title: Low-Mg(2+) treatment increases sensitivity of voltage-gated Na(+) channels to Ca(2+)/calmodulin-mediated modulation in cultured hippocampal neurons.
abstract: Culture of hippocampal neurons in low-Mg(2+) medium (low-Mg(2+) neurons) results in induction of continuous seizure activity. However, the underlying mechanism of the contribution of low Mg(2+) to hyperexcitability of neurons has not been clarified. Our data, obtained using the patch-clamp technique, show that voltage-gated Na(+) channel (VGSC) activity, which is associated with a persistent, noninactivating Na(+) current (INa,P), was modulated by calmodulin (CaM) in a concentration-dependent manner in normal and low-Mg(2+) neurons, but the channel activity was more sensitive to Ca(2+)/CaM regulation in low-Mg(2+) than normal neurons. The increased sensitivity of VGSCs in low-Mg(2+) neurons was partially retained when CaM12 and CaM34, CaM mutants with disabled binding sites in the N or C lobe, were used but was diminished when CaM1234, a CaM mutant in which all four Ca(2+) sites are disabled, was used, indicating that functional Ca(2+)-binding sites from either lobe of CaM are required for modulation of VGSCs in low-Mg(2+) neurons. Furthermore, the number of neurons exhibiting colocalization of CaM with the VGSC subtypes NaV1.1, NaV1.2, and NaV1.3 was significantly higher in low- Mg(2+) than normal neurons, as shown by immunofluorescence. Our main finding is that low-Mg(2+) treatment increases sensitivity of VGSCs to Ca(2+)/CaM-mediated regulation. Our data reveal that CaM, as a core regulating factor, connects the functional roles of the three main intracellular ions, Na(+), Ca(2+), and Mg(2+), by modulating VGSCs and provides a possible explanation for the seizure discharge observed in low-Mg(2+) neurons.
authors: Department of Pharmaceutical Toxicology, School of Pharmacy, China Medical University, Shenyang, China;
authors: Feng
authors: F
authors: Guo
authors: Department of Pharmaceutical Toxicology, School of Pharmacy, China Medical University, Shenyang, China;
authors: Pei-Dong
authors: PD
authors: Zhou
authors: Department of Pharmaceutical Toxicology, School of Pharmacy, China Medical University, Shenyang, China;
authors: Qing-Hua
authors: QH
authors: Gao
authors: Department of Clinical Pharmacy, School of Life Science and Biopharmaceutics, Shenyang Pharmaceutical University, Shenyang, China;
authors: Jian
authors: J
authors: Gong
authors: Department of Pharmaceutical Toxicology, School of Pharmacy, China Medical University, Shenyang, China;
authors: Rui
authors: R
authors: Feng
authors: Department of Neurology, The First Hospital of China Medical University, Shenyang, China; and.
authors: Xiao-Xue
authors: XX
authors: Xu
authors: Department of Pharmaceutical Toxicology, School of Pharmacy, China Medical University, Shenyang, China;
authors: Shu-Yuan
authors: SY
authors: Liu
authors: Department of Pharmaceutical Toxicology, School of Pharmacy, China Medical University, Shenyang, China;
authors: Hui-Yuan
authors: HY
authors: Hu
authors: Department of Pharmaceutical Toxicology, School of Pharmacy, China Medical University, Shenyang, China;
authors: Mei-Mi
authors: MM
authors: Zhao
authors: Department of Pharmacology and Therapeutics, University of Manitoba, Winnipeg, Manitoba, Canada.
authors: Hogan-Cann
authors: HC
authors: Adam
authors: Department of Pharmaceutical Toxicology, School of Pharmacy, China Medical University, Shenyang, China;
authors: Ji-Qun
authors: JQ
authors: Cai
authors: Department of Pharmaceutical Toxicology, School of Pharmacy, China Medical University, Shenyang, China;
authors: Li-Ying
authors: LY
authors: Hao
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D058256:Brain Waves; D002118:Calcium / Q000494:pharmacology*; D002147:Calmodulin / Q000494:pharmacology*; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D006624:Hippocampus / Q000166:cytology*; D006801:Humans; D008274:Magnesium / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D012640:Seizures / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology; D061567:Voltage-Gated Sodium Channel Blockers / Q000494:pharmacology; D061566:Voltage-Gated Sodium Channels / Q000378:metabolism*
chemical_list: D002147:Calmodulin; D061567:Voltage-Gated Sodium Channel Blockers; D061566:Voltage-Gated Sodium Channels; D013779:Tetrodotoxin; D000255:Adenosine Triphosphate; D008274:Magnesium; D002118:Calcium
keywords: calcium; calmodulin; magnesium; voltage-gated sodium channels