scholarly journals Characterization of the calcium-activated chloride channel in isolated guinea-pig hepatocytes.

1994 ◽  
Vol 104 (2) ◽  
pp. 357-373 ◽  
Author(s):  
S Koumi ◽  
R Sato ◽  
T Aramaki
Keyword(s):  
Guinea Pig ◽  
Single Channel ◽  
Hill Coefficient ◽  
Disulfonic Acid ◽  
Dependent Manner ◽  
Channel Activity ◽  
Patch Clamp Technique ◽  
Whole Cell ◽  
Cl Channels ◽  
Inside Out

Macroscopic and unitary currents through Ca(2+)-activated Cl- channels were examined in enzymatically isolated guinea-pig hepatocytes using whole-cell, excised outside-out and inside-out configurations of the patch-clamp technique. When K+ conductances were blocked and the intracellular Ca2+ concentration ([Ca2+]i) was set at 1 microM (pCa = 6), membrane currents were observed under whole-cell voltage-clamp conditions. The reversal potential of the current shifted by approximately 60 mV per 10-fold change in the external Cl- concentration. In addition, the current did not appear when Cl- was omitted from the internal and external solutions, indicating that the current was Cl- selective. The current was activated by increasing [Ca2+]i and was inactivated in Ca(2+)-free, 5 mM EGTA internal solution (pCa > 9). The current was inhibited by bath application of 9-anthracenecarboxylic acid (9-AC) and 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) in a voltage-dependent manner. In single channel recordings from outside-out patches, unitary current activity was observed, whose averaged slope conductance was 7.4 +/- 0.5 pS (n = 18). The single channel activity responded to extracellular Cl- changes as expected for a Cl- channel current. The open time distribution was best described by a single exponential function with mean open lifetime of 97.6 +/- 10.4 ms (n = 11), while at least two exponentials were required to fit the closed time distributions with a time constant for the fast component of 21.5 +/- 2.8 ms (n = 11) and that for the slow component of 411.9 +/- 52.0 ms (n = 11). In excised inside-out patch recordings, channel open probability was sensitive to [Ca2+]i. The relationship between [Ca2+]i and channel activity was fitted by the Hill equation with a Hill coefficient of 3.4 and the half-maximal activation was 0.48 microM. These results suggest that guinea-pig hepatocytes possess Ca(2+)-activated Cl- channels.

Swelling-induced and depolarization-induced C1-channels in normal and cystic fibrosis epithelial cells

1991 ◽  
Vol 261 (4) ◽  
pp. C658-C674 ◽  
Author(s):  
C. K. Solc ◽  
J. J. Wine
Keyword(s):  
Cystic Fibrosis ◽  
Epithelial Cells ◽  
Current Density ◽  
Single Channel ◽  
Cell Swelling ◽  
Disulfonic Acid ◽  
Channel Activity ◽  
Whole Cell ◽  
Cl Channels ◽  
Single Channel Currents

Cl- currents induced by cell swelling were characterized at the whole cell and single-channel levels in primary cultures of normal and cystic fibrosis (CF) epithelial cells and in the T84 cell line. Currents recorded in normal and CF cells were indistinguishable. At 22-24 degrees C with isotonic CsCl in the pipette, initial whole cell outward current density at 100 mV in unswollen cells was 2-4 pA/pF. The current density increased with time during whole cell recording up to 100 pA/pF in isotonic solutions and up to 200 pA/pF in a hypotonic bath, though values typically ranged between 10 and 70 pA/pF. Currents were outwardly rectifying, active at negative voltages, started to inactivate above approximately 40 mV, and were blocked by 4,4'-dinitrostilbene-2,2'-disulfonic acid (DNDS). Single Cl- channels (approximately 50 pS near 0 mV) with an outwardly rectifying current-voltage relation were recorded in cell-attached and outside-out patches from swollen cells. The channels were mostly open at negative voltages and inactivated at positive voltages with a voltage dependence similar to the whole cell currents. Channel activity decreased rapidly (channel rundown) after seal formation. After swelling-induced channel activity had ceased, outwardly rectifying, depolarization-induced Cl- channels (ORDIC channels) were activated in some patches. The swelling-induced and ORDIC single-channel currents were similar, but some consistent differences were observed. ORDIC channels were often closed at resting voltages (-70 to -50 mV), while swelling-induced channels were always open in this voltage range. In addition, ORDIC channels started to inactivate at more positive voltages (approximately 90 vs. approximately 50 mV), rectified more, and had smaller conductances (approximately 25 pS near 0 mV), shorter mean open durations (approximately 70 vs. approximately 350 ms), and more open-channel noise than swelling-induced channels. The two types of currents might arise from separate channel proteins or from a single channel molecule in different states.

