The Effects of Calmodulin on the Voltage-gated Sodium Channels, Nav1.4

• Main Authors: Yi-Ting Tsai, 蔡依廷
• Other Authors: Chien-Yuan Pan
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/35963837666511291813

碩士 === 國立臺灣大學 === 生命科學系 === 102 === Voltage-gated sodium channels (Navs) are essential for the initiation and propagation of action potentials in excitable cells. Calmodulin (CaM) is a calcium sensor protein and can bind to the highly conserved IQ motif at the intracellular C-terminal of Navs to regulate channel activities. Each of the N- and C-lobes in CaM has two EF-hand Ca2+-binding motifs and is known to have distinct effects in modulating channel activities. In this report, we co-expressed CaM and mutations with Nav1.4 to characterize how CaM regulates the channel activities. I expressed these proteins in 293T cells and measured the Na+ currents with patch-clamp technique in whole-cell mode. CaM significantly enhanced the current density from -87.3 ± 8.8 to -137.3 ± 16.5 pA/pF, however, CaM1234, which has no Ca2+ binding capability, had little effect on the current density (-76.5 ± 12.6 pA/pF). CaM34, which has no Ca2+-binding abilities at the C-lobe, significantly enhanced the current density -135.0 ± 15.6 pA/pF; in contrast, CaM12, which loses Ca2+-binding abilities at the N-lobe, did not have the effect in enhancing the current density (-81.2 ± 13.1 pA/pF). Elevating the Ca2+ concentration in the pipette solution to 0.2 and 10 μM further enhanced the current density in the presence of CaM overexpression.CaM co-expression significantly shortened the recovery time of Nav1.4 from 3.3 ± 0.2 to 3.0 ± 0.0 msec. These results demonstrate that, under physiologiucal conditions when the intracellular Ca2+ concentration elevates, CaM activation leads to the enhancement of the Nav1.4 currents to regulate the activities of excitable cells.