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 (H(2)O(2)), is a water-soluble oxidant. [H(2)O(2)](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(o)) 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 [H(2)O(2)](cis) to -1.10 +/- 0.51 pA and 0. 13 +/- 0.04 (for the intermediate subconductance states) in 8.8 mm [H(2)O(2)](cis), respectively. The [H(2)O(2)](cis)-induced decrease in P(o) is mainly due to a decrease in the mean open time T(o). The mechanism of [H(2)O(2)](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 [H(2)O(2)](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 mm removed the inhibitory effects of 8.8 mm [H(2)O(2)](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 mm 4,4'-DTDP to the cis or trans solutions facing an SCl channel already subjected to 0.5 mm [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 H(2)O(2) 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 H(2)O(2) effects on the Ca(2+) countercurrent through the SCl channel are also consistent with H(2)O(2)-modification of the mechanisms involved in the Ca(2+) regulation, which underlies excitation-contraction coupling in skeletal muscle.
Kourie
J I
JI
Membrane Transport Group, Department of Chemistry, The Faculties, The Australian National University, Canberra City, ACT, 0200 Australia.
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D018118:Chloride Channels / Q000037:antagonists & inhibitors*; D004220:Disulfides / Q000494:pharmacology; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000187:drug effects; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism*; D011725:Pyridines / Q000494:pharmacology; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism*
D018118:Chloride Channels; D004220:Disulfides; D011725:Pyridines; C007542:4,4'-dipyridyl disulfide; D000255:Adenosine Triphosphate; D006861:Hydrogen Peroxide