Studies on Liver Cellular Functions by a Novel Ca^<2+>-Binding Protein Regucalcin

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1. Tissue distribution of regucalcinRabbit-anti-regucalcin antiserum, which was raised against regucalcin conjugated by glutaraldehyde to bovine serum albumin, was applied to glutaraldehyde-fixed whole mounts and subsequently visualized using the peroxidase-antiperoxidase methods. Rat hepatic regucalcin immunoreactivity was most pronounced in the liver of rats, while it. was not seen in the duodenum, testicle, spleen, lung and smooth muscle. This was confirmed by the methods of enzyme-immunoassay and Northern bloting for MRNA of regucalcin gene.2. Regulation of liver cell function by regucalcinIn rat liver cytosol, regucalcin completely prevented the activation of Ca^<2+>/ calmodulin-dependent cyclic AMP phosphodiesterase by Ca^<2+> and the inhibition of deoxyuridine 5'-triphosphatase by Ca^<2+>. Also, DNA fragmentation in isolated rat liver nuclei was activated by Ca^<2+>. This activation was completely blocked by the presence of regucalcin. moreover, the liver nuclei is Ca^<2+> transport systems. Especially, regucalcin stimulated Ca^<2+> release from rat liver nuclei, but not it had no effect on Ca^<2+> uptake.