Erythrocyte Membrane Fluidity Research Articles

Damage to the structure of erythrocyte plasma membranes in patients with type-2 hypercholesterolemia

Background: Hypercholesterolemia may decrease the deformability of red blood cells which impairs their hemorheological behavior and promotes atherosclerosis. The study involved 60 hypercholesterolemic patients and 30 healthy individuals as the control group. Methods: The membrane fluidity of erythrocytes was estimated by a spin-label method (5-doxylstearic acid (5-DSA)). The ratio of weakly to strongly (W/S) immobilized residues of erythrocyte membrane-bond maleimide-tempo spin label was studied in oxidative damage to membrane protein. Damage to erythrocyte proteins was also indicated by means of Na + K + ATPase activity. Results: The membranes of hyperlipidemia (hlp) patients contain larger concentrations of cholesterol 2.16±0.24 than do those of the normolipemic individuals 0.31±0.24 ( P<0.001). The level of Na + K + ATPase in the erythrocyte membrane from the control group was higher 103.4±1.3 (nmol Pi/(mg proteins h)) than in the patient group 93.6±3.2 (nmol Pi/(mg proteins h)) ( P<0.001). The order parameter S 5-DSA in the control group was 0.745±0.009 and in hlp patients was 0.755±0.009 ( P<0.001). The W/S ratio in the control group amounted to 2.00±0.09 and in the hlp patient group was 2.50±0.11 ( P<0.001). Conclusion: Type-2 hypercholesterolemia causes changes in the structure and fluidity of erythrocyte plasma membranes since the excess of cholesterol affects the normal rheology of blood through its interaction with erythrocytes. It also impairs the function and structure of plasma membrane proteins.

Hormone replacement therapy improves membrane fluidity of erythrocytes in postmenopausal women: an electron paramagnetic resonance investigation

Background Many studies have shown that hormone replacement therapy (HRT) might provide protection against the development of hypertension and arteriosclerosis in postmenopausal women. However, the precise mechanism underlying its benefits is unclear. This question was addressed in an electron spin resonance (EPR) study of membrane function of erythrocytes in postmenopausal women. The purpose of this study was to investigate the effects of HRT on membrane fluidity of erythrocytes in postmenopausal women by means of the EPR and spin-labeling method. Methods The healthy postmenopausal women were randomly divided into the HRT group ( n = 14) receiving the conjugated estrogen with medroxyprogesterone for 3 months and the non-HRT control group ( n = 14). We measured membrane fluidity of erythrocytes in postmenopausal women before and after the trial period. Results The HRT group showed a significant decrease in blood pressure (BP) after treatment (systolic BP 145.7 ± 5.5 v 123.3 ± 5.1 mm Hg, n = 14, mean ± SEM, P < .05). The order parameter (S) for 5-nitroxide stearate in the EPR spectra of erythrocyte membranes decreased significantly in the HRT group (S: 0.718 ± 0.002 v 0.695 ± 0.002, n = 14, P < .01). The finding indicated that HRT increased the membrane fluidity of erythrocytes and improved the microviscosity of the cell membranes in postmenopausal women. Conclusions These results are consistent with the hypothesis that HRT might have a beneficial effect on the membrane rheologic behavior of erythrocytes and the microcirculation in postmenopausal women.

The effects of verbascoside on plasma lipid peroxidation level and erythrocyte membrane fluidity during immobilization in rabbits: a time course study

