Anestis Andreas, Pörtner Hans O, Lazou Antigone, Michaelidis Basile
Laboratory of Animal Physiology, Department of Zoology, School of Biology, Faculty of Science, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece.
J Exp Biol. 2008 Sep;211(Pt 17):2889-98. doi: 10.1242/jeb.016782.
The present study set out to investigate the thermal limits of the Mediterranean bivalve Modiolus barbatus, acclimated to various temperatures, and includes a comparison of laboratory determined limits with its temperature-dependent restriction to deeper water layers in its natural habitat. Thermal responses and limits were determined by integrating information from various levels of biological organization, including the expression of Hsp70 and Hsp90, the phosphorylation of stress-activated protein kinases, p38 mitogen-activated protein kinase (p38 MAPK) and cJun-N-terminal kinases (JNKs) as well as metabolic adjustments. The latter were assessed by examining temperature effects on the activity of the key glycolytic enzyme pyruvate kinase (PK). The expression of Hsp70 and Hsp90 was activated when mussels were acclimated to temperatures above 20 degrees C. Increased phosphorylation of p38 MAPK and JNKs at about the same temperatures indicate activation of MAPK signaling cascades and their potential involvement in the induction of Hsp genes. As indicated by the activity of PK, Modiolus barbatus maintains some aerobic capacity when acclimated to temperatures up to 24 degrees C, while further warming probably caused metabolic depression and a shift from aerobic to anaerobic metabolism. An increase in mortality occurred in parallel, during acclimation to temperatures above 24 degrees C. Our results indicate that both the biochemical stress indicators and metabolic status respond in parallel once hypoxemia becomes extreme. Comparison with our previous study of thermal limits and vertical distribution in M. galloprovincialis dwelling in shallow waters emphasizes the relevance of maintained aerobic scope over that of passive tolerance for permanent vertical zonation at higher temperatures in the field. These findings and conclusions are in line with the concept of oxygen and capacity limited thermal tolerance and the associated systemic to molecular hierarchy of thermal limitation.
本研究旨在调查适应不同温度的地中海双壳贝类巴氏偏顶蛤的热极限，并将实验室测定的极限与其在自然栖息地中对较深水层的温度依赖性限制进行比较。通过整合来自生物组织各个层面的信息来确定热反应和极限，这些信息包括热休克蛋白70（Hsp70）和热休克蛋白90（Hsp90）的表达、应激激活蛋白激酶（p38丝裂原活化蛋白激酶（p38 MAPK）和cJun氨基末端激酶（JNKs））的磷酸化以及代谢调节。后者通过检查温度对关键糖酵解酶丙酮酸激酶（PK）活性的影响来评估。当贻贝适应高于20摄氏度的温度时，Hsp70和Hsp90的表达被激活。在大约相同温度下p38 MAPK和JNKs磷酸化增加表明MAPK信号级联被激活，并且它们可能参与Hsp基因的诱导。如PK活性所示，巴氏偏顶蛤在适应高达24摄氏度的温度时保持一定的有氧能力，而进一步升温可能导致代谢抑制以及从有氧代谢向无氧代谢的转变。在适应高于24摄氏度的温度期间，死亡率同时增加。我们的结果表明，一旦低氧血症变得极端，生化应激指标和代谢状态会同时做出反应。与我们之前对栖息在浅水区的加利福尼亚偏顶蛤的热极限和垂直分布的研究相比，强调了在野外较高温度下维持有氧范围相对于被动耐受对于永久垂直分区的相关性。这些发现和结论与氧和容量限制热耐受性的概念以及热限制的相关系统到分子层次结构一致。
