Cell-permeable. Coelenterazine is the luminescent substrate for Renilla luciferase and apoaequorin. When coelenterazine combines with luciferase, oxygen, and calcium ions, it produces oxy-coelenterazine and light. This allows coelenterazine to be used for bioluminescent calcium detection and the monitoring of reporter genes in BRET (Bioluminescence Resonance Energy Transfer), ELISA and HTS methods as well as chemiluminescent detection of superoxide anions and peroxynitrite in cells or tissues.