Ca(2+)-dependent Cl- channels in undifferentiated human colonic cells (HT-29). I. Single-channel properties

1993 ◽  
Vol 264 (4) ◽  
pp. C968-C976 ◽  
Author(s):  
A. P. Morris ◽  
R. A. Frizzell
Keyword(s):  
Single Channel ◽  
Voltage Sensitivity ◽  
Channel Activity ◽  
Patch Clamp Technique ◽  
Channel Activation ◽  
Whole Cell ◽  
Multiple Channel ◽  
Cl Channel ◽  
Cl Channels ◽  
Ht 29

The patch-clamp technique was combined with camera-based intracellular Ca2+ concentration ([Ca2+]i) imaging to identify the single-channel basis of the Ca(2+)-dependent Cl- conductance in human colonic adenocarcinoma cells (HT-29). Cl- channels were activated when membrane patches were excised into solutions containing high (1 microM) Ca2+ concentrations. Their single-channel conductance, measured by amplitude histogram analysis, averaged 13 pS at -90 mV and 16 pS at +90 mV membrane potential (MP). In multiple channel patches, Cl- currents showed properties similar to Ca(2+)-activated whole cell currents: outward rectification and time-dependent activation at depolarizing MP. Channel activity disappeared shortly after patch excision from the cell. In cell-attached patches, Cl- channel opening was infrequent at resting [Ca2+]i values (96 +/- 18 nM), but when [Ca2+]i was increased by the Ca2+ ionophore ionomycin (1 microM), Cl- channels were activated with a time course that paralleled the [Ca2+]i rise. Repetitive ionophore exposure produced equivalent rises in [Ca2+]i, but the corresponding Cl- channel activity became progressively reduced. The Ca(2+)-mediated agonist neurotensin (50 nM) elicited a transient Cl- channel activation that preceded the generalized cellular [Ca2+]i rise. Channel activation with neurotensin occurred in the absence of pipette Ca2+ but was abolished by preloading cells with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid. Thus, in response to the Ca(2+)-mediated agonist neurotensin, Cl- channel activation results from Ca2+ mobilization from intracellular pools localized within the vicinity of the plasma membrane. The Ca2+ dependency, voltage sensitivity, and kinetics of this 15-pS Cl- channel indicate that it is the basis of the whole cell Ca(2+)-activated Cl- current.

P2X receptors in mouse Leydig cells

2006 ◽  
Vol 290 (4) ◽  
pp. C1009-C1017 ◽  
Author(s):  
Luiz Artur Poletto Chaves ◽  
Endrigo Piva Pontelli ◽  
Wamberto Antonio Varanda
Keyword(s):  
Leydig Cells ◽  
Pyridoxal Phosphate ◽  
Hill Coefficient ◽  
Disulfonic Acid ◽  
Inward Rectification ◽  
Dependent Manner ◽  
Patch Clamp Technique ◽  
Concentration Dependent Manner ◽  
Apparent Dissociation Constant ◽  
Whole Cell

