Calcium metabolism regulation may be studied by use of a novel purine-based inhibitor of inositol 1,4,5-trisphosphate 3-kinase (IP3K) developed by purine library screening (IC50= 10.2 muM). This new IP3K inhibitor 1 increased Ca2+ ion release as a result of IP3 accumulation in HL60 cells but did not affect any other metabolic enzymes, such as inositol 1,4,5-trisphosphate 5-phosphatase or phospholipase C