Classes of Thiols That Influence the Activity of the Skeletal Muscle Calcium Release Channel*

The skeletal muscle Ca²⁺release channel/ryanodine receptor (RyR1) is a prototypic redox-responsive ion channel. Nearly half of the 101 cysteines per RyR1 subunit are kept in a reduced (free thiol) state under conditions comparable with resting muscle. Here we assessed the effects of physiological determinants of cellular redox state (oxygen tension, reduced (GSH) or oxidized (GSSG) glutathione, and NO/O⨪₂(released by 3-morpholinosydnonimine)) on RyR1 redox state and activity. Oxidation of ∼10 RyR1 thiols (from ∼48 to ∼38 thiols/RyR1 subunit) had little effect on channel activity. Channel activity increased reversibly as the number of thiols was further reduced to ∼23/subunit, whereas more extensive oxidation (to ∼13 thiols/subunit) inactivated the channel irreversibly. NeitherS-nitrosylation nor tyrosine nitration contributed to these effects. The results identify at least three functional classes of RyR1 thiols and suggest that 1) the channel may be protected from oxidation by a large reservoir of functionally inert thiols, 2) the channel may be designed to respond to moderate oxidative stress by a change in activation setpoint, and 3) the channel is susceptible to oxidative injury under more extensive conditions.