An anion channel of sarcoplasmic reticulum incorporated into planar lipid bilayers: Single-channel behavior and conductance properties

1987 ◽  
Vol 99 (2) ◽  
pp. 103-111 ◽  
Author(s):  
Manabu Tanifuji ◽  
Masahiro Sokabe ◽  
Michiki Kasai
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Lipid Bilayers ◽  
Single Channel ◽  
Anion Channel ◽  
Planar Lipid Bilayers

Single cardiac sarcoplasmic reticulum Ca2+-release channel: activation by caffeine

1989 ◽  
Vol 256 (2) ◽  
pp. H328-H333 ◽  
Author(s):  
E. Rousseau ◽  
G. Meissner
Keyword(s):  
Steady State ◽  
Sarcoplasmic Reticulum ◽  
Lipid Bilayers ◽  
Single Channel ◽  
Ruthenium Red ◽  
Planar Lipid Bilayers ◽  
Release Channel ◽  
Cardiac Sarcoplasmic Reticulum ◽  
Channel Activation ◽  
Contraction Coupling

Caffeine is thought to affect excitation-contraction coupling in cardiac muscle by activating the sarcoplasmic reticulum (SR) Ca2+-release channel. The effect of caffeine at the single channel level was studied by incorporating canine cardiac SR vesicles into planar lipid bilayers. Cardiac Ca2+-release channels were activated in a steady-state manner by millimolar cis-caffeine and displayed a unitary conductance (77 pS in 50 mM Ca2+ trans) similar to that previously observed for the Ca2+-activated cardiac channel. The caffeine-activated channel was moderately sensitive to the voltage applied across the bilayer, was sensitive to further activation by ATP, and was inhibited by Mg2+ and ruthenium red. Kinetic analysis showed that at low Ca2+ concentration, caffeine activated the channel by increasing the frequency and the duration of open events.

Ryanodine modifies conductance and gating behavior of single Ca2+ release channel

1987 ◽  
Vol 253 (3) ◽  
pp. C364-C368 ◽  
Author(s):  
E. Rousseau ◽  
J. S. Smith ◽  
G. Meissner
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Lipid Bilayers ◽  
Single Channel ◽  
Ruthenium Red ◽  
Planar Lipid Bilayers ◽  
Open Probability ◽  
Release Channel ◽  
Excitation Contraction Coupling ◽  
Contraction Coupling

Ryanodine affects excitation-contraction coupling in skeletal and cardiac muscle by specifically interacting with the sarcoplasmic reticulum (SR) Ca2+ release channel. The effect of the drug at the single channel level was studied by incorporating skeletal and cardiac SR vesicles into planar lipid bilayers. The two channels were activated by micromolar free Ca2+ and millimolar ATP and inhibited by Mg2+ and ruthenium red. Addition of micromolar concentrations of ryanodine decreased about twofold the unit conductance of the Ca2+- and ATP-activated skeletal and cardiac channels. A second effect of ryanodine was to increase the open probability (Po) of the channels in such a way that Po was close to unity under a variety of activating and inactivating conditions. The effects of ryanodine were long lasting in that removal of ryanodine by perfusion did not return the channels into their fully conducting state.

Ryanodine receptor dysfunction in porcine stunned myocardium

1997 ◽  
Vol 273 (2) ◽  
pp. H796-H804 ◽  
Author(s):  
C. Valdivia ◽  
J. O. Hegge ◽  
R. D. Lasley ◽  
H. H. Valdivia ◽  
R. Mentzer
Keyword(s):  
Coronary Artery ◽  
Lipid Bilayers ◽  
Ryanodine Receptor ◽  
Myocardial Stunning ◽  
Single Channel ◽  
Stunned Myocardium ◽  
Wall Thickening ◽  
Planar Lipid Bilayers ◽  
Open Probability ◽  
Single Channel Recordings

We investigated the effects of myocardial stunning on the function of the two main Ca2+ transport proteins of the sarcoplasmic reticulum (SR), the Ca(2+)-adenosinetriphosphatase and the Ca(2+)-release channel or ryanodine receptor. Regional myocardial stunning was induced in open-chest pigs (n = 6) by a 10-min occlusion of the left anterior descending coronary artery (LAD) and 2 h reperfusion. SR vesicles isolated from the LAD-perfused region (stunned) and the normal left circumflex coronary artery (LC)-perfused region were used to assess the oxalate-supported 45Ca2+ uptake, [3H]ryanodine binding, and single-channel recordings of ryanodine-sensitive Ca(2+)-release channels in planar lipid bilayers. Myocardial stunning decreased LAD systolic wall thickening to 20% of preischemic values. The rate of SR 45Ca2+ uptake in the stunned LAD bed was reduced by 37% compared with that of the normal LC bed (P < 0.05). Stunning was also associated with a 38% reduction in the maximal density of high-affinity [3H]ryanodine binding sites (P < 0.05 vs. normal LC) but had no effect on the dissociation constant. The open probability of ryanodine-sensitive Ca(2+)-release channels determined by single channel recordings in planar lipid bilayers was 26 +/- 2% for control SR (n = 33 channels from 3 animals) and 14 +/- 2% for stunned SR (n = 21 channels; P < 0.05). This depressed activity of SR function observed in postischemic myocardium could be one of the mechanisms underlying myocardial stunning.

