Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, Miami, Florida 33149, USA.
Am J Physiol Regul Integr Comp Physiol. 2011 Dec;301(6):R1682-91. doi: 10.1152/ajpregu.00059.2011. Epub 2011 Aug 24.
The absorption of Cl(-) and water from ingested seawater in the marine fish intestine is accomplished partly through Cl(-)/HCO(3)(-) exchange. Recently, a H(+) pump (vacuolar-type H(+)-ATPase) was found to secrete acid into the intestinal lumen, and it may serve to titrate luminal HCO(3)(-) and facilitate further Cl(-)/HCO(3)(-) exchange, especially in the posterior intestine, where adverse concentration gradients could limit Cl(-)/HCO(3)(-) exchange. The H(+) pump is expressed in all intestinal segments and in gill tissue of gulf toadfish (Opsanus beta) maintained in natural seawater. After acute transfer of toadfish to 60 ppt salinity, H(+) pump expression increased 20-fold in the posterior intestine. In agreement with these observations was a fourfold-increased H(+)-ATPase activity in the posterior intestine of animals acclimated to 60 ppt salinity. Interestingly, Na(+)-K(+)-ATPase activity was elevated in the anterior intestine and gill, but not in the posterior intestine. Apical acid secretion by isolated intestinal tissue mounted in Ussing chambers fitted with pH-stat titration systems increased after acclimation to hypersalinity in the anterior and posterior intestine, titrating >20% of secreted bicarbonate. In addition, net base secretion increased in hypersalinity-acclimated fish and was ∼70% dependent on serosal HCO(3)(-). Protein localization by immunohistochemistry confirmed the presence of the vacuolar-type H(+)-ATPase in the apical region of intestinal enterocytes. These results show that the H(+) pump, especially in the posterior intestine, plays an important role in hypersaline osmoregulation and that it likely has significant effects on HCO(3)(-) accumulation in the intestinal lumen and, therefore, the continued absorption of Cl(-) and water.
肠道通过 Cl(-)/HCO(3)(-)交换来吸收摄入海水中的 Cl(-)和水。最近，人们发现一种 H(+)泵（液泡型 H(+)-ATP 酶）会将酸分泌到肠腔中，它可能用于滴定肠腔中的 HCO(3)(-)，并促进进一步的 Cl(-)/HCO(3)(-)交换，尤其是在后肠，在后肠中，不利的浓度梯度可能会限制 Cl(-)/HCO(3)(-)交换。在 Gulf toadfish（Opsanus beta）的所有肠段和鳃组织中均表达 H(+)泵，这些鱼在天然海水中饲养。将 Gulf toadfish 急性转移到 60 ppt 盐度后，H(+)泵在后肠中的表达增加了 20 倍。与这些观察结果一致的是，在适应 60 ppt 盐度的动物的后肠中，H(+)-ATP 酶活性增加了 4 倍。有趣的是，在前肠和鳃中，Na(+)-K(+)-ATP 酶活性升高，但在后肠中没有。在前肠和后肠中，用配备 pH -stat 滴定系统的 Ussing 室中分离的肠组织进行的顶端酸分泌在适应高盐度后增加，滴定了>20%分泌的 HCO(3)(-)。此外，在适应高盐度的鱼类中，净基础分泌增加，约 70%依赖于浆膜 HCO(3)(-)。免疫组织化学的蛋白质定位证实了液泡型 H(+)-ATP 酶存在于肠上皮细胞的顶端区域。这些结果表明，H(+)泵，特别是在后肠，在高渗渗透压调节中起重要作用，它可能对 HCO(3)(-)在肠腔中的积累产生重大影响，因此，继续吸收 Cl(-)和水。
