Activation of cardiac ryanodine receptors by the calcium channel agonist FPL-64176

2002 ◽  
Vol 283 (1) ◽  
pp. H331-H338 ◽  
Author(s):  
J. Andrew Wasserstrom ◽  
Leslie A. Wasserstrom ◽  
Andrew J. Lokuta ◽  
James E. Kelly ◽  
Sireen T. Reddy ◽  
...  
Keyword(s):  
Single Channel ◽  
Ryanodine Receptors ◽  
Channel Activity ◽  
Open Probability ◽  
Release Channel ◽  
Cardiac Sarcoplasmic Reticulum ◽  
Significant Difference ◽  
Single Channel Activity ◽  
Control Versus ◽  
Channel Agonist

We investigated the possibility that the Ca2+ channel agonist FPL-64176 (FPL) might also activate the cardiac sarcoplasmic reticulum (SR) Ca2+ release channel ryanodine receptor (RyR). The effects of FPL were tested on single channel activity of purified and crude vesicular RyR (RyR2) isolated from human and dog hearts using the planar lipid bilayer technique. FPL (100–200 μM) increased single channel open probability ( P o) when added to the cytoplasmic side of the channel ( P o = 0.070 ± 0.021 in control RyR2; 0.378 ± 0.086 in 150 μM FPL, n = 9, P < 0.01) by prolonging open times and decreasing closed times without changing current magnitude. FPL had no effect on P o when added to the trans (luminal) side of the bilayer ( P o = 0.079 ± 0.036 in control and 0.103 ± 0.066 in FPL, n = 4, no significant difference). The bell-shaped [Ca2+] dependence of [3H]ryanodine binding and of P o was altered by FPL, suggesting that the mechanism by which FPL increases channel activity is by an increase in Ca2+-induced activation at low [Ca2+] (without a change in threshold) and suppression of Ca2+-induced inactivation at high [Ca2+]. However, the fact that inactivation was restored at elevated [Ca2+] suggests a competitive interaction between Ca2+ and FPL on inactivation. FPL had no effect on RyR skeletal channels (RyR1), where P o was 0.039 ± 0.005 in control versus 0.030 ± 0.006 in 150 μM FPL (no significant difference). These results suggest that, in addition to its ability to activate the L-type Ca2+channels, FPL activates cardiac RyR2 primarily by reducing the Ca2+ sensitivity of inactivation.

Activation of purified cardiac ryanodine receptors by dihydropyridine agonists

2001 ◽  
Vol 280 (3) ◽  
pp. H1201-H1207 ◽  
Author(s):  
Toshio Sagawa ◽  
Manabu Nishio ◽  
Kazuko Sagawa ◽  
James E. Kelly ◽  
Andrew J. Lokuta ◽  
...  
Keyword(s):  
Single Channel ◽  
Ryanodine Receptors ◽  
Channel Activity ◽  
Allosteric Site ◽  
Open Probability ◽  
Release Channel ◽  
Inotropic Effects ◽  
Cytoplasmic Face ◽  
Single Channel Activity ◽  
Negative Inotropic Effects

Prior observations have raised the possibility that dihydropyridine (DHP) agonists directly affect the sarcoplasmic reticulum (SR) cardiac Ca2+ release channel [i.e., ryanodine receptor (RyR)]. In single-channel recordings of purified canine cardiac RyR, both DHP agonists (−)-BAY K 8644 and (+)-SDZ202-791 increased the open probability of the RyR when added to the cytoplasmic face of the channel. Importantly, the DHP antagonists nifedipine and (−)-SDZ202-791 had no competitive blocking effects either alone or after channel activation with agonist. Thus there is a stereospecific effect of SDZ202-791, such that the agonist activates the channel, whereas the antagonist has little effect on channel activity. Further experiments showed that DHP agonists changed RyR activation by suppressing Ca2+-induced inactivation of the channel. We concluded that DHP agonists can also influence RyR single-channel activity directly at a unique allosteric site located on the cytoplasmic face of the channel. Similar results were obtained in human purified cardiac RyR. An implication of these data is that RyR activation by DHP agonists is likely to cause a loss of Ca2+ from the SR and to contribute to the negative inotropic effects of these agents reported by other investigators. Our results support this notion that the negative inotropic effects of DHP agonists result in part from direct alteration in the activity of RyRs.

