Viscoelastic and biochemical properties of erythrocytes during storage with SAG-M at +4 degrees C

During storage at +4 degrees C, red blood cells undergo biochemical and physicochemical modifications, which alter their rheological characteristics especially the deformability. Even so until now not precisely defined deformability is undoubtedly a function of whole cell elasticity and viscosity. In a previous study we have investigated changes of elasticity of whole RBCs during a 6 weeks storage by quasi-static experiments using our Cell-Elastometer method. Since the changes in deformability we observed with that experimental approach have not been significant we extended the hard/software capabilities of this instrument to enable dynamic measurements also. We applied this modified hard-/software set-up to examine again changes in viscoelasticity of erythrocytes from concentrates during a six weeks storage at a blood bank. The cells were resuspended in CPD-SAG-M and stored at +4 degrees C. Quasi-static and dynamic experiments were performed on stored erythrocytes and showed for both significant changes in elasticity and viscoelasticity from the fourth week on. So it can be stated that due to our experimental results decrease in deformability of RBCs during storage occurs after a four weeks period of relative stability. To get further insight in changes of underlying or related biochemical properties according experiments have been performed in parallel. Especially the decrease in ATP showed a nearly parallel time course with a significant decrease after the 4th week. All other parameters especially the 2,3 DPG level showed a nearly linear de- or increase with time which are in accordance with the results of the additionally performed elongation experiments. Our quasi-static and dynamic deformability measurements have been proven to provide a simple and reliable tool to follow up erythrocyte senescence during storage where a pronounced change in mechanical properties may be used as an indicator for a change in bioviability. This has to be verified in further experiments.

Complexity analysis of placental blood flow in normal and high-risk pregnancies

Various strategems of complexity analysis of microvascular blood flow were carried out in several fields of medicine in the past, as such as angiology, ophthalmology and neurology. The introduction of colour-angio-mode, a special form of colour coded Doppler sonography, now makes possible to perform complexity analysis of the placental blood displacement even in the absence of information about hydrodynamic details such as directionality, velocity profile and number of displaced blood cells. Algorithms were developed which allows to extract information concerning the time averaged power of phonon-erythrocytes collision events (from the square of the frequencies of back scattered ultrasound recorded during 166 ms) in 20,000 to 40,000 regions of interest. The obtained values are being displayed as false coloured pixels on a video-screen, we succeeded to obtain quantitative data about displacement rates.In cross-sectional and longitudinal studies we generated typical diagrams displaying the "occurrence rate" of various powers of displacement over time. By this mode of display contour plots can be generated, showing a large amount of low intensity pixels and a small amount of high intensity pixels representing the parenchymatous blood flow inside the placenta. As was to be expected, interdependencies between the placental blood flow and the maternal and fetal heart rates as well as the maternal breathing can be found. While there was only limited influence of maternal and fetal heart rate on the placental blood flow, maternal breathing showed striking influence. Surprisingly, during expiration the power of placental blood movement was decreased, and there was a marked increase during inspiration. In cases of severe intrauterine growth retardation, colour pixel intensities were seen to transiently vanish during end-expiration. The power of placental blood displacement was marked increased subsequent to reducing maternal hematocrit during hemodilution therapy by infusion of artificial colloids. These interdependencies could be confirmed by ex vivo examinations perfusing and percolating the placenta after birth in a hemodynamic model. Additionally, we found interdependencies between fetal and maternal blood displacement inside the placenta. By modelling the decrease of fetal inotropic power in the ex vivo examinations, increase in the power of maternal blood displacement in the intervillous space. The two types of placental blood flow are known to be determined by many factors. While it is currently impossible to measure all these parameters determining an parenchymatous blood flow, it is possible to obtain useful informations about the physiologic and pathophysiologic changes of placental blood flow using colour-angio-mode as a tool of complexity analysis based on the distribution of local blood displacement. This new knowledge can help to understand clinically relevant changes in the individual patient as well their underlying causes.

