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Paper | Special issue | Vol 59, No. 2, 2003, pp.613-622
Published online, 1st January, 1970
DOI: 10.3987/COM-02-S62
Photochemical Identification of the Binding Region for (S)-Semotiadil on Sodium Channels: Comparison with that for (R)-Semotiadil on Skeletal Muscle Calcium Channel

Hiromi Yoshikawa, Eisuke Shimizu, Kohichi Kawahara, Akihiko Kuniyasu, Toshiro Shibano, and Hitoshi Nakayama*

*Department of Biofunctional Chemistry, Faculty of Pharmaceutical Sciences, Kumamoto University, 5-1 Oe-hon-machi, Kumamoto 862-0973, Japan

Abstract

To clarify the recognition site of (S)-semotiadil in the Na+ channels, we employed photoaffinity labeling with (S)-[3H]-D51-4700, an azidophenyl derivative of (S)-semotiadil, to Na+ channel preparations from rat brains and porcine hearts, and the results were compared with those by (R)-enantiomer to skeletal muscle Ca2+ channel. Protease-digestion of the photolabeled Na+ channels followed by quantitative immunoprecipitation assay using a site-directed antibody, revealed that 10- and 13- kDa fargments of brain and cardiac Na+ channels, respectively, were located within the regions including IVS6. These regions are corresponding to the 8.3 kDa fragment photolabled by (R)-[3H]-D51-4700 in the skeletal muscle Ca2+ channel. Interestingly, however, the photoincorporation of (S)-[3H]-D51-4700 into the Na+ channel was 2-3 times higher than that of (R)-isomer; and visa versa in the Ca2+ channels.