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PubMed2005

Fleeting glimpses of lipid rafts: how biophysics is being used to track them.

Cell membranes are fluid but can exhibit local order that gives rise to lateral inhomogeneities, often referred to as membrane microdomains. Among the best studied yet least well understood of these microdomains are lipid rafts. Lipid rafts are hypothesized to participate in a variety of physiologic and pathologic pathways important to human health by causing the spatial segregation of proteins and lipids within the plane of the membrane. Despite the widespread implications of the raft model, major questions remain about raft size, composition, and life span. This article discusses how recent biophysical measurements of the dynamic properties of rafts and putative raft-associated proteins and lipids are being used to test the hypothesis that confinement of proteins in rafts slows and/or impairs their ability to sample their microenvironment by lateral diffusion.

Animals↗
PubMed1991

Biophysical and biochemical alterations in erythrocyte membranes from chronic alcoholics.

Erythrocyte membranes from healthy controls and alcoholic patients, examined within 24 h of abstinence, were studied for basal membrane fluidity and membrane sensitivity to ethanol by fluorescence polarization of the apolar probe 1,6-diphenyl-1, 3,5-hexatriene (DPH) and its cationic derivative 1,4(trimethylammonium phenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH). The membrane partition (Kp) of ethanol and phenobarbital, and the concentrations of membrane-bound sialic acid and galactose, were also determined. The apolar hydrocarbon region of the membrane (DPH) was less fluid, in the alcoholics than in the controls (p less than 0.005). In the patients this membrane layer, as well as the polar lipid head group region (TMA-DPH), showed reduced fluidizing effect of ethanol (p less than 0.01). This resistance or tolerance to ethanol correlated with a markedly impaired (-59%, p less than 0.025) partition of ethanol into the membrane. The low Kp of ethanol in turn was partly related to reduced concentrations of polar carbohydrates such as sialic acid and galactose (p less than 0.01) at the membrane surface. The Kp of phenobarbital was reduced in the patients (-59%, p less than 0.005) but, apparently unrelated to the carbohydrate changes. These results indicate that in man, chronic alcohol abuse is associated with complex changes of membrane properties at different membrane levels e.g. at the charged surface, in the polar lipid head group region and in the hydrocarbon core. A partial basis for biophysical membrane tolerance to ethanol is suggested, implying that apart from phospholipid alterations, structural changes in membrane-bound glycoconjugates participate in this adaptive process.

Adult↗
PubMed2003

Biophysical properties of Kv3.1 channels in SH-SY5Y human neuroblastoma cells.

Biophysical properties of delayed rectifier K channels in the human neuroblastoma SH-SY5Y were established using patch clamp recordings. The whole cell K+ conductance activated at membrane potentials positive to -20 mV. The midpoint of current activation was 9.6 +/- 5.1 mV, the equivalent charge was 3.7 +/-.6. Whole-cell currents inactivated slightly with time constants of 700 ms and 5 s. The K+ currents were sensitive to micromolar concentrations of TEA and 4-aminopyridine. RT-PCR experiments amplified a cDNA fragment specific for human Kv3.1 channels. Activation gating parameters in outside-out patches were shifted by approximately 14 mV in the hyperpolarizing direction.

4-Aminopyridine↗
PubMedDate not supplied

The biophysical effects of ultrasound on median nerve distal latencies.

