Department of Biology, York University, Toronto, ON, M3J 1P3, Canada.
Department of Biology, York University, Toronto, ON, M3J 1P3, Canada; Department of Internal Medicine, University of Utah School of Medicine, Salt Lake City, UT, United States.
Aquat Toxicol. 2019 Jun;211:92-104. doi: 10.1016/j.aquatox.2019.03.019. Epub 2019 Mar 27.
The impact of freshwater (FW) salinization on osmoregulation as well as tracheal gill morphology and function was examined in nymphs of the mayfly Hexagenia rigida following exposure to salt contaminated water (SCW, 7.25 g/l NaCl) for a 7-day period. Ionoregulatory homeostasis was perturbed in SCW exposed H. rigida nymphs as indicated by increased hemolymph Na, K and Cl levels as well as hemolymph pH and water content. Despite this, SCW did not alter gill Na-K-ATPase (NKA) or V-type H-ATPase (VA) activity. In addition, NKA and VA immunolocalization in gill ionocytes did not show alterations in enzyme location or changes in ionocyte abundance. The latter observation was confirmed using scanning electron microscopy (SEM) to examine exposed tracheal gill ionocyte numbers. Ionocyte surface morphometrics also revealed that SCW did not change individual ionocyte surface area or ionocyte fractional surface area. Nevertheless, analysis of Na movement across the tracheal gill of mayfly nymphs using scanning ion-selective electrode technique indicated that FW nymphs acquired Na from surrounding water, while tracheal gills of SCW nymphs had the capacity to secrete Na. Because Na secretion across the gill of SCW-exposed animals occurred in the absence of any change in (1) NKA and VA activity or (2) ionocyte numbers/surface exposure, it was reasoned that Na movement across the gill of SCW animals may be occurring, at least in part, through the paracellular pathway. The ultrastructure of tracheal gill septate junctions (SJs) supported this idea as they exhibited morphological alterations indicative of a leakier pathway. Data provide a first look at alterations in osmoregulatory mechanisms that allow H. rigida nymphs to tolerate sub-lethal salinization of their surroundings.
在暴露于受污染盐水 (SCW, 7.25 g/l NaCl) 7 天后，检查了 FW 盐度对蜉蝣 Hexagenia rigida 若虫渗透调节以及气管鳃形态和功能的影响。暴露于 SCW 的 H. rigida 若虫的离子稳态受到干扰，表现为血淋巴 Na、K 和 Cl 水平以及血淋巴 pH 值和水含量升高。尽管如此，SCW 并未改变鳃 Na-K-ATP 酶 (NKA) 或 V 型 H-ATP 酶 (VA) 活性。此外，在鳃离子细胞中，NKA 和 VA 的免疫定位并未显示酶位置的改变或离子细胞丰度的变化。后者的观察结果通过使用扫描电子显微镜 (SEM) 检查暴露的气管鳃离子细胞数量得到证实。离子细胞表面形态计量学还表明，SCW 不会改变单个离子细胞表面积或离子细胞分数表面积。尽管如此，使用扫描离子选择性电极技术分析蜉蝣若虫气管鳃中的 Na 迁移表明，FW 若虫从周围水中摄取 Na，而 SCW 若虫的气管鳃具有分泌 Na 的能力。由于在（1）NKA 和 VA 活性或（2）离子细胞数量/表面积暴露没有任何变化的情况下，SCW 暴露动物的鳃跨膜 Na 分泌发生，因此可以推断，SCW 动物的鳃跨膜 Na 迁移至少部分通过细胞旁途径发生。气管鳃有隔接合处 (SJ) 的超微结构支持了这一观点，因为它们表现出形态改变，表明存在更漏的途径。数据首次提供了有关渗透调节机制改变的信息，这些改变使 H. rigida 若虫能够耐受周围环境的亚致死盐度。
