Stress-induced decrement in the plasticity of the physical properties of chick brain membranes

Coupling between GABA(A)-R ligand-binding activity and membrane organization in β-cyclodextrin-treated synaptosomal membranes from bovine brain cortex: new insights from EPR experiments

Correlations between GABA(A) receptor (GABA(A)-R) activity and molecular organization of synaptosomal membranes (SM) were studied along the protocol for cholesterol (Cho) extraction with β-cyclodextrin (β-CD). The mere pre-incubation (PI) at 37°C accompanying the β-CD treatment was an underlying source of perturbations increasing [(3)H]-FNZ maximal binding (70%) and K (d) (38%), plus a stiffening of SMs' hydrocarbon core region. The latter was inferred from an increased compressibility modulus (K) of SM-derived Langmuir films, a blue-shifted DPH fluorescence emission spectrum and the hysteresis in DPH fluorescence anisotropy (A (DPH)) in SMs submitted to a heating-cooling cycle (4-37-4°C) with A (DPH,heating) < A (DPH,cooling). Compared with PI samples, the β-CD treatment reduced B (max) by 5% which correlated with a 45%-decrement in the relative Cho content of SM, a decrease in K and in the order parameter in the EPR spectrum of a lipid spin probe labeled at C5 (5-SASL), and significantly increased A (TMA-DPH). PI, but not β-CD treatment, could affect the binding affinity. EPR spectra of 5-SASL complexes with β-CD-, SM-partitioned, and free in solution showed that, contrary to what is usually assumed, β-CD is not completely eliminated from the system through centrifugation washings. It was concluded that β-CD treatment involves effects of at least three different types of events affecting membrane organization: (a) effect of PI on membrane annealing, (b) effect of residual β-CD on SM organization, and (c) Cho depletion. Consequently, molecular stiffness increases within the membrane core and decreases near the polar head groups, leading to a net increase in GABA(A)-R density, relative to untreated samples.

Langmuir films from human placental membranes: preparation, rheology, transfer to alkylated glasses, and sigmoidal kinetics of alkaline phosphatase in the resultant Langmuir-Blodgett film

In the present study, we studied the activity of human placental alkaline phosphatase (PLAP) constraint in a planar surface in controlled molecular packing conditions. For the first time, Langmuir films (LFs) were prepared by the spreading of purified placental membranes (PPM) on the air-water interface and their stability and rheological properties were studied. LFs exhibited a collapse pressure pi(C) = 48 mN/m, hysteresis during the compression-decompression cycle (C-D), indicating a plastic deformation, and a compressibility modulus (K) compatible with liquid-expanded phases. A phase transition point appeared at pi(T) = 28 mN/m and, following successive C-D, it moved toward lower surface areas and higher K, suggesting the lost of some non-PLAP proteins as components of vesicles that might protrude from the monolayer (confirmed by combining lipid/protein molar ratio analysis, PAGE-SDS and V(max)). LFs were transferred at 35 mN/m to alkylated glasses to obtain Langmuir-Blodgett films (LB(35)) the stability of which was confirmed by AFM. The kinetics of p-nitrophenyl phosphate (pNPP) hydrolysis at 37 degrees C catalyzed by PPM was Michaelian and exhibited the thermostability at 60 degrees C typical of PLAP. In LB(35), PLAP exhibited a sigmoidal kinetics which resembled the behavior of the partially metalated enzyme but might become from a cross-talk between protein and membrane structures.

Phosphatidylinositol 4,5-Bisphosphate Induced Flunitrazepam Sensitive-GABAA Receptor Increase in Synaptosomes from Chick Forebrain

The flunitrazepam sensitive-GABA(A) receptor density was increased by cytochalasins C and D at 37 degrees C suggesting that microfilament depolymerization induces exposure to the radioligand of a GABA(A) receptor in synaptosomes (Pharm Biochem Behav 72 (2002) 497). Similarly, phosphatidylinositol-4,5-bisphosphate (1-5 microM), but not a mixture of phospholipids, induced an increase of GABA(A) receptors in synaptosomes. Furthermore, N-ethyl maleimide, an inactivator of the sensitive fusion protein, which interacts with GABA(A) receptor, abolished the receptor increase induced by phosphatidylinositol-4,5-bisphosphate. Together, the results suggest that phosphatidylinositol-4,5-bisphosphate, acts via microfilament depolymerization increasing the binding of the radioligand to receptors possibly by modulation of their interaction with proteins involved in trafficking and docking mechanisms.

Dietary lipids modulate fatty acid composition, gamma glutamyltranspeptidase and lipid peroxidation levels of the epididymis tissue in mice

The purpose of this work was to analyze the effect of diets that contain several oils whose composition in fatty acids were different, on the kinetic parameters of the gamma-glutamyltranspeptidase (GGTP) and the lipoperoxidation of the epididymis because GGTP controls the level of the glutathione that is an molecule that regulates the level of oxidation protecting the maturation and survival of sperm in the lumen of the epididymis. The caput portion of the epididymis was chosen because the epithelium of this segment synthesizes GGTP. Weaned BALB-c mice were fed a commercial or semi-synthetic diet that contained 5% added olein. The mice were maintained on corn oil or fish oil diet for the first 4-8 months of age. The kinetic variables of the GGTP enzyme, analyzed by means of multiple regression analysis using dummy variables, showed that values were similar in olein and corn oil samples, whereas in samples from the fish oil fed group the enzyme behaved as that in animals maintained on commercial diets. Although there were no variations in maximum velocity (Vm) of the enzyme, the Km value, was greater (P < 0.0001) for the mice fed the olein and corn diets. These groups contained greater percentages of the monounsaturated fatty acids, palmitoleic (16:1 n-7) and oleic acid, 18:1 n-9. Similarly, the amount of lipid peroxidation was also greater in the olein and corn oil groups with respect to commercial and fish groups. The significant increment in Km of GGTP in the olein and corn groups was correlated with greater amount of monounsaturated fatty acids and lipid peroxidation in the epididymis. In conclusion, modifications of dietary lipid sources differentially modulated the epididymis tissue fatty acid profile, lipid peroxidation amounts, and the Km of GGTP. These effects may alter the metabolism of the natural substrate of GGTP, glutathione, a tripeptide with a powerful antioxidant activity, which is necessary in maintaining the oxidative state of the sperm microenvironment, thereby favoring maturation of the male gametes.