Hydrogen peroxide inhibits chloride channels of the sarcoplasmic reticulum of skeletal muscle

Data obtained with the lipid bilayer technique indicate that cis (cytoplasmic) concentration of 4.4-22 mm hydrogen peroxide (H₂O₂), is a water-soluble oxidant. [H₂O₂](cis) (n = 26) reversibly inhibits the multisubconductance SCl channel of the sarcoplasmic reticulum vesicles from rabbit skeletal muscle. At -40 mV, the mean values of the current amplitude (I) and the probability of the SCl channel being open (P(0)) were reduced significantly (n = 8) from -6.14 ± 0.42 pA and 0.69 ± 0.06 (for all conductance levels) in control 0.0 mM [H₂O₂](cis) to -1.10 ± 0.51 pA and 0.13 ± 0.04 (for the intermediate subconductance states) in 8.8 mu [H₂O₂](cis), respectively. The [H₂O₂](cis)-induced decrease in P(o) is mainly due to a decrease in the mean open time T(o). The mechanism of [H₂O₂](cis) effects on the multiconductance SCl channel is characterized by a mode shift in the channel state from the main conductance state to the low subconductance states. The estimated concentration of the [H₂O₂](cis) for the half inhibitory constant, K(i), was 11.78 mm, higher than the estimated 8.0 and 8.1 mm for the parameters P(o) and T(o), respectively; indicating that the conductance of the SCl channel is less sensitive than the gating kinetics of the channel. After a lag period of between 30 to 60 sec, the lipophilic SH-oxidizing agent 4,4'-dithiodipyridine (4,4'-DTDP) added to the cis side at 1.0 mu removed the inhibitory effects of 8.8 mu [H₂O₂](cis). The 4,4'-DTDP-enhanced SCl channel activity was blocked after the addition of 0.5 mM ATP to the cis side of the channel. The addition of 1.0 mu 4,4'-DTDP to the cis or trans solutions facing an SCl channel already subjected to 0.5 mu [ATP](cis) or [ATP](trans) failed to activate the ATP-inhibited SCl channel. These findings suggest that 4,4'-DTDP is not preventing the binding of ATP to its binding site on the channel protein. The interaction of H₂O₂ with the SCl channel proteins is consistent with a thiol-disulfide redox state model for regulating ion transport, where SH groups can directly modify the function of the channel and/or the availability of regulatory sites on the channel proteins. The H₂O₂ effects on the Ca²⁺ countercurrent through the SCl channel are also consistent with H₂O₂-modification of the mechanisms involved in the Ca²⁺ regulation, which underlies excitation- contraction coupling in skeletal muscle.