We studied the changes in the level of plasma lipid peroxidation indicated by malondialdehyde (MDA) level and erythrocyte membrane fluidity expressed by the value of order parameter (S) during single hindlimb immobilization of 21 days using thiobarbituric acid — reactive substances method and spin label electron spin resonance method, respectively. The impacts of verbascoside that has been proved its antioxidative activity on the measured parameters were examined. 11 New Zealand white rabbits were immobilized and divided into two groups. The rabbits in the verbascoside group were administrated with 0.8 mg/kg of verbascoside twice a day orally throughout the immobilization. The rabbits in the placebo group were treated with normal saline. In placebo group, the results showed that the level of MDA significantly increased on day 3, peaked on day 7, and was still significantly higher on day 14 of immobilization, compared with the value measured before immobilization. The value of S reached the highest on day 7 and subsequently lowered but still higher on day 14 than those measured before immobilization. Compared with placebo group, there were lower MDA level (P < 0.05, 0.001, and 0.05 for days 3, 7, and 14, respectively) and higher erythrocyte membrane fluidity (P < 0.05, 0.001, and 0.001 for days 3, 7, and 14, respectively) in verbascoside group. The data indicated that immobilization caused temporal changes of increase in plasma lipid peroxidation and decrease in erythrocyte membrane fluidity. Verbascoside might have the effects to moderate oxidative stress and erythrocyte membrane fluidity during immobilization.

Nitric oxide is a determinant of membrane fluidity of erythrocytes in postmenopausal women: an electron paramagnetic resonance investigation

In the present study, to determine a possible role of nitric oxide (NO) in the regulation of membrane functions, we examined the relationship between plasma NO level and membrane fluidity of erythrocytes in postmenopausal women. We evaluated the membrane fluidity of erythrocytes obtained from hypertensive and normotensive postmenopausal women by means of an electron paramagnetic resonance (EPR) and spin labeling method. The EPR study revealed that the order parameter (S) for 5-nitroxide stearate in erythrocyte membranes was significantly greater in hypertensive postmenopausal women than in normotensive postmenopausal women. The finding indicated that the membrane fluidity of erythrocytes was decreased in hypertensive postmenopausal women compared with normotensive postmenopausal women. The plasma level of the NO metabolites (nitrite and nitrate) while fasting was significantly lower in hypertensive postmenopausal women than in normotensive postmenopausal women. In addition, the order parameter (S) in the EPR spectra of erythrocyte membranes was inversely correlated with the plasma NO metabolite level, which indicated that the lower membrane fluidity of erythrocytes was associated with the lower plasma NO level in postmenopausal women. These results are consistent with the hypothesis that NO may have a crucial role in the regulation of membrane fluidity of erythrocytes in postmenopausal women.

Effect of oestrone on membrane fluidity of erythrocytes is mediated by a nitric oxide-dependent pathway: An electron paramagnetic resonance study.

1. It has been recognized that hormone replacement therapy (HRT) may have a beneficial effect on protection against cardiovascular diseases. Oestrone is the major component of conjugated equiline oestrogens, which are commonly used in HRT. The present study was performed in order to investigate the effects of oestrone on the membrane fluidity of erythrocytes by means of an electron paramagnetic resonance (EPR) and spin-labelling method. 2. In an in vitro study, oestrone significantly decreased the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (ho/h-1) for 16-nitroxide stearate (16-NS) obtained from EPR spectra of erythrocyte membranes. This finding indicated that oestrone may increase the membrane fluidity and improve the membrane microviscosity of erythrocytes. 3. The effect of oestrone was significantly potentiated by the nitric oxide (NO) donor s-nitroso-N-acetylpenicillamine and the cGMP analogue 8-bromo-cGMP. 4. In contrast, the change in membrane fluidity induced by oestrone was antagonized by the NO synthase inhibitors NG-nitro-l-arginine methyl ester and asymmetric dimethyl-l-arginine. 5. The results of the present study show that oestrone significantly increases membrane fluidity and improves the rigidity of cell membranes, which is partially mediated by a NO- and cGMP-dependent pathway. Furthermore, the data may be consistent with the hypothesis that oestrone could have a beneficial effect on the rheological behaviour of erythrocytes and have a crucial role in the regulation of the microcirculation.

The effect of atorvastatin on erythrocyte membranes and serum lipids in patients with type-2 hypercholesterolemia.

