scholarly journals An Anionic Ryanoid, 10-O-succinoylryanodol, Provides Insights into the Mechanisms Governing the Interaction of Ryanoids and the Subsequent Altered Function of Ryanodine-receptor Channels

2003 ◽  
Vol 121 (6) ◽  
pp. 551-561 ◽  
Author(s):  
Bhavna Tanna ◽  
William Welch ◽  
Luc Ruest ◽  
John L. Sutko ◽  
Alan J. Williams
Keyword(s):  
Ryanodine Receptor ◽  
Transmembrane Potential ◽  
Voltage Dependence ◽  
Major Influence ◽  
Ionic Interactions ◽  
Receptor Affinity ◽  
Flexible Molecule ◽  
Ion Translocation ◽  
Conductance States ◽  
Conductance State

We have investigated the interactions of a novel anionic ryanoid, 10-O-succinoylryanodol, with individual mammalian cardiac muscle ryanodine receptor channels under voltage clamp conditions. As is the case for all ryanoids so far examined, the interaction of 10-O-succinoylryanodol with an individual RyR channel produces profound alterations in both channel gating and rates of ion translocation. In the continued presence of the ryanoid the channel fluctuates between periods of normal and modified gating, indicating a reversible interaction of the ligand with its receptor. Unlike the majority of ryanoids, we observe a range of different fractional conductance states of RyR in the presence of 10-O-succinoylryanodol. We demonstrate that 10-O-succinoylryanodol is a very flexible molecule and propose that each fractional conductance state arises from the interaction of a different conformer of the ryanoid molecule with the RyR channel. The probability of channel modification by 10-O-succinoylryanodol is dependent on the transmembrane holding potential. Comparison of the voltage dependence of channel modification by this novel anionic ryanoid with previous data obtained with cationic and neutral ryanoids reveals that the major influence of transmembrane potential on the probability of RyR channel modification by ryanoids results from an alteration in receptor affinity. These investigations also demonstrate that the charge of the ryanoid has a major influence on the rate of association of the ligand with its receptor indicating that ionic interactions are likely to be involved in this reaction.

scholarly journals The Interaction of a Neutral Ryanoid with the Ryanodine Receptor Channel Provides Insights into the Mechanisms by Which Ryanoid Binding Is Modulated by Voltage

2000 ◽  
Vol 116 (1) ◽  
pp. 1-10 ◽  
Author(s):  
Bhavna Tanna ◽  
William Welch ◽  
Luc Ruest ◽  
John L. Sutko ◽  
Alan J. Williams
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Ryanodine Receptor ◽  
Transmembrane Potential ◽  
Voltage Dependence ◽  
Voltage Drop ◽  
Release Channel ◽  
Receptor Affinity ◽  
A Site ◽  
Positively Charged ◽  
Receptor Channel

In an earlier investigation, we demonstrated that the likelihood of interaction of a positively charged ryanoid, 21-amino-9α-hydroxyryanodine, with the sarcoplasmic reticulum Ca2+-release channel (ryanodine receptor, RyR) is dependent on holding potential (Tanna, B., W. Welch, L. Ruest, J.L. Sutko, and A.J. Williams. 1998. J. Gen. Physiol. 112:55–69) and suggested that voltage dependence could result from either the translocation of the charged ligand to a site within the voltage drop across the channel or a voltage-driven alteration in receptor affinity. We now report experiments that allow us to assess the validity of these alternate mechanisms. Ryanodol is a neutral ryanoid that binds to RyR and induces modification of channel function. By determining the influence of transmembrane potential on the probability of channel modification by ryanodol and the rate constants of ryanodol association and dissociation, we demonstrate that the influence of voltage is qualitatively the same for both the neutral and positively charged ryanoids. These experiments establish that most, if not all, of the modification of ryanoid interaction with RyR by transmembrane holding potential results from a voltage-driven alteration in receptor affinity.

scholarly journals Ryanoid Modification of the Cardiac Muscle Ryanodine Receptor Channel Results in Relocation of the Tetraethylammonium Binding Site

