Goldin Alan L
Department of Microbiology and Molecular Genetics, University of California, Irvine, CA 92697-4025, USA.
J Exp Biol. 2002 Mar;205(Pt 5):575-84. doi: 10.1242/jeb.205.5.575.
Voltage-gated Na(+) channels play important functional roles in the generation of electrical excitability in most vertebrate and invertebrate species. These channels are members of a superfamily that includes voltage-gated K(+), voltage-gated Ca(2+) and cyclic-nucleotide-gated channels. There are nine genes encoding voltage-gated Na(+) channels in mammals, with a tenth homologous gene that has not been shown to encode a functional channel. Other vertebrate and invertebrate species have a smaller number of Na(+) channel genes. The mammalian genes can be classified into five branches in a phylogenetic tree, and they are localized on four chromosomes. Four of the branches representing the four chromosomal locations probably resulted from the chromosomal duplications that led to the four Hox gene clusters. These duplications occurred close to the emergence of the first vertebrates. The fifth branch probably evolved from a separate ancestral Na(+) channel gene. There are two branches in the invertebrate tree, although members of only one of those branches have been demonstrated to encode functional voltage-gated Na(+) channels. It is possible that the other branch may have diverged, so that its members do not represent true voltage-gated Na(+) channels. Vertebrate and invertebrate Na(+) channels appear to be derived from a single primordial channel that subsequently evolved independently in the two lineages.
电压门控性钠通道在大多数脊椎动物和无脊椎动物的电兴奋性产生过程中发挥着重要的功能作用。这些通道属于一个超家族，该超家族还包括电压门控性钾通道、电压门控性钙通道和环核苷酸门控通道。在哺乳动物中，有九个基因编码电压门控性钠通道，还有第十个同源基因，但尚未证明其能编码功能性通道。其他脊椎动物和无脊椎动物物种的钠通道基因数量较少。在系统发育树中，哺乳动物的基因可分为五个分支，它们位于四条染色体上。代表四个染色体位置的四个分支可能源于导致四个Hox基因簇的染色体复制。这些复制发生在第一批脊椎动物出现之时。第五个分支可能是从一个单独的祖先钠通道基因进化而来。在无脊椎动物树中有两个分支，不过只有其中一个分支的成员被证明能编码功能性电压门控性钠通道。另一个分支有可能已经分化，因此其成员并不代表真正的电压门控性钠通道。脊椎动物和无脊椎动物的钠通道似乎源自一个单一的原始通道，该通道随后在这两个谱系中独立进化。