. The beneficial effects of statins on clinical events may involve mechanisms that modify endothelial dysfunction, plaque stability, thrombus formation, and inflammatory responses. To determine the effect of atorvastatin on blood rheology in patients with familial hypercholesterolemia (FH), we prospectively studied serum lipid concentration, red cell cholesterol content, lipid peroxidation and erythrocyte membrane fluidity. The aim of this paper was to evaluate the effects of atorvastatin therapy on the erythrocyte membrane structure and the hypolipemic efficacy in patients with FH. MATERIALS, METHODS AND SUBJECTS STUDIED:. The study involved 31 patients with FH and 20 healthy individuals as a control group. The program lasted 20 weeks. For the first 8 weeks, the patients were on a hypolipemic diet only and for the subsequent 12 weeks, alongside the diet they were given 10 mg atorvastatin per day. Laboratory tests were carried out before and after 4 weeks and 12 weeks of the pharmacological treatment. Erythrocyte membrane fluidity was determined using the spin labeled method. The peroxidation of lipids was measured in whole erythrocytes as well as in erythrocyte plasma membranes by means of the thiobarbituric acid technique. . Treatment with atorvastatin reduced serum total cholesterol concentration from 310+/-29 mg/dl in a basal situation to 203+/-34 mg/dl ( P<0.001) at the end of the treatment and low-density lipoprotein (LDL) cholesterol concentration from 225+/-30 mg/dl to 126+/-30 mg/dl ( P<0.001), respectively. The changes observed in the plasma lipids correlate with a significant decrease in erythrocyte membrane cholesterol, from 2.24+/-1.69 to 1.17+/-0.75 mg/mg protein ( P<0.001) after 12 weeks of treatment. The lipid peroxidation in membranes of erythrocytes was lowered from the basal value 0.171+/-0.097 to 0.100+/-0.024 mmol/mg protein ( P<0.05) after 4 weeks of treatment and to 0.057+/-0.020 mmol/mg protein ( P<0.001) after 12 weeks of treatment, and in total erythrocytes from 4.78+/-1.49 to 3.99+/-1.39 mmol/g Hb ( P<0.02) and 2.43+/-0.87 mmol/g Hb ( P<0.001), respectively. The membrane fluidity was estimated by means of parameter S at the depth of the fifth carbon atom. Atorvastatin in hypercholesterolemic erythrocytes enhances the fluidity of the superficial layer from 0.758+/-0.009 up to the values observed in the control group 0.744+/-0.009 ( P<0.001). There is no impact on the microviscosity of the hydrophobic core observed. . Our findings suggest that the atorvastatin therapy reverses the alteration of erythrocyte plasma membrane properties. It may improve blood rheology in patients with FH. This improvement in blood properties may contribute to the well-known beneficial effects of atorvastatin on cardiovascular risk in patients with severe hyperlipidemia and atherosclerotic vascular disease.

Leptin improves membrane fluidity of erythrocytes in humans via a nitric oxide-dependent mechanism—an electron paramagnetic resonance investigation

Abnormalities in physical properties of the cell membranes may underlie the defects that are strongly linked to hypertension, stroke, and other cardiovascular diseases. Recently, there has been an indication that leptin, the product of the human obesity gene, actively participates not only in the metabolic regulations but also in the control of cardiovascular functions. In the present study, to assess the role of leptin in the regulation of membrane properties, the effects of leptin on membrane fluidity of erythrocytes in humans are examined. The membrane fluidity of erythrocytes in healthy volunteers by means of an electron paramagnetic resonance (EPR) and spin-labeling method is determined. In an in vitro study, leptin decreased the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (ho/h-1) for 16-NS obtained from EPR spectra of erythrocyte membranes in a dose-dependent manner in healthy volunteers. The finding indicated that leptin increased the membrane fluidity and improved the microviscosity of erythrocytes. The effect of leptin on the membrane fluidity was significantly potentiated by the nitric oxide (NO) donors, l-arginine and S-nitroso- N-acetylpenicillamine (SNAP), and a cyclic guanosine monophosphate (cGMP) analog, 8-bromo-cGMP. In contrast, the change evoked by leptin was significantly attenuated in the presence of the NO synthase inhibitors, N G-nitro- l-arginine-methyl-ester ( l-NAME) and asymmetric dimethyl- l-arginine (ADMA). The results of the present study showed that leptin increased the membrane fluidity and improved the rigidity of cell membranes to some extent via an NO- and cGMP-dependent mechanism. Furthermore, the data also suggest that leptin might have a crucial role in the regulation of rheological behavior of erythrocytes and microcirculation in humans.

