Erythrocyte membranes undergo cooperative, pH-sensitive state transitions in the physiological temperature range: evidence from Raman spectroscopy

Shock and detonation waves at an interface and the collision of action potentials

Action potentials in neurons are known to annihilate each other upon collision, while there are cases where they might penetrate each other. The fate of two waves upon collision is critically dependent on the underlying mechanism of propagation and therefore an understanding of possible outcomes of collision under different conditions is important. Previously, compression waves that travel within the plasma membrane of a neuron have been proposed as a thermodynamic basis for the propagation of action potentials. In this context, it was recently shown that two-dimensional compressive shock waves in the model system of lipid monolayers behave strikingly similar to action potentials in neurons and can even annihilate each other upon head-on collision. However, even a qualitative mechanism remained unclear. To this end, we summarise the fundamentals of shock physics as applied to an interface and recap how it explained the observation of threshold and saturation of shockwaves in the lipid monolayer (all - or - none). We then compare the theory with the soliton model that has the same fundamental premise, i.e. the conservation laws and thermodynamics, and was previously proposed as a model for the nerve pulse propagation. We elaborate on how the two approaches make different predictions with regards to collisions and the detailed structure of the wave-front. As a case study and a new qualitative result, we finally show that previously unexplained annihilation of shock waves in the lipid monolayer is a direct consequence of the nature of state changes, i.e. jump conditions, within these shockwaves.

Label-free Optical Imaging of Membrane Potential

Offering high temporal resolution, voltage imaging is an important and essential technique in neuroscience. Among different optical imaging approaches, the label-free approach remains attractive due to its unique value coming from free of exogenous chromophores. The intrinsic voltage-indicating signals arising from membrane deformation, membrane spectral change, phase shift, light scattering, and membrane hydration haven been reported. First demonstrated 70 years ago, label-free optical imaging of membrane potential is still at an early stage and the field is challenged by the relatively small signals generated by the intrinsic optical properties. We review major contrast mechanisms used for label-free voltage imaging and discuss several recent exciting advances that could potentially enable membrane potential imaging in mammalian neurons at high speed and high sensitivity.

Three-Dimensional Cellular Raman Analysis: Evidence of Highly Ordered Lipids Within Cell Nuclei

Striking levels of spatial organization exist among and within interphase cell chromosomes, raising the possibility that other nuclear molecular components may also be organized in ways that facilitate nuclear function. To further examine molecular distributions and organization within cell nuclei, we utilized Raman spectroscopy to map distributions of molecular components, with a focus on cellular lipids. Although the vast majority of cellular lipids are associated with membranes, mapping the 2870/2850 cm^-1 lipid peak ratios revealed that the most highly ordered lipids within interphase cells are found within cell nuclei. This finding was seen in cells from multiple tissue types, noncancerous cells, and in cancer cell lines of different metastatic potential. These highly ordered lipids colocalize with nuclear chromatin, are present throughout the nuclear volume, and remain colocalized with chromatin through mitosis, when the nuclear envelope has dissociated. Phosphatidylinositol is a major component of the highly ordered lipids. The presence of phosphatidylinositol and other lipids in the nuclear interior is well established, but their highly ordered packing has not been reported and represents a unique finding. The molecular interactions involved in the formation and maintenance of these highly ordered lipids, and their potential effects on nuclear activities, remain to be discovered.

Label-Free Vibrational Spectroscopic Imaging of Neuronal Membrane Potential

Detecting membrane potentials is critical for understanding how neuronal networks process information. We report a vibrational spectroscopic signature of neuronal membrane potentials identified through hyperspectral stimulated Raman scattering (SRS) imaging of patched primary neurons. High-speed SRS imaging allowed direct visualization of puff-induced depolarization of multiple neurons in mouse brain slices, confirmed by simultaneous calcium imaging. The observed signature, partially dependent on sodium ion influx, is interpreted as ion interactions on the CH₃ Fermi resonance peak in proteins. By implementing a dual-SRS balanced detection scheme, we detected single action potentials in electrically stimulated neurons. These results collectively demonstrate the potential of sensing neuronal activities at multiple sites with a label-free vibrational microscope.

