Increase in membrane conductance by adrenaline in parotid acinar cells

Summary It is shown that excitation of the - or -adrenoceptors in mouse parotid acinar cells causes a marked reduction of surface cell membrane resistance. The -adrenoceptor induced membrane effect is an increase in K conductance. The -adrenoceptor induced membrane effect does not seem to be mediated by cyclic AMP.     

Induction of dolykaryocytes by vesicular stomatitis virus in XC rat cells]

V.S.V. induced polycaryocytes in rat embryonic fibroblasts, transformed by the Prague strain of Sarcoma Rous (XC cells). This fusion is strictly dependent on the expression of the viral genome and is probably due to the incorporation of viral antigens in the cell membrane. The integrity of cellular RNA synthesis is however not required. The fusion is probably due to a membrane structure characteristic of these transformed cells.     

Ba++ induced square-shaped potential waves in molluscan neurones

Summary Rhythmic slow square-shaped potential waves lasting 20–50 sec are induced in Aplysia neurones when Ca⁺⁺ is replaced by Ba⁺⁺. During the plateau, the membrane is highly permeable to Ba⁺⁺ ions, whereas in the inter-wave period the membrane resistance increases by 60 times. Analysis with slow current ramps suggests that the membrane properties of Ba-treated neurones and normally burst-generating neurones are similar.     

Insulin stimulation of glucose and amino acid transport in mouse fibroblasts with elevated membrane microviscosity

Summary Basal and insulin-stimulated transport of 2-deoxy glucose and of -aminoisobutyric acid in mouse 3T3 fibroblasts were modulated by increasing the lipid microviscosity of the cell plasma membrane. The kinetics indicate that the insulin effect is induced either by recruitment of new transport carriers or by reduction of the translocation activation energy.This investigation was supported by grant No.5-R01-CA-27471-02, awarded by the National Cancer Institute, Department of Health, Education and Welfare.     

An increase in Sendai virus-induced cell fusion of erythrocytes infected with Plasmodium chabaudi

The extent of cell fusion induced by Sendai virus was examined in erythrocytes infected with Plasmodium chabaudi. An increase in cell fusion of erythrocytes with Ehrlich tumor cells and of erythrocytes with erythrocytes was observed with the infected erythrocytes. However, agglutination by the virus was not changed between erythrocytes of normal and malarial mice. These results indicate that the increase in cell fusion occurred in the process of membrane fusion, suggesting that some membrane property of Plasmodium-parasitized erythrocytes is changed in terms of Sendai virus-induced cell fusion.     

Tubular and glomerular nephropathy induced in rabbits by injection of a heterologous antitubular basement membrane serum]

A nephropathy affecting both tubules and glomeruli has been induced in Rabbits by the injection of an heterologous immune serum directed against Rabbit tubular basement membrane. It differs from experimental antiglomerular basement membrane nephropathy by the fixation of antibodies and C3 on tubular basement membrane and by the occurrence of glucosuria.     

Activation of the electrogenic Na-pump of cardiac muscle fibres by ACh in K-free solutions.

The ionic mechanism of the membrane outward current (ACh-current) of bullfrog atrium muscle, induced by acetylcholine in K-free solution, was analyzed by a voltage-clamp experiment. The results suggested that the ACh-current was induced not only by an increase in K-conductance but also by an activation of the electrogenic Na-pump.     

Activation of the electrogenic Na-pump of cardiac muscle fibres by ACh in K-free solutions

Summary The ionic mechanism of the membrane outward current (ACh-current) of bullfrog atrium muscle, induced by acetylcholine in K-free solution, was analyzed by a voltage-clamp experiment. The results suggested that the ACh-current was induced not only by an increase in K-conductance but also by an activation of the electrogenic Na-pump.Acknowledgment. This work was supported by a grant (257037) from the Ministry of Education of Japan.     

Intracellular injection of cAMP and cGMP into snail neurones induces an increase in Na+-conductance

Injection of cAMP and more rarely cGMP into the neurones of the snail Helix pomatia induces an increase in membrane conductance, membrane depolarization and excitation. The effect is theophylline-dependent and has a reversal potential near -10mV.     

