Akiyama Chifumi, Sakata Souhei, Ono Fumihito
Department of Physiology, Division of Life Sciences, Faculty of Medicine, Osaka Medical and Pharmaceutical University, Osaka, Japan.
PLoS Biol. 2025 Apr 24;23(4):e3003137. doi: 10.1371/journal.pbio.3003137. eCollection 2025 Apr.
Extensive studies over decades have firmly established the concept that action potentials (APs) in muscles are indispensable for muscle contraction. To re-examine the significance of APs, we generated zebrafish lacking APs by editing the scn4aa and scn4ab genes, which together encode NaV1.4 (NaVDKO), using the CRISPR-Cas9 system. Surprisingly, the escape response of NaVDKOs to tactile stimuli, both in the embryonic and adult stages, was indistinguishable from that of wild-type (WT) fish. Ca2+ imaging using the calcium indicator protein GCaMP revealed that myofibers isolated from WT fish could be excited by the application of acetylcholine (ACh), even in the presence of tetrodotoxin (TTX) indicating that NaVs are dispensable for skeletal muscle contraction in zebrafish. Mathematical simulations showed that the end-plate potential was able to elicit a change in membrane potential large enough to activate the dihydropyridine receptors of the entire muscle fiber owing to the small fiber size and the disseminated distribution of neuromuscular synapses in both adults and embryos. Our data demonstrate that NaVs are not essential for muscle contraction in zebrafish and that the physiological significance of NaV1.4 in muscle is not uniform across vertebrates.
数十年来的广泛研究已经牢固确立了这样一个概念，即肌肉中的动作电位（APs）对于肌肉收缩是不可或缺的。为了重新审视动作电位的重要性，我们使用CRISPR-Cas9系统编辑了共同编码NaV1.4（NaVDKO）的scn4aa和scn4ab基因，从而培育出缺乏动作电位的斑马鱼。令人惊讶的是，无论是在胚胎期还是成年期，NaVDKO对触觉刺激的逃避反应与野生型（WT）鱼并无差异。使用钙指示剂蛋白GCaMP进行的Ca2+成像显示，即使存在河豚毒素（TTX），从WT鱼分离出的肌纤维也能被乙酰胆碱（ACh）激发，这表明斑马鱼骨骼肌收缩过程中电压门控钠通道（NaVs）并非必需。数学模拟表明，由于成体和胚胎中肌纤维尺寸小以及神经肌肉突触分布分散，终板电位能够引发足以激活整个肌纤维二氢吡啶受体的膜电位变化。我们的数据表明，NaVs对斑马鱼的肌肉收缩并非必不可少，并且NaV1.4在肌肉中的生理意义在脊椎动物中并不一致。
