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Bathing Medium (bathing + medium)
Selected AbstractsPlasma membrane surface potential (,pm) as a determinant of ion bioavailability: A critical analysis of new and published toxicological studies and a simplified method for the computation of plant ,pmENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2006Thomas B. Kinraide Abstract Plasma membranes (PMs) are negatively charged, and this creates a negative PM surface electrical potential ,PM) that is also controlled by the ionic composition of the bathing medium. The ,PM controls the distribution of ions between the PM surface and the medium so that negative potentials increase the surface activity of cations and decrease the surface activity of anions. All cations reduce the negativity of ,PM, and these common ions are effective in the following order: Al3+ > H+ > Cu2+ > Ca2+ , Mg2+ > Na+ , K+. These ions, especially H+, Ca2+, and Mg2+, are known to reduce the uptake and biotic effectiveness of cations and to have the opposite effects on anions. Toxicologists commonly interpret the interactions between toxic cations (commonly metals) and ameliorative cations (commonly H+, Ca2+, and Mg2+) as competitions for binding sites at a PM surface ligand. The ,PM is rarely considered in this biotic ligand model, which incorporates the free ion activity model. The thesis of this article is that ,PM effects are likely to be more important to bioavailability than site-specific competition. Furthermore, ,PM effects could give the false appearance of competition even when it does not occur. The electrostatic approach can account for the bioavailability of anions, whereas the biotic ligand model cannot, and it can account for interactions among cations when competition does not occur. Finally, a simplified procedure is presented for the computation of ,PM for plants, and the possible use of ,PM in a general assessment of the bioavailability of ions is considered. [source] Electrophysiological characterization of laminar synaptic inputs to the olfactory tubercle of the rat studied in vitro: modulation of glutamatergic transmission by cholinergic agents is pathway-specificEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 9 2001G. S. Owen Abstract We have exploited the complementary arrangement of afferents in a coronal slice (300,400 µm) of the rat olfactory tubercle (OT) maintained in vitro to investigate transmission in two separate synaptic pathways. We recorded extracellular responses within the OT dense cell layer in slices and stimulated either the outermost layer to activate primary olfactory fibres or deeper to activate secondary input. Superficial stimulation produced a synaptic potential with superimposed population spike. This interpretation was based on blockade by calcium removal from the bathing medium and the use of the glutamate antagonist DNQX (10 µm); the spike was found to be selectively suppressed by tetrodotoxin applied near the cells. The spike, but not the synaptic wave, was depressed by 12 mm Ca2+ and enhanced by 1 mm Ba2+ in the bathing medium. Deep stimulation to activate association and intrinsic fibres elicited a nerve volley followed by a later response, also blocked by Ca2+ removal or 10 µm DNQX. It was unaffected by high Ca2+ or Ba2+, hence resulting from synaptic and not action current flow. Removal of Mg2+ from the bathing medium revealed an NMDA component of synaptic transmission at both loci that was selectively blocked by D-AP-5. The deep synaptic response, only, was depressed by carbachol IC50 7 µm or muscarine IC50 13 µm. This depression was also induced by AChE inhibitors eserine or tacrine and was antagonized by 1 µm atropine or 5,10 µm clozapine. These results characterize transmission in the OT and demonstrate a role for muscarinic modulation of deeper synapses in the OT that is influenced by psychotherapeutic drugs. [source] The catalytic domain of human neuropathy target esterase mediates an organophosphate-sensitive ionic conductance across liposome membranesJOURNAL OF NEUROCHEMISTRY, Issue 2 2001Philip J. Forshaw In humans and other vertebrates, reaction of organophosphates with a neuronal membrane protein, neuropathy target esterase (NTE), initiates events which culminate in axonal degeneration. The initiation process appears