Physiological role of cyclic ADP-ribose a novel endogenous agonist of ryanodine receptors

Cyclic ADP-ribose(CADPR)is suggested to be a novel messenger of ryanodine receptors(RyR)in various cellular systems.However，the regulation of its synthesis in response to cell stimulation and its functional roles are still unclear。We examined the physiological relevance of cADPR to the messenger role in stimulation-secretion coupling.The pharmacological profile of the effects of various agents on cADPR-induced Ca I D 12+I D 1 release in digitonin-permeabilized cells suggests that cADPR induces release from different pools via a different mechanism from IP3-induced Ca I D 12+i D 1 release.CADPR-induced Ca I D 12+I D 1 release but not caffeine-，ryanodine-，and IP I D 23 I D 2-induced Ca I D 12+I D 1 release was inhibited by FK 506 which bind to FKBPs and dissociate them from the RyR.These evidence suggesting that cADPR may be the ligand for FKBP-RyR complex，resulting in a dynamic regulation of RyR-mediated Ca I D12+i D1 release.ADP-ribosyl cyclase was activated in the membrane preparation from…More cells stimulated with acetylcholine(ACh)，excess KCl，and 8Br-cAMP，ACh-induced activation of ADP-ribosyl cyclase was dependent on the influx of Ca I D12+ii D1 into cells and on the activation of cAMP2-dependent protein kinase.These and previous findings that ACh activates adenylate cyclase by Ca I D 12+i D 1 influx，suggested that ACh induces activation of ADP-ribosyl cyclase and Ca I D 12+I D 1 influx through the cAMP-mediated pathways.ACh causes biphasic[Ca I D 12+i D 1]i rise，an initial transient rise followed by sustained rise，in intact cells.8Br-cADPR，an antagonist of cADPR and FK506 specifically reduced the sustained phases of ACh-induced[Ca I D 12+I D 1]i rise.8Br-cADPR，and FK506 failed to alter ACh-Induced[Ca I D 12+I D 1]i rise pretreated with RyR antagonist，imperatoxin inhibitor(IpTxi)，suggesting that cADPR contributes to[Ca I D 12+I D 1]i rise following peak[Ca I D 12+I i rise.8Br cADPR FK506，and IpTxi reduced CA release in response to ACh in chromaffin cells.These results provide evidence that the synthesis of cADPR Is regulated by cell stimulation，and the cADPR/Ca I D 12+I D 1-induced Ca I D 12+I D 1 release pathway forms a significant signal transduction for secretion.Less：Less

Cyclic ADP-ribose (CADPR) is suggested to be a novel messenger of ryanodine receptors (RyR) in various cellular systems. However, the regulation of its synthesis in response to cell stimulation and its functional roles are still unclear. We examined the physiological relevance of cADPR to the messenger role in stimulation-secretion coupling. The pharmacological profile of the effects of various agents on cADPR-induced CaィイD12+ィエD1 release in digitonin-permeabilized cells suggests that cADPR induces release from different pools via a different mechanism from IP3-induced CaィイD12+ィエD1 release. cADPR-induced CaィイD12+ィエD1 release but not caffeine-, ryanodine-, and IPィイD23ィエD2-induced CaィイD12+ィエD1 release was inhibited by FK506 which bind to FKBPs and dissociate them from the RyR. These evidence suggesting that cADPR may be the ligand for FKBP-RyR complex, resulting in a dynamic regulation of RyR-mediated CaィイD12+ィエD1 release.ADP-ribosyl cyclase was activated in the membrane preparation from … More cells stimulated with acetylcholine (ACh), excess KCl, and 8Br-cAMP, ACh-induced activation of ADP-ribosyl cyclase was dependent on the influx of CaィイD12+ィエD1 into cells and on the activation of cAMP2-dependent protein kinase. These and previous findings that ACh activates adenylate cyclase by CaィイD12+ィエD1 influx, suggested that ACh induces activation of ADP-ribosyl cyclase and CaィイD12+ィエD1 influx through the cAMP-mediated pathways.ACh causes biphasic [CaィイD12+ィエD1]i rise, an initial transient rise followed by sustained rise, in intact cells. 8Br-cADPR, an antagonist of cADPR and FK506 specifically reduced the sustained phases of ACh-induced [CaィイD12+ィエD1]i rise. 8Br-cADPR, and FK506 failed to alter ACh-Induced [CaィイD12+ィエD1]i rise pretreated with RyR antagonist, imperatoxin inhibitor (IpTxi), suggesting that cADPR contributes to [CaィイD12+ィエD1]i rise following peak [CaィイD12+ィエD1]i rise. 8Br cADPR FK506, and IpTxi reduced CA release in response to ACh in chromaffin cells.These results provide evidence that the synthesis of cADPR Is regulated by cell stimulation, and the cADPR/ CaィイD12+ィエD1-induced CaィイD12+ィエD1 release pathway forms a significant signal transduction for secretion. Less