Search results for "membrane potentials"
showing 10 items of 149 documents
Activation of a caspase-3-independent mode of cell death associated with lysosomal destabilization in cultured human retinal pigment epithelial cells…
2008
International audience; Purpose: To characterize the possible cytotoxic effects of oxysterols (7-hydroxycholesterol (7-OH), 25-hydroxycholesterol (25-OH)) in human retinal pigment epithelial cells (ARPE-19) and to detail the relationships between some of these effects. Methods: ARPE-19 cells were treated with 7-OH and 25-OH. Cell viability was measured with the MTT assay. Membrane permeability, mitochondrial potential, and lysosomal integrity were measured by flow cytometry with propidium iodide, DiOC6(3), and acridine orange, respectively. Cell death was characterized by staining with Hoechst 33342, transmission electron microscopy, and analysis of the DNA fragmentation pattern. Caspase ac…
Heat-induced action potential discharges in nociceptive primary sensory neurons of rats.
2009
Although several transducer molecules for noxious stimuli have been identified, little is known about the transformation of the resulting generator currents into action potentials (APs). Therefore we investigated the transformation process for stepped noxious heat stimuli (42-47 degrees C, 3-s duration) into membrane potential changes and subsequent AP discharges using the somata of acutely dissociated small dorsal root ganglion (DRG) neurons (diameteror=32.5 microm) of adult rats as a model for their own peripheral terminals. Three types of heat-induced membrane potential changes were differentiated: type 1, heat-induced AP discharges (approximately 37% of the neurons); type 2, heat-induce…
EGF and HGF levels are increased during active HBV infection and enhance survival signaling through extracellular matrix interactions in primary huma…
2008
The hepatitis B virus (HBV) is a major causative agent of chronic liver disease and subsequent liver cirrhosis worldwide. The reduced sensitivity of virus-infected liver cells to apoptosis may play a role in the failure to remove virus-infected cells and eventually promote viral chronicity. The purpose of our study was to investigate whether survival factors induced during compensatory liver regeneration may protect hepatocytes against apoptosis. We evaluated the serum levels of hepatocyte growth factor (HGF) and epidermal growth factor (EGF) in HBV-infected patients and found significant increases in HGF and EGF in patients with active virus infection. In primary human hepatocytes we show …
Differential electrophysiologic and inotropic effects of phenylephrine in atrial and ventricular heart muscle preparations from rats.
1991
Stimulation of alpha 1-adrenoceptors evokes a different pattern of inotropic responses in atrial and ventricular heart muscle preparations from rats. The inotropic effects are accompanied by different changes in membrane potential. In an attempt to clarify the question whether or to which extent these events are causally related, the effects of phenylephrine on force of contraction, transmembrane potential, Ca2+ current (ICa) and K+ currents were comparatively studied in either tissue. In atrial preparations, phenylephrine 10 mumol/l caused an increase in force of contraction, a marked prolongation of the action potential duration and a depolarization of the membrane at rest. In the ventric…
Electrical and mechanical activity of mammalian heart muscle fibres treated with papaverine
1977
The action of papaverine on electrical and mechanical activity was investigated in ventricular and atrial heart muscle fibres from guinea-pigs and cats. 1. Papaverine (10−5 M–5×10−5M) had positive, negative or no inotropic effects in ventricular preparations; positive inotropic effects were not observed after pretreatment of the animals with reserpine. In atrial preparations, papaverine (2×10−5M) had a positive inotropic effect that was independent of endogenously stored catecholamines. 2. The effects of isoprenaline and dibutyryl cyclic AMP were potentiated by papaverine (10−5 M–2×10−5M). 3. The action potential duration was always prolonged by papaverine in ventricular as well as in atria…
Impact of Surface Charge Directionality on Membrane Potential in Multi-ionic Systems
2020
The membrane potential (Vmem), defined as the electric potential difference across a membrane flanked by two different salt solutions, is central to electrochemical energy harvesting and conversion. Also, Vmem and the ionic concentrations that establish it are important to biophysical chemistry because they regulate crucial cell processes. We study experimentally and theoretically the salt dependence of Vmem in single conical nanopores for the case of multi-ionic systems of different ionic charge numbers. The major advances of this work are (i) to measure Vmem using a series of ions (Na+, K+, Ca2+, Cl-, and SO42-) that are of interest to both energy conversion and cell biochemistry, (ii) to…
Fasting enhances the response of arcuate neuropeptide Y-glucose-inhibited neurons to decreased extracellular glucose
2009
0363-6143 (Print) Comparative Study In Vitro Journal Article Research Support, N.I.H., Extramural; Fasting increases neuropeptide Y (NPY) expression, peptide levels, and the excitability of NPY-expressing neurons in the hypothalamic arcuate (ARC) nucleus. A subpopulation of ARC-NPY neurons ( approximately 40%) are glucose-inhibited (GI)-type glucose-sensing neurons. Hence, they depolarize in response to decreased glucose. Because fasting enhances NPY neurotransmission, we propose that during fasting, GI neurons depolarize in response to smaller decreases in glucose. This increased excitation in response to glucose decreases would increase NPY-GI neuronal excitability and enhance NPY neurotr…
Trefoil factor TFF1-induced protection of conjunctival cells from apoptosis at premitochondrial and postmitochondrial levels.
2008
PURPOSE. Goblet cells of the conjunctival epithelium synthesize and secrete TFF1 (Trefoil factor 1), a small protease-resistant peptide that, together with mucins, is responsible for the rheologic properties of the tear film. This study aimed to determine whether TFF1, whose synthesis increases in inflammatory conditions such as pterygium, could protect conjunctival cells from apoptosis. METHODS. Chang conjunctival cells, either wild-type or expressing TFF1 through stable transfection, were exposed to benzalkonium chloride (BAK) and ultraviolet (UV) irradiation to trigger apoptosis. The authors used cell fractionation to detect lipid raft‐associated proteins, coimmunoprecipitation to explor…
Influence of the drying processes of yeasts on their volatile phenol sorption capacity in model wine.
2009
International audience; Volatile phenols, such as 4-ethylphenol, are responsible for a "horsey" smell in wine. Thus, the study of volatile phenol sorption in yeasts, and their subsequent elimination from wine, helps to optimize eco-friendly wine curative processes. Here, we compared the influences of spray drying, lyophilization and evaporative drying at low water activity on yeast, for improving the 4-ethylphenol sorption capacity in a synthetic model wine. The changes that occur in the physico-chemical characteristics of the yeast surface (surface hydrophobicity, electron-donor character and zeta potential) during these drying processes were determined to assess if any correlation exists …
Mechanisms underlying the toxicity of lactone aroma compounds towards the producing yeast cells
2003
M. A G U E D O , L. B E N E Y , Y. W A C H EA N D J. - M. B E L I N. 2003. Aims: To study the fundamental mechanisms of toxicity of the fruity aroma compound c-decalactone, that lead to alterations in cell viability during its biotechnological production by yeast cells; Yarrowia lipolytica that is able to produce high amounts of this metabolite was used here as a model. Methods and Results: Lactone concentrations above 150 mg l )1 inhibited cell growth, depolarized the living cells and increased membrane fluidity. Infrared spectroscopic measurements revealed that the introduction of the lactone into model phospholipid bilayers, decreased the phase transition temperature. Moreover, the H + -…