A cloned renal epithelial Na+ channel protein displays stretch activation in planar lipid bilayers

1995 ◽  
Vol 268 (6) ◽  
pp. C1450-C1459 ◽  
Author(s):  
M. S. Awayda ◽  
I. I. Ismailov ◽  
B. K. Berdiev ◽  
D. J. Benos
Keyword(s):  
Hydrostatic Pressure ◽  
Pressure Gradient ◽  
Lipid Bilayers ◽  
Single Channel ◽  
Na Channel ◽  
Planar Lipid Bilayers ◽  
Stretch Activation ◽  
Hydrostatic Pressure Gradient ◽  
Epithelial Na Channel

We have previously cloned a bovine renal epithelial channel homologue (alpha-bENaC) belonging to the epithelial Na+ channel (ENaC) family. With the use of a rabbit nuclease-treated in vitro translation system, mRNA coding for alpha-bENaC was translated and the polypeptide products were reconstituted into liposomes. On incorporation into planar lipid bilayers, in vitro-translated alpha-bENaC protein 1) displayed voltage-independent Na+ channel activity with a single-channel conductance of 40 pS, 2) was mechanosensitive in that the single-channel open probability was maximally activated with a hydrostatic pressure gradient of 0.26 mmHg across the bilayer, 3) was blocked by low concentrations of amiloride [apparent inhibitory constant of amiloride (K(i)amil approximately 150 nM], and 4) was cation selective with a Li+:Na+:K+ permselectivity of 2:1:0.14 under nonstretched conditions. These pharmacological and selectivity characteristics were altered to a lower amiloride affinity (K(i)amil > 25 microM) and a lack of monovalent cation selectivity in the presence of a hydrostatic pressure gradient. This observation of stretch activation (SA) of alpha-bENaC was confirmed in dual electrode recordings of heterologously expressed alpha-bENaC whole cell currents in Xenopus oocytes swelled by the injection of 15 nl of a 100 mM KCl solution. We conclude that alpha-bENaC, and by analogy other ENaCs, represent a novel family of cloned SA channels.

Calcium-dependent halothane activation of sarcoplasmic reticulum calcium channels from frog skeletal muscle

1994 ◽  
Vol 266 (2) ◽  
pp. C391-C396 ◽  
Author(s):  
R. Bull ◽  
J. J. Marengo
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Calcium Channels ◽  
Lipid Bilayers ◽  
Single Channel ◽  
Free Calcium ◽  
Frog Skeletal Muscle ◽  
Time Constants ◽  
Calcium Dependent ◽  
Open Time

The effect of halothane on calcium channels present in sarcoplasmic reticulum membranes isolated from frog skeletal muscle was studied at the single channel level after fusing the isolated vesicles into planar lipid bilayers. Addition of 91 microM halothane to the cytosolic compartment containing 1 microM free calcium activated the channel by increasing fractional open time from 0.11 to 0.59, without changing the channel conductance. The activation of the channels by halothane was calcium dependent. At resting calcium concentrations in the cytosolic compartment, halothane failed to activate the channel, whereas maximal activation was found at 10 microM calcium. The free energy of halothane binding to the channel decreased from -5.8 kcal/mol at 1 microM calcium to -6.6 kcal/mol at 10 microM calcium. Halothane increased the open time constants and decreased the closed time constants, indicating that it binds to both the open and the closed configurations of the channel.

Opening of large-conductance calcium-activated potassium channels by the substituted benzimidazolone NS004

1994 ◽  
Vol 71 (5) ◽  
pp. 1873-1882 ◽  
Author(s):  
M. C. McKay ◽  
S. I. Dworetzky ◽  
N. A. Meanwell ◽  
S. P. Olesen ◽  
P. H. Reinhart ◽  
...  
Keyword(s):  
Rat Brain ◽  
Lipid Bilayers ◽  
Single Channel ◽  
Outward Current ◽  
Calcium Sensitivity ◽  
Bk Channels ◽  
Gh3 Cells ◽  
Xenopus Laevis Oocytes ◽  
Planar Lipid Bilayers ◽  
Whole Cell

1. We used electrophysiological techniques to examine the effects of 5-trifluoromethyl-1-(5-chloro-2-hydroxyphenyl)-1,3-dihydro-2H-benzimidaz ole- 2-one (NS004) on large-conductance calcium-activated potassium (BK) channels. 2. We used recordings from excised membrane patches (cell-attached and inside-out single-channel configurations) and whole-cell patch-clamp recordings to examine the effects of NS004 on single BK channels and whole-cell outward currents, respectively, in rat GH3 clonal pituitary tumor cells. We also tested NS004 on voltage-clamped BK channels isolated from rat brain plasma membrane preparations and reconstituted into planar lipid bilayers. Finally, we used two-electrode voltage-clamp techniques to study the effects of NS004 on currents expressed in Xenopus laevis oocytes by the recently described Slo BK clone from Drosophila. 3. In GH3 cells and in Xenopus oocytes expressing the Slo gene product NS004 produced an increase in an iberiotoxin- or tetraethylammonium-sensitive whole-cell outward current, respectively. NS004 produced a significant increase in the activity of single GH3 cell BK channels and rat brain BK channels reconstituted into planar lipid bilayers. In both systems this was characterized by an increase in channel mean open time, a decrease in interburst interval, and an apparent increase in channel voltage/calcium sensitivity. 4. These data indicate that NS004 could be useful for investigating the biophysical and molecular properties of BK channels and for determining the functional consequences of the opening of BK channels.

