Non-Thiol Reagents Regulate Ryanodine Receptor Function by Redox Interactions That Modify Reactive Thiols

Abstract

The Ca(2+) release channel (CRC) from sarcoplasmic reticulum (SR) is rich in thiol groups, and their oxidation/- reduction by thiol reagents activates/inhibits the CRC. Most channel regulators are not thiol reagents, and the mechanism of their action is illusive. Here the authors show that many channel activators act as electron acceptors, while many channel inhibitors act as electron donors in free radical reactions. The channel activator, caffeine, and the CRC inhibitor, tetracaine, are shown to interact competitively, which suggests that there exists a common site(s) on the CRC, that integrates the donor/acceptor effects of ligands. Moreover, channel activators shift the redox potential of reactive thiols on the ryanodine receptor (RyR) to more negative values and decrease the number of reactive thiols, while channel inhibitors shift the redox potential to more positive values and increase the number of reactive thiols. These observations suggest that the non-thiol channel modulators shift the thiol-disulfide balance within CRC by transiently exchanging electrons with the Ca(2+) release protein.

Designing Calcium Release Channel Inhibitors with Enhanced Electron Donor Properties: Stabilizing the Closed State of Ryanodine Receptor Type 1

“…Moreover, more potent channel activators are stronger electron acceptors and more potent channel inhibitors are stronger electron donors (Marinov et al, 2007). In Fig.…”

“…This nontraditional approach toward drug design was motivated by our earlier observations that all RyR activators tested were electron acceptors, whereas channel inhibitors were electron donors. Moreover, there was a strong correlation between the effectiveness of these drugs and their potency as either electron donors (inhibitors) or acceptors (activators) (Marinov et al, 2007).…”

“…In a previous publication, we proposed that nonthiol electron acceptors or donors form a reversible charge transfer complex upon binding to RyR1 (Marinov et al, 2007). Channel activators (electron acceptors) were shown to shift the redox potential of RyR1 to more negative redox potentials (RyR1 oxidizes more readily), and the thiol/disulfide balance of the receptor shifts to a more oxidized state.…”

“…Given these experimental conditions, we were not able to directly measure decreases in o. However, Marinov et al (2007). All measurements were performed under continuous illumination by visible light in a buffer containing 1 mM Tris, 10 M methylene blue, and 100 M XTT, pH 7.4, at room temperature.…”

“…The common characteristic of most channel activators is their ability to act as electron acceptors, and common to the channel inhibitors are their electron donor characteristics. Moreover, there is a strong correlation between the strength of the electron donor/acceptor and its potency as a channel inhibitor/activator (Marinov et al, 2007). It occurred to us that this could serve as a basis and direction for development of new drugs targeting the RyR.…”