Synthetic ciguatoxins selectively activate Nav1.8-derived chimeric sodium channels expressed in HEK293 cells.
The synthetic ciguatoxin CTX3C has been shown to activate tetrodotoxin (TTX)-sensitive sodium channels (Na(v)1.2, Na(v)1.4, and Na(v)1.5) by accelerating activation kinetics and shifting the activation curve toward hyperpolarization (Yamaoka, K., Inoue, M., Miyahara, H., Miyazaki, K., and Hirama, M. (2004) Br. J. Pharmacol. 142, 879-889). In this study, we further explored the effects of CTX3C on the TTX-resistant sodium channel Na(v)1.8. TTX-resistant channels have been shown to be involved in transducing pain and related sensations (Akopian, A. N., Sivilotti, L., and Wood, J. N. (1996) Nature 379, 257-262). Thus, we hypothesized that ciguatoxin-induced activation of the Na(v)1.8 current would account for the neurological symptoms of ciguatera poisoning. We found that 0.1 mum CTX3C preferentially affected the activation process of the Na(v)1.8 channel compared with those of the Na(v)1.2 and Na(v)1.4 channels. Importantly, without stimulation, 0.1 mum CTX3C induced a large leakage current (I (L)). The conductance of the I (L) calculated relative to the maximum conductance (G (max)) was 10 times larger than that of Na(v)1.2 or Na(v)1.4. To determine the molecular domain of Na(v)1.8 responsible for conferring higher sensitivity to CTX3C, we made two chimeric constructs from Na(v)1.4 and Na(v)1.8. Chimeras containing the N-terminal half of Na(v)1.8 exhibited a large response similar to wild-type Na(v)1.8, indicating that the region conferring high sensitivity to ciguatoxin action is located in the D1 or D2 domains.
Yamaoka
Kaoru
K
Department of Physical Therapy, Faculty of Health Sciences, Hiroshima International University, Higashi-Hiroshima 739-2695, Japan. k-yamao@hs.hirokoku-u.ac.jp
Inoue
Masayuki
M
Miyazaki
Keisuke
K
Hirama
Masahiro
M
Kondo
Chie
C
Kinoshita
Eiji
E
Miyoshi
Hiroshi
H
Seyama
Issei
I
D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D036841:Ciguatera Poisoning / Q000235:genetics / Q000378:metabolism*; D002922:Ciguatoxins / Q000494:pharmacology*; D015870:Gene Expression; D006801:Humans; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D062553:NAV1.4 Voltage-Gated Sodium Channel; D062559:NAV1.8 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D010449:Peptide Mapping; D017434:Protein Structure, Tertiary / Q000235:genetics; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015222:Sodium Channels / Q000235:genetics / Q000378:metabolism*
D009124:Muscle Proteins; D062553:NAV1.4 Voltage-Gated Sodium Channel; D062559:NAV1.8 Voltage-Gated Sodium Channel; D009419:Nerve Tissue Proteins; D011993:Recombinant Fusion Proteins; C568317:SCN10A protein, human; C106251:SCN4A protein, human; C568319:Scn10a protein, rat; C466180:Scn4a protein, rat; D015222:Sodium Channels; D002922:Ciguatoxins