1,721,001 research outputs found
Ion transport and metal sensitivity of vacuolar channels from the roots of the aquatic plant Eichhornia crassipes
No full textUsing the patch-clamp technique, we investigated the transport properties of vacuolar ion channels from the roots of water hyacinth, Eichhornia crassipes (Mart. Solms, Pontederiacae). Eichhornia crassipes vacuoles displayed large voltage-dependent rectifying slow-vacuolar (SV) currents, which activated in a few seconds at positive potentials and deactivated at negative voltages in a few hundreds of mill-seconds. Similarly to SV channel previously identified in the tonoplast of terrestrial plants, SV currents in E. crassipes were activated by micromolar concentrations of Ca2+ and current slightly increased (25%) on addition (10 mM) of the reducing agent dithiothreitol (DTT). Eichhornia crassipes SV channels were equally permeable to K+ and Na+. The permeability sequence derived from current values is: K+ ≈ Na+ > Rb+ > NH4+ ≈ Cs+ >>TEA+. Excised membrane patches displayed single channel transitions typical of SV-type single channel openings with a conductance of (83.0 ± 5.6) pS; a smaller channel with a conductance of (31.0 ± 2.7) pS was also identified. Metals such as Ni2+ and Zn2+ decreased the vacuolar current in a reversible manner. However, although Zn2+ inhibition is comparable to that induced by the same metal in vacuoles from the main root of sugar beet (Beta vulgaris L.), the inhibition of the SV currents by Ni2+ is not as substantial in E. crassipes as in sugar beet. To our knowledge, this is the first electrophysiological characterization of ionic transport in E. crassipes, a pervasive troublesome aquatic weed, which has exceptional absorption properties of several water contaminants such as heavy metals, pesticides and phenols
Effects of calcium on the gramicidin A single channel in phosphatidylserine membranes: screening and blocking.
No full textIn phosphatidylserine membranes the decrease in the conductance of the gramicidin A single channel caused by calcium is attributed to a reduction of surface potential and to a direct blocking of the pore (Apell et al. 1979). The aim of this paper is to make a quantitative evaluation of these two effects. We recorded the conductance of gramicidin single channels in 100 mM KCl in the presence of different amounts of CaCl2, MgCl2 or TEACl. The ionic activities at the channel mouth were calculated using the Gouy-Chapman-Stern theory. Our experiments showed that even when the K+ activity at the channel mouth was estimated to be the same, the single channel conductance was lower if divalent cations were present. This effect is attributed to a blocking action of these ions
Modulation of plant ion channels by oxidizing and reducing agents
No full textIon channels are proteins forming hydrophilic pathways through the membranes of all living organisms. They play important roles in the electrogenic transport of ions and metabolites. Because of biophysical properties such as high selectivity for the permeant ion, high turnover rate, and modulation by physico-chemical parameters (e.g., membrane potential, calcium concentration), they are involved in several physiological processes in plant cells (e.g., maintenance of the turgor pressure, stomatal movements, and nutrient absorption by the roots). As plants cannot move, plant metabolism must be flexible and dynamic, to cope with environmental changes, to compete with other living species and to prevent pathogen invasion. An example of this flexibility and dynamic behavior is represented by their handling of the so-called reactive oxygen species, inevitable by-products of aerobic metabolism. Plants cope with these species on one side avoiding their toxic effects, on the other utilizing them as signalling molecules and as a means of defence against pathogens. In this review, we present the state-of-the-art of the modulation of plant ion channels by oxidizing and reducing agents
Effects of cytoplasmic Mg2+ on slowly activating channels in isolated vacuoles of Beta vulgaris
No full textThe slow vacuolar (SV) channel can mediate a large part of the ionic current in plant tonoplasts, but its actual physiological role is still unclear. We demonstrate that in vacuoles from the taproots of sugar beet (Beta vulgaris L.), besides Ca2+, cytoplasmic Mg2+ also plays an important role in promoting the activation of the SV channel. An increase in Mg2+ concentration decreases the time constants of channel activation and deactivation, and determines a consistent shift, towards negative voltages, of the conductance characteristic; as an example, when the free concentration of Mg2+ was increased from the micromolar range up to 10 mM the activation shifted by about -60 mV. The experimental results obtained, which are based on a fast perfusion procedure allowing us to change the solution bathing the vacuole in a few milliseconds, suggest that magnesium-binding is a faster process than the voltage-activation gating of the channel, which constitutes the rate-limiting step controlling channel opening. Interestingly, the activation of the channel mediated by Mg2+ depends on the cooperative binding of at least three magnesium ions. We verified that cytoplasmic magnesium favours the activation of SV channels in the presence of nanomolar cytoplasmic calcium concentrations. A critical discussion on the Calcium Induced Calcium Release (CICR) mechanism proposed for the SV channel is presented
