Experimental fusion of E. histolytica cells by horseradish peroxidase treatment.

The experimental fusion of Entamoeba histolytica cells after their treatment with horseradish peroxidase is reported. This finding is discussed in relation with the general knowledge about the cell fusion process.     

Theoretical considerations regarding the cell membrane function during cold-induced preservation of tissues and organs: new possibilities for optimizing the process

An analysis of the effects of temperature variation on the function of the mammalian cell membrane strongly suggests that during the cold-induced preservation of living tissues and organs the passive flow of micromolecules and ions across the cell membrane is the main factor in determining the state of the cellular biological system. Practically, the optimal organ (tissue) storage could be obtained at low temperatures (exceeding the freezing point) by using preservation fluids with constitutive substances in concentrations equal to those existing in the normal cytoplasm. Consequently, the formulae for adequate preservation fluids must be calculated according to the peculiar cytoplasmic constitution of the cells of each organ and tissue.     

Effect of depletion of monocytes/macrophages on early aortic valve lesion in experimental hyperlipidemia

Monocytes/macrophages are key players throughout atheroma development. The aim of this study was to determine the role of macrophages in lesion formation in heart valves in hyperlipidemia. We examined whether systemic depletion of monocytes/macrophages had a beneficial or adverse effect on the development of lesions in hyperlipemic hamsters injected twice weekly (for 2 months) with clodronate-encapsulated liposomes (H+Lclod), a treatment that selectively induces significant monocyte apoptosis. Hyperlipemic hamsters were employed as controls, as were hyperlipemic hamsters treated with plain liposomes. We assayed serum cholesterol (CH) and triglycerides (TG), the lipid and collagen contents and the size of the valve lesions, the matrix metalloproteinases (MMPs) in the serum and vessel wall, apolipoprotein E (ApoE), interleukin-1β (IL-1β), and superoxide anion production. In comparison with controls, H+Lclod hamsters exhibited: (1) increased lipid and collagen accumulation within the lesions, (2) decreased activity of MMP-9 and MMP-2 in sera and aortic homogenates, (3) decreased serum CH and TG and decreased expression of ApoE in sera and liver, (4) reduced expression of IL-1β in aorta and liver homogenates, and (5) no change in the level of superoxide anion in the aorta. Thus, initially, the presence of the macrophages is beneficial in valvular lesion formation. Depletion of monocytes/macrophages is a two-edged sword having a beneficial effect by decreasing the expression of IL-1β and MMP activities but an adverse effect by inducing a significant increase in the lipid and collagen content and expansion of valvular lesions. This work was supported by the Romanian Academy and a grant from the Romanian Ministry of Education and Research, National Program VIASAN (grant no. 330).     

Calcium Promotes the Formation of Syntaxin 1 Mesoscale Domains through Phosphatidylinositol 4,5-Bisphosphate

Phosphatidylinositol 4,5-bisphosphate (PI(4,5)P₂) is a minor component of total plasma membrane lipids, but it has a substantial role in the regulation of many cellular functions, including exo- and endocytosis. Recently, it was shown that PI(4,5)P₂ and syntaxin 1, a SNARE protein that catalyzes regulated exocytosis, form domains in the plasma membrane that constitute recognition sites for vesicle docking. Also, calcium was shown to promote syntaxin 1 clustering in the plasma membrane, but the molecular mechanism was unknown. Here, using a combination of superresolution stimulated emission depletion microscopy, FRET, and atomic force microscopy, we show that Ca²⁺ acts as a charge bridge that specifically and reversibly connects multiple syntaxin 1/PI(4,5)P₂ complexes into larger mesoscale domains. This transient reorganization of the plasma membrane by physiological Ca²⁺ concentrations is likely to be important for Ca²⁺-regulated secretion.