Stiffness and ATP recovery of stored red blood cells in serum

Biological and genetic determinants of glycolysis: Phosphofructokinase isoforms boost energy status of stored red blood cells and transfusion outcomes

Mature red blood cells (RBCs) lack mitochondria and thus exclusively rely on glycolysis to generate adenosine triphosphate (ATP) during aging in vivo or storage in blood banks. Here, we leveraged 13,029 volunteers from the Recipient Epidemiology and Donor Evaluation Study to identify associations between end-of-storage levels of glycolytic metabolites and donor age, sex, and ancestry-specific genetic polymorphisms in regions encoding phosphofructokinase 1, platelet (detected in mature RBCs); hexokinase 1 (HK1); and ADP-ribosyl cyclase 1 and 2 (CD38/BST1). Gene-metabolite associations were validated in fresh and stored RBCs from 525 Diversity Outbred mice and via multi-omics characterization of 1,929 samples from 643 human RBC units during storage. ATP and hypoxanthine (HYPX) levels-and the genetic traits linked to them-were associated with hemolysis in vitro and in vivo, both in healthy autologous transfusion recipients and in 5,816 critically ill patients receiving heterologous transfusions, suggesting their potential as markers to improve transfusion outcomes.

Endothelial calcium dynamics elicited by ATP release from red blood cells

Red blood cells (RBCs) exhibit an interesting response to hydrodynamic flow, releasing adenosine triphosphate (ATP). Subsequently, these liberated ATP molecules initiate a crucial interaction with endothelial cells (ECs), thereby setting off a cascade involving the release of calcium ions (Ca2 + ). Ca2 + exerts control over a plethora of cellular functions, and acts as a mediator for dilation and contraction of blood vessel walls. This study focuses on the relationship between RBC dynamics and Ca2 + dynamics, based on numerical simulations under Poiseuille flow within a linear two-dimensional channel. It is found that the concentration of ATP depends upon a variety of factors, including RBC density, channel width, and the vigor of the flow. The results of our investigation reveals several features. Firstly, the peak amplitude of Ca2 + per EC escalates in direct proportion to the augmentation of RBC concentration. Secondly, increasing the flow strength induces a reduction in the time taken to reach the peak of Ca2 + concentration, under the condition of a constant channel width. Additionally, when flow strength remains constant, an increase in channel width corresponds to an elevation in calcium peak amplitude, coupled with a decrease in peak time. This implies that Ca2 + signals should transition from relatively unconstrained channels to more confined pathways within real vascular networks. This notion gains support from our examination of calcium propagation in a linear channel. In this scenario, the localized Ca2 + release initiates a propagating wave that gradually encompasses the entire channel. Notably, our computed propagation speed agrees with observations.

Tired and stressed: direct holographic quasi-static stretching of aging echinocytes and discocytes in plasma using optical tweezers [Invited]

Red blood cells (RBCs) undergo a progressive morphological transformation from smooth biconcave discocytes into rounder echinocytes with spicules on their surface during cold storage. The echinocytic morphology impacts RBCs' ability to flow through narrow sections of the circulation and therefore transfusion of RBC units with a high echinocytic content are thought to have a reduced efficiency. We use an optical tweezers-based technique where we directly trap and measure linear stiffness of RBCs under stress without the use of attached spherical probe particles or microfluidic flow to induce shear. We study RBC deformability with over 50 days of storage performing multiple stretches in blood plasma (serum with cold agglutinins removed to eliminate clotting). In particular, we find that discocytes and echinocytes do not show significant changes in linear stiffness in the small strain limit (∼ 20 % change in length) up to day 30 of the storage period, but do find differences between repeated stretches. By day 50 the linear stiffness of discocytes had increased to approximately that measured for echinocytes throughout the entire period of measurements. These changes in stiffness corresponded to recorded morphological changes in the discocytes as they underwent storage lesion. We believe our holographic trapping and direct measurement technique has applications to directly control and quantify forces that stretch other types of cells without the use of attached probes.