scholarly journals Interactions of a Reversible Ryanoid (21-Amino-9α-Hydroxy-Ryanodine) with Single Sheep Cardiac Ryanodine Receptor Channels

1998 ◽  
Vol 112 (1) ◽  
pp. 55-69 ◽  
Author(s):  
Bhavna Tanna ◽  
William Welch ◽  
Luc Ruest ◽  
John L. Sutko ◽  
Alan J. Williams
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Binding Site ◽  
Single Channel ◽  
Single Channels ◽  
Open Probability ◽  
Release Channel ◽  
Cardiac Sarcoplasmic Reticulum ◽  
Channel Protein ◽  
High Affinity ◽  
Conductance State

The binding of ryanodine to a high affinity site on the sarcoplasmic reticulum Ca2+-release channel results in a dramatic alteration in both gating and ion handling; the channel enters a high open probability, reduced-conductance state. Once bound, ryanodine does not dissociate from its site within the time frame of a single channel experiment. In this report, we describe the interactions of a synthetic ryanoid, 21-amino-9α-hydroxy-ryanodine, with the high affinity ryanodine binding site on the sheep cardiac sarcoplasmic reticulum Ca2+-release channel. The interaction of 21-amino-9α-hydroxy-ryanodine with the channel induces the occurrence of a characteristic high open probability, reduced-conductance state; however, in contrast to ryanodine, the interaction of this ryanoid with the channel is reversible under steady state conditions, with dwell times in the modified state lasting seconds. By monitoring the reversible interaction of this ryanoid with single channels under voltage clamp conditions, we have established a number of novel features of the ryanoid binding reaction. (a) Modification of channel function occurs when a single molecule of ryanoid binds to the channel protein. (b) The ryanoid has access to its binding site only from the cytosolic side of the channel and the site is available only when the channel is open. (c) The interaction of 21-amino-9α-hydroxy-ryanodine with its binding site is influenced strongly by transmembrane voltage. We suggest that this voltage dependence is derived from a voltage-driven conformational alteration of the channel protein that changes the affinity of the binding site, rather than the translocation of the ryanoid into the voltage drop across the channel.

Characterization of RyR1-slow, a ryanodine receptor specific to slow-twitch skeletal muscle

2000 ◽  
Vol 279 (5) ◽  
pp. R1889-R1898 ◽  
Author(s):  
Jeffery Morrissette ◽  
Le Xu ◽  
Alexandra Nelson ◽  
Gerhard Meissner ◽  
Barbara A. Block
Keyword(s):  
Skeletal Muscle ◽  
Single Channel ◽  
Fiber Type ◽  
Ryanodine Receptors ◽  
Open Probability ◽  
Dependent Inhibition ◽  
Single Channel Activity ◽  
Intracellular Ca ◽  
Slow Twitch ◽  
Fast Twitch

Two distinct skeletal muscle ryanodine receptors (RyR1s) are expressed in a fiber type–specific manner in fish skeletal muscle (11). In this study, we compare [3H]ryanodine binding and single channel activity of RyR1-slow from fish slow-twitch skeletal muscle with RyR1-fast and RyR3 isolated from fast-twitch skeletal muscle. Scatchard plots indicate that RyR1-slow has a lower affinity for [3H]ryanodine when compared with RyR1-fast. In single channel recordings, RyR1-slow and RyR1-fast had similar slope conductances. However, the maximum open probability (Po) of RyR1-slow was threefold less than the maximum Po of RyR1-fast. Single channel studies also revealed the presence of two populations of RyRs in tuna fast-twitch muscle (RyR1-fast and RyR3). RyR3 had the highest Po of all the RyR channels and displayed less inhibition at millimolar Ca2+. The addition of 5 mM Mg-ATP or 2.5 mM β,γ-methyleneadenosine 5′-triphosphate (AMP-PCP) to the channels increased the Po and [3H]ryanodine binding of both RyR1s but also caused a shift in the Ca2+ dependency curve of RyR1-slow such that Ca2+-dependent inactivation was attenuated. [3H]ryanodine binding data also showed that Mg2+-dependent inhibition of RyR1-slow was reduced in the presence of AMP-PCP. These results indicate differences in the physiological properties of RyRs in fish slow- and fast-twitch skeletal muscle, which may contribute to differences in the way intracellular Ca2+ is regulated in these muscle types.

