0.01). Moreover, we found an altered voltage-dependent Ca2+ influx showing a reduced transport rate (0.42 +/- 0.03 nM/second vs. 0.74 +/- 0.08, P < 0.01). High levels of plasma parathyroid hormone (PTH) were related to augmented Ca2+ entry (r = 0.511, P < 0.05), contributing to maintain a high level of [Ca2+]i. Hemodialysis had no effect on cell calcium level and Ca2+ influx indices. The therapy with Ca2+ antagonists did not modify the values of resting [Ca2+]i or Ca2+ influx indices, but the correlation between PTH and influx indices was lost.

CONCLUSIONS

In conclusion, we found evidence for an alteration of erythrocyte Ca2+ influx caused by uremic toxicity that could be related to some organ disorders in uremia. The chronic increase of cellular calcium may contribute to influx derangement.

Lymphocyte intracellular free calcium concentration is increased in preeclampsia

OBJECTIVES

We tested 2 hypotheses: (1) Preeclampsia is characterized by an increase in intracellular free calcium concentration in lymphocytes. (2) Levels of intracellular free calcium are influenced by the calcium concentration in the extracellular milieu or by parathyroid hormone.

STUDY DESIGN

Intracellular free calcium concentrations were measured in 4 groups of women: nonpregnant women (n = 25), normotensive pregnant women (n = 30), pregnant women with chronic hypertension (n = 15), and women with preeclampsia (n = 15). Intracellular free calcium concentration was measured in the basal state, at varying extracellular calcium ion concentrations, and in the presence of exogenous parathyroid hormone.

RESULTS

Women with preeclampsia had the highest basal lymphocyte intracellular free calcium concentration (121 +/- 7 nmol/L, mean +/- SEM) compared with normotensive pregnant women during the third trimester (94 +/- 3 nmol/L, P <.001) and pregnant women in the third trimester with chronic hypertension (100 +/- 3 nmol/L, P <.01). During the third trimester normotensive women and women with chronic hypertension had significantly higher basal intracellular free calcium concentrations than were found in women during the first trimester. Exposure of lymphocytes to an extracellular milieu of low calcium concentration resulted in an increase in intracellular free calcium concentration. Incubation with parathyroid hormone had no effect on intracellular free calcium concentration.

CONCLUSIONS

Lymphocyte intracellular free calcium concentration is increased in preeclampsia and not in chronic hypertensive pregnancy and is greater during the third trimester than during the first trimester. Extracellular calcium depletion increases lymphocyte intracellular free calcium concentration. These data support the idea that a calcium deficit leading to an increased intracellular free calcium concentration during late pregnancy contributes to the pathogenesis of preeclampsia.

Effect of pravastatin on erythrocyte rheological and biochemical properties in poorly controlled Type 2 diabetic patients

AIMS

The rheological properties of erythrocytes are impaired in diabetes mellitus, especially because of changes in their membrane lipid composition. In hypercholesterolaemic patients, lowering plasma cholesterol is associated with an improvement of the erythrocyte rheological parameters. The aim of this study was to investigate the relationship between erythrocyte deformability, plasma lipids, lipid membrane composition and cytosolic cations in poorly controlled Type 2 diabetic patients and to test the effects of a cholesterol-lowering treatment on these parameters.

METHODS

We compared 37 poorly controlled Type 2 diabetic patients with 26 controls. In 22 of the diabetic patients who showed an impairment in erythrocyte deformability (filtration index >10.5 on the Hanss' haemorheometer), a double-blind randomized trial compared the effect of the inhibitor of HMG CoA reductase pravastatin 20 mg per day for 4 months vs. placebo on the erythrocyte parameters.

RESULTS

Compared with controls, diabetic patients had higher filtration index (FI), erythrocyte sodium and calcium contents and lower free cholesterol-phospholipids ratio in erythrocyte membranes. Erythrocyte sodium content correlated positively with the FI and the membrane free cholesterol-phospholipids ratio. In the pravastatin-treated group (11 patients), fibrinogen decreased significantly, FI reached a normal value (<10) in six patients. Four of the five other patients who still had abnormal FI after 4 months of treatment had either a high plasma triglycerides (> or =4.60 mmol/l) or a high plasma fibrinogen (> or =4 g/l) level at baseline. Only two of the 11 placebo-treated patients achieved a normal FI.