2001 ◽  
Vol 117 (5) ◽  
pp. 385-394 ◽  
Author(s):  
Bhavna Tanna ◽  
William Welch ◽  
Luc Ruest ◽  
John L. Sutko ◽  
Alan J. Williams
Keyword(s):  
Binding Site ◽  
Ryanodine Receptor ◽  
Single Channel ◽  
Voltage Drop ◽  
Structural Features ◽  
Channel Structure ◽  
Open Probability ◽  
Voltage Dependent ◽  
Conductance States ◽  
Conductance State

The interaction of ryanodine and derivatives of ryanodine with the high affinity binding site on the ryanodine receptor (RyR) channel brings about a characteristic modification of channel function. In all cases, channel open probability increases dramatically and single-channel current amplitude is reduced. The amplitude of the ryanoid-modified conductance state is determined by structural features of the ligand. An investigation of ion handling in the ryanodine-modified conductance state has established that reduced conductance results from changes in both the affinity of the channel for permeant ions and the relative permeability of ions within the channel (Lindsay, A.R.G., A. Tinker, and A.J. Williams. 1994. J. Gen. Physiol. 104:425–447). It has been proposed that these alterations result from a reorganization of channel structure induced by the binding of the ryanoid. The experiments reported here provide direct evidence for ryanoid-induced restructuring of RyR. TEA+ is a concentration- and voltage-dependent blocker of RyR in the absence of ryanoids. We have investigated block of K+ current by TEA+ in the unmodified open state and modified conductance states of RyR induced by 21-amino-9α-hydroxyryanodine, 21-azido-9α-hydroxyryanodine, ryanodol, and 21-p-nitrobenzoylamino-9α-hydroxyryanodine. Analysis of the voltage dependence of block indicates that the interaction of ryanoids with RyR leads to an alteration in this parameter with an apparent relocation of the TEA+ blocking site within the voltage drop across the channel and an alteration in the affinity of the channel for the blocker. The degree of change of these parameters correlates broadly with the change in conductance of permeant cations induced by the ryanoids, indicating that modification of RyR channel structure by ryanoids is likely to underlie both phenomena.

Ryanodine receptor dysfunction and triggered activity in the heart

2007 ◽  
Vol 292 (5) ◽  
pp. H2144-H2151 ◽  
Author(s):  
Rodolphe P. Katra ◽  
Toshiyuki Oya ◽  
Gregory S. Hoeker ◽  
Kenneth R. Laurita
Keyword(s):  
Ryanodine Receptor ◽  
Transmembrane Potential ◽  
Calcium Release ◽  
Left Ventricular ◽  
Calcium Handling ◽  
Adrenergic Stimulation ◽  
Triggered Activity ◽  
Multiple Regions ◽  
Rapid Pacing ◽  
Almost All

Arrhythmogenesis has been increasingly linked to cardiac ryanodine receptor (RyR) dysfunction. However, the mechanistic relationship between abnormal RyR function and arrhythmogenesis in the heart is not clear. We hypothesize that, under abnormal RyR conditions, triggered activity will be caused by spontaneous calcium release (SCR) events that depend on transmural heterogeneities of calcium handling. We performed high-resolution optical mapping of intracellular calcium and transmembrane potential in the canine left ventricular wedge preparation ( n = 28). Rapid pacing was used to initiate triggered activity under normal and abnormal RyR conditions induced by FKBP12.6 dissociation and β-adrenergic stimulation (20–150 μM rapamycin, 0.2 μM isoproterenol). Under abnormal RyR conditions, almost all preparations experienced SCRs and triggered activity, in contrast to control, rapamycin, or isoproterenol conditions alone. Furthermore, under abnormal RyR conditions, complex arrhythmias (monomorphic and polymorphic tachycardia) were commonly observed. After washout of rapamycin and isoproterenol, no triggered activity was observed. Surprisingly, triggered activity and SCRs occurred preferentially near the epicardium but not the endocardium ( P < 0.01). Interestingly, the occurrence of triggered activity and SCR events could not be explained by cytoplasmic calcium levels, but rather by fast calcium reuptake kinetics. These data suggest that, under abnormal RyR conditions, triggered activity is caused by multiple SCR events that depend on the faster calcium reuptake kinetics near the epicardium. Furthermore, multiple regions of SCR may be a mechanism for multifocal arrhythmias associated with RyR dysfunction.

