Badr Ahmed, Hassinen Minna, El-Sayed Mohamed F, Vornanen Matti
Department of Environmental and Biological Sciences, University of Eastern Finland, Joensuu, Finland; Department of Zoology, Faculty of Science, Sohag University, Sohag, Egypt.
Department of Environmental and Biological Sciences, University of Eastern Finland, Joensuu, Finland.
Comp Biochem Physiol A Mol Integr Physiol. 2017 Mar;205:15-27. doi: 10.1016/j.cbpa.2016.12.017. Epub 2016 Dec 19.
Temperature sensitivity of electrical excitability is a potential limiting factor for high temperature tolerance of ectotherms. The present study examines whether heat resistance of electrical excitability of cardiac myocytes is modified by seasonal thermal acclimatization in roach (Rutilus rutilus), a eurythermal teleost species. To this end, temperature dependencies of ventricular action potentials (APs), and atrial and ventricular K currents were measured from winter-acclimatized (WiR) and summer-acclimatized (SuR) roach. Under patch-clamp recording conditions, ventricular APs could be triggered over a wide range of temperatures (4-43°C) with prominent changes in resting membrane potential (RMP), AP duration and amplitude. In general, APs of SuR were slightly more tolerant to high temperatures than those of WiR, e.g. the break point temperature (T) of RMP was 37.6±0.4°C in WiR and 41±1°C in SuR (p<0.05). Of the two major cardiac K currents, the inward rectifier K current (I) was particularly heat resistant in both SuR (T 39.4±0.4°C) and WiR (T 40.0±0.4°C) ventricular myocytes. The delayed rectifier K current (I) was not as heat resistant as I. Surprisingly, I of WiR tolerated heat better (T 31.9±0.8°C) than I of SuR (T 24.1±0.5°C) (p<0.05). I (Erg2) channel transcripts of both atrial and ventricular myocytes were up-regulated in WiR. I (Kir2) channel transcripts were not affected by seasonal acclimatization, although ventricular I current was up-regulated in summer. Collectively, these findings show that thermal tolerance limits of K currents in isolated myocytes between seasonally acclimatized roach are much less pronounced than the heat sensitivity of ECG variables in intact fish.
电兴奋性的温度敏感性是变温动物高温耐受性的一个潜在限制因素。本研究考察了广温硬骨鱼拟鲤（Rutilus rutilus）的心肌细胞电兴奋性的耐热性是否会因季节性热适应而改变。为此，我们测量了冬季适应（WiR）和夏季适应（SuR）的拟鲤心室动作电位（APs）以及心房和心室钾电流的温度依赖性。在膜片钳记录条件下，心室APs能在较宽温度范围（4 - 43°C）内被触发，静息膜电位（RMP）、AP持续时间和幅度有显著变化。总体而言，SuR的APs比WiR的对高温稍更耐受，例如，WiR中RMP的断点温度（T）为37.6±0.4°C，SuR中为41±1°C（p<0.05）。在两种主要的心脏钾电流中，内向整流钾电流（I）在SuR（T 39.4±0.4°C）和WiR（T 40.0±0.4°C）的心室肌细胞中都特别耐热。延迟整流钾电流（I）不如I耐热。令人惊讶的是，WiR的I比SuR的I更耐热（T 31.9±0.8°C对T 24.1±0.5°C）（p<0.05）。WiR中心房和心室肌细胞的I（Erg2）通道转录本均上调。I（Kir2）通道转录本不受季节性适应影响，尽管夏季心室I电流上调。总的来说，这些发现表明，季节性适应的拟鲤之间分离的心肌细胞中钾电流的热耐受极限远不如完整鱼心电图变量的热敏感性明显。