ERK activation by Ca2+ ionophores depends on Ca2+ entry in lymphocytes but not in platelets, and does not conduct membrane scrambling

Rapid Ca²⁺-dependent phospholipid (PL) reorganization (scrambling) at the plasma membrane is a mechanism common to hematopoietic cells exposing procoagulant phosphatidylserine (PS). The aim of this research was to determine whether activation of the extracellular signal-regulated kinase (ERK) pathway was required for PL scrambling, based on a single report analyzing both responses induced by Ca²⁺ ionophores in megakaryoblastic HEL cells. Ca²⁺ ionophore-stimulated ERK phosphorylation was induced in platelets without external Ca²⁺, whereas exogenous Ca²⁺ entry was crucial for ERK activation in Jurkat T cells. In both cells, membrane scrambling only occurred following Ca²⁺ entry and was not blocked by inhibiting ERK phosphorylation. Furthermore, ERK proteins are strongly phosphorylated in transformed B lymphoblastic cell lines, which do not expose PS in their resting state. Overall, the data demonstrated that ERK activation and membrane scrambling are independent mechanisms. A. Arachiche, I. Badirou: These authors contributed equally to this work. Received 18 June 2008; received after revision 24 September 2008; accepted 1 October 2008     

Rheological and functional impairments in cholesterol-loaded human erythrocytes

Summary Decreased deformability, slightly increased suspension viscosity and retarded oxygen egress were observed in cholesterol-loaded, human erythrocytes. These functional changes resulted from the decreased membrane fluidity induced by cholesterol.     

Insulin effect in vitro on human erythrocyte plasma membrane

The effect of porcine insulin has been tested in vitro on human erythrocyte plasma membrane (Na+-K+) and Mg2+-ATPase activities as well as on membrane fluidity. The results indicate that the hormonal treatment significantly inhibits (Na+-K+)-ATPase activity, and at the same time decreases membrane fluidity.     

Periostin in vitreoretinal diseases

Proliferative vitreoretinal diseases such as diabetic retinopathy, proliferative vitreoretinopathy (PVR), and age-related macular degeneration are a leading cause of decreased vision and blindness in developed countries. In these diseases, retinal fibro(vascular) membrane (FVM) formation above and beneath the retina plays an important role. Gene expression profiling of human FVMs revealed significant upregulation of periostin. Subsequent analyses demonstrated increased periostin expression in the vitreous of patients with both proliferative diabetic retinopathy and PVR. Immunohistochemical analysis showed co-localization of periostin with α-SMA and M2 macrophage markers in FVMs. In vitro, periostin blockade inhibited migration and adhesion induced by PVR vitreous and transforming growth factor-β2 (TGF-β2). In vivo, a novel single-stranded RNAi agent targeting periostin showed the inhibitory effect on experimental retinal and choroidal FVM formation without affecting the viability of retinal cells. These results indicated that periostin is a pivotal molecule for FVM formation and a promising therapeutic target for these proliferative vitreoretinal diseases.     

Intracellular injection of cAMP and cGMP into snail neurones induces an increase in Na+-conductance

Summary Injection of cAMP and more rarely cGMP into the neurones of the snailHelix pomatia induces an increase in membrane conductance, membrane depolarization and excitation. The effect is theophylline-dependent and has a reversal potential near — 10 mV.     

K-p-nitrophenylphosphatase activity, Na and K content, Na permeability and membrane lipid composition in rabbit myocardium after cholesterol rich diet

The aim of the present study was to investigate the effects of a cholesterol-rich diet on membrane function and lipid composition in rabbit myocardium. The activity and the ouabain sensitivity of the K-p-nitrophenylphosphatase (K-pNPPase), a partial reaction of the Na, K-ATPase, were diminished after a cholesterol/oil or pure cholesterol diet. The content of cholesterol, cholesterol esters and of several classes of phospholipids was enhanced in microsomes. A causal relationship is assumed between cholesterol accumulation and a decrease in membrane fluidity as well as in Na, K-ATPase activity. The intracellular Na content and the Na-Li-exchange rate were higher after the cholesterol diet. The increase in the Na content is supposed to be induced by a lower Na transport and a higher Na permeability. An enhanced Ca flux via the sarcolemma could be the consequence.     

