Department of Biological Sciences, Ohio University, Athens, OH, 45701, USA.
Institute of Arctic Biology, University of Alaska, Fairbanks, AK, 99775, USA.
J Comp Physiol B. 2019 Apr;189(2):213-222. doi: 10.1007/s00360-019-01207-x. Epub 2019 Feb 9.
Disruption of neuronal function is likely to influence limits to thermal tolerance. We hypothesized that with acute warming the structure and function of neuronal membranes in the Antarctic notothenioid fish Chaenocephalus aceratus are more vulnerable to perturbation than membranes in the more thermotolerant notothenioid Notothenia coriiceps. Fluidity was quantified in synaptic membranes, mitochondrial membranes, and myelin from brains of both species of Antarctic fishes. Polar lipid compositions and cholesterol contents were analyzed in myelin; cholesterol was measured in synaptic membranes. Thermal profiles were determined for activities of two membrane-associated proteins, acetylcholinesterase (AChE) and Na/K-ATPase (NKA), from brains of animals maintained at ambient temperature or exposed to their critical thermal maxima (CT). Synaptic membranes of C. aceratus were consistently more fluid than those of N. coriiceps (P < 0.0001). Although the fluidities of both myelin and mitochondrial membranes were similar among species, sensitivity of myelin fluidity to in vitro warming was greater in N. coriiceps than in C. aceratus (P < 0.001), which can be explained by lower cholesterol contents in myelin of N. coriiceps (P < 0.05). Activities of both enzymes, AChE and NKA, declined upon CT exposure in C. aceratus, but not in N. coriiceps. We suggest that hyper-fluidization of synaptic membranes with warming in C. aceratus may explain the greater stenothermy in this species, and that thermal limits in notothenioids are more likely to be influenced by perturbations in synaptic membranes than in other membranes of the nervous system.
神经元功能的紊乱可能会影响热耐受极限。我们假设，在急性变暖的情况下，南极鳕鱼 Chaenocephalus aceratus 的神经元膜的结构和功能比更耐热的南极鳕鱼 Notothenia coriiceps 的神经元膜更容易受到干扰。我们在这两种南极鱼类的脑内突触膜、线粒体膜和髓鞘中量化了流动性。我们分析了髓鞘中的极性脂质组成和胆固醇含量；突触膜中的胆固醇含量也在测量范围。我们从生活在环境温度下的动物或暴露在其临界热极值（CT）下的动物的脑中测定了两种膜相关蛋白，乙酰胆碱酯酶（AChE）和 Na/K-ATP 酶（NKA）的活性的热谱。C. aceratus 的突触膜始终比 N. coriiceps 的突触膜更具流动性（P<0.0001）。尽管两种物种的髓鞘和线粒体膜的流动性相似，但 N. coriiceps 的髓鞘流动性对体外加热的敏感性比 C. aceratus 的更高（P<0.001），这可以用 N. coriiceps 的髓鞘中胆固醇含量较低来解释（P<0.05）。在 C. aceratus 中，两种酶，AChE 和 NKA 的活性在 CT 暴露后下降，但在 N. coriiceps 中没有。我们认为，C. aceratus 中突触膜的超流动性增加可能解释了该物种的更高耐热性，并且在 notothenioids 中，热极限更有可能受到突触膜的干扰，而不是神经系统的其他膜的干扰。