Synergistic role of progesterone and nitric oxide in the regulation of membrane fluidity of erythrocytes in humans: an electron paramagnetic resonance investigation

Background It has been shown that progesterone may actively participate in the regulation of blood pressure and other cardiovascular regulations. However, the precise mechanism underlying its effects is unclear. Methods In the present study, we examined the effects of progesterone on membrane fluidity of erythrocytes in healthy volunteers by means of an electron paramagnetic resonance (EPR) and spin-labeling method. Results In an in vitro study, progesterone significantly decreased the order parameter (S) for 5-nitroxide stearate (5-NS) and the peak height ratio (ho/h-1) for 16-NS obtained from EPR spectra of erythrocyte membranes. The finding indicates that progesterone might increase the membrane fluidity and improve the membrane microviscosity of erythrocytes. The effect of progesterone was significantly potentiated by the nitric oxide (NO) donor, S-nitroso- N-acetylpenicillamine (SNAP) and a cyclic guanosine monophosphate (cGMP) analogue, 8-bromo-cGMP. In contrast, the change in the membrane fluidity evoked by progesterone was attenuated in the presence of the NO synthase inhibitors, N G-nitro- l-arginine-methyl-ester (L-NAME) and asymmetric dimethyl- l-arginine (ADMA). Conclusions The results of the present study showed that progesterone increased the membrane fluidity of erythrocytes and ameliorated the rigidity of cell membranes, at least in part, by an NO-dependent mechanism. Furthermore, the data strongly suggest that progesterone might be involved in the regulation of rheological behavior of erythrocytes and have a crucial role in the improvement of microcirculation in humans.

Domain structure of erythrocyte membranes in psoriasis: an EPR study

Membrane fluidity of erythrocytes from psoriatic patients in active and inactive period of the disease was studied by electron paramagnetic resonance (EPR). Comparison of simulated and experimental EPR spectra of erythrocyte membranes from controls and psoriatics showed that they are essentially superimposition of three components; two regions with a high degree of order of the lipid acyl chains and one region with poor alignments of hydrocarbon chains (with a small order parameter). In psoriatic erythrocytes not only the portion of the most rigid domain was enlarged, but also the order parameter of this domain was increased, while the order parameters of two other domains were the same than in normal erythrocytes. Results obtained in this article showed that the portion of the most rigid domain ( W A) better correlated with polymorphonuclear elastase (PMN elastase) than with PASI score. Additionally, correlation between PMN elastase and W A in the active period of the disease was observed to be higher than in the inactive period. Therefore, portion of the most ordered domain ( W A) seems to be a good marker for evaluation of the disease activity in psoriatic patients.

Biochemical, biophysical and haemorheological effects of dimethylsulphoxide on human erythrocyte calcium loading

The studies using dimethylsulphoxide (DMSO) and/or the 4-bromo-calcium ionophore A23187 (Br-A23187) often neglect the precise knowledge of some of their biochemical, biophysical and haemorheological effects. The aim of the present study was to evaluate these effects on erythrocytes after whole blood incubations with DMSO or Br-A23187 dissolved in DMSO. There were no significant differences between the different aliquots in the values of P50, pH, erythrocyte deformability, erythrocyte membrane fluidity, haemoglobin and intracellular Ca2 concentrations ([Ca2]i). Aliquots with DMSO (independently of the presence of Br-A23187 or added Ca2) had lower erythrocyte aggregation indexes and higher plasma concentrations of K+], Na+] and Ca2 than the aliquots without DMSO (independently of the presence of added Ca2). Aliquots with added calcium (without the presence of Br-A23187 in DMSO) had a significantly higher erythrocyte acetylcholinesterase activity. Our data shows that calcium loading, the usual objective of Br-A23187 incubations, cannot be fulfilled with the studied experimental conditions. The coherence between our results and those obtained by other authors with different biological systems and different modulators of the rise on [Ca2]i suggests a non-specific effect of DMSO, disabling the action of the modulator. It can be reasoned that the decreased erythrocyte aggregation (without significant changes on the deformability or membrane fluidity) can result either from the decrease of t he hydrogen bonding contribution to erythrocyte aggregation or the increased ionic strength influence on the erythrocyte membrane surface.

