Antarctic notothenioids are noted for extreme stenothermy, yet underpinnings of their thermal limits are not fully understood. We hypothesized that properties of ventricular membranes could explain previously observed differences among notothenioids in temperature onset of cardiac arrhythmias and persistent asystole. Microsomes were prepared using ventricles from six species of notothenioids, including four species from the hemoglobin-less (Hb−) family Channichthyidae (icefishes), which also differentially express cardiac myoglobin (Mb), and two species from the (Hb+) Nototheniidae. We determined membrane fluidity and structural integrity by quantifying fluorescence depolarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) and leakage of 5(6)-carboxyfluorescein, respectively, over a temperature range from ambient (0 °C) to 20 °C. Compositions of membrane phospholipids and cholesterol contents were also quantified. Membranes from all four species of icefishes exhibited greater fluidity than membranes from the red-blooded species N. coriiceps. Thermal sensitivity of fluidity did not vary among species. The greatest thermal sensitivity to leakage occurred between 0 and 5 °C for all species, while membranes from the icefish, Chaenocephalus aceratus (Hb−/Mb−) displayed leakage that was nearly 1.5-fold greater than leakage in N. coriiceps (Hb+/Mb+). Contents of phosphatidylethanolamine (PE) were approximately 1.5-fold greater in icefishes than in red-blooded fishes, and phospholipids had a higher degree of unsaturation in icefishes than in Hb + notothenioids. Cholesterol contents were lowest in Champsocephalus gunnari (Hb−/Mb−) and highest in the two Hb+/Mb + species, G. gibberifrons and N. coriiceps. Our results reveal marked differences in membrane properties and indicate a breach in membrane fluidity and structural integrity at a lower temperature in icefishes than in red-blooded notothenioids.

南极类异戊二烯类化合物被认为具有极强的狭窄性，但其热极限的基础尚不完全清楚。我们假设心室膜的性质可以解释以前观察到的类胡萝卜素之间在心律不齐和持续性心律不齐温度发作方面的差异。使用来自六种类胡萝卜素的心室制备微粒体，其中包括来自无血红蛋白（Hb-）的Channichthyidae（icefishes）的四种，它们也差异表达心脏肌红蛋白（Mb），以及来自（Hb +）Nototheniidae的两种。我们通过在环境温度（0°C）范围内分别量化1,6-二苯基-1,3,5-己三烯（DPH）的荧光去极化和5（6）-羧基荧光素的泄漏来确定膜的流动性和结构完整性）至20°C。还定量了膜磷脂的成分和胆固醇含量。四种鱼类的膜的流动性都比红血种的膜好N. coriiceps。流动性的热敏感性在物种之间没有变化。对于所有物种，对泄漏的最大热敏感性发生在0到5°C之间，而来自冰鱼，无头狐猴（Chaenocephalus aceratus）的膜（Hb- / Mb-）所显示的泄漏几乎是Coriicepseps（Hb + / Mb +）。在冰鱼中，磷脂酰乙醇胺（PE）的含量比在红鱼中高约1.5倍，并且在冰鱼中，磷脂的不饱和度比在Hb +异戊二烯类中更高。胆固醇含量分别为最低Champsocephalus gunnari（HB-/ MB-）和最高的两个血红蛋白+ / MB +物种，G. gibberifrons和N. coriiceps。我们的研究结果表明，与红色血液中的类胡萝卜素相比，冰鱼在较低温度下膜的流动性和结构完整性遭到破坏。