Design of an automated robotic microinjection system for batch injection of zebrafish embryos and larvae

This paper presents the design of a vision-based automated robotic microinjection system for batch injection of both zebrafish embryos and larvae. A novel visual recognition algorithm based on an automatic threshold and excessive dilatation is introduced to accurately identify the center of zebrafish embryos and larval yolks. A corresponding software system is developed using the producer-consumer model as the framework structure, and a friendly user interface is designed to allow operators to choose from a range of desired functions according to their different needs. In addition, a novel microstructural agarose device is designed and fabricated to simultaneously immobilize mixed batches of embryos and larvae. Moreover, a prototype microinjection system is fabricated by integrating hardware devices with visual algorithms. An experimental study is conducted to verify the performance of the robotic microinjection system. The results show that the reported system can accurately identify zebrafish embryos and larvae and efficiently complete batch microinjection tasks of the mixtures with an injection success rate of 92.05% in 13.88 s per sample. Compared with manual and existing microinjection systems, the proposed system demonstrates the merits of versatility, excellent efficiency, high success rate, high survival rate, and sufficient stability.

Core-Shell Microfiber Encapsulation Enables Glycerol-Free Cryopreservation of RBCs with High Hematocrit

Cryopreservation of red blood cells (RBCs) provides great potential benefits for providing transfusion timely in emergencies. High concentrations of glycerol (20% or 40%) are used for RBC cryopreservation in current clinical practice, which results in cytotoxicity and osmotic injuries that must be carefully controlled. However, existing studies on the low-glycerol cryopreservation of RBCs still suffer from the bottleneck of low hematocrit levels, which require relatively large storage space and an extra concentration process before transfusion, making it inconvenient (time-consuming, and also may cause injury and sample lose) for clinical applications. To this end, we develop a novel method for the glycerol-free cryopreservation of human RBCs with a high final hematocrit by using trehalose as the sole cryoprotectant to dehydrate RBCs and using core-shell alginate hydrogel microfibers to enhance heat transfer during cryopreservation. Different from previous studies, we achieve the cryopreservation of human RBCs at high hematocrit (> 40%) with high recovery (up to 95%). Additionally, the washed RBCs post-cryopreserved are proved to maintain their morphology, mechanics, and functional properties. This may provide a nontoxic, high-efficiency, and glycerol-free approach for RBC cryopreservation, along with potential clinical transfusion benefits.

Deformability of mouse erythrocytes in different diluents measured using optical tweezers

Optical tweezers are widely used to measure the mechanical properties of erythrocytes, which is crucial to the study of pathology and clinical diagnosis of disease. During the measurement, the blood sample is diluted and suspended in an exogenous physiological fluid, which may affect the elastic properties of the cells in vitro. Here, we investigate the effect of different diluents on the elastic properties of mouse erythrocytes by quantitatively evaluating their elastic constants using optical tweezers. The diluents are plasma extracted from mouse blood, veterinary blood diluent (V-52D), Dulbecco's modified Eagle's medium (DMEM), phosphate-buffered saline (PBS), and normal saline (NS). To create an environment that closely resembles in vivo conditions, the experiment is performed at 36.5 °C. The results show that the spring constant of mouse erythrocytes in plasma is 6.23 ± 0.41 μN m-1. The elasticity of mouse erythrocytes in V-52D and DMEM is 8.21 ± 0.91 and 6.95 ± 0.85 μN m-1, which are higher than that in plasma extracted from blood, whereas, the elasticity in PBS and NS is 4.23 ± 0.85 and 4.68 ± 0.79 μN m-1, which are less than that in plasma extracted from blood. At last, we observe the size and circularity of erythrocytes in different diluents, and consider that the erythrocyte diameter and circularity may affect cell deformability. Our results provide a reference of the diluent choice for measuring the mechanical properties of erythrocytes in vitro.

Integration of Trehalose Lipids with Dissociative Trehalose Enables Cryopreservation of Human RBCs

Cryopreservation of red blood cells (RBCs) is imperative for transfusion therapy, while cryoprotectants are essential to protect RBCs from cryoinjury under freezing temperatures. Trehalose has been considered as a biocompatible cryoprotectant that naturally accumulates in organisms to tolerate anhydrobiosis and cryobiosis. Herein, we report a feasible protocol that enables glycerol-free cryopreservation of human RBCs by integration of the synthesized trehalose lipids and dissociative trehalose through ice tuning and membrane stabilization. Typically, in comparison with sucrose monolaurate or trehalose only, trehalose monolaurate was able to protect cell membranes against freeze stress, achieving 96.9 ± 2.0% cryosurvival after incubation and cryopreservation of human RBCs with 0.8 M trehalose. Moreover, there were slight changes in cell morphology and cell functions. It was further confirmed by isothermal titration calorimetry and osmotic fragility tests that the moderate membrane-binding activity of trehalose lipids exerted cell stabilization for high cryosurvival. The aforementioned study is likely to provide an alternative way for glycerol-free cryopreservation of human RBCs and other types of cells.

