STIMULATORY EFFECT OF CALCIUM ADMINISTRATION ON REGUCALCIN MESSENGER-RNA EXPRESSION IS ATTENUATED IN THE KIDNEY CORTEX OF RATS INGESTED WITH SALINE

The expression of calcium-binding protein regucalcin mRNA in the kidne y cortex of rats ingested with saline was investigated. The alteration in regucalcin mRNA levels was analyzed by Northern blotting using liv er regucalcin complementary DNA (0.9 kb of open reading frame). Rats w ere freely given saline as drinking water for 7 days. Regucalcin mRNA levels in the kidney cortex were suppressed by saline ingestion. When calcium chloride (10 mg Ca/100 g body weight) was intraperitoneally ad ministered to rats ingested with saline for 7 days, the effect of calc ium administration to increase regucalcin mRNA levels was weakened by saline ingestion. Such effect was also seen by the administration of 2 .5 and 5 mg Ca/100 g. Regucalcin mRNA levels in the kidney cortex of s pontaneous hypertensive rats (SHR) were not appreciably increased by t he administration of calcium (10 mg/100 g). Meanwhile, calcium content in the kidney cortex was significantly elevated by the administration of calcium (10 mg/100 g) to normal rats. This increase was weakened i n saline-ingested rats. Moreover, Ca2+/calmodulin-dependent protein ki nase activity in the cytosol of kidney cortex was significantly decrea sed by saline ingestion. These results suggest the possibility that sa line ingestion-induced suppression of regucalcin mRNA expression in th e kidney cortex is partly involved in the attenuation of Ca2+ signalli ng.