Overgaard Johannes, Wang Tobias, Nielsen Ole Baekgaard, Gesser Hans
Department of Zoophysiology, Institute of Biological Sciences, University of Aarhus, Aarhus, Denmark.
Physiol Biochem Zool. 2005 Nov-Dec;78(6):976-95. doi: 10.1086/432853. Epub 2005 Sep 8.
Painted turtles (Chrysemys picta) survive months of anoxic submergence, which is associated with large changes in the extracellular milieu where pH falls by 1, while extracellular K+, Ca++, and adrenaline levels all increase massively. While the effect of each of these changes in the extracellular environment on the heart has been previously characterized in isolation, little is known about their interactions and combined effects. Here we examine the isolated and combined effects of hyperkalemia, acidosis, hypercalcemia, high adrenergic stimulation, and anoxia on twitch force during isometric contractions in isolated ventricular strip preparations from turtles. Experiments were performed on turtles that had been previously acclimated to warm (25 degrees C), cold (5 degrees C), or cold anoxia (submerged in anoxic water at 5 degrees C). The differences between acclimation groups suggest that cold acclimation, but not anoxic acclimation per se, results in a downregulation of processes in the excitation-contraction coupling. Hyperkalemia (10 mmol L(-1) K+) exerted a strong negative inotropic effect and caused irregular contractions; the effect was most pronounced at low temperature (57%-97% reductions in twitch force). Anoxia reduced twitch force at both temperatures (14%-38%), while acidosis reduced force only at 5 degrees C (15%-50%). Adrenergic stimulation (10 micromol L(-1)) increased twitch force by 5%-19%, but increasing extracellular [Ca++] from 2 to 6 mmol L(-1) had only small effects. When all treatments were combined with anoxia, twitch force was higher at 5 degrees C than at 25 degrees C, whereas in normoxia twitch force was higher at 25 degrees C. We propose that hyperkalemia may account for a large part of the depressed cardiac contractility during long-term anoxic submergence.
锦龟（彩龟属）能在缺氧状态下存活数月，这与细胞外环境的巨大变化有关，此时pH值下降1，而细胞外钾离子、钙离子和肾上腺素水平均大幅升高。虽然先前已分别对细胞外环境中这些变化各自对心脏的影响进行了表征，但对它们之间的相互作用和综合影响却知之甚少。在此，我们研究了高钾血症、酸中毒、高钙血症、高肾上腺素能刺激和缺氧对来自海龟的离体心室肌条等长收缩期间抽搐力的单独和联合作用。实验是在先前已适应温暖（25摄氏度）、寒冷（5摄氏度）或冷缺氧（浸没于5摄氏度的缺氧水中）环境的海龟身上进行的。适应组之间的差异表明，冷适应而非缺氧适应本身会导致兴奋 - 收缩偶联过程的下调。高钾血症（10毫摩尔/升钾离子）产生强烈的负性肌力作用并导致不规则收缩；该作用在低温时最为明显（抽搐力降低57% - 97%）。缺氧在两个温度下均降低抽搐力（14% - 38%），而酸中毒仅在5摄氏度时降低抽搐力（15% - 50%）。肾上腺素能刺激（10微摩尔/升）使抽搐力增加5% - 19%，但将细胞外钙离子浓度从2毫摩尔/升增加到6毫摩尔/升的影响较小。当所有处理与缺氧联合时，5摄氏度时的抽搐力高于25摄氏度，而在常氧状态下25摄氏度时的抽搐力更高。我们认为高钾血症可能是长期缺氧浸没期间心脏收缩力降低的主要原因。