Raman Spectroscopy of Blood and Blood Components

Blood is a bodily fluid that is vital for a number of life functions in animals. To a first approximation, blood is a mildly alkaline aqueous fluid (plasma) in which a large number of free-floating red cells (erythrocytes), white cells (leucocytes), and platelets are suspended. The primary function of blood is to transport oxygen from the lungs to all the cells of the body and move carbon dioxide in the return direction after it is produced by the cells' metabolism. Blood also carries nutrients to the cells and brings waste products to the liver and kidneys. Measured levels of oxygen, nutrients, waste, and electrolytes in blood are often used for clinical assessment of human health. Raman spectroscopy is a non-destructive analytical technique that uses the inelastic scattering of light to provide information on chemical composition, and hence has a potential role in this clinical assessment process. Raman spectroscopic probing of blood components and of whole blood has been on-going for more than four decades and has proven useful in applications ranging from the understanding of hemoglobin oxygenation, to the discrimination of cancerous cells from healthy lymphocytes, and the forensic investigation of crime scenes. In this paper, we review the literature in the field, collate the published Raman spectroscopy studies of erythrocytes, leucocytes, platelets, plasma, and whole blood, and attempt to draw general conclusions on the state of the field.

The impact of biochemical composition and nature of paramagnetic species in grains on stress tolerance of oat cultivars

The aim of this work was to investigate the relationships between the chemical composition of oat grains and the tolerance to oxidative stress of oat genotypes. The studies were based on the results of biochemical analyses and both EPR and Raman spectroscopies on whole grains and their parts (embryo, endosperm, seed coat) originating from oat genotypes with different sensitivities to stress. We found that the amounts of fats and especially unsaturated fatty acids, proteins rich in glutamic acid and glycine, as well as phenolics and tocopherols were higher in grains of the tolerant genotype. Moreover, fats and proteins were distributed not only in embryos, but also in endosperms. The grains of tolerant genotypes exhibited high antioxidant activity and contained greater amounts of β-glucan. EPR data pointed to higher concentrations of various kinds of stable organic radicals (semiquinone, tyrosyl and carbon-centered radicals) in whole grains (and their parts) of sensitive genotypes. EPR spectra revealed the character of interactions of paramagnetic transition metal ions Fe(III) and Mn(II) with organic and inorganic structures of grains. The quantitative EPR measurements showed the dependence between the amount of radical species and the content of transition metal ions, mainly Fe(III) bonded to inorganic structures.

The ring-stage of Plasmodium falciparum observed in RBCs of hospitalized malaria patients

Raman spectra of the blood samples obtained directly from hospitalized malaria patients with Plasmodium falciparum (P. falciparum) in the ring-stage were analyzed. Changes observed in the Raman band intensities of the infected patients compared to healthy volunteers are the result of parasite activity inside red blood cells. The obtained spectra were discussed by analyzing differences in particular spectral regions by evaluating changes in the band intensity ratios as well as using PCA analysis. The alterations of erythrocyte membranes caused by parasite penetration are visible by a reduced I1130/I1075 intensity ratio expressing the lowering of the amount of domains arranged in trans conformation. The I2930/I2850 ratio, which is a measure of modifications in structures of membrane proteins and lipids, in infected red blood cells increases, which is caused by malaria protein export to the erythrocyte membrane and expresses the membrane disarrangement. In the pyrrole ring vibration region, the ν4 band marker of the oxygenated-Hb shows at 1371 cm(-1) whereas the ν4 band at 1353 cm(-1) related to the deoxygenated-Hb is observed for malaria patients and is characterized by a higher intensity in infected erythrocytes. The amide I analysis shows the modifications in the secondary structure composition in the infected RBCs. We found that the P. falciparum infection leads to a decrease in the α-helical content and a concurrent increase in undefined (random-coil) structures. It was observed that the Raman spectra changes are also the result of the hemozoin formation process. In the pyrrole ring stretching vibration region, the increase of 1220 cm(-1) (deoxyHb) as against 1248 cm(-1) (oxyHb) may be considered as a signal of hemozoin formation in the RBCs. Relatively intense band patterns at 1560 cm(-1) and also at 1570 cm(-1) and 1552 cm(-1) may be due to the hemozoin that is formed according to parasite activity. The results of medical diagnostic tests had not presented changes in patient RBC parameters. A significant reduction in WBC count was noticed along with a decrease in neutrophil and platelet count when compared with the control group. Although no change is observed in the overall picture of the erythrocytes, pathological changes are evident in the Raman spectrum.

