Bucking Carol, Wood Chris M
Department of Biology, McMaster University, 1280 Main St. West, Hamilton, Ontario, Canada, L82 4K1.
Am J Physiol Regul Integr Comp Physiol. 2006 Dec;291(6):R1764-72. doi: 10.1152/ajpregu.00224.2006. Epub 2006 Aug 10.
The role of the gastrointestinal tract in maintaining ionic homeostasis during digestion, as well as the relative contribution of the diet for providing electrolytes, has been generally overlooked in many aquatic species. An experimental diet that contained an inert reference marker (lead-glass beads) was used to quantify the net transport of Na(+), K(+), and Cl(-) during the digestion and absorption of a single meal (3% ration) by freshwater rainbow trout (Oncorhynchus mykiss). Secretion of Cl(-) into the stomach peaked at 8 and 12 h following feeding at a rate of 1.1 mmol.kg(-1).h(-1), corresponding to a theoretical pH of 0.6 in the secreted fluid (i.e., 240 mmol/l HCl). The majority ( approximately 90%) of dietary Na(+) and K(+) was absorbed in the stomach, whereas subsequent large fluxes of Na(+) and Cl(-) into the anterior intestine corresponded to a large flux of water previously observed. The estimated concentration of Na(+) in fluids secreted into the anterior intestine was approximately 155 mmol/l, equivalent to reported hepatic bile values, whereas the estimated concentration of Cl(-) ( approximately 285 mmol/l) suggested seepage of HCl acid from the stomach in advance of the chyme front. Net absorption of K(+) in the stomach occurred following the cessation of Cl(-) secretion, providing indirect evidence of K(+) involvement with HCl acid production. Overall, 80-90% of the K(+) and Cl(-) contents of the meal were absorbed on a net basis, whereas net Na(+) absorption was negligible. Chyme-to-plasma ion concentration gradients were often opposed to the direction of ion transport, especially for Na(+) and Cl(-).
在许多水生生物中，胃肠道在消化过程中维持离子稳态的作用以及饮食在提供电解质方面的相对贡献通常被忽视。一种含有惰性参考标记物（铅玻璃珠）的实验性饲料被用于量化淡水虹鳟（Oncorhynchus mykiss）单次进食（3%定量）消化和吸收过程中Na⁺、K⁺和Cl⁻的净转运。进食后8小时和12小时，Cl⁻分泌到胃中的速率达到峰值，为1.1 mmol·kg⁻¹·h⁻¹，这相当于分泌液的理论pH值为0.6（即240 mmol/L HCl）。大部分（约90%）的膳食Na⁺和K⁺在胃中被吸收，而随后大量的Na⁺和Cl⁻流入前肠，这与之前观察到的大量水流相对应。估计分泌到前肠的液体中Na⁺的浓度约为155 mmol/L，与报道的肝胆汁值相当，而Cl⁻的估计浓度（约285 mmol/L）表明在食糜前端之前有HCl从胃中渗出。Cl⁻分泌停止后，胃中发生了K⁺的净吸收，这为K⁺参与HCl产生提供了间接证据。总体而言，进食的K⁺和Cl⁻含量有80 - 90%以净吸收的方式被吸收，而Na⁺的净吸收可以忽略不计。食糜与血浆之间的离子浓度梯度常常与离子转运方向相反，尤其是对于Na⁺和Cl⁻。