Dose dependent effects on bone resorption and formation of intermittently administered intravenous ibandronate

The aim of the present paper was to delineate in detail the dose-dependent effects of intermittent intravenous (IV) ibandronate treatment on the dynamics of markers of bone resorption and formation. The study included 73 healthy postmenopausal women between 50 and 70 years of age. Two groups received an IV injection of either 1 mg or 2 mg ibandronate on day 0 and 84 and one group, which received no treatment, served as control. Study duration was 168 days. Bone turnover was estimated by measuring the serum concentration of the C-terminal collagen I telopeptide (s-CTx, bone resorption) and osteocalcin (s-OC, bone formation) at 19 consecutive time-points. Serum CTx decreased rapidly reaching a nadir 7 days after drug administration. Maximal changes from baseline in the 1 and 2 mg ibandronate groups were -81% and -90%, respectively ( P<0.001). However, already 2 weeks after drug administration, s-CTx started to rise again in both treatment groups, reaching -16% and -20% by day 84, i.e. immediately before the second drug administration. In contrast, s-OC showed a slower but progressive decrease over time reaching a nadir at -35% inhibition after 5 months. On a group level, the suppression of bone resorption was greater or equal to the suppression of bone formation at all time points. However, the least significant change (LSC) analysis performed at the individual level highlighted individuals who at certain time points showed apparently greater suppression of formation than resorption, which could also contribute to the inefficacy of this dosing regime. Although the physiological relevance of this latter finding would require further analysis, the results draw attention to the need to optimize the intermittent IV dosing of ibandronate in order to approximate more closely the sustained and balanced anti-resorptive effect provided by daily oral treatment.

The influence of age, sex and other variables on the plasma level of N-terminal pro brain natriuretic peptide in a large sample of the general population

OBJECTIVE

To identify potentially confounding variables for the interpretation of plasma N-terminal pro brain natriuretic peptide (NT-proBNP).

DESIGN

Randomly selected subjects filled in a heart failure questionnaire and underwent pulse and blood pressure measurements, ECG, echocardiography, and blood sampling.

SETTING

Subjects were recruited from four Copenhagen general practices located in the same urban area and were examined in a Copenhagen University Hospital.

PATIENTS

382 women and 290 men in four age groups: 50-59 years (n = 174); 60-69 years (n = 204); 70-79 years (n = 174); and > 80 years (n = 120).

MAIN OUTCOME MEASURES

Associations between the plasma concentration of NT-proBNP and a range of clinical variables.

RESULTS

In the undivided study sample, female sex (p < 0.0001), greater age (p < 0.0001), increasing dyspnoea (p = 0.0001), diabetes mellitus (p = 0.01), valvar heart disease (p = 0.002), low heart rate (p < 0.0001), left ventricular ejection fraction < or = 45% (p < 0.0001), abnormal ECG (p < 0.0001), high log10[plasma creatinine] (p = 0.0009), low log10[plasma glycosylated haemoglobin A1c] (p = 0.0004), and high log10[urine albumin] (p < 0.0001) were independently associated with a high plasma log10[plasma NT-proBNP] by multiple linear regression analysis.

CONCLUSIONS

A single reference interval for the normal value of NT-proBNP is unlikely to suffice. There are several confounders for the interpretation of a given NT-proBNP concentration and at the very least adjustment should be made for the independent effects of age and sex.

Quantitative proton magnetic resonance spectroscopy of children with adrenoleukodystrophy before and after hematopoietic stem cell transplantation

About 35-40 % of boys with X-linked adrenoleukodystrophy (ALD) develop a rapidly progressive cerebral form which leads to severe neurologic disability and death within 3-5 years after onset of clinical symptoms. Because previous proton magnetic resonance spectroscopy (MRS) studies of ALD identified metabolite patterns characteristic of demyelination, gliosis, and neuroaxonal loss, this work tested the hypothesis that MRS--apart from indicating disease progression--provides criteria for the outcome after hematopoietic stem cell transplantation (HSCT) which has been promising at an early stage of the active disease. Follow-up quantitative proton MRS was performed in frontal and occipital white matter of ALD patients (n = 12) before and up to 5 years after HSCT. The observed metabolite alterations were retrospectively correlated with the clinical outcome representing either a stable condition (n = 5), a further deterioration (n = 5), or death (n = 2). While disease progression of patients before HSCT was mainly characterized by a further increase of elevated choline-containing compounds (Cho) as an indicator of active demyelination, a positive outcome after HSCT was correlated with high N-acetylaspartate (tNAA) levels in affected white matter before HSCT yielding positive and negative predictive values for tNAA of 80 %. Although to be confirmed in a larger cohort of patients, the present findings suggest the preservation of neuroaxonal integrity as a prerequisite for an arrested course. Conversely, the combination of increased Cho with markedly reduced tNAA before HSCT apparently reflects a degree of tissue degeneration which precludes a successful therapeutic intervention.