Amine-modified nanoplastics promote the procoagulant activation of isolated human red blood cells and thrombus formation in rats

Background

Microplastics (MPs) and nanoplastics (NPs) formed from decomposed plastic are increasing environmental threats. Although MPs and NPs exposed through various routes enter the systemic circulation, the potential toxicity of those is largely unknown. We investigated whether polystyrene NPs (PS-NPs) promote the coagulation activity of red blood cells (RBCs).

Results

We tested several types of PS-NPs using human RBCs and found that amine-modified 100 nm PS-NPs were the most potent. We measured the uptake of PS-NPs using flow cytometry and confocal microscopy. Electron microscopy revealed morphological changes of RBCs by PS-NPs. PS-NPs induced the externalization of phosphatidylserine, generation of microvesicles in RBCs, and perturbations in the intracellular microenvironment. PS-NPs increased the activity of scramblases responsible for phospholipid translocation in RBCs. PS-NPs modulated the functional interaction to adjacent tissues and coagulation cascade, enhancing RBC adhesion and thrombin generation. Our observations in human RBCs were consistent with those in isolated rat RBCs, showing no inter-species differences. In rat venous thrombosis models, the intravenous administration of PS-NPs enhanced thrombus formation.

Conclusion

Amine-modified PS-NPs induce the prothrombotic activation of RBCs causing thrombus formation. We believe that our study will contribute to understanding the potential toxicity of amine-modified polystyrene particles in blood cells and cardiovascular systems.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-022-00500-y.

Biomechanical properties of native and cultured red blood cells–Interplay of shape, structure and biomechanics

Modern medicine increases the demand for safe blood products. Ex vivo cultured red blood cells (cRBC) are eagerly awaited as a standardized, safe source of RBC. Established culture models still lack the terminal cytoskeletal remodeling from reticulocyte to erythrocyte with changes in the biomechanical properties and interacts with membrane stiffness, viscosity of the cytoplasm and the cytoskeletal network. Comprehensive data on the biomechanical properties of cRBC are needed to take the last step towards translation into clinical use in transfusion medicine. Aim of the study was the comparative analysis of topographical and biomechanical properties of cRBC, generated from human CD34⁺ adult hematopoietic stem/progenitor cells, with native reticulocytes (nRET) and erythrocytes (nRBC) using cell biological and biomechanical technologies. To gain the desired all-encompassing information, a single method was unsatisfactory and only the combination of different methods could lead to the goal. Topographical information was matched with biomechanical data from optical tweezers (OT), atomic force microscopy (AFM) and digital holographic microscopy (DHM). Underlying structures were investigated in detail. Imaging, deformability and recovery time showed a high similarity between cRBC and nRBC. Young’s modulus and plasticity index also confirmed this similarity. No significant differences in membrane and cytoskeletal proteins were found, while lipid deficiency resulted in spherical, vesiculated cells with impaired biomechanical functionality. The combination of techniques has proven successful and experiments underscore a close relationship between lipid content, shape and biomechanical functionality of RBC.

Cyclic Mechanical Stresses Alter Erythrocyte Membrane Composition and Microstructure and Trigger Macrophage Phagocytosis

Red blood cells (RBCs) are cleared from the circulation when they become damaged or display aging signals targeted by macrophages. This process occurs mainly in the spleen, where blood flows through submicrometric constrictions called inter-endothelial slits (IES), subjecting RBCs to large-amplitude deformations. In this work, RBCs are circulated through microfluidic devices containing microchannels that replicate the IES. The cyclic mechanical stresses experienced by the cells affect their biophysical properties and molecular composition, accelerating cell aging. Specifically, RBCs quickly transition to a more spherical, less deformable phenotype that hinders microchannel passage, causing hemolysis. This transition is associated with the release of membrane vesicles, which self-extinguishes as the spacing between membrane-cytoskeleton linkers becomes tighter. Proteomics analysis of the mechanically aged RBCs reveals significant losses of essential proteins involved in antioxidant protection, gas transport, and cell metabolism. Finally, it is shown that these changes make mechanically aged RBCs more susceptible to macrophage phagocytosis. These results provide a comprehensive model explaining how physical stress induces RBC clearance in the spleen. The data also suggest new biomarkers of early "hemodamage" and inflammation preceding hemolysis in RBCs subjected to mechanical stress.

