Else P L, Windmill D J, Markus V
Department of Biomedical Science, University of Wollongong, New South Wales, Australia.
Am J Physiol. 1996 Nov;271(5 Pt 2):R1287-94. doi: 10.1152/ajpregu.1996.271.5.R1287.
Previous research has shown ectotherms to have markedly lower sodium pump metabolism than endotherms. Direct measurement of enzymatic activity of the sodium pump (Na(+)-K(+)-adenosinetriphosphatase) confirmed this difference. To determine the source of this difference, sodium pump density was measured with the use of [3H]ouabain binding. Ectotherms and endotherms were found to share similar sodium pump numbers. Approximate densities (in pmol/g) were 250 for skeletal muscle, 500 for liver, 900 for heart, and 8,000 for kidney and brain. Therefore, differences in sodium pump activity between endotherms and ectotherms were due to differences in turnover rates or molecular activities of sodium pumps. Molecular activities of sodium pumps (in ATP/min) of tissues from endotherms were between 6,000 and 12,000 and, for ectotherms, between 1,500 and 2,500. Exceptions were found that included the heart of Bufo marinus. In a single invertebrate species studied, Charax destructor, the sodium pumps of the heart had a low molecular activity characteristic of ectothermic tissues. These results suggest that during the evolution of endothermy there was a general increase in the molecular activity of the sodium pump.
先前的研究表明，变温动物的钠泵代谢明显低于恒温动物。对钠泵（Na(+)-K(+)-三磷酸腺苷酶）的酶活性进行直接测量证实了这种差异。为了确定这种差异的来源，使用[3H]哇巴因结合法测量了钠泵密度。结果发现变温动物和恒温动物的钠泵数量相似。骨骼肌的近似密度（以皮摩尔/克计）为250，肝脏为500，心脏为900，肾脏和大脑为8000。因此，恒温动物和变温动物之间钠泵活性的差异是由于钠泵周转率或分子活性的差异。恒温动物组织中钠泵的分子活性（以ATP/分钟计）在6000至12000之间，变温动物则在1500至2500之间。不过也有例外，比如海蟾蜍的心脏。在所研究的一个单一无脊椎动物物种——毁灭丽体鱼中，其心脏的钠泵具有变温组织的低分子活性特征。这些结果表明，在恒温动物的进化过程中，钠泵的分子活性普遍增加。