ATP-activated currents were studied in Leydig cells of mice with the patch-clamp technique. Whole cell currents were rapidly activating and slowly desensitizing (55% decrement from the peak value on exposure to 100 μM ATP for 60 s), requiring 3 min of washout to recover 100% of the response. The concentration-response relationships for ATP, adenosine 5′- O-(3-thiotriphosphate) (ATPγS), and 2-methylthio-ATP (2-MeS-ATP) were described by the Hill equation with a concentration evoking 50% of maximal ATP response ( Kd) of 44, 110, and 637 μM, respectively, and a Hill coefficient of 2. The order of efficacy of agonists was ATP ≥ ATPγS > 2-MeS-ATP > 2′,3′- O-(4-benzoylbenzoyl)-ATP (BzATP). αβ-Methylene-ATP (αβ-MeATP), GTP, UTP, cAMP, and adenosine were ineffective. Suramin and pyridoxal phosphate-6-azophenyl-2′,4′-disulfonic acid (PPADS) blocked the responses in a concentration-dependent manner. The ATP-activated currents were dependent on extracellular pH, being maximal at pH 6.5 and decreasing with both acidification and alkalinization (apparent dissociation constant (p Ka) of 5.9 and 7.4, respectively). The whole cell current-voltage relationship showed inward rectification and reversed near 0 mV. Experiments performed in bi-ionic conditions for measurement of reversal potentials showed that this channel is highly permeable to calcium [permeability ( P)Ca/ PNa = 5.32], but not to chloride ( PCl/ PNa = 0.03) or N-methyl-d-glucamine (NMDG) ( PNMDG/ PNa = 0.09). Unitary currents recorded in outside-out patches had a chord conductance of 27 pS (between −90 and −50 mV) and were inward rectifying. The average current passing through the excised patch decreased with time [time constant (τ) = 13 s], resembling desensitization of the macroscopic current. These findings indicate that the ATP receptor present in Leydig cells shows properties most similar to those of cloned homomeric P2X2.

Propofol Inhibits Cardiac L-Type Calcium Current in Guinea Pig Ventricular Myocytes

1996 ◽  
Vol 84 (3) ◽  
pp. 626-635 ◽  
Author(s):  
Ching-Yue Yang ◽  
Chih-Shung Wong ◽  
Chuan-Cheng Yu ◽  
Hsiang-Ning Luk ◽  
Cheng-I Lin
Keyword(s):  
Steady State ◽  
Guinea Pig ◽  
Time Course ◽  
Single Channel ◽  
Ventricular Myocytes ◽  
Hill Coefficient ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Inactivation Curve ◽  
Whole Cell

Background Propofol may exert negative inotropic and chronotropic actions in the heart. Single-channel studies show that propofol affects the kinetics of opening and closing of cardiac L-type calcium channels (ICa(L)) without altering channel conductance. The aim of this study was to investigate the mechanisms of depressant effects of propofol on cardiac whole-cell ICa(L). Methods Single ventricular myocytes were freshly dissciated from guinea pig hearts using enzymatic isolation. One-suction electrode voltage-clamp technique (whole-cell mode) was used. LCa(L) was separated from other contaminated ionic currents. Propofol was applied in the commercial 10% Intralipid emulsion formula (Zeneca, UK). Results In isolated cardiomyocytes, propofol significantly inhibited whole-cell ICa(L) in a concentration-dependent manner (K D = 52.0 microM; Hill coefficient = 1.3). The solvent (Intralipid) did not affect ICa(L). Propofol decreased ICa(L) at all potentials tested along the voltage axis and reduced the slope conductance. The threshold potential for activation and the peak potential of the current-voltage relationship were not changed by propofol. The steady-state activation curves overlapped in the absence and the presence of 56 microM propofol. In contrast, the steady-state inactivation curve was shifted in the hyperpolarizing direction. The time course of the recovery from inactivation was delayed by 56 microM propofol. The blocking action on ICa(L) of propofol shows marked resting block and use-dependent block. Propofol caused more pronounced inhibition at a higher stimulation frequency. The effect of propofol on the inactivation process was even more clear on ICa(L). Conclusions The authors conclude tha propofol, at supratherapeutic concentrations, inhibits cardiac ICa(L). This inhibition is mainly due to a shift of inactivation curve and a reduction in slope conductance.

scholarly journals Heterogeneity of chloride channels in the apical membrane of isolated mitochondria-rich cells from toad skin.