CONCLUSION

These data suggest that in poorly controlled Type 2 diabetic patients there is a link between the chemical composition and the rheological properties of erythrocytes. Erythrocyte deformability may be improved by lowering plasma cholesterol with a statin.

Nisoldipine improves the impaired erythrocyte deformability correlating with elevated intracellular free calcium-ion concentration and poor glycaemic control in NIDDM

AIMS

To explore the mechanisms underlying the impaired erythrocyte deformability (RBC-df) in diabetic patients, the relationship between erythrocyte intracellular free calcium-ion concentration ([Ca2+]i) and RBC-df, and the effects of Ca2+-channel blocker on [Ca2+]i and RBC-df were evaluated.

METHODS

Forty-eight patients with NIDDM and 24 control subjects were enrolled in this study. [Ca2+]i was determined using fura-2, and RBC-df by filtration method expressed as Deformability Index (DI). Erythrocytes were treated with nisoldipine to evaluate the effects of a Ca2+-channel blocker.

RESULTS

[Ca2+]i was significantly higher (82.6 (78.0-87.2) vs 76.6 (74.3-81.2) nmol lRBC-1, P<0.001), and DI was significantly lower (0. 14 (0.09-0.28) vs 0.22 (0.16-0.28), P<0.01) in NIDDM than in controls. There was a significant correlation between HbA1c and [Ca2+]i (r=0.38, P<0.01), between HbA1c and DI (r=-0.51, P<0.01), and between [Ca2+]i and DI (r=-0.42, P<0.01). Stepwise multiple regression analysis revealed HbA1c and [Ca2+]i as independent determinants for the impaired RBC-df. Nisoldipine treatment in vitro significantly decreased [Ca2+]i, and significantly improved RBC-df.

CONCLUSIONS

These data indicate that the impaired RBC-df in NIDDM may at least partly be attributed to the elevated [Ca2+]i and poor glycaemic control. In addition, favorable effects of a Ca2+-channel blocker on both [Ca2+]i and RBC-df have been demonstrated.

Erythrocyte disaggregation shear stress, sialic acid, and cell aging in humans

Erythrocyte aggregation, which plays an important role in the physiological behavior of blood fluidity, was found to be enhanced in hypertension and hypercholesterolemia. While the role of macromolecule bridging force has been widely described, cellular factors related to membrane sialic acid content, which might contribute to the negative charge of cell surface causing the repulsion of erythrocytes, have been less studied. Cell age-dependent changes in membrane sialic acid content (in micromoles per gram of integral membrane protein) were investigated in 24 normotensive and 24 hypertensive matched subjects, each divided into 2 identical subgroups according to a cutoff of 6.2 mmol/L serum cholesterol. A progressive and significant (P<0.001) decrease in membrane sialic acid content associated with an increase (P<0.001) of disaggregation shear rate threshold (laser reflectometry in the presence of dextran) were observed with increased erythrocyte density (erythrocytes fractionated by density using ultracentrifugation) in both normotensive and hypertensive groups regardless of the cholesterol level. However, disaggregation shear rate threshold was significantly higher and sialic acid content was lower (P<0.001) in both hypertensive and normotensive subjects with hypercholesterolemia compared with either normotensive or hypertensive subjects with low cholesterol, respectively. A high membrane sialic acid content variance, beginning in the younger erythrocytes, was due mainly to triglyceride and LDL cholesterol levels (R2=0.49 for low, R2=0.43 for middle, and R2=0.54 for high densities, ie, young, mean, and senescent erythrocytes, respectively). We conclude that an early decrease in erythrocyte sialic acid content may influence the rheological properties of blood by increasing the adhesive energy of erythrocyte aggregates.

Erythrocytic protein kinase C activity in primary hypertension

OBJECTIVES

Increased protein kinase C activity has been reported in erythrocytes from patients with primary hypertension and also from hypertensive rats. In this phenomenological study, we investigated whether a possible increased activity was the result of an augmented amount of enzyme molecules or a more active enzyme.