Sex-Specific Differences of Adenosine Triphosphate Levels in Red Blood Cells Isolated From ApoE/LDLR Double-Deficient Mice

In this study for the first time, we investigated the correlation between sex-specific differences in adenosine triphosphate (ATP) levels in red blood cells (RBCs) and their mechanical, biochemical, and morphological alterations during the progression of atherosclerosis in ApoE/LDLR double-deficient (ApoE/LDLR^−/−) mice. Our results indicate that both sex and age affect alterations in RBCs of both ApoE/LDLR^−/− and C57BL/6J mice. When compared with male RBCs, female RBCs were characterized by lower basal ATP and mean corpuscular hemoglobin concentration (MCHC), higher hemoglobin concentration (HGB), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), deformability, and phosphatidylserine (PS) exposure levels, regardless of age in both, ApoE/LDLR^−/− and C57BL/6J mice. ApoE/LDLR^−/− mice compared with age-matched controls showed lower basal ATP levels regardless of age and sex. Intracellular ATP level of RBCs was decreased solely in senescent female C57BL/6J mice, while it was elevated in males. Basal extracellular ATP levels were 400 times lower than corresponding intracellular level. In conclusion, basal ATP levels, RBC morphology, deformability, PS exposure levels alterations are sex-dependent in mice. Changes in basal ATP levels were correlated with PS exposure and trends of changes in MCV. Trends of changes of the most RBC parameters were similar in both sexes of ApoE/LDLR^−/− mice compared with age-matched controls; however, their kinetics and levels vary greatly between different stages of disease progression.

Melatonin: Regulation of Prion Protein Phase Separation in Cancer Multidrug Resistance

The unique ability to adapt and thrive in inhospitable, stressful tumor microenvironments (TME) also renders cancer cells resistant to traditional chemotherapeutic treatments and/or novel pharmaceuticals. Cancer cells exhibit extensive metabolic alterations involving hypoxia, accelerated glycolysis, oxidative stress, and increased extracellular ATP that may activate ancient, conserved prion adaptive response strategies that exacerbate multidrug resistance (MDR) by exploiting cellular stress to increase cancer metastatic potential and stemness, balance proliferation and differentiation, and amplify resistance to apoptosis. The regulation of prions in MDR is further complicated by important, putative physiological functions of ligand-binding and signal transduction. Melatonin is capable of both enhancing physiological functions and inhibiting oncogenic properties of prion proteins. Through regulation of phase separation of the prion N-terminal domain which targets and interacts with lipid rafts, melatonin may prevent conformational changes that can result in aggregation and/or conversion to pathological, infectious isoforms. As a cancer therapy adjuvant, melatonin could modulate TME oxidative stress levels and hypoxia, reverse pH gradient changes, reduce lipid peroxidation, and protect lipid raft compositions to suppress prion-mediated, non-Mendelian, heritable, but often reversible epigenetic adaptations that facilitate cancer heterogeneity, stemness, metastasis, and drug resistance. This review examines some of the mechanisms that may balance physiological and pathological effects of prions and prion-like proteins achieved through the synergistic use of melatonin to ameliorate MDR, which remains a challenge in cancer treatment.

Deformability of Stored Red Blood Cells

Red blood cells (RBCs) deformability refers to the cells’ ability to adapt their shape to the dynamically changing flow conditions so as to minimize their resistance to flow. The high red cell deformability enables it to pass through small blood vessels and significantly determines erythrocyte survival. Under normal physiological states, the RBCs are attuned to allow for adequate blood flow. However, rigid erythrocytes can disrupt the perfusion of peripheral tissues and directly block microvessels. Therefore, RBC deformability has been recognized as a sensitive indicator of RBC functionality. The loss of deformability, which a change in the cell shape can cause, modification of cell membrane or a shift in cytosol composition, can occur due to various pathological conditions or as a part of normal RBC aging (in vitro or in vivo). However, despite extensive research, we still do not fully understand the processes leading to increased cell rigidity under cold storage conditions in a blood bank (in vitro aging), In the present review, we discuss publications that examined the effect of RBCs’ cold storage on their deformability and the biological mechanisms governing this change. We first discuss the change in the deformability of cells during their cold storage. After that, we consider storage-related alterations in RBCs features, which can lead to impaired cell deformation. Finally, we attempt to trace a causal relationship between the observed phenomena and offer recommendations for improving the functionality of stored cells.