Cypermethrin-induced plasma membrane perturbation on erythrocytes from rats: reduction of fluidity in the hydrophobic core and in glutathione peroxidase activity

The effects of treatment with the synthetic insecticide cypermethrin on plasma membrane fluidity, lipid peroxidation and antioxidant status in rat erythrocytes were investigated. Rats were treated by gavage with a low dose (12.5 mg/kg body weight per day) of cypermethrin in corn oil for 60 days. DPH and TMA-DPH fluorescence anisotropy experiments show that cypermethrin treatment, compared with controls, induced a significant decrease in erythrocyte membrane fluidity measured by DPH, while no changes were observed using TMA-DPH. Cypermethrin treatment also induced a significant increase in the lipid peroxidation, measured by the formation of conjugated dienes. The increased oxidative stress resulted in a significant decrease in the acitivity of glutathione peroxidase. The results are discussed in terms of preferential localization of cypermethrin in the hydrophobic core of the membrane, where it increases lipid packing and consequently decreases membrane fluidity.

In situ assessment of erythrocyte membrane properties during cold storage

Membrane fluidity and overall protein secondary structure of human erythrocytes were studied in situ using Fourier transform infrared spectroscopy (FTIR). Erythrocyte membranes were found to have weakly cooperative phase transitions at 14 degrees C and at 34 degrees C, which were tentatively assigned to the melting of the inner membrane leaflet and the sphingolipid rich outer leaflet, respectively. Cholesterol depletion by methyl-beta-cyclodextrin (MbetaCD) resulted in a large increase in the cooperativity of these transitions, and led to the appearance of another phospholipid transition at 25 degrees C. Multiple, sharp membrane phase transitions were observed after 5 days cold storage (4 degrees C ), which indicated phase separation of the membrane lipids. Using fluorescence microscopy, it was determined that the lipid probe 1,1'-dioctadecyl-3,3,3',3-tetramethyl-indocarbocyanine perchlorate (dil-C18) remained homogeneously distributed in the erythrocyte membrane during cold storage, suggesting that lipid domains were below the resolution limit of the microscope. Using thin layer chromatography, changes in the membrane lipid composition were detected during cold storage. By contrast, assessment of the amide-II band with FTIR showed that the overall protein secondary structure of haemoglobin was stable during cold storage.

Antioxidant Protection of Propofol and Its Recycling in Erythrocyte Membranes

alpha-Tocopherol is a potent antioxidant that effectively protects biological membranes against oxidative injury through coordination with ascorbic acid. Because propofol has a phenolic structure similar to that of alpha-tocopherol, this intravenous anesthetic may also have similar antioxidant activity. To test this hypothesis, the effect of propofol on oxidative injury of human erythrocytes was examined. Propofol inhibited oxidative hemolysis and cis-parinaric acid oxidation in erythrocyte membranes (ED(50) = 6 microM). Although ascorbic acid alone has no appreciable effect, the protective effect of propofol was enhanced by ascorbic acid. An electron spin resonance (ESR) study showed that propofol-derived radicals (g = 2.005) were continuously generated during the oxidation of erythrocyte membranes by an ascorbic acid-inhibitable mechanism. These and other results suggest that propofol interacts with ascorbic acid, thereby exhibiting potent antioxidant activity in and around membranes as does alpha-tocopherol. Kinetic analysis revealed that propofol increased the membrane fluidity of erythrocytes, thereby increasing their resistance to physical and hemodynamic stress. Further, a greater preservation of red blood cell counts was seen after surgery with propofol compared with conventional sevoflurane anesthesia. Thus, propofol may protect erythrocytes against both oxidative and physical stress, indicating its potential as an efficient and safe antioxidant.