Lactate inhibits Ca2+-activated Ca2+-channel activity from skeletal muscle sarcoplasmic reticulum

1997 ◽  
Vol 82 (2) ◽  
pp. 447-452 ◽  
Author(s):  
Terence G. Favero ◽  
, Anthony C. Zable ◽  
, David Colter ◽  
Jonathan J. Abramson
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Single Channel ◽  
Channel Activity ◽  
Release Channel ◽  
Muscle Lactate ◽  
Tension Development ◽  
Contraction Coupling ◽  
Single Channel Activity ◽  
High Concentrations

Favero, Terence G., Anthony C. Zable, David Colter, and Jonathan J. Abramson. Lactate inhibits Ca2+-activated Ca2+-channel activity from skeletal muscle sarcoplasmic reticulum. J. Appl. Physiol. 82(2): 447–452, 1997.—Sarcoplasmic reticulum (SR) Ca2+-release channel function is modified by ligands that are generated during about of exercise. We have examined the effects of lactate on Ca2+- and caffeine-stimulated Ca2+ release, [3H]ryanodine binding, and single Ca2+-release channel activity of SR isolated from rabbit white skeletal muscle. Lactate, at concentrations from 10 to 30 mM, inhibited Ca2+- and caffeine-stimulated [3H]ryanodine binding to and inhibited Ca2+- and caffeine-stimulated Ca2+ release from SR vesicles. Lactate also inhibited caffeine activation of single-channel activity in bilayer reconstitution experiments. These findings suggest that intense muscle activity, which generates high concentrations of lactate, will disrupt excitation-contraction coupling. This may lead to decreases in Ca2+ transients promoting a decline in tension development and contribute to muscle fatigue.

Modification of the gating of the cardiac sarcoplasmic reticulum Ca(2+)-release channel by H2O2 and dithiothreitol

1994 ◽  
Vol 267 (3) ◽  
pp. H1010-H1016 ◽  
Author(s):  
A. Boraso ◽  
A. J. Williams
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Single Channel ◽  
Inhibitory Response ◽  
Dependent Manner ◽  
Open Probability ◽  
Release Channel ◽  
Concentration Dependent Manner ◽  
Cardiac Sarcoplasmic Reticulum ◽  
Gating Mechanism ◽  
Cytosolic Side

The effect of hydrogen peroxide (H2O2) on the sheep cardiac sarcoplasmic reticulum (SR) Ca(2+)-release channel has been investigated under voltage-clamp conditions after incorporation of native membrane vesicles into planar phospholipid bilayers. In the presence of micromolar activating calcium concentrations on the cytosolic side of the membrane, H2O2 (3-5 mM) increased open probability of the channels. H2O2 did not affect the conductance of the channel or the response to activating compounds, such as ATP and caffeine. H2O2 did not alter the inhibitory response to magnesium or the modification of channels by ryanodine. At subactivating calcium concentrations (approximately 45 pM) on the cytosolic side of the membrane, 5 mM H2O2 was still able to open the channel. Analysis of single-channel open and closed lifetimes suggested that H2O2 had a direct effect on the gating mechanism of the channel. Open probability of the SR Ca(2+)-release channel is reduced by millimolar concentrations of dithiothreitol, a sulfhydryl-protecting compound, in a concentration-dependent manner. In conclusion, it is probable that H2O2 activates the SR Ca(2+)-release channel via an oxidation of cysteine thiol groups in the channel protein.

