Nitric Oxide Protects the Skeletal Muscle Ca2+Release Channel from Oxidation Induced Activation

Abstract Reactive oxygen intermediates and nitric oxide modulate the contractile function of skeletal muscle fibers, possibly via direct interaction with the Ca2+ release channel. Oxidants produce disulfide bonds between subunits of the Ca2+ release channel tetramer, and this is accompanied by an increase in channel activity. The sulfhydryl alkylating agentN-ethylmaleimide has three distinct effects on Ca2+ release channel activity: first, channel activity is decreased (phase 1); then with continued exposure the activity is dramatically increased (phase 2); and finally, the channel is again inhibited (phase 3) (Aghdasi, B., Zhang, J. Z., Wu, Y., Reid, M. B., and Hamilton, S. L., (1997) J. Biol. Chem. 272, 3739–3749). Both H2O2 and nitric oxide (NO) block the phase 1 inhibitory effect ofN-ethylmaleimide. NO donors, at concentrations that have no detectable effect on channel activity, block intersubunit cross-linking and prevent activation of the channel by the disulfide inducing agent, diamide. These findings support a model in which NO modulates the activity of the Ca2+ release channel by preventing oxidation of regulatory sulfhydryls. However, higher concentrations of NO donors activate the channel and produce intersubunit cross-links, supporting a bifunctional effect of NO on channel activity. Low NO concentrations prevent oxidation of the Ca2+ release channel whereas higher concentrations oxidize it.