Clostridium difficile the hospital plague

Clostridium difficile infection (CDI) has become one of the major public health threats in the last two decades. An increase has been observed not only in the rate of CDI, but also in its severity and mortality. Symptoms caused by this pathogen are accompanied by intense local and systemic inflammation. We confirmed that Raman microspectroscopy can help us in understanding CDI pathogenesis. A single erythrocyte of patients with CDI shows a difference, approximately 10 times, in the intensity of the Raman spectra at the beginning of hospitalization and after one week of treatment. The intensity level is an indicator of the spread of the inflammation within the cell, confirmed by standard laboratory tests. Many of the observed bands with enormously enhanced intensity, e.g. 1587, 1344, 1253, 1118 and 664 cm(-1), come from the symmetric vibration of the pyrrole ring. Heme variation of recovered cells in the acute CDI state between the first and the seventh day of treatment seems to show increased levels of oxygenated hemoglobin. Intense inflammation alters the conformation of the protein which is reflected in the significant changes in the amide I, II and III bands. There is an observed shift and a significant intensity increase of 1253 and 970 cm(-1) amide III and skeletal protein backbone CC stretching vibration bands, respectively. Principal Component Analysis (PCA) was used to find the variance in the data collected on the first and seventh day. PC2 loading in the 1645-1500 cm(-1) range shows an increase of heme, Tyr, Trp, or Phe vibrations because of changes in the protein microenvironment due to their exposure. Positive maxima at 1621, 1563 and 1550 in the PC2 loading originated from the ring vibrations. These observations indicate that Clostridium difficile toxins induce cytopathogenicity by altering cellular proteins.

Stable radicals and biochemical compounds in embryos and endosperm of wheat grains differentiating sensitive and tolerant genotypes--EPR and Raman studies

The aim of this study was to uncover the specific species in grains that might differentiate the wheat genotypes according to their tolerance to oxidative stress. Measurements by EPR and Raman spectroscopy techniques were used to examine whole grains and their parts (embryo, endosperm, seed coat) originating from four wheat genotypes with differing tolerance to drought stress. Raman spectra showed that, in spite of the similar amounts of proteins in whole grains from tolerant and sensitive genotypes, in tolerant ones they were accumulated mainly in embryos. Moreover, in embryos from these grains, a higher content of unsaturated fatty acids was observed. Endosperm of grains from the tolerant genotype, richer with starch than that of sensitive one, exhibited higher content of amylopectin. Detailed analysis of EPR signals and simulation procedures of the spectra allowed the estimation of the nature of interactions of Fe(III) and Mn(II) with organic and inorganic structures of grains and the character of organic stable radicals. Three types of these radicals: carbohydrate, semiquinone and phenoxyl, were identified. The amounts of these radicals were higher in grains of sensitive genotypes, mostly because of differences in carbohydrate radical content in endosperm. Taking into account the level of radical concentration and greater capacity for radical formation in grains from plants of lower tolerance to stress, the content of radicals, especially of a carbohydrate nature, was considered as a marker of the plant resistance to stress conditions.

Inhibitory effect of NaCl on hog kidney mitochondrial membrane-bound monoamine oxidase: pH and temperature dependences

For a further understanding of the inhibitory effect of NaCl on hog kidney mitochondrial monoamine oxidase (MAO), the activity for benzylamine as substrate was assayed spectrophotometrically in the absence and presence of NaCl for mitochondrial outer membrane preparations as well as whole mitochondria. The effect of CaCl2 was also examined for comparison. The inhibition by NaCl but not CaCl2 was strongly pH dependent. The pH dependence of the inhibitory effect of NaCl in phosphate buffer was parallel to the pH dependence of the MAO activity itself. The point at which the slope of the Arrhenius plot in the absence of NaCl decreases with increasing temperature was to be 32.3 degrees C at pH 7.0 and 30.4 degrees C at pH 7.5 in phosphate buffer, while the Arrhenius plot in the presence of NaCl exhibited discontinuities without change in the slope in small temperature ranges, 39.2 degrees C-40.0 degrees C and 33.0 degrees C-34.2 degrees C. It was estimated that the inhibitory effect of NaCl was due to a pH and temperature sensitive cooperative state change involving MAO protein and boundary lipids, while the effect of CaCl2 could be induced by specific Ca2+ binding to acidic phospholipids.

