Identification of oxygen gas channels involved in gas secretion into the swimbladder

点击翻译按钮获取中文摘要

The gas in the swimbladder of teleost fish is composed primarily of O_2, and the swimbladder volume is regulated by O_2 transfer between the luminal space of the swimbladder and the blood. In the swimbladder, lactic acid generation by anaerobic glycolysis in the gas gland epithelial cells and its recycling through the rete mirabile bundles of countercurrent capillaries are essential for local blood acidification and oxygen liberation from hemoglobin by the "Root effect."To identify genes involved in the local blood acidification, we analyzed the swimbladder of fugu(Takifugu rubripes) by genome database mining, expression analyses, and immunohistochemistry. Gas gland cells contained glycogen, GAPDH, and a gluconeogenesis enzyme FBP1 at high levels, suggesting that a futile cycle consumes ATP and generates heat. In basolateral membrane of gas gland cells, GLUT6 and a cinnamate-insensitive low-affinity/high-conductance lactic acid transporter MCT4b were highly expressed and may mediate glucose uptake and lactic acid secretion, respectively. Acinnamate-sensitive high-affinity lactic acid transporter MCT1b was highly expressed in arterial, but not venous, capillary endothelial cells in rete mirabile and may mediate recycling of lactic acid in rete mirabile. Two aquaporins were expressed in apical membrane of gas gland cells, and may mediate O_2 secretion as gas channels. These results provide new insights for how swimbladder secretes O_2 and inflates under water pressure.