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.

Activation of cardiac ryanodine receptors by cardiac glycosides

2002 ◽  
Vol 282 (3) ◽  
pp. H1118-H1126 ◽  
Author(s):  
Toshio Sagawa ◽  
Kazuko Sagawa ◽  
James E. Kelly ◽  
Robert G. Tsushima ◽  
J. Andrew Wasserstrom
Keyword(s):  
Lipid Bilayers ◽  
Cardiac Glycosides ◽  
Single Channel ◽  
Lower Sensitivity ◽  
Maximal Effect ◽  
Channel Activity ◽  
Cardiac Sarcoplasmic Reticulum ◽  
Channel Activation ◽  
Single Channel Activity ◽  
Ryr2 Channel

This study investigated the effects of cardiac glycosides on single-channel activity of the cardiac sarcoplasmic reticulum (SR) Ca2+ release channels or ryanodine receptor (RyR2) channels and how this action might contribute to their inotropic and/or toxic actions. Heavy SR vesicles isolated from canine left ventricle were fused with artificial planar lipid bilayers to measure single RyR2 channel activity. Digoxin and actodigin increased single-channel activity at low concentrations normally associated with therapeutic plasma levels, yielding a 50% of maximal effect of ∼0.2 nM for each agent. Channel activation by glycosides did not require MgATP and occurred only when digoxin was applied to the cytoplasmic side of the channel. Similar results were obtained in human RyR2 channels; however, neither the crude skeletal nor the purified cardiac channel was activated by glycosides. Channel activation was dependent on [Ca2+] on the luminal side of the bilayer with maximal stimulation occurring between 0.3 and 10 mM. Rat RyR2 channels were activated by digoxin only at 1 μM, consistent with the lower sensitivity to glycosides in rat heart. These results suggest a model in which RyR2 channel activation by digoxin occurs only when luminal [Ca2+] was increased above 300 μM (in the physiological range). Consequently, increasing SR load (by Na+ pump inhibition) serves to amplify SR release by promoting direct RyR2 channel activation via a luminal Ca2+-sensitive mechanism. This high-affinity effect of glycosides could contribute to increased SR Ca2+ release and might play a role in the inotropic and/or toxic actions of glycosides in vivo.

Acetylcholine-sensitive potassium channels in human atrial myocytes

1990 ◽  
Vol 259 (6) ◽  
pp. H1730-H1735 ◽  
Author(s):  
R. Sato ◽  
I. Hisatome ◽  
J. A. Wasserstrom ◽  
C. E. Arentzen ◽  
D. H. Singer
Keyword(s):  
Single Channel ◽  
K Channel ◽  
Channel Activity ◽  
Atrial Myocytes ◽  
Open Probability ◽  
Human Atrial Myocytes ◽  
Open Time ◽  
Patch Pipette ◽  
Single Channel Activity ◽  
Gamma S

Single channel recording techniques were used to study acetylcholine (ACh)-sensitive K+ channel activity in human atrial myocytes isolated from specimens obtained during corrective cardiac surgery. Under conditions of cell-attached patch, the presence of ACh in the patch pipette activated K+ channels. Single channel activity occurred in periodic bursts. The channels exhibited a slope conductance of 46 +/- 2 pS inwardly (means +/- SD, n = 4). During a burst, both open and closed time histograms were fitted by a single exponential curve, suggesting the existence of one open and one closed state during a burst. Open probability increased directly with ACh concentration without affecting open time. The channel could be activated by GTP and guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) (in the presence and absence of ACh in the pipette, respectively). Slope conductance, the response to GTP and GTP gamma S, and the independence of activation from Ca2+ were similar to those for other species. In contrast, sensitivity to ACh appeared diminished compared with frog atrial myocytes.

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