Effects of hyperthermia on the membrane potential and Na+ transport of V79 fibroblasts

The effects of hyperthermia (41-43 degrees C) on the membrane potential (calculated from the transmembrane distribution of [3H]tetraphenylphosphonium) and Na+ transport of Chinese hamster V79 fibroblasts were studied. At 41 degrees C, hyperthermia induced a membrane hyperpolarization of log phase cells (5 to 26 mV) that was reversible upon returning to 37 degrees C. The hyperpolarization was inhibited 50% by 1 mM ouabain or 0.25 mM amiloride, an inhibitor of Na+:H+ exchange. Shifting temperature to 41 degrees C increased ouabain-sensitive Rb+ uptake indicating activation of the electrogenic Na+ pump. At 43 degrees C for 60 min, the membrane potential of log phase cells depolarized (20-35 mV). Parallel studies demonstrated enhanced Na+ uptake at 41 degrees C only in the presence of ouabain. At 43 degrees C, Na+ uptake was increased relative to controls with or without ouabain present. At both 41 and 43 degrees C, 0.25 mM amiloride inhibited heat-stimulated Na+ uptake. Na+ efflux was enhanced at 41 degrees C in a process inhibited by ouabain. Thus, one consequence of heat treatment at 41 degrees C is activation of Na+:H+ exchange with the resultant increase in cytosolic [Na+] activating the electrogenic Na+ pump. At temperatures greater than or equal to 43 degrees C, the Na+ pump is inhibited.

Temperature-specific inhibition of human red cell Na+/K+ ATPase by 2,450-MHz microwave radiation

The ATPase activity in human red blood cell membranes was investigated in vitro as a function of temperature and exposure to 2,450-MHz continuous wave microwave radiation to confirm and extend a report of Na+ transport inhibition under certain conditions of temperature and exposure. Assays were conducted spectrophotometrically during microwave exposure with a custom-made spectrophotometer-waveguide apparatus. Temperature profiles of total ATPase and Ca+2 ATPase (ouabain-inhibited) activity between 17 and 31 degrees C were graphed as an Arrhenius plot. Each data set was fitted to two straight lines which intersect between 23 and 24 degrees C. The difference between the total and Ca+2 ATPase activities, which represented the Na+/K+ ATPase activity, was also plotted and treated similarly to yield an intersection near 25 degrees C. Exposure of membrane suspensions to electromagnetic radiation, at a dose rate of 6 W/kg and at five temperatures between 23 and 27 degrees C, resulted in an activity change only for the Na+/K+ ATPase at 25 degrees C. The activity decreased by approximately 35% compared to sham-irradiated samples. A possible explanation for the unusual temperature/microwave interaction is proposed.

Membrane effects of ionizing radiation and hyperthermia

Results of numerous studies demonstrate that membranes are important sites of cell damage by both ionizing radiation and hyperthermia. Modification of membrane properties (mainly lipid fluidity) affects the cellular responses to radiation and hyperthermia but former concepts that membrane rigidification sensitizes cells to radiation while membrane fluidization potentiates hyperthermic damage have now been seriously challenged. It seems that the effects of membrane fluidity on cell responses to hyperthermia and radiation are due to an indirect influence on functional membrane proteins. The major role of lipid peroxidation in radiation damage to membranes has also been questioned. The existing evidence makes it unlikely that the interaction between radiation and hyperthermia is determined by the action of both agents on the same membrane components.

Spectrin involvement in a 40 degrees C structural transition of the red blood cell membrane

Proteins involved in a structural transition detected in red blood cell membranes at 40 degrees C by spin labeling methods have been investigated. Antibodies specific for spectrin, band 3, and protein 4.1 have been used as specific probes to modify membrane thermotropic properties. Spectrin seems to be involved in a 40 degrees C transition detected in ghosts by both a stearic acid spin label (16-doxyl stearic) and a sulfhydryl-specific maleimide analogue spin label. Circular dichroism and maleimide spin labeling studies of purified spectrin show a slow unfolding of the protein structure starting at 25-30 degrees C and a massive transition with an onset temperature of 48 and 40 degrees C, respectively. This thermotropic behavior of spectrin could be the process that modifies membrane physicochemical properties above 40 degrees C that are detected by the stearic acid spin label. The transition detected by the stearic acid spin label was modified both by antispectrin antibodies and anti-4.1 protein antibodies, but not by antibodies specific for the cytoplasmic domain of band 3. These results suggest an involvement of protein 4.1 in regulating spectrin unfolding at the membrane level. A selective inhibition of the transition detected by the maleimide spin label has been obtained with a monoclonal antispectrin antibody at 1:1 molar ratio. The involvement in this transition of a localized spectrin domain(s) containing few exposed sulfhydryl groups is proposed.

