Cyclic ADP-ribose does not affect cardiac or skeletal muscle ryanodine receptors

The cardiac muscle isoform of the ryanodine receptor/Ca²⁺ release channel (RYR) has been proposed to be an important target of cyclic ADP-ribose (cADPR) action in mammalian cells. However, we now demonstrate that neither cADPR (0.1-5 μM), nor the related metabolites, β-NAD⁺ (0.1-30 mM) and ADP-ribose (0.1-5 μM), affected cardiac RYR activity as determined by [³H]ryanodine binding to cardiac sarcoplasmic reticulum (SR) vesicles. Similarly, cADPR (1 μM) failed to activate single cardiac RYR channels in planar lipid bilayers. Skeletal muscle SR [³H]ryanodine binding was also unaffected by cADPR (up to 30 μM). These results argue against a direct role for the well-characterized RYRs of cardiac or skeletal muscle in mediating cADPR-activated Ca²⁺ release.