Cloning and Distribution of a Putative Tetrodotoxin-Resistant Na^+ Channel in Newt Retina(Physiology)

概要

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Overlapping cDNA clones spanning the entire coding region of a Na^+ channel were isolated from newt retina. The coding region predicts a 2,007 amino acid protein, designated nRNaCh (newt retina sodium channel), which is homologous to other Na^+ channels. In situ hybridization indicated that nRNaCh is expressed exclusively in spiking neurons, where a tetrodotoxin (TTX)-resistant Na^+ current has been recorded. Therefore, nRNaCh cDNA is sure to encode the TTX-resistant Na^+ channel of newt retina. Sequence comparisons show that nRNaCh is more homologous to TTX-sensitive Na^+ channels than to TTX-resistant Na^+ channels. The length of the S5-S6 loop of repeat I of nRNaCh is similar to that of TTX-sensitive channels, whereas TTX-resistant Na^+ channels have a deletion. The 3^<rd> position in the SS2 region of repeat I of nRNaCh is a non-aromatic amino acid (Ala), which is a common feature of TTX-resistant channels. These findings suggest that whether the amino acid at the 3^<rd> position in the SS2 region of repeat I is aromatic or non-aromatic determines the TTX sensitivity of Na^+ channels, not the overall structure of the channel.
社団法人日本動物学会の論文
1999-08-15