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Abstract：
Placozoa are small disc-shaped animals, representing the simplest known, possibly ancestral, organization of free-living animals. With only six morphological distinct cell types, without any recognized neurons or muscle, placozoans exhibit fast effector reactions and complex behaviors. However, little is known about electrogenic mechanisms in these animals. Here, we showed the presence of rapid action potentials in four species of placozoans (Trichoplax adhaerens [H1 haplotype], Trichoplax sp.[H2], Hoilungia hongkongensis [H13], and Hoilungia sp. [H4]). These action potentials are sodium-dependent and can be inducible. The molecular analysis suggests the presence of 5-7 different types of voltage-gated sodium channels, which showed substantial evolutionary radiation compared to many other metazoans. Such unexpected diversity of sodium channels in early-branched metazoan lineages reflect both duplication events and parallel evolution of unique behavioral integration in these nerveless animals.
摘要：
胎盘动物是小的圆盘形动物，代表已知的最简单的，可能是祖先,自由生活的动物组织。只有六种形态不同的细胞类型，没有任何识别的神经元或肌肉，胎盘动物表现出快速的效应子反应和复杂的行为。然而,对这些动物的电机制知之甚少。这里,我们显示了四种placozoans中存在快速动作电位（Trichoplaxadhaerens[H1单倍型]，Trichoplaxsp.[H2],香港海伦佳[H13]，和Hoilungiasp.[H4])。这些动作电位是钠依赖性的并且可以是可诱导的。分子分析表明存在5-7种不同类型的电压门控钠通道，与许多其他后生动物相比，它显示出大量的进化辐射。早期分支后生动物谱系中钠通道的这种出乎意料的多样性反映了这些无神经动物中重复事件和独特行为整合的平行进化。