Raman studies of structural rearrangements induced in human plasma lipoprotein carotenoids by malondialdehyde

Raman and resonance Raman spectra of plasma lipoproteins +/- malondialdehyde were studied at concentrations which block the normal receptor-mediated uptake by cells. The strong resonance Raman bands at about 1010, 1162 and 1530 cm-1, due to the presence of carotenoids in the lipoproteins, are envisaged as structural probes. High resolution resonance Raman spectra of the 1500-1600 cm-1 region reveal multiple features suggesting the coexistence of several structural populations of beta-carotene whose precise assignment is complex. When plasma lipoproteins are reacted with malondialdehyde, a complex change occurs in the resonance Raman banding of beta-carotene in the 1500-1600 cm-1 region. Malonaldehyde (MDA) also modifies the acoustical region (70-200 cm-1 of low density lipoprotein (LDL) lipids. We suggest that malondialdehyde association with plasma lipoproteins alters the lipid structure via apoprotein or apoprotein/lipid associations.

Effects of metabolic acidosis on viability of cells exposed to anoxia

The effects of metabolic acidosis were examined in isolated rat hepatocytes under substrate-free oxygenated or anoxic conditions. Lowering extracellular pH to 6.6 under aerobic conditions had no deleterious effects on the cells as determined by trypan blue exclusion, lactate dehydrogenase (LDH) release, cellular K+ and Ca2+ content, and ability to increase ATP levels after nutrients and adenosine were added to media. Cytosolic pH was measured in aerobic cells at varying extracellular pH using 6-carboxyfluorescein. By using values for cytosolic pH obtained in this manner together with 5,5-dimethyl[2-14C]oxazolidine-2,4-dione (DMO) distribution data, a method was derived for determining intramitochondrial pH. The pH gradient across the mitochondrial membrane was found not to change with a decrease in extracellular pH from 7.4 to 6.9. At pH 6.9 hepatocytes were protected against anoxic injury as compared with cells incubated at pH 7.5 or 6.6. This protection was manifested by a decrease in vital dye uptake and LDH release, maintenance of higher cellular K+ content, less stimulation of respiration with succinate, improved recovery of ATP levels after return to an oxygenated nutrient environment, and maintenance of normal cellular Ca2+ content after reoxygenation. Recovery of cellular ATP content was independent of ATP levels, total adenine nucleotide pool, and energy charge ratio at the end of the anoxic period. Measurement of cytoplasmic pH in anaerobic cells by [14C]DMO distribution showed progressive cellular acidification with lowering of extracellular pH. The protective effects observed at pH 6.9 are not unique to hepatocytes since isolated renal cortical tubules exposed to anoxia have improved ATP levels on reoxygenation at this pH when compared with tubules incubated at pH 7.5.

FACS analysis of a hyperthermia-induced alteration in Hoechst 33342 permeability and direct measurement of its relationship to cell survival

Heat-induced alterations in CHO-10B cell Hoechst 33342 (Ho342) permeability in vitro were analyzed by flow cytometry. Immediately after 45.5 degrees C heating, uptake was decreased in a dose-dependent manner with cytotoxicity. Kinetic analysis indicated that a treatment that reduced cell survival to approximately 10%, reduced the maximal velocity, Vmax, to 53% of control and increased the dissociation constant, Km, to 156% of control. Also, little change in Ho342 efflux was found to occur from control up to 90 min after heating. Upon incubation at 37 degrees C after the heat treatment from 1 to 24 hr (depending on the severity of the dose) diffuse heterogeneity of Ho342 staining developed which was not evident immediately after heating. The altered staining was not due to the presence of trypan blue staining cells. Membrane permeabilization and nuclei isolation studies indicated that the lesion responsible was most likely a plasma membrane event. Induction of the heterogenous staining was not inhibited by either actinomycin D or hydroxyurea but was inhibited by incubation at 4 degrees C. An inverse correlation existed between Ho342 permeability and clonogenicity, with nearly a 10-fold difference in survival between the high and low fluorescence intensity sorted cells. Also, larger fractions of heat-sensitive S and G2M-phase cells were found in the highly fluorescent sorted fractions. These results are discussed in terms of the putative molecular events that may be involved in hyperthermic modulation of Ho342 permeability.

