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Lipid perturbation by corticosteroids: an anisotropic study

Abstract Corticosteroids are the group of steroid hormones which influence the intermediary metabolism. Normal membrane fluidity, necessary for normal functioning of cells, is affected by different drugs. It has been reported previously by us and by other workers that the nature of membrane perturbation by drugs is closely related to their biochemical actions. In this paper we have studied the nature of liquid perturbation by some corticosteroids (hydrocortisone, prednisolone, betamethasone and dexamethasone) in the liposomal membrane of dipalmitoyl phosphatidyl choline using fluorescence polarisation of 1,6-diphenyl-1,3,5-hexatriene. Our result shows that all the corticosteroids fluidise or disorder the liposomal membrane only before phase transition. The two stereoisomers, betamethasone and dexamethasone, have the same effect on the fluidity throughout the experimental temperature range. An explanation for the observed results has been sought in terms of interaction between the lipid and drug molecules at the molecular level.

Nonlinear conduction in bilayer lipid membranes – effect of temperature

We present here our investigation on the effect of temperature on the reversible nonlinearity as manifested in the DC I–V characteristic of bilayer lipid membrane (BLM). Vc and Ic, the values of voltage and current at the onset of nonlinearity, have been found to be functions of temperature, and the nonlinearity has been found to decrease with increase in temperature. By proper scaling of voltage and current by Vc and Ic, respectively, the I–V curves taken at different temperatures collapse into one single curve, showing the universality in their nature. A log–log plot of Ic vs. σ0 (linear conductance) is a straight line where Ic scales with σ0 as Ic∼σ01.56. A possible mode of charge conduction in BLM, which is a disordered composite system of lipid and water molecules, has been proposed on the basis of these experimental results.

Photoinduced changes in structure and function of hexadecyl merocyanine dyes incorporated into lipid membranes

Abstract In the purple membrane of Halobacterium halobium, bacteriorhodopsin (BR) acts as a proton pump leading to a transmembrane potential difference. A biomimetic system can be formed using merocyanine derivative dye which, when incorporated into a bilayer lipid membrane, creates a potential difference across the membrane. In this system, the dye molecules in combination with the lipid molecules act as a proton transport pump due to a light-induced conformational change of the dye. In this paper, we report the photovoltaic properties and crystal structure of hexadecyl merocyanine dye, together with the change in peak intensity in the X-ray diffraction pattern of the dye and dye-lipid system after illumination. We show that, at room temperature (σ300 K), merocyanine dyes exhibit a crystalline form with a long-chain, fibre-like structure (diameter, 2.89 nm). However, on interaction with light, the crystalline form of the dye changes but the diameter remains the same.

Effect of n-decane on lecithin phase transition temperatures: a microscopic study

Lipid, a major membrane-constituent molecule, being amphiphilic in nature, can adopt different aggregated structures in the presence of different agents. Using polarized light microscopy, we report here our study on how the incorporation of n-decane in the dipalmitoyl lecithin–water system can produce a change from lamellar to non-lamellar phase and affect the different phase transition temperatures as well.

SPECTRAL ANALYSIS OF CURRENT-NOISE DATA FOR BILAYER LIPID MEMBRANE

We report the spectral analysis of current-noise data obtained under voltage clamp condition in bilayer lipid membrane, using Lomb Scargle Periodogram. Such spectral analysis shows evidence of crossover from an uncorrelated phenomenon towards a state of long range correlation in time and space with the increase of applied bias. Based on these observations a probable mechanism of transmembrane charge conduction has been outlined in the light of self-organized criticality.