Distinct roles of CaM and Ca²⁺/CaM-dependent protein kinase II in Ca²⁺-dependent facilitation and inactivation of cardiac L-type Ca²⁺ channels

Abstract

L-type Ca²⁺ channels have two opposing forms of autoregulatory feedback, Ca²⁺-dependent facilitation (CDF) and Ca²⁺-dependent inactivation (CDI). To explore the underlying mechanisms, we investigated the effects of CaM and CaMKII inhibitors on CDF and CDI with patch clamp technique in guinea-pig ventricular myocytes. We found that both CDF and CDI were depressed and finally abolished by CaM inhibitors, chlorpromazine (1-100 μM) and calmidazolium (1 μM). In contrast, CaMKII inhibitors, KN-62 (0.1-3 μM) and autocamtide 2-related inhibitory peptide (1 μM), delayed the development of CDF and CDI significantly, but did not depress both CDF and CDI. A CaM-binding GST-fusion peptide containing a. a. 1509-1791 of the C-terminal region of guinea-pig Cav1.2 (CT1) is prepared. In pull-down assay, CT1 treated with CaMKII shows a higher affinity for CaM than that treated with phosphatase. Conclusion: Both CaMKII phosphorylation and binding of CaM to the channel are involved in the process of CDF and CDI. We propose a hypothesis that CaM is a key molecule to bifurcate Ca²⁺ signal to CDF and CDI, while CaMKII plays a modulatory role. Acknowledgements: This work was supported by the grants from the Japan Society for the Promotion of Science and the National Natural Science Foundation of China (No.30670761). [J Physiol Sci. 2008;58 Suppl:S46]