1996 ◽  
Vol 108 (5) ◽  
pp. 421-433 ◽  
Author(s):  
J B Sørensen ◽  
E H Larsen
Keyword(s):  
Chloride Channels ◽  
Single Channel ◽  
Apical Membrane ◽  
Single Cells ◽  
Membrane Depolarization ◽  
Equilibrium Potential ◽  
Toad Skin ◽  
Patch Clamp Technique ◽  
Cl Channels ◽  
Inside Out

The isolated epithelium of toad skin was disintegrated into single cells by treatment with collagenase and trypsine. Chloride channels of cell-attached and excised inside-out apical membrane-patches of mitochondria-rich cells were studied by the patch-clamp technique. The major population of Cl- channels constituted small 7-pS linear channels in symmetrical solutions (125 mM Cl-). In cell-attached and inside-out patches the single channel i/V-relationship could be described by electrodiffusion of Cl- with a Goldmann-Hodgkin-Katz permeability of, PCl = 1.2 x 10(-14) - 2.6 x 10(-14) cm3. s-1. The channel exhibited voltage-independent activity and could be activated by cAMP. This channel is a likely candidate for mediating the well known cAMP-induced transepithelial Cl- conductance of the amphibian skin epithelium. Another population of Cl- channels exhibited large, highly variable conductances (upper limit conductances, 150-550 pS) and could be activated by membrane depolarization. A group of intermediate-sized Cl(-)-channels included: (a) channels (mean conductance, 30 pS) with linear or slightly outwardly rectifying i/V-relationships and activity occurring in distinct "bursts," (b) channels (conductance-range, 10-27 pS) with marked depolarization-induced activity, and (c) channels with unresolvable kinetics. The variance of current fluctuations of such "noisy" patches exhibited a minimum close to the equilibrium-potential for Cl-. With channels occurring in only 38% of sealed patches and an even lower frequency of voltage-activated channels, the chloride conductance of the apical membrane of mitochondria-rich cells did not match quantitatively that previously estimated from macroscopic Ussing-chamber experiments. From a qualitative point of view, however, we have succeeded in demonstrating the existence of Cl-channels in the apical membrane with features comparable to macroscopic predictions, i.e., activation of channel gating by cAMP and, in a few patches, also by membrane depolarization.

Delayed-rectifier potassium channel activity in isolated membrane patches of guinea pig ventricular myocytes

1991 ◽  
Vol 260 (4) ◽  
pp. H1390-H1393 ◽  
Author(s):  
K. B. Walsh ◽  
J. P. Arena ◽  
W. M. Kwok ◽  
L. Freeman ◽  
R. S. Kass
Keyword(s):  
Guinea Pig ◽  
Single Channel ◽  
Ventricular Myocytes ◽  
Outward Current ◽  
Time Dependent ◽  
Delayed Rectifier ◽  
Potential Range ◽  
Ammonium Compound ◽  
Channel Activity ◽  
Patch Clamp Technique

When the patch-clamp technique was used, a slowly activating, time-dependent outward current was identified in both cell-attached and excised membrane patches obtained from guinea pig ventricular myocytes. This macroscopic patch current was present in approximately 50% of patches studied and could be observed both in the presence and absence of unitary single channel activity (i.e., ATP-sensitive K+ channels). The time course of activation of the patch current resembled that of the whole cell delayed-rectifier K+ current (IK) recorded under similar ionic conditions, and the patch current and IK were activated over a similar membrane potential range. The time-dependent patch current could be eliminated when the Nernst potential for K+ equaled that of the pulse voltage. The patch current was inhibited by external addition of the tertiary ammonium compound LY 97241 (50 microM) and was augmented after internal application of the catalytic subunit of adenosine 3',5'-cyclic monophosphate-dependent protein kinase (500 nM). Deactivating tail currents with kinetics similar to those of IK could be recorded to cell-attached and excised patches. Unitary single channel events underlying the time-dependent patch current could not be resolved despite various attempts to increase single channel conductance. Thus our results suggest that a major component of delayed rectification in guinea pig ventricular cells is due to the activity of a high-density, extremely low conductance K+ channel.

