Histological demonstration of glucose transporters, fructose-1, 6-bisphosphatase, and glycogen in gas gland cells of the swimbladder : is a metabolic futile cycle operating
Histological demonstration of glucose transporters, fructose-1, 6-bisphosphatase, and glycogen in gas gland cells of the swimbladder : is a metabolic futile cycle operating
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鱼鳔气腺细胞中葡萄糖转运蛋白、果糖-1、6-双磷酸酶和糖原的组织学证明：是一个代谢无效循环运行
DOI：
10.1016/j.bbrc.2011.12.006
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发表时间：
2012
期刊：
影响因子：
--
通讯作者：
Kato A.
中科院分区：
文献类型：
--
作者：
Munakata K;Ookata K;Doi H;Baba O;Terashima T;Hirose S;Kato A.
鱼鳔的管腔表面被气腺上皮细胞覆盖，负责通过根效应血红蛋白产生 O2 使鱼鳔膨胀，而根效应血红蛋白在酸性条件下释放 O2。血液的酸化是通过气腺细胞分泌的乳酸实现的，气腺细胞缺乏线粒体，但糖酵解活性丰富。酸性条件由称为 rete mirabile 的逆流毛细管系统局部维持。为了了解气腺细胞中葡萄糖无氧代谢的调节，我们分析了气腺细胞中表达的葡萄糖转运蛋白以及糖酵解产生的 ATP 的命运。后者很重要，因为 ATP 应该立即消耗，否则它会强烈抑制糖酵解，使细胞无法再产生乳酸。通过 RT-PCR 和原位杂交对红鳍东方鳔中的葡萄糖转运蛋白 (glut) 基因进行表达分析，结果表明 glut1a 和 glut6 在气腺细胞中表达。代谢酶的免疫组织化学分析表明，糖异生酶果糖-1,6-二磷酸酶（Fbp1）和糖酵解酶甘油醛-3-磷酸脱氢酶（Gapdh）在气腺细胞中高度表达。糖酵解和糖异生反应的同时催化表明气腺细胞中存在无效循环，以维持较低的 ATP 水平并产生有助于降低 O2 溶解度的热量。
Luminal surface of the swimbladder is covered by gas gland epithelial cells and is responsible for inflating the swimbladder by generating O2from Root-effect hemoglobin that releases O2under acidic conditions. Acidification of blood is achieved by lactic acid secreted from gas gland cells, which are poor in mitochondria but rich in the glycolytic activity. The acidic conditions are locally maintained by a countercurrent capillary system called rete mirabile. To understand the regulation of anaerobic metabolism of glucose in the gas gland cells, we analyzed the glucose transporter expressed there and the fate of ATP generated by glycolysis. The latter is important because the ATP should be immediately consumed otherwise it strongly inhibits the glycolysis rendering the cells unable to produce lactic acid anymore. Expression analyses of glucose transporter (glut) genes in the swimbladder of fugu (Takifugu rubripes) by RT-PCR and in situ hybridization demonstrated that glut1a and glut6 are expressed in gas gland cells. Immunohistochemical analyses of metabolic enzymes demonstrated that a gluconeogenesis enzyme fructose-1,6-bisphosphatase (Fbp1) and a glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (Gapdh) are highly expressed in gas gland cells. The simultaneous catalyses of glycolysis and gluconeogenesis reactions suggest the presence of a futile cycle in gas gland cells to maintain the levels of ATP low and to generate heat that helps reduce the solubility of O2.