SULFHYDRYLS ASSOCIATED WITH H2O2-INDUCED CHANNEL ACTIVATION ARE ON LUMINAL SIDE OF RYANODINE RECEPTORS

The mechanism underlying H2O2-induced activation of frog skeletal musc le ryanodine receptors was studied using skinned fibers and by measuri ng single Ca2+-release channel current. Exposure of skinned fibers to 3-10 mM H2O2 elicited spontaneous contractures. H2O2 at 1 mM potentiat ed caffeine contracture. When the Ca2+-release channels were incorpora ted into lipid bilayers, open probability (P-o) and open time constant s were increased on intraluminal addition of H2O2 in the presence of c is catalase, but unitary conductance and reversal potential were not a ffected. Exposure to cis H2O2 at 1.5 mM failed to activate the channel in the presence of trans catalase. Application of 1.5 mM H2O2 to the trans side of a channel th at had been oxidized by cis p-chloromercuri phenyl-sulfonic acid (pCMPS; 50 mu M) still led to an increase in P-o, comparable to that elicited by trans 1.5 mM H2O2 without pCMPS. Addit ion of cis pCMPS to channels that had been treated with or without tra ns H2O2 rapidly resulted in high P-o followed by closure of the channe l. These results suggest that oxidation of luminal sulfhydryls in the Ca2+-release channel may contribute to H2O2-induced channel activation and muscle contracture.