Abstract
In previous studies, we have demonstrated that the interaction of ryanoids with the sarcoplasmic reticulum Ca2+-release channel [ryanodine receptor (RyR)] incorporated into planar lipid bilayers reduced the effectiveness of tetraethylammonium (TEA+) as a blocker of K+ translocation (J Gen Physiol 117: 385-393, 2001). In the current study, we investigated both the effect of TEA+ on [3H]ryanodine binding and the actions of this impermeant cation on the interaction of the reversible ryanoid 21-amino-9α-hydroxyryanodine with individual, voltage-clamped RyR channels. A dose-dependent inhibition of [3H]ryanodine binding was observed in the presence of TEA+, suggesting that the cation and alkaloid compete for access to a common site of interaction. Single channel studies gave further insights into the mechanism of the competition between the two classes of ligands. TEA+ decreases the association rate of 21-amino-9α-hydroxyryanodine with its receptor, whereas the dissociation rate of the ryanoid from the channel was unaffected. Our results demonstrate that TEA+ inhibits both K+ translocation through RyR, and ryanoid interaction at the high affinity ryanodine site on the channel. These actions involve binding of TEA+ to different, but weakly interacting, sites in the RyR channel.
- Received December 12, 2005.
- Accepted March 15, 2006.
- The American Society for Pharmacology and Experimental Therapeutics
MolPharm articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|