Table 1

Effect of oxygen-derived free radicals generated by hypoxanthine-xanthine oxidase reaction responsible for calmodulin on Cai and Ca2+-ATPase activity for SR

Experimental additionNative SREGTA SR
CaiCa2+-ATPase activityCaiCa2+-ATPase activity
nmol/mg nmol Pi/mg/min nmol/mg nmol Pi/mg/min
XO32.8  ± 4.686.6  ± 5.614.3  ± 0.51-e 92.4  ± 6.8
HX/XO16.1  ± 1.21-a 70.9  ± 9.613.8  ± 1.682.6  ± 8.3
SOD plus HX/XO26.4  ± 1.61-b 72.8  ± 5.3
CaM plus XO48.3  ± 4.81-a 91.8  ± 10.129.4  ± 2.41-a 74.8  ± 11.8
CaM plus HX/XO30.4  ± 2.7bc 80.7  ± 7.912.4  ± 1.91-c 81.9  ± 9.9
CaM plus HX/XO*42.9  ± 3.81-d 82.6  ± 4.823.8  ± 1.61-d 94.6  ± 16.5
CaM plus SOD plus HX/XO25.0  ± 2.81-d 76.3  ± 6.6
Ryanodine plus XO52.6  ± 5.91-a 88.4  ± 4.633.2  ± 2.51-a 82.9  ± 7.4
Ryanodine plus HX/XO46.2  ± 3.81-b 84.9  ± 3.428.8  ± 3.878.8  ± 10.2
Ryanodine plus CaM plus HX/XO31.6  ± 3.11-d 83.2  ± 5.9

For determination of Cai or Ca2+-ATPase activity, time sequence addition was designed to ensure exposure of the native and EGTA-washed SR vesicles to the oxygen-derived free radical generating system [20 μm hypoxanthine (HX) plus 0.1 unit/ml xanthine oxidase (XO)] for 2.0 min before initiation of the reaction. SOD (10 μg/ml) or calmodulin (CaM) (2.0 μm or 10 μm*) was added before the free radical exposure. The SR vesicles were preincubated with or without ryanodine (300 μm) for 10 min; then, the reaction was initiated. Values are mean ± standard error (five to seven experiments).p-values are the result of analysis of variance and Dunnett’s multiple-range test.

    • ↵1-a p < 0.01 versus corresponding XO alone.

    • ↵1-b p < 0.01 versus corresponding HX/XO.

    • ↵1-c p < 0.01 versus corresponding XO alone in the presence of 2.0 μm CaM.

    • ↵1-d p < 0.01 versus corresponding HX/XO in the presence of 2.0 μm CaM.

    • ↵1-e p < 0.01 versus corresponding XO alone in native SR.