Blockade of the TTX-resistant Na+ channel by multivalent cations in dorsal root ganglion neurons

• Main Authors: Chen Wan Yu, 陳婉瑜
• Other Authors: Kuo Chung Chin
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/66738233537446350819

碩士 === 國立臺灣大學 === 生理學研究所 === 90 === TTX（tetrodotoxin）is a common animal toxin to block the Na+ channel. According to the sensitivity to the TTX, Na+ channel can be divided into two groups, the TTX-sensitive Na+ channels and the TTX-resistant Na+ channels. TTX-resistant Na+ channels have been found in peripheral nervous systems, and may play an important in the transmission of slow pain. The TTX-resistant Na+ channels have lower affinity to TTX, much slower activation and inactivation rate, and more sensitive to inorganic Ca2+ channel blockers（Cd2+、Co2+、Mn2+、Zn2+、Ni2+、La3+） than TTX-sensitive ones. However, the mechanism underlying the block of the TTX-resistant Na+ channels by the inorganic cations remains unknown. We found that the blocking effect of these cations on the TTX-resistant Na+ channels in dorsal root ganglion neurons are both concentration dependent and flow dependent. The blocking effect is much more manifest in the presence of inward Na+ current than outward Na+ current, with the blocking potency La3+> Zn2+> Ni2+> Co2+>Mn2+. On the other hand, the voltage dependence is Mn2+>Co2+>Ni2+ >Zn2+>La3+. These findings suggest that these cations and Na+ ion can bind to a single-file multi-ion region in TTX-resistant Na+ channels, and these region may contain ion binding sites consisting of carboxyl groups, sulfhydryl groups, and/or oxygen-containing groups.