Role of membrane thermotropic properties on hypotonic hemolysis and hypertonic cryohemolysis of human red blood cells

The hypothesis of a correlation between the effects of temperature on red blood cells hypotonic hemolysis and hypertonic cryohemolysis and two thermotropic structural transitions evidenced by EPR studies has been tested. Hypertonic cryohemolysis of red blood cells shows critical temperatures at 7 degrees C and 19 degrees C. In hypotonic solution, the osmotic resistance increases near 10 degrees C and levels off above 20 degrees C. EPR studies of red blood cell membrane of a 16-dinyloxyl stearic acid spin label show, in the 0-50 degrees C range, the presence of three thermotropic transitions at 8, 20, and 40 degrees C. Treatments of red blood cells with acidic or alkaline pH, glutaraldehyde, and chlorpromazine abolish hypertonic cryohemolysis and reduce the effect of temperature on hypotonic hemolysis. 16-Dinyloxyl stearic acid spectra of red blood cells treated with glutaraldehyde and chlorpromazine show the disappearance of the 8 degrees C transition. Both the 8 degrees C and the 20 degrees C transitions were abolished by acidic pH treatment. The correlation between the temperature dependence of red blood cell lysis and thermotropic breaks might be indicative of the presence of structural transitions producing areas of mismatching between differently ordered membrane components where the osmotic resistance is decreased.

Membrane structural alterations in malignant and normal avian lymphocytes: a Raman investigation

Resonance and nonresonance Raman spectra have been obtained from neoplastically transformed and normal avian lymphocytes. The acyl chains of membrane phospholipids of neoplastic cells are more highly unsaturated than those of normal cells. The observation of prominent carotenoid bands in both cell populations indicates the availability of a sensitive, intrinsic probe of membrane potential and local membrane environment.

Characterization of thermotropic structural transitions of the erythrocyte membrane: a biochemical and electron-paramagnetic resonance approach

The relationship between membrane structural properties and functions has been generally inferred from observed thermotropic phenomena. By the use of 16-dinyloxyl stearic acid spin probe we investigated the red blood cell membrane components involved in three characteristic thermotropic structural transitions occurring at 8, 20, and 40 degrees C. The transition at 8 degrees C is removed by chymotrypsin treatment at the cytoplasmic membrane layer. The 20 degrees C phase transition is unmodified after chymotrypsin treatment and occurs at 15 degrees C after complete proteolysis of intramembrane chymotrypsin-insensitive peptides. Liposomes from the total lipid extract of RBC show only one thermotropic transition at 15 degrees C. The 40 degrees C phase transition is absent in vesicles free of skeletal proteins, in vesicles obtained after RBC storage, and in low-ionic-strength resealed ghosts. Transitions at 8 degrees C and 40 degrees C appear to be due to the interactions of cytoplasmic exposed proteins with membrane, whereas the 20 degrees C transition is intrinsic to the lipid component.

A protein anomaly in erythrocyte membranes of patients with Duchenne muscular dystrophy

Raman spectroscopic comparisons of erythrocyte membranes from 20 patients with Duchenne muscular dystrophy and 8 age-matched controls indicate a prominent and consistent protein anomaly in the patient samples. This was apparent in the following: (a) CH-stretching signals from control membranes reveal a thermotropic transition at 15.6 degrees C, attributable to a protein/lipid phase that is lacking in dystrophic membranes. (b) CH-stretching signals from control membranes also show a protein transition at 39 degrees C [pH 7.4] that is shifted to 45 degrees in dystrophic membranes. (c) A reduction in pH to 5.7 shifts this transition from 39 degrees C to 7 degrees C in normal membranes and from 45 degrees C to 24 degrees C in dystrophic membranes. (d) The Amide I/Amide III regions indicate a significant proportion of beta-structured peptide in dystrophic but not normal membranes. (e) Analysis of tyrosine signals indicates greater polar exposure of tyrosine hydroxyl groups in dystrophic vs normal membranes. All of the differences between dystrophic and normal membranes are highly significant (P less than 0.001).