to involve modification of a property of the protein distinct from its esterase activity, subsequent to formation of a negatively charged adduct with the active site serine residue. Here, we show that membrane patches from liposomes containing NEST, a recombinant hydrophobic polypeptide comprising the esterase domain of human NTE, display a transmembrane ionic conductance with both stable and high-frequency flickering components. An asymmetric current,voltage relationship suggested that ion flow was favoured in one direction relative to the membrane and its associated NEST molecules. Flow of anions was slightly favoured compared with cations. The flickering current formed a much larger proportion of the overall conductance in patches containing wild-type NEST compared with the catalytically inactive S966A mutant form of the protein. The conductance across patches containing NEST, but not those with the S966A mutant, was significantly reduced after adding neuropathic organophosphates to the bathing medium. By contrast, non-neuropathic covalent inhibitors of the catalytic activity of NEST did not reduce NEST-mediated conductance. Future work may establish whether NTE itself mediates an organophosphate-sensitive ion flux across intracellular membranes within intact cells. [source] Grass cells ingested by ruminants undergo autolysis which differs from senescence: implications for grass breeding targets and livestock productionPLANT CELL & ENVIRONMENT, Issue 10 2002E. M. Beha Abstract It is widely believed that the initial degradation of proteins contained in grazed forage is mediated by rumen micro-organisms, but the authors' recent work suggests that the plant cells themselves contribute to their own demise. In the present study the responses of Lolium perenne leaves to the rumen environment were investigated by using an in vitro system which simulates the main stresses of the rumen but from which rumen micro-organisms were excluded. Degradation of leaf protein and the accumulation of amino acids in tissue and bathing medium occurred over a time-scale that is relevant to rumen function, and in a near 1 : 1 ratio. Significant loss of nuclear material was observed after 6 h incubation and chloroplasts became morphologically more spherical as the incubation progressed. In situ localization suggested that ribulose 1,5 bisphosphate carboxylase/oxygenase was broken down within chloroplasts which from cytology were judged to be intact. We conclude from these data that plant metabolism may play a significant role in breaking down plant proteins within relatively intact organelles in the rumen. The determinations of chlorophyll content and cell viability revealed that the plant processes occurring in the simulated rumen were similar but not identical to those of natural senescence. [source] Lack of effectiveness of botulinum neurotoxin A on isolated detrusor strips and whole bladders from mice and guinea-pigs in vitroBJU INTERNATIONAL, Issue 10 2009Sarah Howles OBJECTIVE To differentiate between the effects of parasympathetic and sensorimotor stimulation of isolated mouse and guinea-pig bladders in vitro by measuring the pressure increases to electrical field stimulation (EFS) and then comparing the effects of botulinum neurotoxin A (BoNT-A) applied either to the lumen or to the external bathing medium. MATERIALS AND METHODS Isolated mouse and guinea-pig bladders and detrusor strips were exposed to EFS in vitro before and after the addition of BoNT-A. The rationale of this method was that BoNT-A applied to the outside of the bladder would first affect the parasympathetic nerves before diffusing inwards to affect the sensorimotor innervation. BoNT-A applied intravesically would first reach the sensorimotor nerves and only later the parasympathetic nerves. Initial experiments on strips of detrusor were conducted to establish the correct dosage and application time of BoNT-A. RESULTS Contrary to our expectations, BoNT-A application failed to produce any significant effects on either the detrusor strips or whole bladders. CONCLUSIONS Our experimental design failed to show any effect of BoNT-A on the contractility of detrusor muscle strips or whole bladders from mice and guinea-pigs. The reason for this is unclear, but may be related to tissue spending inadequate time incubated