Mechanisms of cyclic ADP-ribose-induced Ca^<2+> mobilization and its physiological role

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The calcium channels/ryanodine receptors (RyRs) are potential/putative target of cyclic ADP-ribose (cADPR) action in many tissue systems. However, the regulation of its synthesis in response to cell stimulation, and the mechanisms by which cADPR activates RyRs, and its functional roles are still unclear. We have demonstrated that cADPR synthesis is stimulated by cAMP-dependent mechanism. There is increasing evidence indicating that FK506 binding proteins (FKBP)12/12.6 play an important role in the regulation of the RyRs channel gating. It is believed that dissociation from RyRs activates or delays their inactivation. The present study was designed to determine whether FKBP, an accessory protein of the RyRs, plays a role in cADPR-induced activation of RyR channels and whether the physiological relevance of cADPR to the messenger role in several cells (bovine adrenal chromaffin cells, canin parotide cells and human neutrophils) using a cADPR antagonist, 8Br-cADPR, and FK506 and rapamycin … More which bind to FKBPs and dissociate them from the RyRIn permeabilized cells, cADPR-induced Ca^<2+> release but not caffeine-and ryanodine -induced Ca^<2+> release was inhibited by a cADPR antagonist, 8Br-cADPR, and FK506 and rapamycin. Furthermore, anti-FKBP 12/12.6 antibody also attenuated the cADPR-induced Ca^<2+> release. The evidence suggests that cADPR may be the ligand for FKBP-RyR complex, resulting in a dynamic regulation of RyR-mediated Ca^<2+> release. ACh and fMLP causes biphasic intracellular free Ca^<2+> concentration ([Ca^<2+>]i) rise, an initial transient rise followed by sustained rise, in intact cells. 8Br-cADPR, FK506 and rapamycin but not cyclospolin A specifically reduced the sustained phases of stimulation-induced [Ca^<2+>]i rise, suggesting that cADPR contributes to sustained [Ca^<2+>]_i rise. 8Br-cADPR, FK506, and rapamycin reduced ACh-induced adrenal catecholamine release and fMLP-induced neutrophils migrationThese results provide evidence that the synthesis of cADPR is regulated by cell stimulation, and the cADPR/Ca^<2+>-induced Ca^<2+> release pathway forms a positive feedback to stimulation-induced response Less