碱度胁迫对尼罗罗非鱼鳃离子细胞形态以及鳃、肾和肠中HCO3^-转运因子的影响

Effects of Alkalinity on Morphology of Gill Ionocytes and HCO_3^- Transporters in Gill, Kidney and Intestine of Nile Tilapia (Oreochromis niloticus)

采用扫描电镜观察了不同碱度(0、2、4 g/L Na HCO_3)胁迫对尼罗罗非鱼(Oreochromis niloticus)鳃离子细胞形态变化的影响,并采用免疫组化技术观察了鳃、肾、肠中4个HCO_3^-转运因子碳酸酐酶(CAⅡ、CAⅣ)、碳酸氢钠协同转运载体(SLC4A4)、Cl^-/HCO_3^-离子交换体(SLC26A6)的阳性反应变化。扫描电镜结果表明,鳃离子细胞分布在鳃小片基部。根据其表面开孔形状和尺寸,可分为Ⅰ型、Ⅱ型、Ⅲ型和Ⅳ型4种亚型,各亚型离子细胞的开孔尺寸随碱度胁迫强度增高呈正比增大,Ⅲ型离子细胞开孔尺寸变化最明显(P<0.01);离子细胞总数目也随碱度升高而增加,Ⅲ型离子细胞数目上升最为显著(P<0.01)。免疫组化结果表明,在淡水、碱水组中,CAⅡ、CAⅣ、SLC4A4、SLC26A6在鳃小片基部和肾中均有阳性反应,且随着碱度升高,阳性反应增强,但在肠道中未观察到阳性反应。本研究结果初步表明,尼罗罗非鱼可通过鳃离子细胞形态和数量调节适应碱度变化,鳃和肾为主要应答调节器官。

The effect of alkalinity （0, 2 and 4 g/L NaHCO3） stress on morphology of gill ionocytes in Nile Tilapia （Oreochromis niloticus） was studied by scanning electron microscopy, and four HCO3- transporters including carbonic anhydrase （CAⅡ, CAⅣ）, Na＋/HCO3- cotransporter （SLC4A4）, and Cl-/HCO3- exchanger （SLC26A6） in gill, kidney and intestine were also observed by immunohistochemistry. The surface scanning of the gills showed that ionocytes cells were distributed close to the inter-lamellar regions of gill filaments （Fig. 1）. According to the apical shape and size, the ionocytes cells could be divided into four subtypes, subtype Ⅰ, subtype Ⅱ, subtype Ⅲ and subtype Ⅳ （Fig. 2）. The apical size of each subtype of ionocytes was positively correlated with the alkalinity stress strength, and the size of subtype Ⅲ cells was changed most obviously （P 〈 0.01） （Table 1）; The ionocytes number increased significantly with the increase of alkalinity stress strength, and the number of subtype Ⅲ cells was increased most significantly （P 〈 0.01） （Table 1）. The results of immunohistochemistry showed that CAⅡ, CAⅣ, SLC4A4 and SLC26A6 were expressed in gill and kidney of O. niloticus at fresh water and alkaline water （Fig. 3, Fig. 4）. With the increase of alkalinity, the positive reactions became stronger （Table 2）. However, no positive reaction was detected in intestinal at fresh water and alkaline water （Fig. 5）. This result suggest that O. niloticus may change the quantity and morphological structure of ionocytes to adapt to alkaline environment, and that gill and kidney may play a key role in alkalinity regulation.