with BoNT-A under physiological conditions. [source] Vasoconstrictor activity of novel endothelin peptide, ET-1(1 , 31), in human mammary and coronary arteries in vitroBRITISH JOURNAL OF PHARMACOLOGY, Issue 6 2001Janet J Maguire The ability of the putative chymase product of big endothelin-1 (big ET-1), ET-1(1 , 31), to constrict isolated endothelium-denuded preparations of human coronary and internal mammary artery was determined. pD2 values in coronary and mammary artery respectively were 8.21±0.12 (n=14) and 8.55±0.11 (n=12) for ET-1, 6.74±0.11 (n=16) and 7.10±0.08 (n=16) for ET-1(1 , 31) and 6.92±0.10 (n=15) and 7.23±0.11 (n=12) for big ET-1. ET-1(1 , 31) was significantly less potent than ET-1 (P<0.001, Student's t -test) and equipotent with big ET-1. Vasoconstrictor responses to 100 , 700 nM ET-1(1 , 31) were significantly (P<0.05, Student's paired t -test) attenuated by the ETA antagonist PD156707 (100 nM). There was no effect of the ECE inhibitor PD159790 (30 ,M), the ECE/NEP inhibitor phosphoramidon (100 ,M) or the serine protease inhibitor chymostatin (100 ,M) on ET-1(1 , 31) responses in either artery. Radioimmunoassay detected significant levels of mature ET in the bathing medium of coronary (1.6±0.5 nM, n=14) and mammary (2.1±0.6 nM, n=14) arteries, suggesting that conversion of ET-1(1 , 31) to ET-1 contributed to the observed vasoconstriction. ET-1(1 , 31) competed for specific [125I]-ET-1 binding to ETA and ETB receptors in human left ventricle with a pooled KD of 71.6±7.0 nM (n=3). Therefore, in human arteries the novel peptide ET-1(1 , 31) mediated vasoconstriction via activation of the ETA receptor. The conversion of ET-1(1 , 31) to ET-1, by an as yet unidentified protease, must contribute wholly or partly to the observed constrictor response. Chymase generated ET-1(1 , 31) may therefore represent an alternative precursor for ET-1 production in the human vasculature. British Journal of Pharmacology (2001) 134, 1360,1366; doi:10.1038/sj.bjp.0704384 [source] Effects of binocular form deprivation on the excitatory post-synaptic currents mediated by N-methyl-D-aspartate receptors in rat visual cortexCLINICAL & EXPERIMENTAL OPHTHALMOLOGY, Issue 3 2004Wei Qin MD Abstract Purpose:,To investigate the effects of binocular form deprivation (BFD) on the excitatory post-synaptic currents (EPSCs) mediated by the N-methyl-D-aspartate (NMDA) receptor (NMDA-EPSCs), and the proportion of NMDA-EPSCs relative to glutamate receptor currents (glutamate-EPSCs) in rat visual cortex. Methods:,Binocular form deprivation was achieved by suturing the eyelids of Wistar rats at postnatal day (PD) 14, before eye-opening. Visual cortical slices (300 µm) were prepared from normal and BFD Wistar rats aged PD 14, 21 and 28. Recordings were obtained in slices from layer II to IV using the whole-cell patch-clamp technique. Glutamate-EPSCs were isolated in the presence of bicuculline methiodide (20 µmol/L) in the bathing medium, and NMDA-EPSCs were isolated with a combination of bicuculline methiodide (20 µmol/L) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 20 µmol/L). In addition, D,L-2-amino-5-phosphonovalerate (AP-5, 20 µmol/L) was applied to study the NMDA-only mediated currents. For each cell, the ratio of peak NMDA to glutamate EPSCs was calculated. Results:,During visual development, the decay time constant of NMDA-EPSCs became shorter after eye-opening in normal rats (F = 5.949, P <0.05; PD 28 vs PD 14, P = 0.027), but not in rats with BFD (P > 0.05). The weighted time constant of NMDA-EPSCs in the visual cortex became shorter after the rats' eyes were opened in the normal group (F2,37 = 4.727, P = 0.015; PD 28 vs PD 14, P = 0.035), but not in the BFD group (P > 0.05). However, the rise time constant and peak value of NMDA-EPSCs showed no significant changes in normal and BFD groups (P > 0.05). The ratio of NMDA-EPSCs to glutamate-EPSCs became gradually smaller with age in the normal rats (F = 4.661, P < 0.05; PD 28 vs PD 14, P = 0.025), but not in the BFD group (P > 0.05). Conclusions:,These studies reveal that the proportion of NMDA-EPSCs relative to glutamate-EPSCs and the decay time constant of NMDA-EPSCs are influenced by BFD. These changes may reflect important experience-dependent modifications of neuronal synapses in visual cortex. [source] | |||||||||||||