RT Journal Article SR Electronic T1 Differential effects of heparin on inositol 1,4,5-trisphosphate binding, metabolism, and calcium release activity in the bovine adrenal cortex. JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 339 OP 344 VO 35 IS 3 A1 Guillemette, G A1 Lamontagne, S A1 Boulay, G A1 Mouillac, B YR 1989 UL http://molpharm.aspetjournals.org/content/35/3/339.abstract AB In a wide variety of cells, inositol-1,4,5-triphosphate is a second messenger that interacts with specific intracellular receptors and triggers the release of sequestered Ca2+ from an intracellular store. We have looked at the influence of heparin on the action and metabolism of inositol-1,4,5-triphosphate in the bovine adrenal cortex. Heparin blocked inositol-1,4,5-trisphosphate binding with half-maximal efficiency around 10 micrograms/ml. Scatchard analyses revealed that heparin did not change the affinity but decreased the number of available binding sites. The Ca2+-releasing activity of inositol-1,4,5-trisphosphate was monitored with the fluorescent indicator, fura-2. Heparin blocked this activity with half-maximal effeciency around 10 micrograms/ml. The effect of heparin could be overcome by a supramaximal dose of inositol-1,4,5-trisphosphate (25 microM). The activity of inositol-1,4,5-trisphosphate-3-kinase from bovine adrenal cortex cytosol was also studied. Heparin inhibited the activity of the kinase with a half-maximal effeciency around 0.4 microgram/ml. Lineweaver-Burk plots revealed that this potent effect was noncompetitive. Finally, we observed that heparin is without effect on inositol-1,4,5-trisphosphate-5-phosphatase (at concentrations as high as 2 mg/ml). These results are consistent with the suggestion that the binding sites for inositol-1,4,5-trisphosphate are the intracellular receptors responsible for the Ca2+-mobilizing effects of inositol-1,4,5-trisphosphate. These results also show that the kinase, the phosphatase, and the receptor are three different molecular entities, which are affected in a different manner by heparin.