Spremembe v pretočnosti plazemske membrane rakavih tkiv

Plasma membrane is a heterogeneous structure with several coexisting domains having different fluidity characteristics. It plays an important role in the control of cell growth, differentiation and transformation. Fluidity of the whole plasma membrane reflects the ordering and dynamics of phospholipid acyl chains in specific membrane domains, as well as the fraction of each domain inthe membrane. Changes in the membrane fluidity affect processes on the membrane such as transport, enzyme activities and expression of the redeptors.In this paper we present results of our recent electron paramagneticresonance (EPR) studies of plasma membrane fluidity characteristics, which take into account heterogeneous nature of the plasma membrane, By the computer simulation of the EPR spectra line-shapes, the number of coexisting domains in the plasma membrane, their relative portion inthe membrane as well as the ordering and dynamics of each domain be determined. Therefore, we could distinguish the contribution of the relative portion of each domain from the contribution of fulidity alterations in the domain to the entire fluidity changes in the membrane. Two examples will be discussed: membrane fluidity characteristics of excised lung tumor tissues andinfluence of microtubule depolymerizing agent vinblastine on membrane fluidity of vinblastine sensitive and resistant HeLa cells

EPR of the Sodium Laurate-Water Lyotropic Mesophases and Micellar Solution

The local orienta>tional order of molecules in lameilar and hexagonal mesophases as well as in micellar aggregates of the sodium laurate - water system was studied by EPR. As a paramagnetic probe a fatty acid spin label, dissolved in the hydrophobic environment was used. 1t was found that the ordering parameter decreases cont1nously over the whole concentration and temperature range of the mesophases irrespective of the phase transitions. From the local ordering parameter observed in cylindrical micelles, the variation of cylinder dimensions with tempeirature and concentration was estimated. In the micellar solution the concentration range where cylindrical micelles were the most stable was determined, and its relation to the maximal stab.ility region in the hexagonal phase was discussed. The rate of molecular tumbling around the cylindrical axes in the hexagonal phase was found faster t han 108 sec-1 at 100 °c

Magnetic resonances in biomedical research

Prikazana je primjena metoda magnetskih rezonancija - elektronske magnetske rezonancije (EPR) i nuklearne magnetske rezonancije (NMR) u biomedicinskim istraživanjima. Opisani su primjeri istraživanja u kojima se metoda EPR koristi za određivanje mikrogeografije aktivnog centra enzima acetilkolinesteraze i mjerenje konformacijskih promjena pod utjecajem kolinergičnih supstancija, za proučavanje promjena u fluidnosti staničnih membrana pod utjecajem neurotoksina, za određivanje transporta kokarcinogena, forbolestera kroz stanične membrane, te transporta molekula kroz tkiva s pomoću gradijenta magnetskog polja. Opisani primjeri istraživanja metodom NMR odnose se na njenu primjenu za proučavanje metaboličkih osobina skeletnih mišića, karakterizaciju tumora mozga in vitro i moguću dijagnozu tumora i raznih drugih patoloških stanja in vivo.Magnetic resonances are spectroscopic methods by which some structural changes and metabolic processes in biological systems can be followed on the molecular level. There are two main types of magnetic resonance methods: nuclear magnetic resonance (NMR) and electron paramagnetic (spin) resonance (EPR or ESR). By NMR are followed the atomic nuclei with the magnetic moment; in biological systems these are usually lH, 13C, 31P. By EPR are followed paramagnetic centres in biological systems; these are ions of the transition metal group (Fe3+, Cu2+, Mn2+), which appear as cofactors of the enzymes, or free radicals, which are intermediates in biochemical reactions. Instead of paramagnetic centres, which are native in biological systems, very often the molecules with a free radical are incorporated into the system - spin labels or spin probes. Centres with the magnetic moment serve as markers conveying the information about the metabolic f recesses in biological systems and about the changes in these processes in pathological conditions or under the influence of biologically active substances. In this work several typical applications of EPR and NMR in biomedical research are described showing a great variety of issues where magnetic resonances can be used. EPR experiments, Study of the microgeography of acetylcholinesterase active centre and the conformational changes of this centre under the influence of cholinergic substances. Changes in cell membrane fluidity under the influence of neurotoxins. Transport of cocarcinogens, forbolesters, through the cell membrane. Application of magnetic field gradient to the investigation of transport through the tissues. NMR experiments: Application of 1H-NMR to characterization of brain tumours in vitro and possible application of NMR tomography in vivo to diagnosis of tumours and other pathological conditions. Application of 31P-NMR for investigation of metabolic properties of skeletal muscles

EPR of the Sodium Laurate-Water Lyotropic Mesophases and Micellar Solution

The local orienta>tional order of molecules in lameilar and hexagonal mesophases as well as in micellar aggregates of the sodium laurate - water system was studied by EPR. As a paramagnetic probe a fatty acid spin label, dissolved in the hydrophobic environment was used. 1t was found that the ordering parameter decreases cont1nously over the whole concentration and temperature range of the mesophases irrespective of the phase transitions. From the local ordering parameter observed in cylindrical micelles, the variation of cylinder dimensions with tempeirature and concentration was estimated. In the micellar solution the concentration range where cylindrical micelles were the most stable was determined, and its relation to the maximal stab.ility region in the hexagonal phase was discussed. The rate of molecular tumbling around the cylindrical axes in the hexagonal phase was found faster t han 108 sec-1 at 100 °c