Search results for "membrane permeability"
showing 10 items of 134 documents
Rapid quantitative method for measuring phagocytosis of Leishmania promastigotes using a double radiolabelling method.
1990
A double radiolabelling method is described for the measurement of phagocytosis of Leishmania major promastigotes in cultures of murine resident peritoneal macrophages. L. major promastigotes were radiolabelled during exponential growth in RPMI supplemented with [125I]5-iodo-2-deoxyuridine. They were used to infect sodium [51Cr]chromate-labelled macrophages. Phagocytosis was evaluated by measuring the radioactivity of the 125IUdR-labelled parasites detectable inside 51Cr-labelled macrophages by a Beckmann gamma 5500 counting system. This was able to count simultaneously, in two different windows the radioactivity of (a) the parasites and (b) the cells. The technique compares favorably with …
Variability of permeability estimation from different protocols of subculture and transport experiments in cell monolayers.
2014
Abstract Introduction In vitro models with high predictive ability have been revealed as strong tools for pharmaceutical industry. However, the variability in permeability estimations complicates the comparison and combination of data from different laboratories and it makes necessary the careful validation of the model and the continuous suitability demonstration. The adequate standardization of pre-experimental, experimental and post-experimental factors might help to reduce the inter- and intra-laboratory variability in permeability values. Methods The objective of this paper is the evaluation of the effect of passage number, experimental protocol, time after seeding and calculation meth…
Über die Wirkung von Prostaglandin E1 auf den Ca-Haushalt isolierter Meerschweinchenherzen
1967
The stimulatory effect of PGE1 on different functions of isolated guinea-pig hearts (Langendorff method, Tyrode solution) was coupled with an increase in the rate of45Ca uptake from the perfusion medium. The total myocardial Ca content and the amount of exchangeable cellular Ca were not affected. This action of PGE1 on the myocardial Ca metabolism seems to be related to the positive inotropic action of PGE1 and can most probably be explained by an increase in the membrane permeability to Ca ions (similar to the action of epinephrine).
�ber den Mechanismus der positiv inotropen Wirkung von Theophyllin am Warmbl�terherzen
1971
In order to further elucidate the mechanism of the positive inotropiceffect of theophylline (T) in mammalian cardiac muscle, the influence of T on contractile force, extracellular space,45Ca uptake,45Ca release, and total myocardial calcium concentration was investigated in isolated, electrically driven (frequency 170 beats/min) or quiescent left guinea-pig atria. The investigations were performed in Tyrode solution containing 0.45 mM CaCl2. T concentration was 5×10−4 g/ml. Under these conditions, T exerted maximal positive inotropic but no toxic effects, that is, it did not cause contractures or arrythmias within 60 min (Fig. 1). The experiments provide evidence that T increases the rate o…
Der Einflu� von Monojodessigs�ure auf das Aktionspotential des Rattenzwerchfells
1959
1. The action of iodoacetic acid (IA) was studied on the isolated rat diaphragm at 20–22° C. Membrane and action potentials were led off with intracellular microelectrodes. 2. IA causes a contracture which is complete in 4 hours. As long as t he contracture develops, the membrane potential remains constant. A contracture identical with that seen in a normal preparation can be produced by IA in the presence of isotonic K2SO4. 3. The amplitude of the action potential is only slightly reduced during the first two hours after addition of IA. The duration of the action potential is significantly increased. Finally, action potentials with a plateau are obtained which resemble those of normal vent…
Distinctive phytotoxic effects of Cd and Ni on membrane functionality.
2009
Metal ions essential for plant growth, such as Fe, Mn, Ni, Cu or Zn, are taken up by plants from the soil solution through metal transporters at the plasma membrane, mainly of the ZIP and Nramp families. These transport systems, however, can also give entry to other metals (Al, Cd, Hg, Pb). Non-nutritive elements, as well as the essential nutrients at higher than metabolic concentrations, can cause phytotoxicity. We have studied previously the effects of an essential (Ni) and a non essential (Cd) heavy metal on root cell plasma membranes, the first selective barrier encountered when entering the plant, using rice as model plant. Distinctive effects of Cd and Ni on membrane function (i.e., E…
A lipocentric view of peptide-induced pores
2010
Although lipid membranes serve as effective sealing barriers for the passage of most polar solutes, nonmediated leakage is not completely improbable. A high activation energy normally keeps unassisted bilayer permeation at a very low frequency, but lipids are able to self-organize as pores even in peptide-free and protein-free membranes. The probability of leakage phenomena increases under conditions such as phase coexistence, external stress or perturbation associated to binding of nonlipidic molecules. Here, we argue that pore formation can be viewed as an intrinsic property of lipid bilayers, with strong similarities in the structure and mechanism between pores formed with participation …
Functional size of complement and perforin pores compared by confocal laser scanning microscopy and fluorescence microphotolysis
1991
Abstract Confocal laser scanning microscopy and fluorescence microphotolysis (also referred to as fluorescence photobleaching recovery) were employed to study the transport of hydrophilic fluorescent tracers through complement and perforin pores. By optimizing the confocal effect it was possible to determine the exclusion limit of the pores in situ, i.e. without separation of cells and tracer solution. Single-cell flux measurements by fluorescence microphotolysis yielded information on the sample population distribution of flux rates. By these means a direct comparison of complement and perforin pores was made in sheep erythrocyte membranes. In accordance with previous studies employing a v…
Novel path to apoptosis: small transmembrane pores created by staphylococcal alpha-toxin in T lymphocytes evoke internucleosomal DNA degradation.
1994
Peripheral-blood human T lymphocytes were treated with Staphylococcus aureus alpha-toxin. Membrane permeabilization was assessed by measuring efflux of K+ and Rb+ and influx of Na+, Ca2+, and propidium iodide. Cellular ATP and [3H]thymidine incorporation following lectin stimulation were measured as parameters for cell viability. Internucleosomal cleavage characteristic of programmed cell death was assessed by agarose gel electrophoresis and by quantifying low-molecular-weight, [3H]thymidine-labeled DNA fragments. Nanomolar concentrations of alpha-toxin evoked protracted, irreversible ATP depletion in both activated and resting T lymphocytes. Toxin-damaged cells also lost their ability to i…
Nuclear Translocation of Nuclear Transcription Factor-κB by α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid Receptors Leads to Transcription of …
2003
We describe a new molecular mechanism of cell death by excitotoxicity mediated through nuclear transcription factor κB (NFκB) in rat embryonic cultures of dopaminergic neurons. Treatment of mesencephalic cultures with α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) resulted in a number of changes that occurred selectively in dopaminergic neurons, including persistent elevation in intracellular Ca2+ monitored with Fura-2, and a significant increase in intramitochondrial oxidation of dihydrorhodamine 123, probably associated with transient increase of mitochondrial permeability, cytochrome c release, nuclear translocation of NFκB, and transcriptional activation of the oncogenep53.…