Lipid diffusibility in the intact erythrocyte membrane

The lateral diffusion of fluorescent lipid analogues in the plasma membrane of intact erythrocytes from man, mouse, rabbit, and frog has been measured by fluorescence photobleaching recovery (FPR). Intact cells from dystrophic, normoblastic, hemolytic, and spherocytotic mouse mutants; from hypercholesterolemic rabbits and humans; and from prenatal, neonatal, and juvenile mice have been compared with corresponding normals. The lateral diffusion coefficient (D) for 3,3'-dioctadecylindodicarbocyanine iodide (DiI[5]) in intact normal human erythrocytes is D = 8.2 +/- 1.2 X 10(-9) cm2/s at 25 degrees C and D = 2.1 +/- 0.4 X 10(-8) cm2/s at 37 degrees C, and varies approximately 50-fold between 1 degree and 42 degrees C. The diffusion constants of lipid analogue rhodamine-B phosphatidylethanolamine (RBPE) are about twice those of DiI[5]. The temperature dependence and magnitude of D vary by up to a factor of 3 between species and are only influenced by donor age in prenatals. DiI[5] diffusibility is not perturbed by the presence of calcium or local anesthetics or by spectrin depletion (via mutation). However, lipid-analogue diffusibility in erythrocyte ghosts may differ from intact cells. Dietary hypercholesterolemia in rabbits reduces the diffusion coefficient and eliminates the characteristic break in Arrhenius plots of D found in all other cells studied except frog.

Thermotropic state transition in isolated platelet membranes studied by Raman spectroscopy

The thermotropic state transition of the lipids in isolated platelet membranes has been studied by Raman spectroscopy in the temperature range from -3 degrees C to +45 degrees C using the (C-H) stretching vibrations, carotenoid(s) vibrations at 1530 cm-1 and 1160 cm-1, as well as the skeletal optical vibrations. 1. The increase of temperature causes a decrease in intensity of the 2885 cm-1 band relative to the 2855 cm-1 one. The evaluation of the ratio I2885/I2855 as a function of temperature indicates a double thermotropic state transition of platelet membrane lipids: the first one near 5 degrees C and the second near 17.5 degrees C. 2. The ratio I1530/I1160 shows that the intensity variations in the carotenoid(s) peaks follow the second lipid transition. Thus, it seems that the platelet membrane carotenoid(s) might be linked to the lipids which undergo transition near 17.5 degrees C. 3. The spectral changes in the skeletal optical range suggest a considerable proportion of all trans chains in the membrane lipids at lower temperatures whereas gauche structures seem to be introduced at higher temperatures.

Protein-dependent lipid lateral phase separation as a mechanism of human erythrocyte ghost resealing

The hypothesis of a correlation between a 10 degrees-20 degrees C lipid phase transition and the resealing process of human erythrocyte membrane has been investigated. The conditions required to reseal human erythrocyte ghosts have been studied by measuring the amount of fluorescein-labeled dextran (FD) that is trapped into the membrane. Temperature per se was sufficient to induce membrane resealing: (1) at 5 mM sodium phosphate, pH 7.8 (5P8), resealing began at 12 degrees C; (2) at salt concentrations above 8 mM sodium phosphate, it occurred at lower temperature; and (3) in isotonic saline was detected just above 5 degrees C. The removal of peripheral membrane proteins from unsealed membranes by chymotrypsin at 0 degree C in 5P8 was followed by membrane resealing. This seems to imply that the presence of proteins is necessary to maintain the membrane unsealed. Protein-induced lateral phase separation of lipids may be a reasonable mechanism for the observed phenomena. In fact, the permeability of phosphatidylserine-phosphatidylcholine mixed liposomes to FD is modified by lipid lateral phase separation induced by pH or poly-L-lysine. Electron spin resonance studies of membrane fluidity by a spin labeled stearic acid showed a fluidity break around 11 degrees C, which may be due to a gel-liquid phase transition. Fluidity changes are abolished by chymotrypsin treatment. It is suggested that a lateral phase separation is responsible for the permeability of open ghosts to FD. Accordingly, disruption of phase separation apparently produces membrane reconstitution. In this respect peripheral proteins and particularly the spectrin-actin network, may play a major role in membrane resealing.

Effects of temperature and pH on the water exchange through erythrocyte membranes: nuclear magnetic resonance studies

The temperature and pH dependence of water exchange has been studied on isolated erythrocytes suspended in isotonic buffered solutions. At pH 7.4 a break in the Arrhenius plot of water exchange time at around 26 degrees C was found. The mean value of the apparent activation energy of the water exchange time at temperatures higher than that of the discontinuity was 5.7 kcal/mole (+/- 0.4); at lower temperatures the values of the apparent activation energy were below 1.4 kcal/mole. The pH dependence of water exchange time of isolated erythrocytes revealed a marked increase of the water exchange time values in the acid range of pH; a much smaller variation of the same parameter occurs between pH 7.0 and 8.0. These finding could be correlated with other processes involving erythrocyte membranes that showed similar pH and temperature dependence and were considered to indicate state transitions in the membranes. It is suggested that the temperature and pH effects on water diffusion indicate that conformational changes and cooperative effects are implicated in the mechanism of this transport process.

