Department of Environmental and Biological Sciences, University of Eastern Finland, 80101 Joensuu, Finland.
Department of Human and Animal Physiology, Lomonosov Moscow State University, Leninskiye Gory 1-12, 119234 Moscow, Russia.
J Exp Biol. 2021 Apr 15;224(8). doi: 10.1242/jeb.241067. Epub 2021 Apr 16.
Heat tolerance of heart rate in fish is suggested to be limited by impaired electrical excitation of the ventricle due to the antagonistic effects of high temperature on Na+ (INa) and K+ (IK1) ion currents (INa is depressed at high temperatures while IK1 is resistant to them). To examine the role of Na+ channel proteins in heat tolerance of INa, we compared temperature dependencies of zebrafish (Danio rerio, warm-dwelling subtropical species) and rainbow trout (Oncorhynchus mykiss, cold-active temperate species) ventricular INa, and INa generated by the cloned zebrafish and rainbow trout NaV1.4 and NaV1.5 Na+ channels in human embryonic kidney (HEK) cells. Whole-cell patch-clamp recordings showed that zebrafish ventricular INa has better heat tolerance and slower inactivation kinetics than rainbow trout ventricular INa. In contrast, heat tolerance and inactivation kinetics of zebrafish and rainbow trout NaV1.4 channels are similar when expressed in the identical cellular environment of HEK cells. The same applies to NaV1.5 channels. These findings indicate that thermal adaptation of ventricular INa is largely achieved by differential expression of Na+ channel alpha subunits: zebrafish that tolerate higher temperatures mainly express the slower NaV1.5 isoform, while rainbow trout that prefer cold waters mainly express the faster NaV1.4 isoform. Differences in elasticity (stiffness) of the lipid bilayer and/or accessory protein subunits of the channel assembly may also be involved in thermal adaptation of INa. The results are consistent with the hypothesis that slow Na+ channel kinetics are associated with increased heat tolerance of cardiac excitation.
鱼类的心率耐热性被认为受到心室电兴奋的限制，这是由于高温对钠离子（INa）和钾离子（IK1）离子电流的拮抗作用所致（INa 在高温下被抑制，而 IK1 则对其具有抗性）。为了研究钠离子通道蛋白在 INa 耐热性中的作用，我们比较了斑马鱼（Danio rerio，热带亚热带温水物种）和虹鳟鱼（Oncorhynchus mykiss，冷水活性温带物种）心室 INa 的温度依赖性，以及克隆的斑马鱼和虹鳟鱼 NaV1.4 和 NaV1.5 钠离子通道在人胚肾（HEK）细胞中产生的 INa。全细胞膜片钳记录显示，斑马鱼心室 INa 具有更好的耐热性和更慢的失活动力学，而虹鳟鱼心室 INa 则相反。相比之下，当在相同的 HEK 细胞细胞环境中表达时，斑马鱼和虹鳟鱼 NaV1.4 通道的耐热性和失活动力学相似。NaV1.5 通道也是如此。这些发现表明，心室 INa 的热适应主要是通过钠离子通道α亚基的差异表达来实现的：能耐受更高温度的斑马鱼主要表达较慢的 NaV1.5 同工型，而更喜欢冷水的虹鳟鱼主要表达较快的 NaV1.4 同工型。通道组装的脂质双层和/或辅助蛋白亚基的弹性（硬度）差异也可能参与 INa 的热适应。这些结果与慢钠离子通道动力学与心脏兴奋耐热性增加相关的假设一致。
