Calmodulin inhibits inositol 1,4,5-trisphosphate-induced calcium release through the purified and reconstituted inositol 1,4,5-trisphosphate receptortype 1

Our previous studies have demonstrated that calmodulin binds to IP3R type I (IP(3)R1) in a Ca2+ dependent manner, which suggests that calmodulin regul ates the IP(3)R1 channel. In the present study, we investigated real-time k inetics of interactions between calmodulin and IP(3)R1 as well as effects o f calmodulin on IP3-induced Ca2+ release by purified and reconstituted IP(3 )R1. Kinetic analysis revealed that calmodulin binds to IP(3)R1 in a Ca2+ d ependent manner and that both association and dissociation phase consist of two components with time constants of k(a) = 4.46 x 10(2) and > 10(4) M-1 s(-1), k(d) = 1.44 x 10(-2) and 1.17 x 10(-1) s(-1). The apparent dissociat ion constant was calculated to be 27.3 . The IP3-induced Ca2+ release throu gh the purified and reconstituted IP(3)R1 was inhibited by Ca2+/calmodulin, in a dose dependent manner. We interpret our findings to mean that calmodu lin binds to IP(3)R1 in a Ca2+ dependent manner to exert inhibitory effect on IP3R channel activity, This event may be one of the mechanisms governing the negative feedback regulation of IP3-induced Ca2+ release by Ca2+. (C) 1999 Federation of European Biochemical Societies.