PURPOSE: Previous studies have documented the lack of ultrasound's non-thermal effects on nerve conduction using frequencies of 1 MHz and 870 kHz. The analyses and conclusions were reached, despite only one study incorporating pulsed ultrasound. The purpose of this study was to determine the biophysical effects of continuous wave (CW) and pulsed wave (PW) ultrasound on median nerve motor and sensory latencies using common frequencies of 1.0 and 3.0 MHz. SUBJECTS: Fifteen healthy subjects (8 males, 7 females, age = 23.5 + 4.44 yrs, height = 171.2 + 10.7 cm, weight = 67.5 + 7.9 kg) without a history of neurological or musculoskeletal injury to their non-dominant arm volunteered for testing. METHODS AND MATERIALS: Subjects were exposed in counterbalanced order to five ultrasound treatment conditions: (1) 1 MHz, 1.0 W/cm2, 8 min., (2) 1 MHz, 1.0 W/cm2, 50% PW, 8 min., (3) 3.0 MHz, 1.0 W/cm2, CW, 8 min., (4) 3.0 MHz, 1.0 W/cm2, 50% PW, 8 min., (5) placebo, 0.0 W/cm2, 8 min. Dependent measures for motor and sensory latencies, and subcutaneous temperatures were taken pretreatment, at 2, 4 and 6 minutes during treatment, and immediately post-treatment. Separate two within repeated measures ANOVA were used for each dependent measure. RESULTS: Analysis revealed significant interactions for motor latencies [F (16,224) = 52.77, p < .001], sensory latencies [F (16,224) = 41.10, p < .001], and subcutaneous temperatures [F (16,224) = 52.77, p < .001]. Tukey's HSD post hoc analyses confirmed that nerve latencies responded similarly to subcutaneous temperature changes during and after ultrasound treatment. CONCLUSIONS: Alterations in nerve latencies from ultrasound on healthy nerves appeared to be related to temperature changes induced by ultrasound's thermal effects, and not by non-thermal or mechanical effects.

Adult↗
PubMedDate not supplied

[Biophysical foundations of the neuronal activity].

OBJECTIVE: It is sought to expose in a simple but rigorous way the fundamental basis of the classical biophysics. DEVELOPMENT: I start from the basic properties of a simple system (two solutions separated by a semipermeable membrane) in order to analyze the process of development of differences of potential. It is analyzed with special interest the development of the Nernst and Nernst-Planck equations. Then it is studied how this difference potential can originate, with different ionic species, the resting potential (Goldman, Hodgkin and Katz model). The next step consists in to analyze how the action potential arises. To do this, it will be of capital importance the mathematical model developed by Hodgkin and Huxley in the fifties; for it will be analyzed it thoroughly. Finally, some properties of the ionic channels will be commented that symbolize the biological implementation of the previous model. CONCLUSION: The fundamental property of the nervous system that constitutes its biological sense is the handling of the information in a quick and sure way. This information codes it basically in form of potentials and its changes. For it, it would be important for clinical neurophysiologists, neurologists, neurosurgeons and psychiatrists to understand the mechanisms that underlie into the behavior of the nervous system.

Animals↗
PubMed2000

[Combination of the computerized analysis of fetal heart rate and amniotic fluid index in the prediction of neonatal acidemia: a modified biophysical profile].

OBJECTIVE: To study the use of a modification of the classical biophysical profile by the combination of computerized analysis of fetal heart rate (cCTG) and the amniotic fluid index (AFI) in the prediction of neonatal acidemia at birth. METHODS: We considered 89 singleton third trimester high risk pregnancies delivered by cesarean section, with an AFI evaluated within 24 hrs from birth, and an antepartum cCTG performed within 6 hrs from delivery. We assigned values for AFI (oligo/anhydramnios = 1, normal = 0) and cCTG (Dawes-Redman criteria, not satisfied = 1, satisfied = 0). The endpoint was to predict an abnormal neonatal outcome as defined by an umbilical artery (UA) pH < or = 7.2. RESULTS: Fifteen neonates presented an UA pH < or = 7.2. By performing a logistic regression, we found that cCTG + AFI score (abnormal value 1-2) was able to significantly predict a pH value (< or = 7.20) with an Odds Ratio = 2.83 (p < 0.02). The diagnostic accuracy of the combination of cCTG + AFI was as follows: sensitivity: 80%, specificity: 58%. COMMENT: We suggest that the combination of cCTG + AFI included in the simple score we propose, may be of value in the prediction of neonatal acidemia and help in the management of third trimester high risk pregnancies.

Amniotic Fluid↗
PubMed1989

Biophysics in space.

Biophysics is an interdisciplinary field of study where various disciplines work together, with results of much interest to many scientists and students of the life sciences. Since physics is not always accessible to and understandable to biologists and life sometimes too simplified, this presentation focusses on models to help understand the biological effects of space factors, with emphasis on free radicals.