DESIGN

Collect blood samples, separate erythrocytes from other blood cells. After partial purification of protein kinase C in the erythrocyte lysate, assay the enzyme activity under optimal conditions using a specific peptide substrate.

SETTING

Central Hospital in Eskilstuna and University Hospital in Uppsala, Sweden.

SUBJECTS

Healthy individuals: 47 persons (20 women and 27 men). Ten patients with untreated primary hypertension.

MAIN OUTCOME MEASURES

Erythrocytes were separated from leucocytes and platelets by passing through a cellulose column followed by repeated washings. Some proteins in the erythrocyte lysate interfering with protein kinase C assay were removed by chromatography on DEAE-cellulose.

RESULTS

The mean protein kinase C activity in erythrocytes from healthy individuals was 0.18 +/- 0.02 pmol [32P]phosphate min(-1) x 10(6) cells, regardless of sex and age. The corresponding value for patients with primary hypertension was 0.16 +/- 0.04 pmol [32P]phosphate min(-1) x 10(6) cells.

CONCLUSIONS

The amount of protein kinase C, measured as the activity at optimal assay conditions, in erythrocytes from patients with primary hypertension is not critical for the development of moderate hypertension.

Characterization of voltage-dependent calcium influx in human erythrocytes by fura-2

Thus far, the methods used to determine erythrocyte Ca2+ influx have not allowed the assessment of the kinetics of ion uptake. To overcome this drawback, we studied a new method, using the fluorescent Ca2+-chelator fura-2, which directly quantifies intracellular Ca2+ changes in human erythrocytes. This method has the advantage over previous techniques that it monitors continuously cellular Ca2+ levels. The Ca2+ influx is modulated by cellular membrane potential in the presence of a transmembrane Ca2+ concentration gradient and exhibits a first slow increase of the intracellular Ca2+ concentration, followed, after the reachment of a threshold value of 125 +/- 13 nM Ca2+, by a faster increase until a plateau is reached. The influx rate is inhibited by dihydropyridines in the micromolar range. These findings support the hypothesis that erythrocyte Ca2+ influx is mediated by a carrier similar to the slow Ca2+ channels and is dependent on membrane depolarization.

Hemorrheological indices, catecholamines, neuropeptide Y and serotonin in patients with essential hypertension

Hemorrheological and humoral abnormalities and excessive platelet activity can predict the development of cardiovascular complications in patients with essential hypertension. A study was conducted to assess the influence of gender on these factors and the interrelations between changes in hemorrheology and the sympatho-adrenal system in 54 patients (18 women, 36 men) with essential hypertension (aged 39.6 +/- 9.7 years) and 25 healthy volunteers (10 women, 15 men; aged 36.0 +/- 7.2 years). A decrease in erythrocyte deformability (p < 0.01) was found in the hypertensive men compared with the hypertensive women. Hematocrit (p < 0.01), blood viscosity at the shear rates of 0.3 s-1 (p < 0.01) and 6 s-1 (p < 0.01), plasma viscosity (p < 0.01), erythrocyte aggregation (p < 0.01), and neuropeptide Y (p < 0.02) concentrations were higher in the hypertensive men than in the hypertensive women. A positive correlation between blood fibrinogen and serotonin was found in the pooled hypertensive group and in the hypertensive men (p < 0.01) and between blood viscosity (shear rate 6 s-1) and neuropeptide Y in the pooled hypertensive group (p < 0.01). Neuropeptide Y correlated with filtration time of 1 mL blood in the hypertensive men (p < 0.05) and in the pooled normotensive group (p < 0.01) and with beta-thromboglobulin in the hypertensive women (p < 0.001). A positive correlation was also found in the hypertensive men between erythrocyte and platelet aggregation (p < 0.01) and between beta-thromboglobulin and adrenaline (p < 0.01). Hemorrheological and humoral abnormalities are more pronounced in men than in women with essential hypertension and may contribute to the increased incidence of cardiovascular events in men.