Depression of delayed outward K+ current by Co2+ in guinea pig ventricular myocytes

1991 ◽  
Vol 261 (1) ◽  
pp. C23-C31 ◽  
Author(s):  
Z. Fan ◽  
M. Hiraoka
Keyword(s):  
Guinea Pig ◽  
Ventricular Myocytes ◽  
Hill Coefficient ◽  
Maximal Response ◽  
Fluctuation Analysis ◽  
Dependent Manner ◽  
Surface Charges ◽  
Patch Clamp Technique ◽  
Voltage Range ◽  
K Current

Effects of Co2+ on the delayed outward K+ current (IK) in guinea pig ventricular myocytes were studied using the whole cell patch-clamp technique. IK was activated by depolarizing voltage pulses positive to -30 mV and reached half-maximal activation at +24 mV. Co2+ shifted the activation curve to a more depolarized voltage range in a concentration-dependent manner, with a Co2+ concentration at which half-maximal response occurs (IC50) of 8 mM and a saturation value of +38 mV. The voltage dependency of IK gatings showed a shift similar to that of activation. In both cases the shift could be explained by screening of surface potential. The density of total negative surface charges sensed by Co2+ was estimated to be 1 e/225 A2. Co2+ also reduced the fully activated IK [IK(full)], and the dose-response curve had a Hill coefficient of 0.5 and an IC50 of 1 mM at 0 mV. Depression of IK(full) was mainly voltage independent. The single-channel unitary current estimated by fluctuation analysis was approximately 0.1 pA at -30 mV either in the absence or presence of Co2+. Therefore, the depression of IK(full) is due to an equivalent reduction in the number of functional channels. It is concluded that Co2+ depressed IK through multiple mechanisms.

Adenosine triphosphate regulates the activity of guinea pig Cav1.2 channel by direct binding to the channel in a dose-dependent manner

2014 ◽  
Vol 306 (9) ◽  
pp. C856-C863 ◽  
Author(s):  
Rui Feng ◽  
Jianjun Xu ◽  
Etsuko Minobe ◽  
Asako Kameyama ◽  
Lei Yang ◽  
...  
Keyword(s):  
Amino Acids ◽  
Guinea Pig ◽  
Terminal Region ◽  
Atp Binding ◽  
Dependent Manner ◽  
Channel Activity ◽  
Fusion Peptides ◽  
Patch Clamp Technique ◽  
Binding Effect ◽  
Dose Dependent

The present study is to investigate the mechanism by which ATP regulates Cav1.2 channel activity. Ventricular tissue was obtained from adult guinea pig hearts using collagenase. Ca2+ channel activity was monitored using the patch-clamp technique. Proteins were purified using wheat germ agglutinin-Sepharose, and the concentration was determined using the Coomassie brilliant blue technique. ATP binding to the Cav1.2 channel was examined using the photoaffinity method. EDA-ATP-biotin maintains Ca2+ channel activity in inside-out membrane patches. ATP directly bound to the Cav1.2 channel in a dose-dependent manner, and at least two molecules of ATP bound to one molecule of the Cav1.2 channel. Low levels of calmodulin (CaM) increased ATP binding to the Cav1.2 channel, but higher levels of CaM decreased ATP binding to the Cav1.2 channel. In addition, Ca2+ was another regulator for ATP binding to the Cav1.2 channel. Furthermore, ATP bound to GST-fusion peptides of NH2-terminal region (amino acids 6–140) and proximal COOH-terminal region (amino acids 1,509–1,789) of the main subunit (α1C) of the Cav1.2 channel. Our data suggest that ATP might regulate Cav1.2 channel activity by directly binding to the Cav1.2 channel in a dose-dependent manner. In addition, the ATP-binding effect to the Cav1.2 channel was both CaM- and Ca2+ dependent.

