Department of Zoology, University of British Columbia, 6270 University Boulevard, Vancouver, British Columbia, Canada.
Proc Biol Sci. 2010 May 22;277(1687):1553-60. doi: 10.1098/rspb.2009.1545. Epub 2010 Jan 13.
This is the first direct physiological evidence in support of the ionoregulatory hypothesis, challenging the long-held assumption that teleost gills develop initially for gas exchange. Resting unidirectional sodium (Na(+)) uptake and oxygen (O(2)) uptake across the skin and gills were measured simultaneously in larval rainbow trout, Oncorhynchus mykiss, during development. In soft and hard water, Na(+) uptake shifted to the gills by 15 and 16 days post-hatch (dph) while O(2) uptake took 50-80% longer and shifted by 23 and 28 dph, respectively. This suggests that gills are required for ionoregulation prior to gas exchange in developing rainbow trout. The age of transition for Na(+) uptake, gill Na(+), K(+)-ATPase (NKA) alpha-subunit protein expression and gill NKA enzyme activity were not significantly different between soft and hard water-reared groups, which suggests a lack of plasticity in gill ionoregulatory development. In rainbow trout, the gills assume a dominant role in ionoregulation before gas exchange, suggesting that ionoregulation may be the initial driving force for gill development. Further investigation is required to determine whether this pattern is consistent with other teleosts and more basal fishes during early development to gain insight into the role of ionoregulation in vertebrate gill evolution.
这是支持离子调节假说的首个直接生理证据，挑战了长期以来的假设，即硬骨鱼类的鳃最初是为气体交换而发育的。在发育过程中，同时测量了幼鲑鱼（Oncorhynchus mykiss）在软、硬水中的皮肤和鳃的静息单向钠（Na(+))摄取和氧气（O(2))摄取。在软、硬水中，Na(+)摄取分别在孵化后 15 天和 16 天转移到鳃，而 O(2)摄取则需要更长的时间（分别为 50-80%），并分别在孵化后 23 天和 28 天转移到鳃。这表明，在发育中的虹鳟鱼中，鳃在气体交换之前就需要进行离子调节。在软、硬水中，Na(+)摄取的过渡年龄、鳃 Na(+), K(+)-ATP 酶（NKA）α亚基蛋白表达和鳃 NKA 酶活性没有显著差异，这表明鳃离子调节发育缺乏可塑性。在虹鳟鱼中，鳃在离子调节方面先于气体交换发挥主导作用，这表明离子调节可能是鳃发育的初始驱动力。需要进一步研究以确定这种模式是否与其他硬骨鱼和早期发育的更基础鱼类一致，以深入了解离子调节在脊椎动物鳃进化中的作用。