scholarly journals New Insights on the Voltage Dependence of the KCa3.1 Channel Block by Internal TBA

2004 ◽  
Vol 124 (4) ◽  
pp. 333-348 ◽  
Author(s):  
Umberto Banderali ◽  
Hélène Klein ◽  
Line Garneau ◽  
Manuel Simoes ◽  
Lucie Parent ◽  
...  
Keyword(s):  
Transmembrane Potential ◽  
Voltage Dependence ◽  
Selectivity Filter ◽  
Channel Structure ◽  
Potential Profile ◽  
Ammonium Ion ◽  
Channel Pore ◽  
Internal Medium ◽  
K Concentration ◽  
External K

We present in this work a structural model of the open IKCa (KCa3.1) channel derived by homology modeling from the MthK channel structure, and used this model to compute the transmembrane potential profile along the channel pore. This analysis showed that the selectivity filter and the region extending from the channel inner cavity to the internal medium should respectively account for 81% and 16% of the transmembrane potential difference. We found however that the voltage dependence of the IKCa block by the quaternary ammonium ion TBA applied internally is compatible with an apparent electrical distance δ of 0.49 ± 0.02 (n = 6) for negative potentials. To reconcile this observation with the electrostatic potential profile predicted for the channel pore, we modeled the IKCa block by TBA assuming that the voltage dependence of the block is governed by both the difference in potential between the channel cavity and the internal medium, and the potential profile along the selectivity filter region through an effect on the filter ion occupancy states. The resulting model predicts that δ should be voltage dependent, being larger at negative than positive potentials. The model also indicates that raising the internal K+ concentration should decrease the value of δ measured at negative potentials independently of the external K+ concentration, whereas raising the external K+ concentration should minimally affect δ for concentrations &gt;50 mM. All these predictions are born out by our current experimental results. Finally, we found that the substitutions V275C and V275A increased the voltage sensitivity of the TBA block, suggesting that TBA could move further into the pore, thus leading to stronger interactions between TBA and the ions in the selectivity filter. Globally, these results support a model whereby the voltage dependence of the TBA block in IKCa is mainly governed by the voltage dependence of the ion occupancy states of the selectivity filter.

scholarly journals Investigations of the Contribution of a Putative Glycine Hinge to Ryanodine Receptor Channel Gating

2013 ◽  
Vol 288 (23) ◽  
pp. 16671-16679 ◽  
Author(s):  
Joanne Euden ◽  
Sammy A. Mason ◽  
Cedric Viero ◽  
N. Lowri Thomas ◽  
Alan J. Williams
Keyword(s):  
Ryanodine Receptor ◽  
Striated Muscle ◽  
Transmembrane Helix ◽  
Channel Gating ◽  
Disease Process ◽  
Structural Data ◽  
Structural Basis ◽  
Detailed Knowledge ◽  
Ion Translocation ◽  
Channel Opening

Ryanodine receptor channels (RyR) are key components of striated muscle excitation-contraction coupling, and alterations in their function underlie both inherited and acquired disease. A full understanding of the disease process will require a detailed knowledge of the mechanisms and structures involved in RyR function. Unfortunately, high-resolution structural data, such as exist for K+-selective channels, are not available for RyR. In the absence of these data, we have used modeling to identify similarities in the structural elements of K+ channel pore-forming regions and postulated equivalent regions of RyR. This has identified a sequence of residues in the cytosolic cavity-lining transmembrane helix of RyR (G4864LIIDA4869 in RyR2) analogous to the glycine hinge motif present in many K+ channels. Gating in these K+ channels can be disrupted by substitution of residues for the hinge glycine. We investigated the involvement of glycine 4864 in RyR2 gating by monitoring properties of recombinant human RyR2 channels in which this glycine is replaced by residues that alter gating in K+ channels. Our data demonstrate that introducing alanine at position 4864 produces no significant change in RyR2 function. In contrast, function is altered when glycine 4864 is replaced by either valine or proline, the former preventing channel opening and the latter modifying both ion translocation and gating. Our studies reveal novel information on the structural basis of RyR gating, identifying both similarities with, and differences from, K+ channels. Glycine 4864 is not absolutely required for channel gating, but some flexibility at this point in the cavity-lining transmembrane helix is necessary for normal RyR function.