Aerospace Medicine↗
PubMed2002

Changes of biophysical behavior of k562 cells for p16 gene transfer.

p16 gene was transferred into human erythroleukemia cell line K562 that had been subjected to p16 deletion. The changes of biophysical behavior of K562 cells after gene transfer were studied with the micropipette technique. The micropipette data were analyzed with a standard solid viscoelastic model. In comparison to untransfected control K562 cells and the cells transfected with an empty vector, the p16-transfected K562 cells showed an increase in the elastic element K(1), which is inversely proportional to the maximum deformation over a long period of time, whereas the viscous element mu and the other elastic element K(2) showed no significant difference. The results indicate that K562 cells became more rigid after p16 transfer. The p16-transfected K562 cells also had a higher surface charge density. This study contributes to our knowledge about the suppression effect of p16 gene on tumor cell migration and about its use in gene therapy.

Biophysical Phenomena↗
PubMedDate not supplied

[A new method of identifying a systems based on the minimal quadratic discrepancy criterion for biophysics problems].

A wide range of biophysical systems are described by nonlinear dynamic models mathematically presented as a set of ordinary differential equations in the Cauchy explicit form: [formula: see text] Fij(X1(t),..,XN(t),t), (i = 1,...,N, j = 1,...,M), where Fij (X1(t), ..., XN(t), t) is a set of basis functions satisfying the Lipschitz condition. We investigate the problem of evaluation of model constants aij (the system identification) using experimental data about the time dependence of the dynamic parameters of the system Xi(t). A new method of system identification for the class of similar nonlinear dynamic models is proposed. It is shown that the problem of identifying an initial nonlinear model can be reduced to the solution of a system of linear equations for the matrix of the dynamic model constants [aj]i. It is proposed to determine the set of dynamic model constants aij using the criterion of minimal quadratic discrepancy for the time dependence of the set of dynamic parameters Xi(t). An important special case of the nonlinear model, the quadratic model, is considered. Test problems of identification using this method are presented for two nonlinear systems: the Van der Pol type multiparametric nonlinear oscillator and the strange attractor of Ressler, a widely known example of dynamic systems showing the stochastic behavior.

Algorithms↗
PubMed1992

The biophysical and histologic properties of capsules formed by smooth and textured silicone implants in the rabbit.

Capsular contracture remains the major complication of reconstructive and aesthetic breast surgery. The purpose of this investigation was to determine if a silicone implant with a textured surface will form a capsule of significantly different biophysical and histologic properties than conventional smooth silicone. Thirty smooth and 30 textured silicone tissue expanders were implanted under the panniculus carnosus of rabbits. After 3 months, measurements related to contracture were performed on anesthetized animals in an investigator-blinded, controlled manner. Intraexpander pressures were measured as saline was injected over time. We found a significant correlation between intraexpander pressures, applanation tonometry, and Baker class. Histology revealed a thicker, more adherent, and inflammatory capsule around the textured silicone implants as compared with the smooth silicone implants. Dynamic pressures were plotted against volume of saline within the two types of implants. Statistical analysis revealed that the textured implants form a tighter and thicker capsule than the smooth implants after 3 months of observation (p less than 0.005).

Animals↗
PubMedDate not supplied

[Biophysical modeling of radiation induced genetic damage to cells].

The paper deals with the new approach for high accurate prediction of ionising radiation induced lesions of the cellular genetic structures. The previous techniques mainly were based on the assumption of the random radiation-induced breakage of the cellular DNA. They did not consider higher-order DNA organisation in the chromatin and in the interphase chromosomes. The paper discusses the new methods of the biophysical modelling of DNA breakage following high LET irradiation which takes into account the information on 3-dimensional structural organisation of DNA in interphase chromosomes. On this basis the influence of DNA organisation in the chromosomes on both dsb clusters induction and on repair were quantitatively studied, that was impossible by the means of previous computational techniques.

Biophysical Phenomena↗
PubMedDate not supplied

[The clinico-biophysical parallels of mixed saliva in odontogenic inflammatory diseases].

