Garner Molly, Barber Riley G, Cussins Jace, Hall Diarmid, Reisinger Jessica, Stecyk Jonathan A W
Department of Biological Sciences, University of Alaska Anchorage, Anchorage, AK, 99508, USA.
Curr Res Physiol. 2022 Jul 8;5:292-301. doi: 10.1016/j.crphys.2022.07.002. eCollection 2022.
Previous studies have reported evidence of atrio-ventricular (AV) block in the oxygen-limited heart. However, if cardiac arrhythmia occurs in live turtles during prolonged anoxia exposure remains unknown. Here, we compare the effects of prolonged anoxic submergence and subsequent reoxygenation on cardiac electrical activity through electrocardiogram (ECG) recordings of 21 °C- and 5 °C-acclimated turtles to assess the prevalence of cardiac arrhythmia. Additionally, to elucidate the influence of extracellular conditions on the prominence of cardiac arrhythmia, we exposed spontaneously contracting right atrium and electrically coupled ventricle strip preparations to extracellular conditions that sequentially and additively approximated the shift from the normoxic to anoxic extracellular condition of warm- and cold-acclimated turtles. Cardiac arrhythmia was prominent in 21 °C anoxic turtles. Arrhythmia was qualitatively evidenced by groupings of contractions in pairs and trios and quantified by an increased coefficient of variation of the RR interval. Similarly, exposure to combined anoxia, acidosis, and hyperkalemia induced arrhythmia that was not counteracted by hypercalcemia or combined hypercalcemia and heightened adrenergic stimulation. By comparison, cold acclimation primed the turtle heart to be resilient to cardiac arrhythmia. Although cardiac irregularities were present intermittently, no change in the variation of the RR interval occurred with prolonged anoxia exposure at 5 °C. Moreover, the studies at 5 °C highlighted the importance of adrenergic stimulation in counteracting AV block. Finally, at both acclimation temperatures, cardiac arrhythmia and irregularities ceased upon reoxygenation, indicating that the heart recovers from anoxia-induced disruptions to cardiac excitation.
先前的研究报告了缺氧心脏中存在房室（AV）阻滞的证据。然而，在长期缺氧暴露期间活龟是否会发生心律失常仍不清楚。在这里，我们通过对适应21°C和5°C环境的海龟进行心电图（ECG）记录，比较了长期缺氧潜水及随后复氧对心脏电活动的影响，以评估心律失常的发生率。此外，为了阐明细胞外环境对心律失常显著程度的影响，我们将自发收缩的右心房和电耦合心室肌条标本暴露于依次叠加模拟适应温暖和寒冷环境海龟从常氧到缺氧细胞外环境转变的细胞外环境中。在适应21°C环境的缺氧海龟中，心律失常很明显。心律失常在定性上表现为成对和三联的收缩群，在定量上表现为RR间期变异系数增加。同样，暴露于缺氧、酸中毒和高钾血症的联合环境中会诱发心律失常，高钙血症或高钙血症与增强的肾上腺素能刺激联合作用并不能抵消这种心律失常。相比之下，冷适应使海龟心脏对心律失常具有抵抗力。虽然心脏不规则现象间歇性出现，但在5°C下长期缺氧暴露时，RR间期的变异没有变化。此外，在5°C下的研究突出了肾上腺素能刺激在对抗房室阻滞中的重要性。最后，在两个适应温度下，复氧后心律失常和不规则现象均停止，这表明心脏从缺氧引起的心电活动紊乱中恢复过来。