The influence of blood pressure on intracellular Ca2+ content in erythrocytes: effects of cadmium chloride and nifedipine

Cellular abnormalities associated with elevated Ca2+ concentrations have been postulated to be involved in the pathogenesis of hypertension. The present study was undertaken to investigate the effects of blood pressure changes on cytosolic Ca2+ levels in erythrocytes. Cadmium, which has been implicated in the etiology of hypertension was used as the hypertensive agent and the classical blocker of voltage-operated calcium channels nifedipine was used to treat hypertension. 10 weeks old male rats were divided into four groups; control, CdCl2, CdCl2 and nifedipine, nifedipine groups. CdCl2 caused elevations in blood pressure and in the cytosolic erythrocyte Ca2+ levels both of which were reduced after nifedipine administration. After nifedipine alone, cytosolic Ca2+ levels were increased. These findings suggest that cytosolic Ca2+ content decreasing action of nifedipine in the CdCl2 and nifedipine applied group could be secondary to the antihypertensive action.

Disturbed energy balance in skeletal muscle of patients with untreated primary hypertension

OBJECTIVE

It has been shown that the distribution of Na+ and Ca2+ in various cells is abnormal in patients with untreated primary hypertension, indicating an altered membrane permeability in these cells. This would activate certain ion pumps and thereby enhance ATP turnover. We investigated possible alterations in energy economy of skeletal muscle tissue.

DESIGN

Skeletal muscle energetics were studied in vitro and in vivo in patients with untreated primary hypertension. Phosphocreatine (PCr), energy charge (EC) and total adenylate values were assessed.

SETTING

The study was performed at the outpatient clinic of a general hospital and at a university clinical chemistry department and at a specialized bioenergetic laboratory.

SUBJECTS

Altogether, 17 patients with untreated primary hypertension were examined together with matched, healthy and normotensive controls with normal body-mass index.

MAIN OUTCOME MEASURES

Skeletal muscle biopsies were obtained from 10 patients and 10 controls for analysis of high energy phosphate compounds. Another seven patients were enrolled for in vivo NMR spectroscopy.

RESULTS

We found a decrease of 30% (P < 0.01) of PCr content in the patients, whilst EC and total adenylates were unchanged. Nuclear magnetic resonance spectroscopy showed an abnormal decrease of PCr during exercise followed by a markedly slower regeneration of PCr during post-exercise recovery parallelled by a slower recovery of pH. This phenomenon was mirrored by a more pronounced decrease of ATP/Pi in patients during exercise and a slower recovery of ATP/Pi.

CONCLUSION

The data are compatible with an increased ATP turnover in skeletal muscle cells of patients with untreated primary hypertension although ATP was favoured and kept at a normal resting level at the expense of the PCr store.

Alzheimer amyloid beta-peptides exhibit ionophore-like properties in human erythrocytes

There is growing evidence that the amyloid beta-peptide (beta 1-40) is involved in the aetiology of Alzheimer's disease also implicating an altered calcium homeostasis of affected cells. Beta 1-40 has been proposed to form calcium channels in synthetic bilayer membranes [1]. We wanted to investigate in the present study whether beta 1-40 (or fragments thereof) could act as ionophores in a biological membrane like the one in human erythrocytes. Incubation of the cells for 2 h and 4 h at 37 degrees C together with 6 mumol L-1 of beta 1-40 or of fragments beta 1-28 and beta 25-35, resulted in a significantly decreased energy charge qualitatively similar to the one obtained by a known calcium ionophore (A 23187, 0.05 mumol L-1). Moreover, beta 1-40 and its two fragments induced a significant alteration of 45Ca permeability in human red blood cells of the same type as the one achieved by the calcium ionophore. The ionophoric action of beta 1-40 and its two fragments may lead to an increase of the intracellular calcium ion concentration, in turn resulting in enhanced Ca(2+)-ATPase activity and a decrease in energy charge. This may be valid also for neuronal plasma membranes and could, therefore, be a possible aetiological mechanism in Alzheimer's disease.