Mixed salivary pools of 102 patients suffering from odontogenic inflammations were examined in microwave field over the period of 3 to 42 days from the disease onset. Immunoglobulins of the three main classes were measured in these salivary pools starting from the fourth through the 28th day of the disease. Graphs reflecting the time course of the coefficient of biophysical parameters and immunoglobulin levels in patients' mixed saliva were plotted and a mathematical model of an odontogenic inflammation described for the first time, and the markers of the phases of these inflammations defined.

Adolescent↗
PubMed1989

[The auditory area of the cat cerebral cortex after implantation of electrodes into the inner ear (morphologic and biophysical research)].

The article presents the findings of experimental studies of morphological and biophysical changes in the A1 hearing zone of the cerebral cortex depending on the period of the electrodes implantation in the inner ear. The studies showed that in the process of long implantation in the neurones of the hearing zone one can notice the disorders of water-electrolytic exchanges. There is a definite correlation between structural changes in microsome membranes of A1 zone and morphological data.

Animals↗
PubMed1989

The biophysics of nasal airflow.

The biophysics of nasal airflow involve the measurement, analysis, and understanding of bulk airflow or momentum transport through the nasal cavity and of the exchange of mass and heat laterally between the air stream and the walls. In both of these areas, optimal progress depends on judicious, combined, and continuous use of physical models, mathematical calculations, and measurements made on human subjects. The progress that has been made to date is both fascinating and encouraging and suggests that great improvement in understanding, diagnosis, and treatment of nasal and upper airway disease will be possible in the future through closer contact and cooperation between clinicians and physical and biological scientists.

Airway Resistance↗
PubMed1989

Locomotion of white blood cells: a biophysical analysis.

We determined some biophysical properties of human granulocytes, monocytes, and lymphocytes in respect to their locomotion. Granulocytes were exposed to plasma and were allowed to crawl on uncoated or glycol methacrylate coated glass plates. Monocytes did not migrate on uncoated glass, but did so on glycol methacrylated glass. Lymphocytes did not move on glass or glycol methacrylated glass, but moved on plexiglas coverslips. Granulocytes and monocytes showed a pronounced, directed movement towards a lysed erythrocyte (necrotaxis), lymphocytes showed no necrotactic response. The information collected by the granulocytes and monocytes in the necrotactic gradient was between 1 and 2 bits. This small amount of information indicated that the cellular decision in favor of a new direction of migration is based on a mechanism involving instability. We showed that the necrotactic response of granulocytes and monocytes is the product of the chemokinetic activity and the polar order parameter (= McCutcheon index) indicating that the cellular decision for a new direction of migration is independent of the speed of the cell movement. The movement of monocytes can be characterized in a similar way to that of granulocytes: the angle of deviation from a straight line path is nearly a fixed value (+/- 35 degrees). Lymphocytes stay in a restricted area after straight line movement. Particular attention was focused on cellular properties involved in locomotion. The characteristic time of the internal clock controlling the locomotion was 0.9 minutes for granulocytes and 2 minutes for monocytes. We were not able to determine the characteristic time of lymphocytes. We were able to determine the internal program responsible for the change in direction of movement. The directional memory time for granulocytes was 0.9 minutes. Monocytes had two directional memory times, short (2 minutes) and long (greater than 18 minutes). Lymphocytes had a very short directional memory time of 40 seconds. The distribution of the track velocities of migrating granulocytes and monocytes was described by bell shaped curves indicating homogeneous populations of cells. The distribution for lymphocytes had two maxima.

Biophysical Phenomena↗
PubMed1989

Dendritic spines of CA 1 pyramidal cells in the rat hippocampus: serial electron microscopy with reference to their biophysical characteristics.

