Novel mechanisms involved in superoxide anion radical-triggered Ca2+ release from cardiac sarcoplasmic reticulum linked to cyclic ADP-ribose stimulation.
It has been suggested that cyclic adenosine 5'-diphosphoribose (cADPR) directly activates the cardiac isoform of the ryanodine receptor (RyR)/Ca2+ release channel. We have previously shown that selective activation of RyR/Ca2+ release channel by superoxide anion radical (O2.-) is dependent of the presence of calmodulin and identified calmodulin as a functional mediator of O2.- -triggered Ca2+ release through the RyR/Ca2+ release channel of cardiac sarcoplasmic reticulum (SR). We now demonstrate that although the effect of O2.- on Ca2+ efflux from RyR/Ca2+ release channel at higher concentrations ( >5 microM) is due to its ability to produce a loss in function of calmodulin thereby decreasing calmodulin inhibition, O2.- radicals at lower concentrations (<5 microM) may be able to stimulate Ca2+ release only in the presence of calmodulin from the SR via increased cADPR synthesis; it is also shown that cADPR is a modulator that can activate the Ca2+-release mechanism when it is in a sensitized state by the presence of calmodulin, possibly, at physiological concentration. In addition, the SR vesicles immediately upon addition of cADPR, but not NAD+, did exhibit Ca2+ efflux stimulation. When heart homogenate was incubated with O2.-, conversion of NAD+ into cADPR was stimulated; the reduction of homogenate Ca2+ uptake (by increasing Ca2+ efflux through RyR/Ca2+ release channel) occurred. Thus O2.- radical is responsible for cADPR formation from NAD+ in the cellular environment outside of the SR of heart muscle. The results presented here provide the first evidence of a messenger role for O2.- radical in cADPR-mediated Ca2+ mobilization in myocardium.
Department of Pharmacology, Kanagawa Dental College, Yokosuka, Kanagawa, Japan.
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Kumasaka
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Shoji
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Okabe
D000246:Adenosine Diphosphate Ribose / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002132:Calcium Radioisotopes / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism*; D036563:Cyclic ADP-Ribose / Q000031:analogs & derivatives; D004285:Dogs; D004578:Electron Spin Resonance Spectroscopy; D019271:Hypoxanthine / Q000378:metabolism; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D009243:NAD / Q000378:metabolism; D012433:Ryanodine / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000494:pharmacology; D013481:Superoxides / Q000378:metabolism*; D014969:Xanthine Oxidase / Q000378:metabolism
D002121:Calcium Channel Blockers; D002132:Calcium Radioisotopes; D002147:Calmodulin; D019837:Ryanodine Receptor Calcium Release Channel; D009243:NAD; D013481:Superoxides; D036563:Cyclic ADP-Ribose; C082175:8-aminoadenosine cyclic 3',5'-(hydrogen phosphate) 5'-ribofuranosyl ester; D012433:Ryanodine; D000246:Adenosine Diphosphate Ribose; D019271:Hypoxanthine; D013482:Superoxide Dismutase; D014969:Xanthine Oxidase; D002118:Calcium