中国水产科学2017，Vol.24Issue(4)：681-689,9.DOI:10.3724/SP.J.1118.2017.16369
高碱环境下青海湖裸鲤氮废物排泄及相关基因的表达规律
Nitrogenous waste excretion and gene expression of nitrogen trans-porter in Gymnocypris przewalskii in high alkaline environment
摘要
Abstract
Saline-alkaline water bodies are widely distributed in China. High alkalinity is one of the main stressors for the survival of aquatic animals in saline-alkaline water. Previous studies have established that ammonia excre-tion is inhibited when fish are acutely exposed to alkaline water. Przewalskii's naked carp, also known as Gymno-cypris przewalskii or the scale-less carp, is endemic to the austere environment of Lake Qinghai. Lake Qinghai has a high salinity (13 ppt) and a strong alkalinity (carbonate alkalinity approximately 29 mmol/L, pH 9.1–9.5). Due to high evaporative water loss and extensive water diversion for agricultural use, the water level of the lake is de-creasing by 10 cm per year and the salinity and alkalinity levels are increasing by 7% and 0.5% per year, respec-tively. Some studies showed that G. przewalskii had evolved a variety of mechanisms, such as osmoregulation and ion regulation with low energy consumption, regulation of HCO3– secretion in intestines, and compensatory car-bonic anhydrase expression mechanism under metabolic alkalosis, to adapt to saline-alkaline environments. However, the mechanism of nitrogenous waste excretion is less well studied. In order to evaluate the effect of carbonate alkalinity stress on nitrogenous waste excretion in G. przewalskii, we exposed juvenile G. przewalskii to 32 mmol/L and 64 mmol/L carbonate alkalinity water and measured ammonia and urea excretion rate after –6 h (pre-transfer), 4 h, 8 h, 12 h, 16 h, 20 h, 24 h, 48 h, 72 h, 96 h, and 120 h (recovery) after initial exposure. We also measured Rhesus type b glycoproteins (Rhbg), Rhesus type c2 glycoproteins (Rhcg2), and urea transporter (Ut) expression in gill and kidney of G. przewalskii by real-time PCR. The results showed that G. przewalskii in alka-line water reduced ammonia excretion but increased urea excretion. Ammonia excretion rate decreased signifi-cantly over the entire exposure period in 32 mmol/L carbonate alkalinity water and the initial exposure period in 64 mmol/L carbonate alkalinity water. Ammonia excretion is expected to be inhibited when fish are subjected to alkaline water because of a decrease in the extent of the protonation of NH3 to NH4+. Consequently, at high pH water caused by high carbonate alkalinity, the partial pressure of NH3 (PNH3) is predicted to rise in water adjacent to the gill, thus reducing the PNH3 gradient that drives NH3 diffusion. However, in the 64 mmol/L group, the am-monia excretion rate recovered to the level of pre-transfer after 24–72 h and 8–20 h. This indicated that G. prze-walskii may excrete ammonia by re-establishing a favorable NH3 partial pressure gradient under high carbonate alkalinity. Urea excretion rate increased significantly after 12–16 h and 20–24 h in 32 mmol/L carbonate alkalinity water and 16–48 h in 64 mmol/L carbonate alkalinity water. The real-time PCR results showed that Rhbg, Rhcg2, and Ut genes were up-regulated under carbonate alkalinity stress. The expression of Rhbg in gills was significantly up-regulated after 12 h in 32 mmol/L carbonate alkalinity water, while Rhcg2 was significantly up-regulated in gills after 6 h, 48 h, and 72 h and in kidneys at 6 h in 64 mmol/L carbonate alkalinity water. Ut expression in gills was significantly up-regulated after 6 h in the 64 mmol/L carbonate alkalinity group. These results revealed that al-though ammonia excretion was inhibited in highly alkaline environments, G. przewalskii could excrete nitrogen waste by up-regulating Rh and Ut expression, recovering ammonia excretion, and excreting more urea. This study provided evidence of the nitrogenous waste excretion mechanism in G. przewalskii in high alkaline environments. We speculate that the special mechanism of nitrogenous waste excretion facilitate the adaptation of G. przewalskii to highly alkaline environments. Nonetheless, these findings raise more questions than answers, and further studies are needed to clarify the distribution and expression level of Rh protein in cells and tissues.关键词
青海湖裸鲤/碳酸盐碱度/氮废物排泄/Rh基因/Ut基因Key words
Gymnocypris przewalskii/carbonate alkalinity/nitrogenous waste excretion/Rhesus glycoproteins (Rh) gene/urea transporter (Ut) gene分类
农业科技引用本文复制引用
衣晓飞,来琦芳,史建全,高鹏程,周凯,祁洪芳,王慧,么宗利..高碱环境下青海湖裸鲤氮废物排泄及相关基因的表达规律[J].中国水产科学,2017,24(4):681-689,9.基金项目
上海市科学技术委员会科研计划项目(14ZR1449800) （14ZR1449800）
中央级公益性科研院所基本科研业务费专项(中国水产科学研究院东海水产研究所)(2012M05). （中国水产科学研究院东海水产研究所）