Physiological and hemolytic toxicity of some aminophosphonates.

The effect of novel synthesized aminophosphonates on membrane potential and electrical conductance of internodal cells of Nitellopsis obtusa and hemolysis of erythrocytes (RBC) was studied. It was found that those the organophosphorous compounds, when present at 10-100 microM concentrations, caused depolarization and increased electrical conductance of alga membranes. They also influenced fluidity of erythrocyte membranes. When used at higher concentrations aminophosphonates caused hemolysis of RBC. The changes observed depended on structural features of the aminophosphonates, i.e., substituents at the carbon, phosphorus and nitrogen atoms, and, most probably, may be the result of direct interaction of the aminophosphonates with the lipid phase of the plasma membrane and the induced structural changes. Two modes of interaction are proposed.

Electron paramagnetic resonance investigation on modulatory effect of 17beta-estradiol on membrane fluidity of erythrocytes in postmenopausal women.

Many studies have shown that estrogen may exert cardioprotective effects and reduce the risk of hypertension and coronary events. On the other hand, it has been proposed that cell membrane abnormalities play a role in the pathophysiology of hypertension, although it is not clear whether estrogen would influence membrane function in essential hypertension. The present study was performed to investigate the effects of 17beta-estradiol (E(2)) on membrane fluidity of erythrocytes in normotensive and hypertensive postmenopausal women. We determined the membrane fluidity of erythrocytes by means of an electron paramagnetic resonance and spin-labeling method. In an in vitro study, E(2) significantly decreased the order parameter for 5-nitroxide stearate and the peak height ratio for 16-nitroxide stearate obtained from electron paramagnetic resonance spectra of erythrocyte membranes in normotensive postmenopausal women. The finding indicates that E(2) might increase the membrane fluidity of erythrocytes. The effect of E(2) was significantly potentiated by the NO donor, S-nitroso-N-acetylpenicillamine, and a cGMP analogue, 8-bromo-cGMP. In contrast, the change in the membrane fluidity evoked by E(2) was attenuated in the presence of the NO synthase inhibitor, N(G)-nitro-L-arginine methyl ester, and asymmetric dimethyl-L-arginine. In hypertensive postmenopausal women, the membrane fluidity of erythrocytes was significantly lower than that in normotensive postmenopausal women. The effect of E(2) on membrane fluidity was significantly more pronounced in the erythrocytes of hypertensive postmenopausal women than in the erythrocytes of normotensive postmenopausal women. The results of the present study showed that E(2) significantly increased the membrane fluidity and improved the microviscosity of erythrocyte membranes, partially mediated by an NO- and cGMP-dependent pathway. Furthermore, the greater action of E(2) in hypertension might be consistent with the hypothesis that E(2) could have a beneficial effect in regulating rheological behavior of erythrocytes and could have a crucial role in the improvement of the microcirculation in hypertension.

Erythrocyte membrane fluidity changes in psoriasis: an EPR study

The aim of the study was to find the cause of membrane fluidity decrease in psoriasis, observed by other authors, in different types of cells and its clinical consequences. To this end, we have examined the influence of different clinical and biochemical factors on erythrocyte membrane fluidity changes in psoriatic patients. Membrane fluidity was studied by the electron paramagnetic resonance spin-labeling method. The data revealed that the decrease of membrane fluidity corresponded with exacerbation of skin lesions. The results clearly indicate that the increased lipid peroxidation may be the essential mechanism of membrane fluidity decrease in psoriasis.

