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Ryanoid modification of the cardiac muscle ryanodine receptor channel results in relocation of the tetraethylammonium binding site.

Tanna B, Welch W, Ruest L, Sutko JL, Williams AJ - J. Gen. Physiol. (2001)

Bottom Line: In all cases, channel open probability increases dramatically and single-channel current amplitude is reduced.It has been proposed that these alterations result from a reorganization of channel structure induced by the binding of the ryanoid.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Cardiac Medicine, National Heart and Lung Institute, Imperial College of Science, Technology and Medicine, London SW3 6LY, United Kingdom.

ABSTRACT
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-9alpha-hydroxyryanodine, 21-azido-9alpha-hydroxyryanodine, ryanodol, and 21-p-nitrobenzoylamino-9alpha-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.

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Relationship between relative conductance (i/io) produced by TEA+ in the ryanoid-modified state at + 80 mV and FC of the ryanoid-modified state. The line plotted through the data is of no theoretical significance.
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Figure 8: Relationship between relative conductance (i/io) produced by TEA+ in the ryanoid-modified state at + 80 mV and FC of the ryanoid-modified state. The line plotted through the data is of no theoretical significance.

Mentions: Overall, our investigations of the influence of holding potential on block by TEA+ of ryanoid-modified conductance states of RyR indicate that there are marked quantitative differences in the degree of block produced by TEA+ in the modified states induced by the various ryanoids. The alteration of the effectiveness of TEA+ as a blocker appears to be correlated with the FC of the ryanoid. A comparison of the degree of block (expressed as relative current; single-channel current in the presence of TEA+ divided by single-channel current in the absence of TEA+) produced by 20 mM TEA+ at a holding potential of +80 mV of the various ryanoid-modified conductance states monitored in this study is presented in Fig. 8. The degree of block induced by TEA+ increases as FC rises from 0.17 to 0.67; block in the ryanodol-modified state is essentially the same as that in the RyR channel in the absence of ryanoid (FC = 1.0).


Ryanoid modification of the cardiac muscle ryanodine receptor channel results in relocation of the tetraethylammonium binding site.

Tanna B, Welch W, Ruest L, Sutko JL, Williams AJ - J. Gen. Physiol. (2001)

Relationship between relative conductance (i/io) produced by TEA+ in the ryanoid-modified state at + 80 mV and FC of the ryanoid-modified state. The line plotted through the data is of no theoretical significance.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2233661&req=5

Figure 8: Relationship between relative conductance (i/io) produced by TEA+ in the ryanoid-modified state at + 80 mV and FC of the ryanoid-modified state. The line plotted through the data is of no theoretical significance.
Mentions: Overall, our investigations of the influence of holding potential on block by TEA+ of ryanoid-modified conductance states of RyR indicate that there are marked quantitative differences in the degree of block produced by TEA+ in the modified states induced by the various ryanoids. The alteration of the effectiveness of TEA+ as a blocker appears to be correlated with the FC of the ryanoid. A comparison of the degree of block (expressed as relative current; single-channel current in the presence of TEA+ divided by single-channel current in the absence of TEA+) produced by 20 mM TEA+ at a holding potential of +80 mV of the various ryanoid-modified conductance states monitored in this study is presented in Fig. 8. The degree of block induced by TEA+ increases as FC rises from 0.17 to 0.67; block in the ryanodol-modified state is essentially the same as that in the RyR channel in the absence of ryanoid (FC = 1.0).

Bottom Line: In all cases, channel open probability increases dramatically and single-channel current amplitude is reduced.It has been proposed that these alterations result from a reorganization of channel structure induced by the binding of the ryanoid.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Cardiac Medicine, National Heart and Lung Institute, Imperial College of Science, Technology and Medicine, London SW3 6LY, United Kingdom.

ABSTRACT
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-9alpha-hydroxyryanodine, 21-azido-9alpha-hydroxyryanodine, ryanodol, and 21-p-nitrobenzoylamino-9alpha-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.

Show MeSH
Related in: MedlinePlus