Effects of Calmodulin Antagonists on the Mitochondrial and Microsomal Ca^<2+> Uptake in Apple Fruit

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In apple fruit, active ATP-dependent microsomal Ca^<2+> uptake and respiration-dependent mitochondrial Ca^<2+> uptake were observed. The mitochondrial Ca^<2+> uptake was depressed by the calmodulin antagonists chlorpromazine hydrochloride (CPZ) and N-(6-aminohexyl)-5-chloro-1-naphthalene-sulfonamide hydrochloride (W-7). The Ca^<2+>_ATPase from apple mitochondria was also inhibited by CPZ or W-7. The apparent K_m Value for Ca^<2+> in mitochondrial Ca^<2+> uptake (Km=0.35 mM) was similar to that of mitochondrial Ca^<2+>_ATPase (Km=0.32 mM). The inhibitory effect of W-7 on the activity of the mitochondrial Ca^<2+> uptake was closely correlated with the inhibition by W-7 of mitochondrial Ca^<2+>-ATPase (r=0.996). These findings indicate that the mitochondrial uptake of Ca^<2+> in apple fruit depends on the calmodulin-mediated activation of Ca^<2+>-ATPase. The microsomal Ca^<2+> uptake was. depressed by CPZ, suggesting that the microsomal Ca^<2+> uptake may also be modulated by calmodulin.
日本植物生理学会の論文