Calmodulin (CaM) is well known as an activator of calcium/calmodulin-dependent protein kinase II (CaMKII). Voltage-gated sodium channels (VGSCs) are basic signaling molecules in excitable cells and are crucial molecular targets for nervous system agents. However, the way in which Ca²⁺/CaM/CaMKII cascade modulates Na_V1.1 IQ (isoleucine and glutamine) domain of VGSCs remains obscure. In this study, the binding of CaM, its mutants at calcium binding sites (CaM₁₂, CaM₃₄, and CaM₁₂₃₄), and truncated proteins (N-lobe and C-lobe) to Na_V1.1 IQ domain were detected by pull-down assay. Our data showed that the binding of Ca²⁺/CaM to the Na_V1.1 IQ was concentration-dependent. ApoCaM (Ca²⁺-free form of calmodulin) bound to Na_V1.1 IQ domain preferentially more than Ca²⁺/CaM. Additionally, the C-lobe of CaM was the predominant domain involved in apoCaM binding to Na_V1.1 IQ domain. By contrast, the N-lobe of CaM was predominant in the binding of Ca²⁺/CaM to Na_V1.1 IQ domain. Moreover, CaMKII-mediated phosphorylation increased the binding of Ca²⁺/CaM to Na_V1.1 IQ domain due to one or several phosphorylation sites in T1909, S1918, and T1934 of Na_V1.1 IQ domain. This study provides novel mechanisms for the modulation of Na_V1.1 by the Ca²⁺/CaM/CaMKII axis. For the first time, we uncover the effect of Ca²⁺, lobe-specificity and CaMKII on CaM binding to Na_V1.1.

In recent years, there are increasing evidences of epidemiology and clinic which indicate that vitamin D deficiency has relationship with cardiovascular disease. It was found the levels of vitamin D were negatively correlated with cardiovascular events such as hypertension, heart failure, atrial fibrillation and coronary heart disease. This article reviews the connection between cardiovascular diseases and vitamin D, and explains the underlying mechanisms including regulating renin-angiotensin system or endothelial function, inhibition of natriuretic peptide expression or the release of parathyroid hormone, effects on inflammation or obesity, bioenergetics, activation of extracellular Ca²⁺, inhibition of oxidative stress, and so on. These mechanisms provide novel strategy for the treatment of these cardiovascular diseases.

Reperfusion after ischemia would cause massive myocardial injury, which leads to oxidative stress (OS). Calcium homeostasis imbalance plays an essential role in myocardial OS injury. Ca_V1.2 calcium channel mediates calcium influx into cardiomyocytes, and its activity is modulated by a region of calpastatin (CAST) domain L, CS_L54-64. In this study, the effect of Ahf-caltide, derived from CS_L54-64, on myocardial OS injury was investigated. Ahf-caltide decreased the levels of LDH, MDA and ROS and increased heart rate, coronary flow, cell survival and SOD activity during OS. In addition, Ahf-caltide permeated into H9c2 cells and increased Ca_V1.2, Ca_Vβ2 and CAST levels by inhibiting protein degradation. At different Ca²⁺ concentrations (25 nM, 10 μM, 1 mM), the binding of CS_L to the IQ motif in the C terminus of the Ca_V1.2 channel was increased in a H₂O₂ concentration-dependent manner. CS_L54-64 was predicted to be responsible for the binding of CS_L to Ca_V1.2. In conclusion, Ahf-caltide exerted a cardioprotective effect on myocardial OS injury by stabilizing Ca_V1.2 protein expression. Our study, for the first time, proposed that restoring calcium homeostasis by targeting the Ca_V1.2 calcium channel and its regulating factor CAST could be a novel treatment for myocardial OS injury.