The distribution and expression of mRNA encoding the Ca2+-binding protein regucalcin in rats were investigated by Northern blot analyses. Liver regucalcin cDNA (0.6 kb) was used as a probe. The analyses of total RNAs extracted from various tissues of rat indicated that regucalcin mRNA was mainly present in liver but only slightly in kidney with a size of 1.8 kb. The expression level decreased with increasing age (3, 10 and 25 weeks). A single intraperitoneal administration of calcium chloride (15 mg Ca/100 g body weight) induced a remarkable increase in regucalcin mRNA in liver; the level was about 200% of control at 30 min after the administration. Subsequently, the expression level began to decrease with time and was about 40% of control level at 120 min after the administration. The increase in regucalcin mRNA levels at 30 min after calcium administration was dose-dependent. These observations show that the expression of regucalcin mRNA is specific in liver of various tissues, and that it is regulated by Ca2+ administration. Regucalcin may have a role as regulatory protein for calcium homeostasis in liver cells.