Large-conductance Ca2+-activated potassium channel in mitochondria of endothelial EA.hy926 cells

2013 ◽  
Vol 304 (11) ◽  
pp. H1415-H1427 ◽  
Author(s):  
Piotr Bednarczyk ◽  
Agnieszka Koziel ◽  
Wieslawa Jarmuszkiewicz ◽  
Adam Szewczyk
Keyword(s):  
Potassium Channel ◽  
Mitochondrial Membrane ◽  
Single Channel ◽  
Dependent Manner ◽  
Channel Activity ◽  
Inner Mitochondrial Membrane ◽  
Patch Clamp Technique ◽  
Open Probability ◽  
Α Subunit ◽  
Ea.Hy926 Cells

In the present study, we describe the existence of a large-conductance Ca2+-activated potassium (BKCa) channel in the mitochondria of the human endothelial cell line EA.hy926. A single-channel current was recorded from endothelial mitoplasts (i.e., inner mitochondrial membrane) using the patch-clamp technique in the mitoplast-attached mode. A potassium-selective current was recorded with a mean conductance equal to 270 ± 10 pS in a symmetrical 150/150 mM KCl isotonic solution. The channel activity, which was determined as the open probability, increased with the addition of calcium ions and the potassium channel opener NS1619. Conversely, the activity of the channel was irreversibly blocked by paxilline and iberiotoxin, BKCa channel inhibitors. The open-state probability was found to be voltage dependent. The substances known to modulate BKCa channel activity influenced the bioenergetics of mitochondria isolated from human endothelial EA.hy926 cells. In isolated mitochondria, 100 μM Ca2+, 10 μM NS1619, and 0.5 μM NS11021 depolarized the mitochondrial membrane potential and stimulated nonphosphorylating respiration. These effects were blocked by iberiotoxin and paxilline in a potassium-dependent manner. Under phosphorylating conditions, NS1619-induced, iberiotoxin-sensitive uncoupling diverted energy from ATP synthesis during the phosphorylating respiration of the endothelial mitochondria. Immunological analysis with antibodies raised against proteins of the plasma membrane BKCa channel identified a pore-forming α-subunit and an auxiliary β2-subunit of the channel in the endothelial mitochondrial inner membrane. In conclusion, we show for the first time that the inner mitochondrial membrane in human endothelial EA.hy926 cells contains a large-conductance calcium-dependent potassium channel with properties similar to those of the surface membrane BKCa channel.

A maxi Cl(−) channel in cultured pavement cells from the gills of the freshwater rainbow trout Oncorhynchus mykiss

2001 ◽  
Vol 204 (10) ◽  
pp. 1783-1794 ◽  
Author(s):  
M.J. O'Donnell ◽  
S.P. Kelly ◽  
C.A. Nurse ◽  
C.M. Wood
Keyword(s):  
Rainbow Trout ◽  
Oncorhynchus Mykiss ◽  
Single Channel ◽  
Primary Cultures ◽  
Channel Activity ◽  
Patch Clamp Technique ◽  
Pavement Cells ◽  
Cl Channel ◽  
Rainbow Trout Oncorhynchus Mykiss ◽  
Inside Out

Primary cultures of pavement cells from the gills of a freshwater fish, the rainbow trout Oncorhynchus mykiss, have been studied for the first time using the patch-clamp technique. Gigaohm seals were obtained in approximately 95 % of cells studied, and channel activity was evident in a high proportion (>90 %). A large-conductance Cl(−) channel was evident in 6 % of cell-attached and in 31 % of inside-out patches. Single-channel conductance in inside-out patches was 372 pS, and current/voltage relationships were linear over the range −60 to +60 mV. The channel was activated by patch excision, and activation was often associated with polarization of the patch. The mean number of channels per patch was 1.9, and there were several subconductance states. The relationship between channel activity (NP(o)) and voltage was in the form of an inverted U, and channel activity was highest between 0 and +20 mV. Large-conductance Cl(−) channels showed a progressive time-dependent reduction in current in response to sustained polarization to voltages outside the range −20 mV to +20 mV. Permeability ratios (P) of Cl(−) to other anions were P(HCO3)/P(Cl)=0.81, P(SO4)/P(Cl)=0.31 and P(isethionate)/P(Cl)=0.53. The channel was blocked by Zn(2+), SITS, DIDS and diphenylamine carboxylate. This is the first description of a large-conductance Cl(−) channel in gill cells from freshwater or marine species. Possible functions of the channel are discussed.

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