Centre of Marine Sciences (CCMar), CIMAR-Laboratório Associado, Universidade do Algarve, Faro, Portugal.
J Comp Physiol B. 2012 Dec;182(8):1069-80. doi: 10.1007/s00360-012-0685-4. Epub 2012 Jun 30.
In the marine fish intestine luminal, HCO₃⁻ can remove divalent ions (calcium and magnesium) by precipitation in the form of carbonate aggregates. The process of epithelial HCO₃⁻ secretion is under endocrine control, therefore, in this study we aimed to characterize the involvement of transmembrane (tmACs) and soluble (sACs) adenylyl cyclases on the regulation of bicarbonate secretion (BCS) and water absorption in the intestine of the sea bream (Sparus aurata). We observed that all sections of sea bream intestine are able to secrete bicarbonate as measured by pH-Stat in Ussing chambers. In addition, gut sac preparations reveal net water absorption in all segments of the intestine, with significantly higher absorption rates in the anterior intestine that in the rectum. BCS and water absorption are positively correlated in all regions of the sea bream intestinal tract. Furthermore, stimulation of tmACs (10 μM FK + 500 μM IBMX) causes a significant decrease in BCS, bulk water absorption and short circuit current (Isc) in a region dependent manner. In turn, stimulation of sACs with elevated HCO₃⁻ results in a significant increase in BCS, and bulk water absorption in the anterior intestine, an action completely reversed by the sAC inhibitor KH7 (200 μM). Overall, the results reveal a functional relationship between BCS and water absorption in marine fish intestine and modulation by tmACs and sAC. In light of the present observations, it is hypothesized that the endocrine effects on intestinal BCS and water absorption mediated by tmACs are locally and reciprocally modulated by the action of sACs in the fish enterocyte, thus fine-tuning the process of carbonate aggregate production in the intestinal lumen.
在海洋鱼类肠道腔中，HCO₃⁻可以通过沉淀的形式将二价离子（钙和镁）以碳酸盐聚集体的形式去除。上皮 HCO₃⁻分泌的过程受内分泌控制，因此，在这项研究中，我们旨在研究跨膜（tmAC）和可溶性（sAC）腺苷酸环化酶对海鲈（Sparus aurata）肠道中 HCO₃⁻分泌（BCS）和水吸收的调节作用。我们观察到，在用 pH-Stat 在 Ussing 室中测量时，海鲈肠道的所有部分都能够分泌 HCO₃⁻。此外，肠道囊制备物显示出所有肠道段的净水分吸收，前肠的吸收速率明显高于直肠。BCS 和水吸收在海鲈肠道的所有区域都呈正相关。此外，tmAC 的刺激（10 μM FK + 500 μM IBMX）以区域依赖性方式导致 BCS、大量水分吸收和短路电流（Isc）显著降低。相反，用升高的 HCO₃⁻刺激 sAC 会导致前肠的 BCS 和大量水分吸收显著增加，而 sAC 抑制剂 KH7（200 μM）完全逆转了这一作用。总的来说，这些结果揭示了海洋鱼类肠道中 BCS 和水吸收之间的功能关系，以及 tmAC 和 sAC 的调节作用。鉴于目前的观察结果，假设 tmAC 对肠道 BCS 和水吸收的内分泌作用通过 sAC 在鱼肠细胞中的作用被局部和相互调节，从而精细调节肠道腔中碳酸盐聚集体的产生过程。
