Effects of Nppb and Niflumic Acid on Outward K+ and Cl- Currents Across the Plasma Membrane of Wheat Root Protoplasts

1996 ◽  
Vol 23 (4) ◽  
pp. 527 ◽  
Author(s):  
A Garrill ◽  
SD Tyerman ◽  
GP Findlay ◽  
PR Ryan
Keyword(s):  
Plasma Membrane ◽  
Single Channel ◽  
Wheat Root ◽  
Niflumic Acid ◽  
Channel Blockers ◽  
Anion Channels ◽  
Intact Cells ◽  
Ic50 Values ◽  
Plant Membranes ◽  
O 10

We have tested the effects of the reported Cl- channel blockers NPPB (5-nitro-2-(3- phenylpropylamino)benzoic acid) and niflumic acid (trifluoromethyl-3-phenylamino-2-nicotinic acid) on the slow-activating K+ (IKK.out) and fast-activating Cl- (IClCl.out) outward rectifying currents across the plasma membrane of wheat root protoplasts. Both compounds display a greater potency against IKK.out(half maximal inhibition (IC50) values of 8.7 μM for NPPB and 5.3 μM for niflumic acid with [K+]o= 10 mM) than against IClCl.out(IC50 values of 150 and 100 μM respectively). Single-channel studies using detached patches show that these blockers reduce the percentage of time that IKK.out out channels are in their open state. The data show that caution is necessary when using these compounds on intact cells to ascribe physiological functions to anion channels in plant membranes.

scholarly journals Cytosolic [Ca2+] regulation of InsP3-evoked puffs

2012 ◽  
Vol 449 (1) ◽  
pp. 167-173 ◽  
Author(s):  
Michiko Yamasaki-Mann ◽  
Angelo Demuro ◽  
Ian Parker
Keyword(s):  
Plasma Membrane ◽  
Nicotinic Acetylcholine Receptors ◽  
Acetylcholine Receptors ◽  
Xenopus Oocytes ◽  
Single Channel ◽  
Building Blocks ◽  
Electrochemical Gradient ◽  
Intact Cells ◽  
Nicotinic Acetylcholine ◽  
Insp3 Receptors

InsP3-mediated puffs are fundamental building blocks of cellular Ca2+ signalling, and arise through the concerted opening of clustered InsP3Rs (InsP3 receptors) co-ordinated via Ca2+-induced Ca2+ release. Although the Ca2+ dependency of InsP3Rs has been extensively studied at the single channel level, little is known as to how changes in basal cytosolic [Ca2+] would alter the dynamics of InsP3-evoked Ca2+ signals in intact cells. To explore this question, we expressed Ca2+-permeable channels (nicotinic acetylcholine receptors) in the plasma membrane of voltage-clamped Xenopus oocytes to regulate cytosolic [Ca2+] by changing the electrochemical gradient for extracellular Ca2+ entry, and imaged Ca2+ liberation evoked by photolysis of caged InsP3. Elevation of basal cytosolic [Ca2+] strongly increased the amplitude and shortened the latency of global Ca2+ waves. In oocytes loaded with EGTA to localize Ca2+ signals, the number of sites at which puffs were observed and the frequency and latency of puffs were strongly dependent on cytosolic [Ca2+], whereas puff amplitudes were only weakly affected. The results of the present study indicate that basal cytosolic [Ca2+] strongly affects the triggering of puffs, but has less of an effect on puffs once they have been initiated.

Anion channels influence ECC by modulating L-type Ca2+ channel in ventricular myocytes

2002 ◽  
Vol 93 (5) ◽  
pp. 1660-1668 ◽  
Author(s):  
Shi-Sheng Zhou ◽  
Zhan Gao ◽  
Ling Dong ◽  
Yan-Feng Ding ◽  
Xiao-Dong Zhang ◽  
...  
Keyword(s):  
Ventricular Myocytes ◽  
Anion Channel ◽  
Niflumic Acid ◽  
Cardiac Contraction ◽  
Channel Blockers ◽  
Dependent Manner ◽  
Anion Channels ◽  
Cell Shortening ◽  
Fluorescence Measurements ◽  
Intracellular Ca