Oral ibandronate: changes in markers of bone turnover during adequately dosed continuous and weekly therapy and during different suboptimally dosed treatment regimens

The aims of the present study were to investigate how changes in the cumulative dose and the frequency of dosing influence the short-term antiresorptive efficacy of oral ibandronate treatment and whether serial measurements of bone markers could provide a useful diagnostic tool for the revelation of noncompliance to established treatments with antiresorptive drugs. Study participants were 200 healthy women 50-70 years old (mean 63.1 years) with a lumbar spine BMD t-score of -1 to -5. Women were randomly allocated to receive treatment with oral ibandronate according to one of the following eight dosing regimes: (1) 2.5 mg daily for 84 days; (2) 20 mg weekly for 84 days; (3) 2.5 mg daily for 28 days + no treatment for 56 days; (4) 2.5 mg daily for 28 days + 2.5 mg weekly for 56 days; (5) 2.5 mg daily for 28 days + 2.5 mg three times weekly for 56 days; (6) 2.5 mg daily for 14 days + 2.5 mg three times weekly for 56 days; (7) 2.5 mg three times weekly for 84 days; (8) no treatment for 168 days. Study parameters were the serum concentration of the C-terminal telopeptide of collagen type I (s-CTX, resorption marker) and N-MID osteocalcin (formation marker) measured by enzyme-linked immunosorbent assay. Oral treatment with ibandronate 20 mg weekly (cumulative dose 240 mg) resulted in greater final inhibition in s-CTX and area under the curve (AUC) compared to the 2.5 mg daily treatment (cumulative dose 210 mg), indicating that as long as optimal doses are administered the frequency of dosing has secondary importance for overall efficacy. When the cumulative dose was 130 mg or less, the final degree of inhibition was still the function of the cumulative dose, but the overall efficacy estimated by the AUC was also under the influence of the frequency of dosing. These observations suggest that serial measurements of s-CTX may provide a useful diagnostic tool for the early revelation of suboptimal dosing or noncompliance to already optimized therapies with antiresorptive agents.

Ultrafractionation in A7 human malignant glioma in nude mice

PURPOSE

Low-dose hyperradiosensitivity (HRS) has been demonstrated in numerous cell lines in vitro, including a number of radioresistant human malignant glioma cell lines such as A7. The aim of our experiment was to show whether HRS can be exploited by using ultrafractionated irradiation (UF) to improve local control of A7 tumours growing in nude mice. Extrapolation of the in vitro results predict a 3.7-fold difference in the efficacy of UF compared with conventional fractionation (CF).

MATERIAL AND METHODS

Subcutaneuously growing A7 tumours were irradiated either with UF (126 fractions in 6 weeks, 0.4 Gy per fraction) or CF (30 fractions in 6 weeks, 1.68 Gy per fraction). The total dose was 50.4 Gy in both experimental arms. Fractionated irradiations were given under ambient conditions and followed by graded top-up doses under clamp hypoxia. Endpoints were tumour growth delay and local tumour control 180 days after the end of treatment.

RESULTS

UF resulted in a significant decrease of tumour growth delay and in a significant increase of the top-up TCD(50) compared with CF (40.0 Gy [95% CI 29; 61 Gy] versus 28.3 Gy [24; 35 Gy], p=0.047).

CONCLUSIONS

Despite a pronounced HRS phenomenon in vitro, UF was significantly less effective than CF in A7 human malignant glioma in nude mice. These results neither disprove the existence of HRS nor do they exclude a possible clinical value of UF. The findings rather indicate that simplistic extrapolation from results obtained after single-dose exposure or few fractions in vitro is not sufficient to predict outcome of UF in vivo and that comprehensive evaluation of novel treatment options in animal models continues to be an essential requirement for clinical translation.

Factors associated with the consumption of psychotropic drugs in a cohort of men and women aged 50 and over

OBJECTIVES

The use of psychotropic drugs has increased continuously over recent years in industrialized countries. In Europe, France has the highest consumption of such drugs. The aim of this study was to identify the sociodemographic and medical factors associated with the use of psychotropic agents.

METHODS

Data, collected as part of the SUVIMAX (SUpplementation en VItamines et sels Mineraux AntioXydants) prevention trial, from a self- administered questionnaire involving 7299 subjects aged 45-60 years, were subjected to logistic regression analysis.