Hemodynamic actions of insulin

There is accumulating evidence that insulin has a physiological role to vasodilate skeletal muscle vasculature in humans. This effect occurs in a dose-dependent fashion within a half-maximal response of approximately 40 microU/ml. This vasodilating action is impaired in states of insulin resistance such as obesity, non-insulin-dependent diabetes, and elevated blood pressure. The precise physiological role of insulin-mediated vasodilation is not known. Data indicate that the degree of skeletal muscle perfusion can be an important determinant of insulin-mediated glucose uptake. Therefore, it is possible that insulin-mediated vasodilation is an integral aspect of insulin's overall action to stimulate glucose uptake; thus defective vasodilation could potentially contribute to insulin resistance. In addition, insulin-mediated vasodilation may play a role in the regulation of vascular tone. Data are provided to indicate that the pressor response to systemic norepinephrine infusions is increased in obese insulin-resistant subjects. Moreover, the normal effect of insulin to shift the norepinephrine pressor dose-response curve to the right is impaired in these patients. Therefore, impaired insulin-mediated vasodilation could further contribute to the increased prevalence of hypertension observed in states of insulin resistance. Finally, data are presented to indicate that, via a yet unknown interaction with the endothelium, insulin is able to increase nitric oxide synthesis and release and through this mechanism vasodilate. It is interesting to speculate that states of insulin resistance might also be associated with a defect in insulin's action to modulate the nitric oxide system.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations of membrane properties in erythrocytes of salt hypertensive Sabra rats

This study was designed to investigate the effects of a hypertensive stimulus, high salt intake, in hypertension-prone (SBH) and -resistant (SBN) Sabra rats on erythrocyte Na+ content (Na+i), Ca2+ influx and cytosolic Ca2+ concentration ([Ca2+]i). The relationships of these parameters to plasma lipids, circulating digoxin-like immunoreactivity and membrane microviscosity, determined by the fluorescence anisotropy of trimethylamino-diphenylhexatriene (TMA-DPH) and diphenylhexatriene (DPH), were also evaluated. Erythrocytes of SBH rats were characterized by increased [Ca2+]i, unchanged Ca2+ influx and reduced Na+i. There were no significant differences in the plasma digoxin-like immunoreactivity between the two strains. High-salt intake decreased membrane microviscosity (DPH anisotropy) in SBH rats but did not alter the above parameters. Erythrocyte [Ca2+]i correlated positively with diastolic blood pressure and negatively with erythrocyte Na+i. Membrane dynamics evaluated by the two fluorescent probes did not correlate with [Ca2+]i, Ca2+ influx or Na+i whereas DPH anisotropy was inversely related to blood pressure. These relationships were independent of plasma cholesterol or triglycerides. It can be concluded that 1) similarly to earlier observations in essential hypertension and spontaneously hypertensive rats, erythrocyte [Ca2+]i correlates positively with blood pressure in salt-dependent hypertension, and 2) increased erythrocyte Na+ content need not be a hallmark of hypertension.

Erythrocyte Ca2+ handling in the spontaneously hypertensive rat, effect of vanadate ions

Cytosolic Ca2+ concentration ([Ca2+]i) and 45Ca2+ influx were investigated in erythrocytes from conscious spontaneously hypertensive rats (SHR) and their normotensive controls Wistar-Kyoto (WKY). [Ca2+]i was evaluated with fura-2 and intra- and extra-cellular calibration parameters were compared. Irrespective of the calibration parameters used, erythrocyte [Ca2+]i was always significantly higher in SHR than in WKY and Wistar rats (by 25 and 40%, p < 0.01 and 0.001). A rise of the external Ca2+ concentration from 1 to 2 mmol/l increased less [Ca2+]i in SHR than in WKY erythrocytes (17 vs 37%, p < 0.01). SHR erythrocytes incorporated more 45Ca2+ than those from WKY, with an initial rate of 45Ca2+ uptake higher by 57% than that of WKY erythrocytes (p < 0.05). Vanadate ions, after corrections of their quenching effect on red cell and fura-2 fluorescence signals, increased [Ca2+]i by 19% in WKY erythrocytes (p = 0.05), but did not modify the SHR values. They also increased 45Ca2+ accumulation and the initial rate of 45Ca2+ influx in WKY erythrocytes only (p < 0.01). This study indicates that, when compared to WKY rats, erythrocytes from SHR are characterized by higher [Ca2+]i values, higher initial rate of Ca2+ influx and low sensitivity to vanadate ions.