Metabolite Ratios as Quality Indicators for Pre-Analytical Variation in Serum and EDTA Plasma

In clinical diagnostics and research, blood samples are one of the most frequently used materials. Nevertheless, exploring the chemical composition of human plasma and serum is challenging due to the highly dynamic influence of pre-analytical variation. A prominent example is the variability in pre-centrifugation delay (time-to-centrifugation; TTC). Quality indicators (QI) reflecting sample TTC are of utmost importance in assessing sample history and resulting sample quality, which is essential for accurate diagnostics and conclusive, reproducible research. In the present study, we subjected human blood to varying TTCs at room temperature prior to processing for plasma or serum preparation. Potential sample QIs were identified by Ultra high pressure liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) based metabolite profiling in samples from healthy volunteers (n = 10). Selected QIs were validated by a targeted MS/MS approach in two independent sets of samples from patients (n = 40 and n = 70). In serum, the hypoxanthine/guanosine (HG) and hypoxanthine/inosine (HI) ratios demonstrated high diagnostic performance (Sensitivity/Specificity > 80%) for the discrimination of samples with a TTC > 1 h. We identified several eicosanoids, such as 12-HETE, 15-(S)-HETE, 8-(S)-HETE, 12-oxo-HETE, (±)13-HODE and 12-(S)-HEPE as QIs for a pre-centrifugation delay > 2 h. 12-HETE, 12-oxo-HETE, 8-(S)-HETE, and 12-(S)-HEPE, and the HI- and HG-ratios could be validated in patient samples.

Real-time red blood cell counting and osmolarity analysis using a photoacoustic-based microfluidic system

Counting the number of red blood cells (RBCs) in blood samples is a common clinical diagnostic procedure, but conventional methods are unable to provide the size and other physical properties of RBCs at the same time. In this work, we explore photoacoustic (PA) detection as a rapid label-free and noninvasive analysis technique that can potentially be used for single RBC characterization based on their photoabsorption properties. We have demonstrated an on-chip PA flow cytometry system using a simple microfluidic chip combined with a PA imaging system to count and characterize up to ∼60 RBCs per second. Compared with existing microfluidic-based RBC analysis methods, which typically use camera-captured image sequences to characterize cell morphology and deformation, the PA method discussed here requires only the processing of one-dimensional time-series data instead of two- or three-dimensional time-series data acquired by computer vision methods. Therefore, the PA method will have significantly lower computational requirements when large numbers of RBCs are to be analyzed. Moreover, we have demonstrated that the PA signals of RBCs flowing in a microfluidic device could be directly used to acquire the osmolarity conditions (in the range of 124 to 497 mOsm L-1) of the medium surrounding the RBCs. This finding suggests a potential extension of applicability to blood tests via PA-based biomedical detection.

Efficient encapsulation of functional proteins into erythrocytes by controlled shear-mediated membrane deformation

Red blood cells (RBCs) are attractive carriers of biomolecular payloads due to their biocompatibility and the ability to shelter their encapsulated cargo. Commonly employed strategies to encapsulate payloads into RBCs, such as hypotonic shock, membrane fusion or electroporation, often suffer from low throughput and unrecoverable membrane impairment. This work describes an investigation of a method to encapsulate protein payloads into RBCs by controlling membrane deformation either transiently or extendedly in a microfluidic channel. Under the optimized conditions, the loading efficiency of enhanced green fluorescent protein into mouse RBCs increased was about 2.5- and 4-fold compared to that with osmotic entrapment using transient and extended deformation, respectively. Significantly, mouse RBCs loaded with human arginase exhibit higher enzymatic activity and membrane integrity compared to their counterparts loaded by osmotic entrapment. These features together with the fact that this shear-mediated encapsulation strategy allows loading with physiological buffers highlight the key advantages of this approach compared to traditional osmotic entrapment.

In vitro analysis of multiple blood flow determinants using red blood cell dynamics under oscillatory flow

The flow behavior of blood is determined mainly by red blood cell (RBC) deformation and aggregation as well as blood viscoelasticity. These intricately interdependent parameters should be monitored by healthcare providers to understand all aspects of circulatory flow dynamics under numerous cases including cardiovascular and infectious diseases. Current medical instruments and microfluidic systems lack the ability to quantify these parameters all at once and in physiologically relevant flow conditions. This work presents a handheld platform and a measurement method for quantitative analysis of multiple of these parameters from 50 μl undiluted blood inside a miniaturized channel. The assay is based on an optical transmission analysis of collective RBC deformation and aggregation under near-infrared illumination during a 1 s damped oscillatory flow and at stasis, respectively. Measurements with blood of different hemo-rheological properties demonstrate that the presented approach holds a potential for initiating simultaneous and routine on-chip blood flow analysis even in resource-poor settings.

