Department of Biology, York University, Toronto, Ontario, Canada, M3J 1P3.
Department of Biology, York University, Toronto, Ontario, Canada, M3J 1P3
J Exp Biol. 2019 Apr 1;222(Pt 7):jeb187484. doi: 10.1242/jeb.187484.
Trout caeca are vermiform structures projecting from the anterior intestine of the gastrointestinal tract. Despite their simple gross morphology, these appendages are physically distinct along the anterior-posterior axis, and ultrastructural evidence suggests zonation of function within the structures. Individual caeca from three sections (anterior, middle and posterior) were removed from the intestine of freshwater rainbow trout and investigated for ion transport and enzyme activity. Ca absorption appeared as a combination of active and passive movement, with Michaelis-Menten kinetics observable under symmetrical conditions, and was inhibited by several pharmacological agents (ouabain, La and a calmodulin antagonist). There was a decrease in ion transport function from adjacent to the intestine (proximal) to the distal tip of each caecum, along with decreasing transport from anterior to posterior for the proximal portion alone. Feeding increased the and for Ca absorption within all sections, whereas ion-poor water (IPW) exposure further increased the and for Ca transport in the anterior and middle sections. Increased Na/K-ATPase (NKA) and citrate synthase (CS) activity rates paralleled trends seen in Ca transport. Feeding in freshwater and IPW exposure increased the glycolytic capacity of the caeca via increased pyruvate kinase (PK) and decreased lactate dehydrogenase (LDH) activity, while amino acid metabolism increased with IPW exposure through increased glutamate dehydrogenase (GDH) activity. Overall, feeding and IPW exposure each altered ionoregulation within the caeca of freshwater rainbow trout in a zone-specific pattern, with the anterior and proximal portions of the caeca being most affected. Increased carbohydrate and protein metabolism fueled the increased ATP demand of NKA through CS.
盲囊是从消化道前肠突出的蠕虫状结构。尽管它们的宏观形态简单，但这些附属物在前后轴向上具有明显的物理差异，超微结构证据表明结构内存在功能分区。从淡水虹鳟鱼的肠道中取出三个部分（前、中、后）的单个盲囊，研究其离子转运和酶活性。Ca 吸收似乎是主动和被动运动的结合，在对称条件下可观察到米氏动力学，并且被几种药理学试剂（哇巴因、La 和钙调蛋白拮抗剂）抑制。从肠道（近端）到每个盲囊的远端尖端，离子转运功能逐渐下降，而仅在前部部分从近端到后端的转运减少。摄食增加了所有部分的 Ca 吸收的 和 ，而低离子水（IPW）暴露进一步增加了前、中部分的 Ca 转运的 和 。增加的 Na/K-ATP 酶（NKA）和柠檬酸合酶（CS）活性与 Ca 转运的趋势平行。在淡水和 IPW 暴露中摄食通过增加丙酮酸激酶（PK）和降低乳酸脱氢酶（LDH）活性增加了盲囊的糖酵解能力，而氨基酸代谢通过增加谷氨酸脱氢酶（GDH）活性随着 IPW 暴露而增加。总的来说，摄食和 IPW 暴露以特定区域的方式改变了淡水虹鳟鱼盲囊的离子调节，盲囊的前部和近端部分受影响最大。增加的碳水化合物和蛋白质代谢通过 CS 为 NKA 的增加的 ATP 需求提供燃料。
