Else Paul L
School of Medicine (IHMRI), University of Wollongong, Wollongong, NSW 2522, Australia
J Exp Biol. 2016 Jul 15;219(Pt 14):2098-102. doi: 10.1242/jeb.136747. Epub 2016 May 9.
The thermal dependence (0-40°C) of Na(+) flux in isolated liver cells of three endotherms (mice, rat and rabbit) was compared with that of ectotherms in the form of a thermally tolerant amphibian (cane toad), a cold-water fish (rainbow trout) and a thermophilic reptile (lizard). Mammals were found to share similar high rates of Na(+) flux (3.0-3.7 nmol Na(+) mg(-1) protein min(-1)) at their normal body temperatures (36-39°C). These Na(+) flux rates were significantly greater (P<0.0004-0.0001) than those of the ectotherms, which shared similar low rates of Na(+) flux (0.7-1.3 nmol Na(+) mg(-1) protein min(-1)) at their very different normal acclimated body temperatures (15°C for trout, 25°C for toad and 37°C for the lizard species). Trout, which possess highly unsaturated membranes (similar to those of mammals), showed a Na(+) flux with high thermal sensitivity at low temperatures similar to that found in mammals at higher temperatures. The thermal sensitivity of toad Na(+) flux was significantly less (P<0.05-0.01) than that of rat and rabbit. Trout Na(+) flux did not increase with increasing temperature much above 20°C, whereas all other species measured increased their Na(+) flux with increasing temperature up to 40°C. In conclusion, at normal operating body temperatures, the rate of Na(+) flux is much lower in ectotherms.
将三种恒温动物（小鼠、大鼠和兔子）分离肝细胞中钠（Na⁺）通量的热依赖性（0 - 40°C）与变温动物进行了比较，变温动物包括耐热两栖动物（甘蔗蟾蜍）、冷水鱼（虹鳟鱼）和嗜热爬行动物（蜥蜴）。研究发现，哺乳动物在其正常体温（36 - 39°C）下钠（Na⁺）通量的速率相似且较高（3.0 - 3.7 nmol Na⁺ mg⁻¹蛋白质 min⁻¹）。这些钠（Na⁺）通量速率显著高于变温动物（P < 0.0004 - 0.0001），变温动物在其差异很大的正常驯化体温下钠（Na⁺）通量速率相似且较低（0.7 - 1.3 nmol Na⁺ mg⁻¹蛋白质 min⁻¹）（虹鳟鱼为15°C，蟾蜍为25°C，蜥蜴物种为37°C）。具有高度不饱和膜（与哺乳动物相似）的虹鳟鱼在低温下钠（Na⁺）通量具有较高的热敏感性，类似于哺乳动物在较高温度下的情况。蟾蜍钠（Na⁺）通量的热敏感性显著低于大鼠和兔子（P < 0.05 - 0.01）。虹鳟鱼的钠（Na⁺）通量在温度高于20°C时增加不多，而其他所有被测物种的钠（Na⁺）通量随温度升高至40°C而增加。总之，在正常工作体温下，变温动物的钠（Na⁺）通量速率要低得多。