Excess noise in modified conductance states following the interaction of ryanoids with cardiac ryanodine receptor channels

FEBS Letters ◽  
2002 ◽  
Vol 516 (1-3) ◽  
pp. 35-39 ◽  
Author(s):  
Bhavna Tanna ◽  
William Welch ◽  
Luc Ruest ◽  
John L Sutko ◽  
Alan J Williams
Keyword(s):  
Ryanodine Receptor ◽  
Excess Noise ◽  
Conductance States ◽  
Cardiac Ryanodine Receptor

scholarly journals Block by acetylcholine of mouse muscle nicotinic receptors, stably expressed in fibroblasts.

1995 ◽  
Vol 106 (1) ◽  
pp. 113-147 ◽  
Author(s):  
D J Maconochie ◽  
J H Steinbach
Keyword(s):  
Nicotinic Receptors ◽  
Open Channel ◽  
Transmembrane Potential ◽  
Voltage Dependence ◽  
Fibroblast Cell ◽  
Open Channel Block ◽  
Adult Type ◽  
Mouse Muscle ◽  
Transmembrane Potentials ◽  
Rate Of Recovery

We have measured the concentration and voltage dependence of block by acetylcholine (ACh) of fetal- and adult-type mouse muscle nicotinic receptors, expressed in a fibroblast cell line. Data, obtained at a transmembrane potential of -60 mV and with ACh concentrations of 1 mM and above, are broadly consistent with the occlusion of an open channel with a single ACh+ ion (simple open channel block). The rate of recovery from block is approximately 40,000s-1 and has only a weak voltage dependence. This is in contrast to the strong voltage dependence observed for the degree of block. Deviations from the predictions of the simple model are seen in data collected at positive transmembrane potentials and at negative potentials for ACh concentrations &lt; 1 mM. Less concentration dependence is observed than expected. Of a number of models tested, we demonstrate that two models incorporating both a high and a low affinity blocking site can predict our data.

Elastomeric Ionomers

1984 ◽  
Vol 57 (3) ◽  
pp. 652-663 ◽  
Author(s):  
W. J. MacKnight ◽  
R. D. Lundberg
Keyword(s):  
Polymer Chain ◽  
Inorganic Salt ◽  
Maximum Level ◽  
Major Influence ◽  
Ionic Interactions ◽  
Polymer Systems ◽  
Ionic Groups ◽  
Polymer Properties ◽  
Hydrocarbon Polymer ◽  
Commercial Polymers

Abstract Ionomers are a class of materials which are emerging as important commercial polymers but yet have many intriguing scientific characteristics. Typically, ionomers consist of a low level of inorganic salt groups pendent to a polymer chain. For this article, we will consider ionomers to possess a maximum level of about 10 mol% ionic groups pendent to a hydrocarbon polymer chain. While this definition is somewhat arbitrary, it is one generally accepted in the polymer field. Unlike homogeneous polymer systems, the pendent ionic groups can interact to form ion-rich aggregates contained in the nonpolar polymer matrix. The resulting ionic interactions can have a major influence on polymer properties and applications which have made this area an extremely fertile one for research and development.

scholarly journals Voltage-Sensitive Equilibrium between Two States within a Ryanoid-Modified Conductance State of the Ryanodine Receptor Channel

2005 ◽  
Vol 88 (4) ◽  
pp. 2585-2596 ◽  
Author(s):  
Bhavna Tanna ◽  
William Welch ◽  
Luc Ruest ◽  
John L. Sutko ◽  
Alan J. Williams
Keyword(s):  
Ryanodine Receptor ◽  
Conductance State ◽  
Receptor Channel
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