The effect of ryanodine on oxygen free radical-induced dysfunction of cardiac sarcoplasmic reticulum.
The effect of the plant alkaloid ryanodine on the cardiac sarcoplasmic reticulum (SR) function, which plays a major role in the regulation of intracellular calcium and thereby in the generation of force, was studied by determining oxalate-supported calcium uptake, steady-state calcium load, calcium permeability, intravesicular-free calcium and Ca,Mg-adenosine triphosphatase (ATPase) activity of "heavy" vesicles in the presence or absence of the oxygen-free radical-generating system. In vitro generation of oxygen-free radicals by xanthine oxidase (0.09 u/ml), acting on xanthine (25 microM) as a substrate, increased the permeability of the vesicles to calcium, determined by measuring net efflux of calcium after stopping pump-mediated fluxes, and decreased oxalate-supported calcium uptake and steady-state calcium load with no effect on Ca,Mg-ATPase activity. This effect of oxygen-free radicals was inhibited completely by superoxide dismutase, which eliminated completely superoxide anion radical production and caused an anticipated increase in hydrogen peroxide from the xanthine-xanthine oxidase reaction in our system. The xanthine-xanthine oxidase reaction decreased intravesicular-free calcium. The diminished level of intravesicular-free calcium, which was reflected by the decreased steady-state calcium load induced by oxygen-free radicals, was prevented by specific closure of the SR calcium release channel by ryanodine under established optimal conditions; under the same conditions, ryanodine also prevented superoxide dismutase-inhibitable reduction of calcium uptake induced by oxygen-free radicals in the presence or absence of oxalate. Ryanodine was without effect on Ca,Mg-ATPase activity by itself and had no effect on any of the changes in calcium permeability mediated by the generation of oxygen-free radicals under the experimental conditions used.(ABSTRACT TRUNCATED AT 250 WORDS)
Okabe
E
E
Department of Pharmacology, Kanagawa Dental College, Japan.
Kuse
K
K
Sekishita
T
T
Suyama
N
N
Tanaka
K
K
Ito
H
H
D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D004285:Dogs; D005609:Free Radicals; D006321:Heart / Q000187:drug effects*; D009206:Myocardium / Q000201:enzymology / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism*; D012433:Ryanodine / Q000494:pharmacology*; D012519:Sarcoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism; D013482:Superoxide Dismutase / Q000378:metabolism; D014969:Xanthine Oxidase / Q000378:metabolism
D015220:Calcium Channels; D005609:Free Radicals; D012433:Ryanodine; D013482:Superoxide Dismutase; D014969:Xanthine Oxidase; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D010100:Oxygen; D002118:Calcium