Red Blood Cell Stiffness and Adhesion Are Species-Specific Properties Strongly Affected by Temperature and Medium Changes in Single Cell Force Spectroscopy

Besides human red blood cells (RBC), a standard model used in AFM-single cell force spectroscopy (SCFS), little is known about apparent Young's modulus (Ea) or adhesion of animal RBCs displaying distinct cellular features. To close this knowledge gap, we probed chicken, horse, camel, and human fetal RBCs and compared data with human adults serving as a repository for future studies. Additionally, we assessed how measurements are affected under physiological conditions (species-specific temperature in autologous plasma vs. 25 °C in aqueous NaCl solution). In all RBC types, Ea decreased with increasing temperature irrespective of the suspension medium. In mammalian RBCs, adhesion increased with elevated temperatures and scaled with reported membrane sialic acid concentrations. In chicken only adhesion decreased with higher temperature, which we attribute to the lower AE-1 concentration allowing more membrane undulations. Ea decreased further in plasma at every test temperature, and adhesion was completely abolished, pointing to functional cell enlargement by adsorption of plasma components. This halo elevated RBC size by several hundreds of nanometers, blunted the thermal input, and will affect the coupling of RBCs with the flowing plasma. The study evidences the presence of a RBC surface layer and discusses the tremendous effects when RBCs are probed at physiological conditions.

Role of glucose in the repair of cell membrane damage during squeeze distortion of erythrocytes in microfluidic capillaries

The rapid development of portable precision detection methods and the crisis of insufficient blood supply worldwide has led scientists to study mechanical visualization features beyond the biochemical properties of erythrocytes. Combined evaluation of currently known biochemical biomarkers and mechanical morphological biomarkers will become the mainstream of single-cell detection in the future. To explore the mechanical morphology of erythrocytes, a microfluidic capillary system was constructed in vitro, with flow velocity and glucose concentration as the main variables, and the morphology and ability of erythrocytes to recover from deformation as the main objects of analysis. We showed the mechanical distortion of erythrocytes under various experimental conditions. Our results showed that glucose plays important roles in improving the ability of erythrocytes to recover from deformation and in repairing the damage caused to the cell membrane during the repeated squeeze process. These protective effects were also confirmed in in vivo experiments. Our results provide visual detection markers for single-cell chips and may be useful for future studies in cell aging.

Differential dielectroscopic data on the relation of erythrocyte membrane skeleton to erythrocyte deformability and flicker

Two dielectric relaxations, βsp (1.5 MHz) and γ1sp (7 MHz), have been detected on spectrin-based membrane skeleton (MS) of red blood cells (RBCs) using the plot of admittance changes at the spectrin denaturation temperature (Ivanov and Paarvanova in Bioelectrochemistry 110: 59-68, 2016, Electrochim Acta 317: 289-300, 2019a). In this study, we treated RBCs and RBC ghost membranes with agents that make membranes rigid and suppress membrane flicker, and studied the effect on βsp and γ1sp relaxations. Diamide (diazene dicarboxylic acid bis-(N,N-dimethylamide)) (up to 0.85 mM), taurine mustard (tris(2-chloroethyl)amine) (up to 2 mM), known to specifically cross-link and stiffen spectrin, and glutaraldehyde (up to 0.044%) all inhibited the relaxations in RBC ghost membranes. Similar inhibition was obtained resealing RBC ghost membranes with 2,3-diphosphoglicerate (up to 15 mM), binding WGA (wheat germ agglutinin) (up to 0.025 mg/ml) to exofacial aspect of RBCs, incubating RBCs in hypotonic (200 mOsm) and hypertonic (600-900 mOsm) media and depleting RBCs of ATP. By contrast, concanavalin A (1 mg/ml) and DIDS (4,4'-diiso-thiocyanato stilbene-2,2'-disulfonic acid) (75 μM, pH 8.2), both known to bind specifically band 3 integral protein of RBCs without effect on RBC membrane rigidity, did not affect the relaxations. We conclude there might be a relation between the strength of dielectric relaxations on MS spectrin and the deformability and flicker of RBC membrane.