In vivo and in vitro influence of etretinate on erythrocyte membrane fluidity

The molecular mechanisms underlying the action of synthetic retinoids have been studied intensively, but they are not fully understood yet. It is well known that retinoids exert their effects on gene expression via the retinoic acid receptor. Some observations suggest that the main aromatic retinoid etretinate (Tigason) exerts its therapeutic effect in psoriasis also through an action on the cell membrane. In this paper, we present the results of previously unreleased experiments (when Tigason was still in use) concerning the in vivo and in vitro influence of etretinate on erythrocyte membrane fluidity in psoriatic patients. Erythrocytes from healthy subjects and topically treated psoriatics were chosen as control groups. Membrane fluidity was measured by the electron paramagnetic resonance (EPR) spin-labelling technique. Erythrocytes from psoriatic patients had lower membrane fluidity, a lower antioxidant activity and a greater susceptibility to peroxidation than those from healthy subjects. After treatment with etretinate, a significant increase in erythrocyte membrane fluidity and in antioxidant activity as well as a decrease in lipid peroxidation were observed in erythrocytes from patients. Local therapy of psoriatic lesions had no influence on the improvement in membrane fluidity and antioxidant activity of erythrocytes. Incubation of erythrocytes from healthy controls and topically treated psoriatics with etretinate in vitro confirmed its fluidizing effect on erythrocyte membranes. These data may indicate that two mechanisms lead to an increase in erythrocyte membrane fluidity in psoriatic patients treated with Tigason: the first one, indirect, by improvement of the antioxidant defence system and cell protection against lipid peroxidation, and the second one, by a direct fluidizing effect of etretinate on the erythrocyte membrane.

Ethnic differences in erythrocyte membrane fluidity and the association with serum triacylglycerols

Ethnic differences in erythrocyte membrane fluidity and the association with serum triacylglycerols

Ethnic differences in erythrocyte membrane fluidity and the association with serum triacylglycerols

The objectives of this study were to determine whether there are differences between black and white individuals with regard to the membrane fluidity of isolated erythrocytes, and/or in the relationships between membrane fluidity, gender and circulating lipids. Fluorescent polarization anisotropy, as an index of membrane fluidity, was determined using the fluorescent probe 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) in 52 black and 52 white individuals, of whom 39 pairs were matched for age, sex and blood pressure. In the 39 matched pairs, the TMA-DPH anisotropy was significantly higher in the black (0.262+/-0.007) compared with the white (0.258+/-0.005) subjects (P<0.005). There was also a significant difference in serum lipids. Gender differences in TMA-DPH anisotropy were observed in the white but not in the black individuals. The associations between membrane fluidity and serum lipids were examined in the total group, separated according to ethnic group. Although the associations were in the same direction in both groups, the association was only significant in the white subjects (r= - 0.42; P<0.02). The ethnic difference in membrane fluidity was abolished when adjusting for serum triacylglycerols. In conclusion, ethnic differences in erythrocyte membrane fluidity, as determined by the use of TMA-DPH anisotropy, appear to be the result of ethnic differences in the level of serum triacylglycerols.

Hyperinsulinemia and membrane fluidity: Hyperinsulinemia is a determinant of membrane fluidity of erythrocytes in essential hypertension

In the present study, to determine a possible role of insulin in the regulation of membrane functions, we have examined the relationship between plasma insulin level and membrane fluidity of erythrocytes in patients with essential hypertension and normotensive subjects. Membrane fluidity of erythrocytes obtained from hypertensive and normotensive subjects were evaluated by means of an electron paramagnetic resonance and spin-labeling method. The order parameter (S for 5-nitroxide stearate) and the peak height ratio (ho/h-1 for 16-nitroxide stearate) obtained from electron paramagnetic resonance spectra of erythrocyte membranes were significantly higher in patients with essential hypertension than in normotensive subjects. The finding indicated that the erythrocyte membrane fluidity was lower in essential hypertension than in normotensive controls. The plasma concentration of insulin while fasting was also significantly greater in hypertensive patients than in normotensive subjects. In addition, the plasma insulin level was significantly correlated with the values of the order parameter (S) and the peak height ratio (ho/h-1), which showed that the higher plasma insulin was associated with the lower membrane fluidity of erythrocytes. These results support the hypothesis that insulin may actively participate in the regulation of membrane fluidity of erythrocytes in essential hypertension.