RESULTS

A total of 467 subjects used psychotropic drugs (8.4% of the women, 4.6% of the men). Use of psychotropic drugs increased in subjects of both sexes with past history of depression, perception of poor health and use of other drug treatments. Widowhood in men [odds ratio (OR) = 3.4; 95% CI = 1.6-7.3] and divorce in women (OR = 2; 95% CI = 1.2-3.2) were also associated with an increased use of psychotropic drugs. Interaction was demonstrated between educational level and occupational satisfaction in men (OR = 2.9; 95% CI = 1.5-5.8) and between perception of health status and use of other types of medication in women (OR = 6.5; 95% CI = 4.6-9.5).

CONCLUSION

The results of our study are consistent with those of others in demonstrating that specific socio-occupational factors in men and specific medical factors in women influence extent of use of psychotropic drugs.

A haptic sensor-actor-system based on ultrasound elastography and electrorheological fluids for virtual reality applications in medicine

Mechanical properties of biological tissue represent important diagnostic information and are of histological relevance (hard lesions, "nodes" in organs: tumors; calcifications in vessels: arteriosclerosis). The problem is, that such information is usually obtained by digital palpation only, which is limited with respect to sensitivity. It requires intuitive assessment and does not allow quantitative documentation. A suitable sensor is required for quantitative detection of mechanical tissue properties. On the other hand, there is also some need for a realistic mechanical display of those tissue properties. Suitable actuator arrays with high spatial resolution and real-time capabilities are required operating in a haptic sensor actuator system with different applications. The sensor system uses real time ultrasonic elastography whereas the tactile actuator is based on electrorheological fluids. Due to their small size the actuator array elements have to be manufactured by micro-mechanical production methods. In order to supply the actuator elements with individual high voltages a sophisticated switching and control concept have been designed. This haptic system has the potential of inducing real time substantial forces, using a compact lightweight mechanism which can be applied to numerous areas including intraoperative navigation, telemedicine, teaching, space and telecommunication.

Distribution of 16alpha-[18F]fluoro-estradiol-3,17beta-disulfamate in rats, tumour-bearing mice and piglets

Based on a high affinity to the enzyme estrone sulfatase (ES), 16alpha-[18F]fluoroestradiol-3,17beta-disulfamate ([18F]FESDS) has been suggested as a potential PET radiotracer for imaging steroid-dependent breast tumours. The distribution of [18F]FESDS was studied in rats, tumour-bearing nude mice and piglets. In all species evidence for binding to a second target, the enzyme carbonic anhydrase (CA), was obtained. ES and CA inhibitors significantly reduced the radiotracer uptake in various organs but not in tumours. It is concluded that [18F]FESDS binds to ES and CA in vivo but this binding is not strong enough to allow tumour imaging with positron emission tomography (PET).

Preparation of porous n-type silicon sample plates for desorption/ionization on silicon mass spectrometry (DIOS-MS)

This study focuses on porous silicon (pSi) fabrication methods and properties for desorption ionization on silicon mass spectrometry (DIOS-MS). PSi was prepared using electrochemical etching of n-type silicon in HF-ethanol solution. Porous areas were defined by a double-sided illumination arrangement: front-side porous areas were masked by a stencil mask, eliminating the need for standard photolithography, and backside illumination was used for the backside ohmic contact. Backside illumination improved the uniformity of the porosified areas. Porosification conditions, surface derivatizations and storage conditions were explored to optimize pSi area, pore size and pore depth. Chemical derivatization of the pSi surfaces improved the DIOS-MS performance providing better ionization efficiency and signal stability with lower laser energy. Droplet spreading and drying patterns on pSi were also examined. Pore sizes of 50-200 nm were found to be optimal for droplet evaporation and pore filling with the sample liquid, as measured by DIOS efficiency. With DIOS, significantly better detection sensitivity was obtained (e.g. 150 fmol for midazolam) than with desorption ionization from a standard MALDI steel plate without matrix addition (30 pmol for midazolam). Also the noise that disturbs the detection of low-molecular weight compounds at m/z < 500 with MALDI could be clearly reduced with DIOS. Low background MS spectra and good detection sensitivity at the 100-150 fmol level for pharmaceutical compounds were achieved with DIOS-MS.

Long term visual outcome in amblyopia treatment

AIM

To evaluate long term visual outcome of treatment for amblyopia.

METHODS

In a previous study, 44 children with unilateral amblyopia caused by strabismus or anisometropia were enrolled in a prospective study investigating the results of treatment. All children were regularly examined up to at least 8 years of age and outcome was evaluated. All subjects were invited to a re-examination and in total 26 subjects attended. Two of these were excluded because of insufficient records. The final sample consists of 24 subjects. Mean follow up time was 10.4 (SD 1.9) years.

