Time-dependent cadmium-neurotoxicity in rat brain synaptosomal plasma membranes

• 1.1. The modulation of lipid dynamics and lipid protein interactions were studied in rat brain synaptosomal plasma membranes (SPM) up to 24 hr after exposure to cadmium (Cd).
• 2.2. The activity of acetylcholinesterase and adenylate cyclase showed a considerable decrease after 6 hr of Cd exposure, followed by a progressive increase up to 24 hr.
• 3.3. SPM chemiluminescence showed a maximum decrease at 12 hr, demonstrating a considerable increase in lipid peroxidation.
• 4.4. SPM of Cd-exposed animals showed a statistical significant increase in fluorescence anisotropy parameter [(r₀/r) — 1]⁻¹ at 18 and 24 hr compared to SPM of the control, indicating a decrease of membrane fluidity.

     

Identification of a phospholipase A1 in plasma membranes of rat liver

1.

1. A fraction rich in plasma membranes was isolated from the rat liver cell by zonal centrifugation, and the amounts of nitochondria, microsomes, and lysosomes in the fraction were determined by the use of marker enzymes for these organelles. Recovery of the marker enzymes indicated that 94% of the fraction was plasma membranes.     

Effect of bovine milk antigens and egg lysozyme on the binding of 59Fe-lactoferrin to platelet plasma membranes

• 1.1. Platelets bind specifically to lactoferrin. A significant similarity between human lactoferrin and some bovine milk proteins has been established.
• 2.2. Because of the structural homology of lactoferrin and cows milk proteins they are able to influence lactoferrins regulatory function on the level of its binding to membrane receptors on platelets.
• 3.3. An inhibitory effect of bovine α-lactalbumin and of β-lactoglobulin on lactoferrin-receptor interaction was shown.
• 4.4. Bovine α-lactalbumin competes with lactoferrin for the binding sites.
• 5.5. Scatchard plot analysis of data shows one binding site for lactoferrin in the presence of α-lactalbumin with an affinity constant, Ka = 0.46 × 10⁹ mol/1 and 335 receptors/cell.
• 6.6. The inhibitory effect of β-lactoglobulin reaches 62% and is different for the common fraction ⨿-lactoglobulin and the genetic variants β-lactoglobulin A and B.
• 7.7. β-lactoglobulin does not compete with lactoferrin for the membrane receptors.
• 8.8. Bovine casein and egg lysozyme stimulate ⁵⁹Fe-lactoferrin binding to the receptors. The mechanism of these effects is still unknown.
• 9.9. Tested alimentary antigens are able to interact with lactoferrin and also with some platelet membrane structures.
• 10.10. Established changes in lactoferrin binding to the platelet membrane might be in relation to lactoferrins regulatory function and (or) eliminating mechanisms of these alimentary antigens.

     

Permeability of isolated rat hepatocyte plasma membranes for molecules of dimethyl sulfoxide

We have studied permeability of isolated rat hepatocyte membranes for molecules of dimethyl sulfoxide (DMSO) at different hypertonicity of a cryoprotective medium. The permeability coefficient of hepatocyte membranes k ₁ for DMSO molecules was shown to be the differential function of osmotic pressure between a cell and an extracellular medium. Ten-fold augmentation of DMSO concentration in the cryoprotective medium causes the decrease of permeability coefficients k ₁ probably associated with the increased viscosity in membrane-adjacent liquid layers as well as partial limitations appeared as a result of change in cell membrane shape after hepatocyte dehydration. We have found out that in aqueous solutions of NaCl (2246 mOsm/L) and DMSO (2250 mOsm/L) the filtration coefficient L _p in the presence of a penetrating cryoprotectant (L _pDMSO = (4.45 ± 0.04) · 10^?14 m³/Ns) is 3 orders lower compared to the case with electrolyte (L _pNaCl = (2.25 ± 0.25) · 10^?11 m³/Ns). This phenomenon is stipulated by the cross impact of flows of a cryoprotectant and water at the stage of cell dehydration. Pronounced lipophilicity of DMSO, geometric parameters of its molecule as well as the presence of large aqueous pores in rat hepatocyte membranes allow of suggesting the availability of two ways of penetrating this cryoprotectant into the cells by non-specific diffusion through membrane lipid areas and hydrophilic channels.     

Large scale isolation and storage of Neurospora plasma membranes.

Functionally inverted plasma membrane vesieles isolated from the eukaryotic microorganism Neurospora crassa generate and maintain a transmembrane electrical potential via ATP hydrolysis catalyzed by a plasma membrane ATPase (G. A. Scarborough, 1976, Proc. Nat. Acad. Sci. USA73, 1485–1488). In order to facilitate investigation of the molecular mechanism of the electrogenic ATPase, and other transport systems, we have developed a method for the large scale isolation and storage of Neurospora plasma membranes in a stable form. Large quantities of open plasma membrane sheets (ghosts) are isolated by a scaled-up modification of the original method (G. A. Scarborough, 1975, J. Biol. Chem.250, 1106–1111) and stored at ?26°C in 60% glycerol ($\text{v}\text{v}$). As needed, the ghosts are washed free of glycerol and then converted to closed vesicles by a modification of the original method. With this technique, plasma membrane vesicles with normal electrogenic pump activity can be prepared daily in approximately 2.5 h.