The photochemical reactions occurring in the cell membranes, sensitized photo-oxidation and psoralen photoaddition to lipids, are briefly reviewed. Phospholipid dynamics in the membrane structure, based on erythrocyte lipid organization, are described. Evidence for alterations of cell membrane functions under psoralen plus UVA radiation (PUVA) treatment in a variety of mammalian cells is presented. Cell receptor dysfunctions under PUVA treatment are demonstrated in a number of biological investigations.The purpose of this survey is to illustrate the feasibility of studying psoralen photobiology with phospholipids. The reaction of psoralens with phospholipids is considered to be one of the triggering mechanisms of the subsequent physiological responses, which may be relevant to PUVA photochemotherapy.
The induced effects by radiation with gamma (γ) and thermal neutrons (N) on the radiophotoluminiscence, microhardness indentation number as well as the electric resistivity of the cellulose acetate films are investigated. The results indicate uniform and linear changes in these physical parameters with increasing absorbed doses D γ and D N for both types of irradiation. Furthermore, the dose response as a function of these induced changes promises a dosimetric use of cellulose acetate (CA) over the ranges from 10 0 to 10 5 Gy (1 Gy = 100 rad) and from 0.3 to 50 cSv (1 Sv = 100 cSv = 100 rem, i.e. 1 cSv= 1 rem) for gamma and thermal neutron radiation doses, respectively. The fading behaviour in CA as a radiation detector is found to be stabilized after 28 days and attained relative values 10–15% considering the three different techniques of measurements.
In the homologous series of long hydrocarbon chain surface active compounds, their various biological activities increase progressively with increasing chain length up to a critical point, beyond which the compounds cease to be active. The paper reviews several hypotheses of this cut-off effect in biological activities and experimental evidences supporting them. It is suggested that the lateral expansion of the phospholipid bilayer of biological membranes caused by the intercalation of long-chain amphiphile molecules between the phospholipid molecules and the mismatch between their hydrocarbon chain lengths results in the creation of free volume in the bilayer hydrophobic region. The elimination of the free volume via the hydrocarbon chain trans-gauche isomerisation or interdigitation results in the bilayer thickness change or in its destabilisation and formation of non-bilayer phase(s). In combination with the partition and ionisation equilibria of amphiphiles in the lipid/aqueous phase systems, the free volume predicts similar chain length and pH dependencies as observed in biological experiments. It is suggested that the free volume mechanism, in combination with other mechanisms, could be responsible for the cut-off effects in biological activities of amphiphiles.
External electric field tends to deform a nearly spherical phospholipid vesicle into a rotational ellipsoid, with the rotational axis parallel to the field [1]. The key parameters that govern the extent of deformation are the field strength, its frequency, the size of the vesicle, the membrane tension, the membrane bending elastic constant, and the electric properties of both the membrane and the surrounding medium. The vesicles of average diameter about 20 m were prepared from commercially available 1-palmitoyl-2-oleoyl-sn-3-phosphatidylcholine (POPC) using the standard procedure [2], in both pure water and 0.1 mol/l sucrose solution. The observation was performed by means of a phase contrast microscope and a CCD video camera attached to it. The observed picture of vesicle cross-section was digitized, and the appropriate Fourier coefficients describing the contour were calculated. In the experiment, more than 100 vesicles have been observed. The strength of the applied AC electric field ranged up to 18 kV/m, while the frequency was varied from 1 to 100 kHz. The deformation of a vesicle was measured as the ratio of ellipsoid semiaxes. At low field strengths its value was increasing proportionally to the square of the field strength, whereas at higher field strengths a region with much smaller further
The combined employment of protein chemistry, electrophysiology and neurochemistry enabled the chemical and pharmacological characterization of two classes of neurotoxin polypeptides, the excitatory and the depressant, derived from the venom of Buthinae scorpions which selectively paralyze and kill insects. These insect selective neurotoxins: 1. Affect insect neuronal sodium conductance; 2. Serve as unique and exclusive probes of the insect voltage gated sodium channels; 3. Bind to these channels through multipoint attachment sites which include segments of external loops in domains I, III and IV of the insect sodium channel; 4. Distinguish among sodium channels of different groups of insects; 5. Are employed as pharmacological tools for the study of insect excitability and the design of future selective insecticides.