An increase in Sendai virus-induced cell fusion of erythrocytes infected withPlasmodium chabaudi

Summary The extent of cell fusion induced by Sendai virus was examined in erythrocytes infected withPlasmodium chabaudi. An increase in cell fusion of erythrocytes with Ehrlich tumor cells and of erythrocytes with erythrocytes was observed wit the infected erythrocytes. However, agglutination by the virus was not changed between erythrocytes of normal and malarial mice. These results indicate that the increase in cell fusion occurred in the process of membrane fusion, suggesting that some membrane property ofPlasmodium-parasitized erythrocytes is changed in terms of Sendai virus-induced cell fusion.We thank Drs George L. Gerton, T. Matsuyama and M. Niwa for their comments on this work and Mr I. Kimata for preparing photographs.     

K-p-Nitrophenylphosphatase activity,Na and K content,Na permeability and membrane lipid composition in rabbit myocardium after cholesterol rich diet

Summary The aim of the present study was to investigate the effects of a cholesterol-rich diet on membrane function and lipid composition in rabbit myocardium. The activity and the ouabain sensitivity of the K-p-nitrophenylphosphatase (K-pNPPase), a partial reaction of the Na, K-ATPase, were diminished after a cholesterol/oil or pure cholesterol diet. The content of cholesterol, cholesterol esters and of several classes of phospholipids was enhanced in microsomes. A causal relationship is assumed between cholesterol accumulation and a decrease in membrane fluidity as well as in Na, K-ATPase activity. The intracellular Na content and the Na-Li-exchange rate were higher after the cholesterol diet. The increase in the Na content is supposed to be induced by a lower Na transport and a higher Na permeability. An enhanced Ca flux via the sarcolemma could be the consequence.To whom reprints should be addressed     

Pressure-induced variations of K+-permeability as related to a possible reversible electrical breakdown in human erythrocytes

Summary Above a hydrostatic pressure of about 600 b a pronounced reversible increase in the net K⁺-efflux from human erythrocytes is observed. The effect is explained in terms of an electro-mechanical compression of the membrane, resulting in a reversible breakdown of the membrane.Acknowledgments. This work was supported by a grant from the Sonderforschungsbereich 160 to U.Z. and by grant No.2.4511.76 from the FRFC to R.G.     

A novel interplay between membrane and nuclear melatonin receptors in human lymphocytes: significance in IL-2 production

Human lymphocyte melatonin, through membrane and nuclear receptors binding, acts as an activator in IL-2 production. Antagonism of membrane melatonin receptors using luzindole exacerbates the drop of the IL-2 production induced by PGE₂ in peripheral blood mononuclear and Jurkat cells. This paper studies the melatonin membrane and nuclear receptors interplay in PGE₂-diminished IL-2 production. The decrease in IL-2 production after PGE₂ and/or luzindole administration correlated with downregulation in the nuclear receptor RORα. We also highlighted a role of cAMP in the pathway, because forskolin mimicked the effects of luzindole and/or PGE₂ in the RORα expression. Finally, a significant RORα downregulation was observed in T cells permanently transfected with inducible MT₁ antisense. In conclusion, we show a novel connection between melatonin membrane receptor signalling and RORα expression, opening a new way to understand melatonin regulation in lymphocyte physiology. Received 23 September 2008; received after revision 19 November 2008; accepted 21 November 2008     

The effects of two neutral polymers on the geometry and deformability of the human erythrocyte.

Polyvinylpyrrolidone and dextran decrease cellular deformability. Changes in volume do not wholly account for the changes which imply a stiffening of the plasma membrane. The effects differ from those induced by charged macromolecules.