Effects of mono- and multi-valent cations on the inward-rectifying potassium channel in isolated protoplasts from maize roots
No full textChloride channels activated by hypotonicity in N2A neuroblastoma cell line
No full textBy using the patch-clamp technique we have shown that, in hypotonic extracellular solutions, the mouse neuroblastoma cells Neuro2A (N2A) develop ionic currents mediated by a chloride-selective channel which is also permeable to other anions in accordance with the permeability sequence: I->Br->Cl->gluconate->glutamate-. The currents persist for several hours when Mg-ATP is present in the recording pipette but occur only transiently in the absence of Mg-ATP. Typical blockers of anions channels such as La3+ and Zn2+ do not affect the hypotonicity-activated channel; conversely, the stilbene sulfonate-derivatives, 4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid (SITS) and 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), reversibly inhibit the channel in a voltage-dependent manner. Also intact cells exposed to hyposmotic solutions activate volume-regulation mechanisms which decrease the transient volume increase that develops immediately after the application of the hyposmotic challenge. Since N2A neurons have been used as an expression system of exogenous channels, the presence of osmolarity-regulated channels in these cells is an important aspect that deserves the attention of researchers who may wish to express and study the properties of transport proteins in this cell line
On the interaction of neomycin with the slow vacuolar channel of Arabidopsis thaliana
No full textThis study investigates the interaction of the aminoglycoside antibiotic neomycin with the slow vacuolar (SV) channel in vacuoles from Arabidopsis thaliana mesophyll cells. Patch-clamp experiments in the excised patch configuration revealed a complex pattern of neomycin effects on the channel: applied at concentrations in the submicromolar to millimolar range neomycin (a) blocked macroscopic SV currents in a voltage- and concentration-dependent manner, (b) slowed down activation and deactivation kinetics of the channel, and most interestingly, (c) at concentrations above 10 muM, neomycin shifted the SV activation threshold towards negative membrane potentials, causing a two-phasic activation at high concentrations. Single channel experiments showed that neomycin causes these macroscopic effects by combining a decrease of the single channel conductance with a concomitant increase of the channel's open probability. Our results clearly demonstrate that the SV channel can be activated at physiologically relevant tonoplast potentials in the presence of an organic effector molecule. We therefore propose the existence of a cellular equivalent regulating the activity of the SV channel in vivo
Fast and slow activation of voltage-dependent ion channels in radish vacuoles.
No full textThe molecular processes associated with voltage-dependent opening and closing (gating) of ion channels were investigated using a new preparation from plant cells, i.e., voltage and calcium-activated ion channels in radish root vacuoles. These channels display a main single channel conductance of approximately 90 pS and are characterized by long activation times lasting several hundreds of milliseconds. Here, we demonstrate that these channels have a second kinetically distinct activation mode which is characterized by even longer activation times. Different membrane potential protocols allowed to switch between the fast and the slow mode in a controlled and reversible manner. At transmembrane potentials of -100 mV, the ratio between the fast and slow activation time constant was around 1:5. Correspondingly, activation times lasting several seconds were observed in the slow mode. The molecular process controlling fast and slow activation may represent an effective modulator of voltage-dependent gating of ion channels in other plant and animal systems
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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