In vivo shear flow and erythrocyte membrane fluidity in hypertensive patients

1. To evaluate the response of red blood cells subjected to the shear flow in hypertension, the relationships between wall shear phenomena determined in vivo in the brachial artery of hypertensive patients and the modifications of the membrane dynamics measured in vitro in erythrocyte ghosts of 32 patients were investigated. 2. Two fluorescent probes, diphenylhexatriene (DPH) and its trimethylamino-derivative (TMA-DPH), localized respectively in the lipid membrane core and at the lipid-water interface, were used. 3. Shear rate, shear stress and blood velocity were positively correlated with TMA-DPH anisotropy (P = 0.015, 0.005 and 0.026, respectively), but not with that of DPH. This indicates that wall shear forces were associated with the microviscosity of the outer part of the cell membrane. 4. The changes in wall shear forces and erythrocyte membrane microviscosity probed by TMA-DPH or DPH were observed to vary in parallel under nitrendipine therapy. 5. These results suggest that in vivo shear forces participate in the control of erythrocyte membrane fluidity or that erythrocytes adapt their membrane properties to blood flow conditions.

Dissipation of the calcium gradient in human erythrocytes results in increased heat production

Heat production rates were measured by a microcalorimetric method in suspended human erythrocytes in the absence and presence of different concentrations of the divalent cationophore A23187. Determinations were carried out during 60 min under static conditions on erythrocytes incubated in various isotonic media at 37 degrees C, pH 7.35. In incubations containing the ionophore, time-power curves showed an early peak followed by a descending slope levelling off at a steady state after 30-60 min. In contrast, the controls lacked the early peak, showing hyperbolic ascending curve profiles before reaching steady state. The appearance of the early peak in the presence of ionophore was dependent upon the composition of the medium, both Mg2+ ions and glucose being decisive. Likewise, dose-response relationships concerning heat production at 60 min depended on the composition of the media. In a basic incubation medium lacking Mg2+ and glucose, no effect was seen on heat production by the ionophore (1-3 mumol/l). Rather modest effects were obtained by the ionophore at 2 and 3 mumol/l when Mg2+ was present. A clear-cut dose-response relationship was observed in a Mg2+ and glucose enriched medium for the ionophore from 1-3 mumol/l. The significant increase in heat production observed at 60 min with 2 mumol/l of A23187 in the Mg2+ and glucose enriched medium was abolished by 1 mmol/l EGTA. Calmidazolium, a calmodulin antagonist, could only marginally reduce the ionophoric effect on heat production. It was concluded that the appearance of the early peak was not the result of an increase in glycolytic rate but rather a consequence of the ionophoric action on the Ca2+ gradient.

Erythrocyte anion exchanger activity and intracellular pH in essential hypertension

The present study was designed to examine the activity of the sodium-independent chloride-bicarbonate anion exchanger and the sodium-proton exchanger in erythrocytes of 30 normotensive and 35 hypertensive subjects and its relation to the previously reported decrease in erythrocyte pH. Erythrocyte cytosolic pH was measured by the pH-sensitive fluorescent probe 2'-7'-bis(2-carboxyethyl)- 5(6)-carboxyfluorescein. The activity of the anion exchanger was determined by acidifying cell pH and measuring the initial rate of the net sodium-independent, 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid-sensitive, bicarbonate influx driven by an outward proton gradient. The activity of the sodium-proton exchanger was determined by acidifying cell pH and measuring the initial rate of the net sodium-dependent proton efflux driven by an outward proton gradient. The activity of the anion exchanger was higher in hypertensive than control individuals (18,863 +/- 1081 vs 15,629 +/- 897 mmol/L cells per hour, P < .05). The activity of the sodium-proton exchanger was higher in hypertensive than control individuals (301 +/- 45 vs 162 +/- 23 mmol/L cells per hour, P < .005). Basal erythrocyte pH was lower in hypertensive than control individuals (7.27 +/- 0.02 vs 7.33 +/- 0.01, mean +/- SEM, P < .05). With the 100% confidence (lower) limit of the normotensive population as a cutoff point, a subgroup of 11 hypertensive patients had an abnormally low erythrocyte pH (< 7.19).(ABSTRACT TRUNCATED AT 250 WORDS)

