Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada, M5S 3G5.
Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada, T6G 2E9.
J Exp Biol. 2021 Oct 1;224(19). doi: 10.1242/jeb.242793. Epub 2021 Oct 6.
In most vertebrates, anoxia drastically reduces the production of the essential adenosine triphosphate (ATP) to power its many necessary functions, and, consequently, cell death occurs within minutes. However, some vertebrates, such as the painted turtle (Chrysemys picta bellii), have evolved the ability to survive months without oxygen by simultaneously decreasing ATP supply and demand, surviving the anoxic period without any apparent cellular damage. The impact of anoxia on the metabolic function of painted turtles has received a lot of attention. However, the impact of low temperature has received less attention and the interactive effect of anoxia and temperature even less. In the present study, we investigated the interactive impacts of reduced temperature and severe hypoxia on the electrophysiological properties of pyramidal neurons in painted turtle cerebral cortex. Our results show that an acute reduction in temperature from 20 to 5°C decreases membrane potential, action potential width and amplitude, and whole-cell conductance. Importantly, acute exposure to 5°C considerably slows membrane repolarization by voltage-gated K+ channels. Exposing pyramidal cells to severe hypoxia in addition to an acute temperature change slightly depolarized membrane potential but did not alter action potential amplitude or width and whole-cell conductance. These results suggest that acclimation to low temperatures, preceding severe environmental hypoxia, induces cellular responses in pyramidal neurons that facilitate survival under low oxygen concentrations. In particular, our results show that temperature acclimation invokes a change in voltage-gated K+ channel kinetics that overcomes the acute inhibition of the channel.
在大多数脊椎动物中，缺氧会极大地减少产生维持其许多必要功能的必需三磷酸腺苷 (ATP)，因此，细胞会在数分钟内死亡。然而，一些脊椎动物，如彩龟 (Chrysemys picta bellii)，已经进化出了在没有氧气的情况下存活数月的能力，同时降低 ATP 的供应和需求，在没有任何明显细胞损伤的情况下度过缺氧期。缺氧对彩龟代谢功能的影响已经引起了广泛关注。然而，低温的影响却受到较少关注，缺氧和温度的交互作用甚至更少受到关注。在本研究中，我们研究了低温和严重缺氧对彩龟大脑皮层锥体神经元电生理特性的交互影响。我们的结果表明，急性降温从 20°C 降至 5°C 会降低膜电位、动作电位宽度和幅度以及全细胞电导。重要的是，急性暴露于 5°C 会显著减慢电压门控 K+ 通道的膜复极化。除了急性温度变化外，将锥体细胞暴露于严重缺氧中仅使膜电位轻微去极化，但不改变动作电位幅度、宽度和全细胞电导。这些结果表明，在严重环境缺氧之前适应低温会诱导锥体神经元产生细胞反应，从而促进在低氧浓度下的生存。特别是，我们的研究结果表明，温度适应会引起电压门控 K+ 通道动力学的变化，从而克服通道的急性抑制。