Anion channels are extensively expressed in the heart, but their roles in cardiac excitation-contraction coupling (ECC) are poorly understood. We, therefore, investigated the effects of anion channels on cardiac ventricular ECC. Edge detection, fura 2 fluorescence measurements, and whole cell patch-clamp techniques were used to measure cell shortening, the intracellular Ca2+ transient, and the L-type Ca2+ current ( I Ca,L) in single rat ventricular myocytes. The anion channel blockers 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) and niflumic acid reversibly inhibited the Ca2+ transients and cell shortening in a dose-dependent manner. Comparable results were observed when the majority of the extracellular Cl− was replaced with the relatively impermeant anions glutamate (Glt−) and aspartate (Asp−). NPPB and niflumic acid or the Cl− substitutes did not affect the resting intracellular Ca2+ concentration but significantly inhibited I Ca,L. In contrast, replacement of extracellular Cl− with the permeant anions NO[Formula: see text], SCN−, and Br− supported the ECC and I Ca,L, which were still sensitive to blockade by NPPB. Exposure of cardiac ventricular myocytes to a hypotonic bath solution enhanced the amplitude of cell shortening and supported I Ca,L, whereas hypertonic stress depressed the contraction and I Ca,L. Moreover, cardiac contraction was completely abolished by NPPB (50 μM) under hypotonic conditions. It is concluded that a swelling-activated anion channel may be involved in the regulation of cardiac ECC through modulating L-type Ca2+ channel activity.

Modulation of frequency and height of cytosolic calcium spikes by plasma membrane anion channels in guard cells

2021 ◽  
Author(s):  
Md Tahjib-Ul-Arif ◽  
Shintaro Munemasa ◽  
Toshiyuki Nakamura ◽  
Yoshimasa Nakamura ◽  
Yoshiyuki Murata
Keyword(s):  
Plasma Membrane ◽  
Stomatal Closure ◽  
Anion Channel ◽  
Guard Cells ◽  
Cytosolic Calcium ◽  
Peak Height ◽  
Extracellular Calcium ◽  
Wild Type ◽  
Anion Channels ◽  
In The Wild

Abstract Cytosolic calcium ([Ca2+]cyt) elevation activates plasma membrane anion channels in guard cells, which is required for stomatal closure. However, involvement of the anion channels in the [Ca2+]cyt elevation remains unclear. We investigated the involvement using Arabidopsis thaliana anion channel mutants, slac1-4 slah3-3 and slac1-4 almt12-1. Extracellular calcium induced stomatal closure in the wild-type plants but not in the anion channel mutant plants whereas extracellular calcium induced [Ca2+]cyt elevation both in the wild-type guard cells and in the mutant guard cells. The peak height and the number of the [Ca2+]cyt spike were lower and larger in the slac1-4 slah3-3 than in the wild-type and the height and the number in the slac1-4 almt12-1 were much lower and much larger than in the wild-type. These results suggest that the anion channels are involved in the regulation of [Ca2+]cyt elevation in guard cells.

scholarly journals Voltage-dependent block of endothelial volume-regulated anion channels by calix[4]arenes

1998 ◽  
Vol 275 (3) ◽  
pp. C646-C652 ◽  
Author(s):  
Guy Droogmans ◽  
Jean Prenen ◽  
Jan Eggermont ◽  
Thomas Voets ◽  
Bernd Nilius
Keyword(s):  
Open Channel ◽  
Single Channel ◽  
Anion Channel ◽  
Anion Channels ◽  
Channel Conductance ◽  
Open Channel Block ◽  
Maximum Inhibition ◽  
Voltage Dependent ◽  
A Site ◽  
Maximal Block

We have studied the effects of calix[4]arenes on the volume-regulated anion channel (VRAC) currents in cultured calf pulmonary artery endothelial cells. TS- and TS-TM-calix[4]arenes induced a fast inhibition at positive potentials but were ineffective at negative potentials. Maximal block occurred at potentials between 30 and 50 mV. Lowering extracellular pH enhanced the block and shifted the maximum inhibition to more negative potentials. Current inhibition was also accompanied by an increased current noise. From the analysis of the calix[4]arene-induced noise, we obtained a single-channel conductance of 9.3 ± 2.1 pS ( n = 9) at +30 mV. The voltage- and time-dependent block were described using a model in which calix[4]arenes bind to a site at an electrical distance of 0.25 inside the channel with an affinity of 220 μM at 0 mV. Binding occludes VRAC at moderately positive potentials, but calix[4]arenes permeate the channel at more positive potentials. In conclusion, our data suggest an open-channel block of VRAC by calix[4]arenes that also depends on the protonation of the binding site within the pore.