RESULTS

For the amblyopic eyes, 17% deteriorated in visual acuity, 50% were stable, and 33% gained in visual acuity. For the non-amblyopic eyes, 8% lost one line in visual acuity, 38% were stable, and 54% gained in visual acuity. No eye in any subject shifted more than 0.2 logMAR units. The increase in visual acuity for the non-amblyopic eyes was significant, while the increase for the amblyopic eyes was not. All straight eyed anisometropic amblyopes showed a distinct decrease in magnitude of anisometropia.

CONCLUSIONS

Visual acuity was essentially stable in the amblyopic eyes 10 years after cessation of treatment in the studied population.

[Autonomy attitudes in the treatment compliance of a cohort of subjects with continuous psychotropic drug administration]

Prescriptions for psychotropic drugs are part of a general practitioner's daily routine. As with all drugs, they need to be controlled by a phenomenon of observance. Respecting prescriptions is in fact a major public health concern. Our problematic is centred on the analysis of the association between observance and autonomy in order to gain a better understanding of the links between the drug, how it is to be taken, and how the patients adapt and control it. Identifying and comparing autonomous practices psychotrope users associated with attitudes put into play by those who claim to observe or not to observe their treatment is the aim of this project. The qualitative analysis of the speech is based on the categorial analysis of the contents of 46 transcriptions of 23 women et 23 men continuous (regular monthly intake for at least 5 years), aged between 50 and 65. The majority live in couples, have professional activities, and are executives. The psychotropes with the largest consumption are: anxiolytics and antidepressors. The average duration of their consumption is more than 17 years. Two types of attitude can be distinguished through the qualitative analyse. The attitudes of non-observers towards the psychotropic drug and dependence show controlled, autonomous acts. Autonomy is an influencing factor in their observation of the prescribed treatment, it is a major component of their non-observance regarding psychotropes; thus our hypothesis is confirmed. The strategy adopted around the medication arises from autonomy of action. Organising the treatment is seen as a sign of autonomy, as taking an initiative in relation to the medical prescription, and not as rebellious, or carefree behaviour, or as a sign of inconsistency. Non-observers seem more to be involved in a step towards self-regulation. Active taking verbs such as stop, diminish, increase , and success verbs succeed the I is greatly used, reinforced in some cases by myself ; this vocabulary situates the patient as an actor facing the drug and shows that he is capable of action. For observers, taking the drug is qualified as regular and some users categorically refuse to bypass the doctor's advice never . Looking for additional information is an act of autonomy. It is found partly with the doctor; but also from the media, the exchanges with the others and the reading of the notes. But talking to other people and reading the information leaflets are more often done by non-observers. Recognizing oneself in the indications and the dosage marked on the leaflet seems to be the first step to adopting the drug so as to know it better and to gain mastery of it. Autonomy is gained through finding alternative, substitutive or complementary solutions with a large share left to herbal medicine and homeopathy. Non-observers seem to be more active than observers in diminishing or stopping taking psychotropes. Affirming one's autonomy is also shown in the direction given to each person's trajectory of life, behaviour referring to it, the projection into the future, and the dynamics of life. These actions underlie a capacity of resistance, non-observers using evocative terms such as taking things in hand , recognizing the while, in certain cases, the need to be supported. This capacity of action is far less present in observers who acknowledge their difficulties in facing up to events. The intentionality and the determination of their behaviour and their choices depend on the autonomy of willpower. Adjusting the amount taken is shown by expressions of intention, and justifies self-regulation. Non-observers direct their behaviour towards a reduction in the medication and commit themselves not to go over a certain amount. Stopping usage is declared as certain , it is planned. On the other hand, it remains unpredictable for observers for whom consumption is linked to the description of a need to have long-lasting health. Observers describe taking their medication as automatic, routine, and easy. A sort of fatality and resignation is attached to the prescription, linked to a negative perception of their health. The medication is at the same time nourishing and destructive . The disagreeable sensations caused by its suppression and the secondary effects appear less important than the benefits to be had from it. Autonomy can be recognized in the type of commitment established with the professional. It can be shown around a prescription negociated for treatment and delivered in mutual agreement. It places the patient in an active partnership. The presence of I and of more frequent active verbs in non-observers shows the role played by the patient. His conversation organizes itself round how the medication is to be taken. Systematic use of the prescription reinforces the instrumental recourse to the doctor for a renewal especially for non-observers. For observers, the prescription is followed despite disagreements. The professional is appreciated for his expertise in advice, how to use the medication . Confidence results from this know-how. The feeling of fear inspired by the psychotrope puts taking the medication into perspective and removes the guilt from non-observance. This process contributes to the patient's carrying on taking the medication. The positive effects found again thanks to the medication strengthen the later's perpetuation. When the patient is asked to participate in the prescription, this participation is described differently in the two groups. In observers, it is understood from the viewpoint of the doctor-patient association with, us and for the other group from the viewpoint of cooperation I, one . In non-observers, a type of delegation is highlighted leave it to be managed , the patient's confidence in the doctor lets him manage his medication under medical control . The autonomy of willpower is shown by the degree of openness to the Other Person. Non-observers have quite open and trendy character traits and give a rather positive image of themselves. These elements are absent from the speech of observers in favour of a negative self-image. The autonomy of willpower shows up in their free expression within the family, and with friends, the patient is freed from the influence of other people. For non-observers it is admitted easily . Observers show reserve through a concern of being discrete; rules of good behaviour do not allow them to speak about their consumption since it lifts the veil on their person and its affects. Two types of attitude can be distinguished: Observers for whom the psychotrope supports them against an unhappy life and is part of a habit which is hidden from other people, they keep to the prescribed doses and don't try to change them, they have absolute confidence in the medical profession; non-observers for whom psychotropes are a crutch which they mistrust. They are conscious of the bad effects and state their intention and their will to control this medication by planning on a reduction in, or even an end to, consumption. In order to give a meaning to the prescription and to avoid too great a feeling of guilt, they legitimize the later by an obligation created by a need, and by an improvement in symptomatology, and they minimize the quantity and the effects of taking the medication. They cooperate with the doctor and are involved in a close relationship with my doctor . They show a certain familiarity to the medication and talk openly about their consumption. Autonomy is a means to responsibility and to valorise a part of the patients in particular those which are non-observing so as to strengthen their capacity to manage their health as best they can. It contributes to a better observance of treatment in as much as autonomous patients are more inclined to negotiate with their doctors. Looking for self-regulatory behaviour allows us a better understanding of those patients non-observers who are willing, and helps them to develop their aptitude to face up to their illness.

