Regucalcin-induced Ca2+ release from rat liver microsomes: the effect is inhibited by heparin

The effect of heparin on the calcium-binding protein regucalcin-stimulated Ca2+ release from rat liver microsomes was investigated. Ca2+ release was assayed by the method of Millipore filtration to estimate microsomal 45Ca2+ accumulation following the addition of 10 mM adenosine triphosphate. The addition of regucalcin (1.0 microM) or inositol 1,4,5-trisphosphate [Ins(1,4,5)P3; 1.0 microM] stimulated 45Ca2+ release from rat liver microsomes. These effects were completely inhibited by the presence of heparin (10.0 micrograms/ml). Regucalcin did not enhance the effect of Ins(1,4,5)P3. These results suggest that regucalcin affects 45Ca2+ release involved in Ins(1,4,5)P3 action in rat liver microsomes.