Calcium-regulated anion channels in the plasma membrane of Lilium longiflorum pollen protoplasts

2011 ◽  
Vol 192 (1) ◽  
pp. 45-60 ◽  
Author(s):  
Bárbara Tavares ◽  
Pedro Nuno Dias ◽  
Patrícia Domingos ◽  
Teresa Fonseca Moura ◽  
José Alberto Feijó ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Lilium Longiflorum ◽  
Anion Channels

Ionic channels in corneal endothelium

1996 ◽  
Vol 270 (4) ◽  
pp. C975-C989 ◽  
Author(s):  
J. L. Rae ◽  
M. A. Watsky
Keyword(s):  
Patch Clamp ◽  
Corneal Endothelium ◽  
Single Channel ◽  
Cell Voltage ◽  
Anion Channel ◽  
Ionic Channels ◽  
K Channel ◽  
Na Channel ◽  
Channel Blockers ◽  
K Currents

Single-channel patch-clamp techniques as well as standard and perforated-patch whole cell voltage-clamp techniques have been applied to the study of ionic channels in the corneal endothelium of several species. These studies have revealed two major K+ currents. One is due to an anion- and temperature-stimulated channel that is blocked by Cs+ but not by most other K+ channel blockers, and the other is similar to the family of A-currents found in excitable cells. The A-current is transient after a depolarizing voltage step and is blocked by both 4-aminopyridine and quinidine. These two currents are probably responsible for setting the -50 to -60 mV resting voltage reported for these cells. A Ca(2+)-activated ATP-inhibited nonselective cation channel and a tetrodotoxin-blocked Na+ channel are possible Na+ inflow pathways, but, given their gating properties, it is not certain that either channel works under physiological conditions. A large-conductance anion channel has also been identified by single-channel patch-clamp techniques. Single corneal endothelial cells have input resistances of 5-10 G omega and have steady-state K+ currents that are approximately 10 pA at the resting voltage. Pairs or monolayers of cells are electrically coupled and dye coupled through gap junctions.

scholarly journals Chemical aspect of the influence of cobalt ions on atpase activity

2000 ◽  
Vol 65 (7) ◽  
pp. 507-515 ◽  
Author(s):  
Ljubica Vujisic ◽  
Danijela Krstic ◽  
Jovan Vucetic
Keyword(s):  
Experimental Data ◽  
Plasma Membrane ◽  
Atpase Activity ◽  
Kinetic Analysis ◽  
Synaptic Plasma Membrane ◽  
Cobalt Ions ◽  
Dependent Inhibition ◽  
Ic50 Values ◽  
Dose Dependent Inhibition ◽  
Dose Dependent

The influence of Co 2+ ions on the activities of Na+/K+-ATPase and Mg2+ -ATPase, enzymes from rat brain synaptic plasma membrane, was studied. The aim of this study was to investigate the inhibition of both ATPases activities byexposure tocobalt ions as a function of experimentally added CoSO4. The "free" Co2+ concentrations in the reaction mixturewere also calculated and discussed. CoSO4 induced a dose-dependent inhibition of both enzymes. The IC50 values of Co 2+, as calculated from the experimental curves, were 168 mM for Na+/K+-ATPase and 262 mMfor Mg 2+-ATPase, and for the recalculated free Co 2+ concentration 75.4 mM for Na+/K+-ATPase and 136 mM for Mg 2+-ATPase. The obtained linear Dixon's plot for Na+/K+-ATPase implies equilibium binding of cobalt with inhibitory sites on the enzyme. The kinetic parameters for both enzymes in presence and absence of CoSO4 were calculated from the experimental data. The results of the kinetic analysis show that inhibition of Na+/K+-ATPase induced by CoSO4 is non-competitive, and for Mg 2+-ATPase that there are two sites of different sensitivities or two different enzymes.

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