The release mechanism regulating SR Ca2+ homeostasis is significantly more sensitive than the uptake mechanisms. The exquisite sensitivity exhibited by ryanodine-sensitive Ca2+ channel complexes (i.e., ryanodine receptors, RyRs) to functional perturbation by chemically diverse sulfhydryl-modifying compounds can include phases of activation and inhibition that are dependent on the concentration of the reagent used, the length of exposure, and the nature of the chemical reaction the reagent undertakes with sulfhydryl groups. However the exquisite sensitivity of RyR function to sulfhydryl modification has been generally viewed as significant only in pathophysiological processes. The present paper addresses possible physiological importance of the redox sensing properties of the ryanodine receptor complexes (RyRs) and proposes an underlying mechanism. New data is presented that directly measure the pKa of hyperreactive thiols that occur when the closed conformation of the RyR channel complex is assumed, and that appear to be an integral component of the redox sensor.