scholarly journals Divalent cation activation and inhibition of single calcium release channels from sheep cardiac sarcoplasmic reticulum.

1990 ◽  
Vol 95 (5) ◽  
pp. 981-1005 ◽  
Author(s):  
R H Ashley ◽  
A J Williams
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Lipid Bilayers ◽  
Calcium Release ◽  
Single Channel ◽  
Fluctuation Analysis ◽  
Open Probability ◽  
Cardiac Sarcoplasmic Reticulum ◽  
Channel Opening ◽  
Lifetime Analysis ◽  
Single Channel Currents

Single Ca2+ release channels from vesicles of sheep cardiac junctional sarcoplasmic reticulum have been incorporated into uncharged planar lipid bilayers. Single-channel currents were recorded from Ca2(+)-activated channels that had a Ca2+ conductance of approximately 90 pS. Channel open probability increased sublinearly as the concentration of free Ca2+ was raised at the myoplasmic face, and without additional agonists the channels could not be fully activated even by 100 microM free Ca2+. Lifetime analysis revealed a minimum of two open and three closed states, and indicates that Ca2+ activated the channels by interacting with at least one of the closed states to increase the rate of channel opening. Correlations between adjacent lifetimes suggested there were at least two pathways between the open- and closed-state aggregates. An analysis of bursting behavior also revealed correlations between successive burst lengths and the number of openings per burst. The latter had two geometric components, providing additional evidence for at least two open states. One component appeared to comprise unit bursts, and the lifetime of most of these fell within the dominant shorter open-time distribution associated with over 90% of all openings. A cyclic gating scheme is proposed, with channel activation regulated by the binding of Ca2+ to a closed conformation of the channel protein. Mg2+ may inhibit activation by competing for this binding site, but lifetime and fluctuation analysis suggested that once activated the channels continue to gate normally.

Cation channels from Tetrahymena cilia incorporated into planar lipid bilayers

1985 ◽  
Vol 249 (1) ◽  
pp. C177-C179 ◽  
Author(s):  
Y. Oosawa ◽  
M. Sokabe
Keyword(s):  
Lipid Bilayers ◽  
Single Channel ◽  
Cation Channel ◽  
Cation Channels ◽  
Planar Lipid Bilayers ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
Ciliary Membrane ◽  
Voltage Dependent

A single cation channel from Tetrahymena cilia was incorporated into planar lipid bilayers. This channel selected for K+, Na+, and Li+ over Cl- and gluconate-, and its single channel conductance (at +25 mV) was 211 +/- 8 pS (mean +/- SE) in 100 mM K+-gluconate. The channel was not voltage dependent and may contribute to the resting K+ conductance of ciliary membrane.

Ethanol enhances caffeine-induced Ca2+-release channel activation in skeletal muscle sarcoplasmic reticulum

1997 ◽  
Vol 272 (2) ◽  
pp. C622-C627 ◽  
Author(s):  
T. Oba ◽  
M. Koshita ◽  
M. Yamaguchi
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Lipid Bilayers ◽  
Skeletal Muscles ◽  
Single Channel ◽  
Channel Activity ◽  
Electrical Parameters ◽  
Open Probability ◽  
Release Channel ◽  
Channel Current ◽  
Open Time

When sarcoplasmic reticulum (SR) vesicles prepared from frog skeletal muscles were actively loaded with Ca2+, pretreatment of the SR with 2.2 mM (0.01%) ethanol for 30 s significantly potentiated 5 mM caffeine-induced release of Ca2+ from 16.7 +/- 3.7 nmol/mg protein in control without ethanol to 28.0 +/- 2.6 nmol/mg (P < 0.05, n = 5). Ethanol alone caused no release of Ca2+ from the SR. Exposure of the Ca2+-release channel, incorporated into planar lipid bilayers, to 2 mM caffeine significantly increased open probability (Po) and mean open time, but unitary conductance was not affected. Ethanol (2.2 mM) enhanced caffeine-induced Ca2+-release channel activity, with Po reaching 3.02-fold and mean open time 2.85-fold the values in the absence of ethanol. However, ethanol alone did not affect electrical parameters of single-channel current, over a concentration range of 2.2 mM (0.01%) to 217 mM (1%). The synergistic action of ethanol and caffeine on the channel activity could be attributable to enhancement of caffeine-induced release of Ca2+ from the SR vesicles in the presence of ethanol.

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