Calmodulin inhibits inositol 1,4,5-trisphosphate-induced calcium release through the purified and reconstituted inositol 1,4,5-trisphosphate receptor type 1.
Our previous studies have demonstrated that calmodulin binds to IP3R type I (IP3R1) in a Ca2+ dependent manner, which suggests that calmodulin regulates the IP3R1 channel. In the present study, we investigated real-time kinetics of interactions between calmodulin and IP3R1 as well as effects of calmodulin on IP3-induced Ca2+ release by purified and reconstituted IP3R1. Kinetic analysis revealed that calmodulin binds to IP3R1 in a Ca2+ dependent 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 dissociation constant was calculated to be 27.3 microM. The IP3-induced Ca2+ release through the purified and reconstituted IP3R1 was inhibited by Ca2+/calmodulin, in a dose dependent manner. We interpret our findings to mean that calmodulin binds to IP3R1 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+.
Hirota
J
J
Mikoshiba Calciosignal Net Project, Exploratory Research for Advanced Technology, Japan Science and Technology Corporation, Tokyo, Japan. jhirota@ims.u-tokyo.ac.jp
Michikawa
T
T
Natsume
T
T
Furuichi
T
T
Mikoshiba
K
K
D000818:Animals; D015374:Biosensing Techniques; D015220:Calcium Channels / Q000187:drug effects* / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects*; D002147:Calmodulin / Q000378:metabolism / Q000494:pharmacology*; D005246:Feedback; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism / Q000494:pharmacology*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D017136:Ion Transport / Q000187:drug effects; D007700:Kinetics; D051379:Mice; D018160:Receptors, Cytoplasmic and Nuclear / Q000187:drug effects* / Q000378:metabolism*
D015220:Calcium Channels; D002147:Calmodulin; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D015544:Inositol 1,4,5-Trisphosphate