ACTIONS OF SULFHYDRYL-REAGENTS ON SINGLE RYANODINE RECEPTOR CA2-RELEASE CHANNELS FROM SHEEP MYOCARDIUM()

Effects of the reactive disulfides, 2,2'- and 4,4'-dithiodipyridine, o n single cardiac ryanodine receptor (RyR) ion channels incorporated in to lipid bilayers are reported. RyRs are activated within minutes of a ddition of the reactive disulfides (10(-7) to 10(-3) M) with an irreve rsible loss of channel activity after the activation at concentrations greater than or equal to 10(-4) M. This activation, followed by loss of activity, is seen over a wide range of cytoplasmic (cis) Ca2+ conce ntration between 10(-9) and 2 x 10(-2) M. and occurs more rapidly with higher reactive disulfide concentrations or when RyRs are initially a ctive at 10(-5) or 10(-3) M Ca2+. The reactive disulfides increase the channel open probability by introducing long components into the open time distributions, increasing the mean channel open time by up to 50 -fold. Closed time distributions are not altered by the sulfhydryl rea gents. The effects of the reactive disulfides are prevented by the red ucing agents dithiothreitol and glutathione (1-10 mM). The results sug gest that cysteine residues on the RyR complex can regulate the ion ch annel gating mechanisms.