Hypertonic cryohemolysis of human red blood cells

Hypertonic cryohemolysis of human erythrocytes is caused by incubation of the cells in hypertonic medium at a temperature of 20--50 degrees C (stage 1), with subsequent cooling to 0 degrees C (stage 2). In 0.86 M sucrose hemolysis increases, with increasing stage 1 temperature, whereas in 1 M NaCl cryohemolysis has a temperature optimum at a stage 1 temperature of about 30 degrees C. Cryohmeolysis is inhibited by preceding ATP depletion of the cells and by preincubation of the cells in hypertonic medium at 0 degrees C. In general, anesthetics inhibit cryohemolysis strongly. Only in 1 M NaCl at stage 1 temperatures in the range of 40--50 degrees C is cryohemolysis stimulated by these drugs, if present during the entire incubation period. This effect is abolished, however, when the anesthetic is added after prior incubation of the cells at 40--50 degrees C in 1 M NaCl. Ghost-bound ANS fluorescence indicates complicated conformation changes in the membrane structure during the various experimental stages leading to cryohemolysis. Some of the experimental results can be considered as examples of molecular hysteresis, thus indicating several different metastable structures of the membrane, under various experimental conditions. The described results support the working hypothesis of Green and Jung that the experimental procedure results in membrane protein damage, preventing normal adaptation of the membrane during cooling.

Zeaxanthin ([3R,3'R]-beta, beta-carotene-3-3'diol) as a resonance Raman and visible absorption probe of membrane structure

When zeaxanthin ([3R,3R']-beta, beta-carotene-3,3'diol) is inserted into phospholipid dispersions and the latter heated through their gel-liquid crystal phase transitions, large changes are noted in the resonance Raman and absorption spectra of the carotenoid molecule. By analogy with the data of Carey and co-workers (J. Raman Spectrosc. 6:282) who studied the aggregation of zeaxanthin in acetone-water solutions, it is suggested that the carotenoid aggregates in the phospholipid gel state while forming a monomer in liquid crystal phases. The alterations in both the visible absorption and resonance Raman data have been used to monitor phospholipid phase behavior in dipalmitoylphosphatidylcholine and distearoylphosphatidylcholine, (DSPC) one-component systems and binary mixtures. The phase diagram obtained for the binary system, as constructed from visible absorption and resonance Raman data, is compared with that of Shimshick and McConnell (Biochemistry. 12:2351) obtained from electron spin resonance (ESR) studies. Although the agreement between absorption and ESR data is generally satisfactory, onset temperatures for phase separation at low DSPC mole fractions deduced from resonance Raman measurements are several degrees lower than those from the other methods. Nevertheless, the use of zeaxanthin as a resonance Raman and visible absorption probe behavior will be useful in some situations where ordinary Raman spectroscopic data cannot be obtained easily. The advantage of the resonance Raman approach is illustrated in a study of the phase behavior of a phospholipid extract of a cel- mutant of Neurospora crassa. A phase separation region is observed with onset and completion temperatures of -19 and -6 degrees C, respectively.

Effect of transmembrane ion gradients on Raman spectra of sealed, hemoglobin-free erythrocyte membrane vesicles

Sealed hemoglobin-free erythrocyte vesicles have been isolated. Imposition of transmembrane cation gradients increases the intensity of Raman scattering in the CH3-stretching region as observed with unsealed ghosts at temperatures greater than 38 degrees C and pH less than 7.0 [Verma, S. P. & Wallach, D. F. H. (1976) Proc. Natl. Acad. Sci. USA 73, 3358--3561]. Modifications in the amide I and amide III frequencies consistent with increased helicity of membrane proteins are observed upon imposition of a cation gradient. Spectrin-free vesicles also demonstrate cation gradient-sensitive intensity changes in the CH3-stretching region. However, no evidence for cation gradient-related protein conformation changes is found with these vesicles. The transmembrane potential of these vesicles has been altered by variations in anion composition and the electrogenic activity of Na+,K+-ATPase. The membrane potential was monitored by cyanine dye fluorescence. Imposition of a membrane potential (negative inside) also increased the intensity of Raman scattering in the CH3-stretching region. These results suggest that a transmembrane potential (negative inside) and/or cation gradient can energize membranes by compression of the apolar region and transfer of protein methyl residues into polar regions.