Status Epilepticus Induces Changes in the Expression and Localization of Endogenous Palmitoyl-Protein Thioesterase 1

Kainic acid (KA)-induced experimental epilepsy, a model of excitotoxicity, leads to selective neuronal death and synaptic restructuring. We used this model to investigate the effects of neuronal hyperactivation on palmitoyl-protein thioesterase 1 (PPT1), the deficiency of which causes drastic neurodegeneration. Immunological stainings showed that epileptic seizures in adult rats led to a progressive and remarkable increase of PPT1 in limbic areas of the brain. Within 1 week, the maximal expression was observed in CA3 and CA1 pyramidal neurons of the hippocampus. In the surviving pyramidal neurons, PPT1 localized in vesicular structures in cell soma and neuritic extensions. After seizures, colocalization of PPT1 with synaptic membrane marker (NMDAR2B) was enhanced. Further, synaptic fractionation revealed that after seizures PPT1 was readily observed on the presynaptic side of synaptic junction. These data suggest that PPT1 may protect neurons from excitotoxicity and have a role in synaptic plasticity.

Cell fusion generates an inhomogeneous distribution of elasticity and rigidity in plasma membranes

The post-electrofusion oscillation cycle of human erythrocytes (doublets) was evaluated for the first four pump events in order to quantify the spectrin-network rearrangement in the fusion zone. Experiments were carried out on control cells and on cells that received a 40 degree C and a 45 degree C 20-min heat treatment. The amplitude of the geometrical changes depended on the heat-treatment procedure, whereas the roundness on entering the pump event was always identical. The rigid influence of the fusion zone prevented the doublets from adopting a spherical shape. The fusion zone was characterized by a linear elongation modulus that could be calculated from geometrical measurements and earlier findings on erythrocyte membrane mechanics, and that ranged between 1.44E6 Nm(-2) for control doublets and 0.99E6 Nm(-2) after 45 degrees C heat treatment. The membrane composition of the fusion zone differs greatly from that of the other membrane parts not involved in fusion processes and evidence is given that this inhomogeneity stems from a rearrangement of the triangulated spectrin network and other membrane skeletal proteins in the fusion zone.