Activation of the Cardiac Ryanodine Receptor by Sulfhydryl Oxidation is Modified by Mg2+ and ATP

Activation of the Cardiac Ryanodine Receptor by Sulfhydryl Oxidation is Modified by Mg2+ and ATP The reactive disulfide 4,4′-dithiodipyridine (4,4′DTDP) was added to single cardiac ryanodine receptors (RyRs) in lipid bilayers. The activity of native RyRs, with cytoplasmic (cis) [Ca2+] of 10−7 m (in the absence of Mg2+ and ATP), increased within ∼1 min of addition of 1 mm 4,4′-DTDP, and then irreversibly ceased 5 to 6 min after the addition. Channels, inhibited by either 1 mm cis Mg2+ (10−7 m cis Ca2+) or by 10 mm cis Mg2+ (10−3 m cis Ca2+), or activated by 4 mm ATP (10−7 m cis Ca2+), also responded to 1 mm cis 4,4′-DTDP with activation and then loss of activity. P o and mean open time (T o ) of the maximally activated channels were lower in the presence of Mg2+ than in its absence, and the number of openings within the long time constant components of the open time distribution was reduced. In contrast to the reduced activation by 1 mm 4,4′-DTDP in channels inhibited by Mg2+, and the previously reported enhanced activation by 4,4′-DTDP in channels activated by Ca2+ or caffeine (Eager et al., 1997), the activation produced by 1 mm cis 4,4′-DTDP was the same in the presence and absence of ATP. These results suggest that there is a physical interaction between the ATP binding domain of the cardiac RyR and the SH groups whose oxidation leads to channel activation. The Journal of Membrane Biology Springer Journals

Activation of the Cardiac Ryanodine Receptor by Sulfhydryl Oxidation is Modified by Mg2+ and ATP

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Copyright © Inc. by 1998 Springer-Verlag New York
Life Sciences; Biochemistry, general; Human Physiology
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