Regucalcin increases Ca2+-ATPase activity in the mitochondria of brain tissues of normal and transgenic rats

The role of regucalcin, which is a regulatory protein in intracellular signaling, in the regulation of Ca2+-ATPase activity in the mitochondria of brain tissues was investigated. The addition of regucalcin (10−10 to 10−8 M), which is a physiologic concentration in rat brain tissues, into the enzyme reaction mixture containing 25 µM calcium chloride caused a significant increase in Ca2+-ATPase activity, while it did not significantly change in Mg2+-ATPase activity. The effect of regucalcin (10−9 M) in increasing mitochondrial Ca2+-ATPase activity was completely inhibited in the presence of ruthenium red (10−7 M) or lanthanum chloride (10−7 M), both of which are inhibitors of mitochondrial uniporter activity. Whether the effect of regucalcin is modulated in the presence of calmodulin or dibutyryl cyclic AMP (DcAMP) was examined. The effect of regucalcin (10−9 M) in increasing Ca2+-ATPase activity was not significantly enhanced in the presence of calmodulin (2.5 µg/ml) which significantly increased the enzyme activity. DcAMP (10−6 to 10−4 M) did not have a significant effect on Ca2+-ATPase activity. The effect of regucalcin (10−9 M) in increasing Ca2+-ATPase activity was not seen in the presence of DcAMP (10−4 M). Regucalcin levels were significantly increased in the brain tissues or the mitochondria obtained from regucalcin transgenic (RC TG) rats. The mitochondrial Ca2+-ATPase activity was significantly increased in RC TG rats as compared with that of wild-type rats. This study demonstrates that regucalcin has a role in the regulation of Ca2+-ATPase activity in the brain mitochondria of rats. J. Cell. Biochem. 104: 795–804, 2008. © 2008 Wiley-Liss, Inc.