Red blood cell sodium-proton exchange in hypertensive blacks with insulin-resistant glucose disposal

To define the potential pathogenic role of hyperinsulinemia as a mediator of alterations in sodium transport, we have examined red blood cell Na(+)-H+ and Na(+)-Li+ exchanges in a young adult black population characterized for blood pressure and insulin-mediated glucose disposal. Normotensive and mildly hypertensive blacks (blood pressure, 120 +/- 2/76 +/- 2 and 139 +/- 3/94 +/- 2 mm Hg, respectively) with a mean age of 26.1 years were studied for insulin sensitivity with the euglycemic hyperinsulinemic clamp (molar index of insulin sensitivity, M/I = moles glucose metabolized/insulin in milliliters of plasma). Na(+)-H+ exchange (U = mmol/L cell.h) was measured before and after the insulin clamp as a function of cell pH to determine the maximum transport rate. In the normotensive subjects, 18 were insulin sensitive (M/I = 9.37 +/- 0.6 x 10(4)) and 4 were insulin resistant (M/I = 3.64 +/- 0.6 x 10(4)). In the hypertensive subjects, 4 were insulin sensitive (M/I = 9.15 +/- 1.1 x 10(4)) and 16 were insulin resistant (M/I = 3.02 +/- 0.3 x 10(4)). The maximum rate of Na(+)-H+ exchange was significantly higher in all hypertensive vs normotensive individuals (35 +/- 3 vs 23 +/- 3 U, P < .005). Na(+)-H+ exchange activity was higher in insulin-resistant vs insulin-sensitive hypertensive subjects (40 +/- 3 vs 20 +/- 2 U, P < .001) but not in insulin-resistant normotensive subjects. Na(+)-Li+ exchange was not different in hypertensive and normotensive individuals but was higher in all insulin-resistant compared with all insulin-sensitive subjects (0.26 +/- 0.03 vs 0.16 +/- 0.02 U, P < .01). Na(+)-Li+ exchange also was higher in insulin-resistant vs insulin-sensitive normotensive subjects (0.35 +/- 0.03 vs 0.15 +/- 0.02 U, P < .001) and in insulin-resistant hypertensive subjects vs insulin-sensitive normotensive subjects (0.24 +/- 0.03 vs 0.15 +/- 0.02 U, P < .001). A stepwise multiple regression analysis for all variables revealed that with Na(+)-H+ exchange as a dependent variable the main determinant was blood pressure, which in turn had insulin sensitivity as the main determinant. In conclusion, these results indicate that in hypertensive blacks, insulin-resistant glucose disposal is strongly associated with elevated red blood cell Na(+)-H+ exchange activity. Thus, despite impaired insulin-mediated glucose disposal, cellular Na+ gain via enhanced activity of Na(+)-H+ exchange is not blunted in hypertensive blacks.

Ca2+ ATPase activity in essential and renal hypertension

In 15 patients with essential hypertension, 16 patients with renal hypertension and in 12 healthy subjects Ca2+ ATPase activity was determined in red blood cells both in the basal state and after maximal stimulation with calmodulin. Normal subjects showed a basal and maximal activity of 7.1 +/- 3.6 and 16.0 +/- 2.3 pmol phosphate/min.10(6) RBC, respectively. Renal hypertensives had a similar basal Ca2+ ATPase activity (5.4 +/- 4.1 pmol phosphate/min.10(6) RBC) and a lowered maximal Ca2+ ATPase activity (9.8 +/- 5.4 pmol phosphate/min.10(6) RBC, p < 0.05). In essential hypertensives basal and maximal Ca2+ ATPase activity was 9.0 +/- 5.3 and 35.4 +/- 14.4 pmol phosphate/min.10(6) RBC, respectively, the latter being significantly increased (p < 0.01). This finding, which is in contrast to earlier results indicating a lowered Ca2+ ATPase activity in essential hypertension, may be explained as a consequence of an increased Ca2+ influx in essential hypertension. A lowered Ca2+ ATPase activity does not seem to be involved in the pathogenesis of essential hypertension.