Serial electron microscopy and 3-D reconstructions of dendritic spines from hippocampal area CA 1 dendrites were obtained to evaluate 2 questions about relationships between spine geometry and synaptic efficacy. First, under what biophysical conditions are the spine necks likely to reduce the magnitude of charge transferred from the synapses on the spine heads to the recipient dendrite? Simulation software provided by Charles Wilson (1984) was used to determine that if synaptic conductance is 1 nS or less, only 1% of the hippocampal spine necks are sufficiently thin and long to reduce charge transfer by more than 10%. If synaptic conductance approaches 5 nS, however, 33% of the hippocampal spine necks are sufficiently thin and long to reduce charge transfer by more than 10%. Second, is spine geometry associated with other anatomical indicators of synaptic efficacy, including the area of the postsynaptic density and the number of vesicles in the presynaptic axon? Reconstructed spines were graphically edited into head and neck compartments, and their dimensions were measured, the areas of the postsynaptic densities (PSD) were measured, and all of the vesicles in the presynaptic axonal varicosities were counted. The dimensions of the spine head were well correlated with the area of PSD and the number of vesicles in the presynaptic axonal varicosity. Spine neck diameter and length were not correlated with PSD area, head volume, or the number of vesicles. These results suggest that the dimensions of the spine head, but not the spine neck, reflect differences in synaptic efficacy. We suggest that the constricted necks of hippocampal dendritic spines might reduce diffusion of activated molecules to neighboring synapses, thereby attributing specificity to activated or potentiated synapses.

Animals↗
PubMed1988

[Direct biophysical effects of ultrasonic stimulation on the living rabbit lower limb].

Ultrasonic applications of low up to high intensity during 2 minutes led to biophysically provable changes (behaviour of bioimpedance, pO2, and temperature) in vital tissues (musculature, periosteum, and bone marrow). The most effective application was noticed by static ultrasonic therapy of 0.2 W/cm2. Repeated ultrasonic therapies of low intensity effected involved, for instance, an adaptation of the temperature and an increase of the electrophysical stimulation (bioimpedance).

Animals↗
PubMed1987

Biophysical and physiological integration of proper clothing for exercise.

In this chapter, I have presented a potpourri of examples of proper clothing to wear during various exercise demands in different environments. These examples are not wholly exact for all persons. For example, during the 1984 Olympics in Los Angeles, clothing wear related to the particular environment was totally different. We have already described the aerodynamic necessities of cyclists and runners. At the other extreme, equestrians had to contend with a warm, moderately humid environment, plus a solar load that added to the effective heat stress, while wearing clothing having clo values of nearly 0.8-0.9, plus headgear that limited evaporative heat loss. Obviously, garments with high water vapor permeation and bellows properties were necessary. Runners in the marathon faced equal thermal challenges. In addition, they incurred variable levels of hypovolemia and cardiovascular strain. A. Salazar, for example, was advised to omit shower sprays, and he ran with a prototype high-permeability singlet. The excessive wetting plus time to maneuver to the spray was deemed of no value, since Mr. Salazar chafes easily from wet clothes (L. Armstrong, personnel communication). One interesting response to this advice is to consider the clothed runner as a wet globe thermometer under forced convection. A high-contact fabric, especially one like cotton, does allow evaporative cooling, provided that the skin-ambient vapor pressure gradient is not diminished by high relative humidity. Salts in sweat may reduce the skin's vapor pressure ; however, Woodcock and Breckenridge point out that "secreted sweat (especially with heat acclimation) is so dilute that no appreciable lowering of vapor pressure would occur unless sweat were concentrated many times by evaporation." Thus, the degree of "human" wet bulb depression simulated by a completely wet runner may or may not be an advantage, since all other variables are also constant (i.e., humidity, weight of clothing as in Figure 13, etc.) or the level of hypovolemia is not excessive and the person is fully heat acclimated. Problems such as these may be theoretical, but they serve to show that the thermal biophysics and physiology of exercise follow similar fundamental pathways that can be highly pertinent. As we sought to point out in this chapter, these pathways have merged in the last 30 years with developments such as warmth without bulk for backpackers (which is a welcomed contrast to heavy arctic wear), materials that allow athletes to remain somewhat comfortable while sweating, and other advances that luckily have replaced the less appealing sports apparel such as the old woolen baseball uniform.(ABSTRACT TRUNCATED AT 400 WORDS)

Biophysical Phenomena↗