Department of Biology, York University, 4700 Keele Street, Toronto, ON M3J 1P3, Canada.
J Comp Physiol B. 2011 Apr;181(3):343-52. doi: 10.1007/s00360-010-0526-2.
The physiological response of larval Chironomus riparius was examined following direct transfer from freshwater (FW) to brackish water (BW; 20% seawater). Endpoints of hydromineral status (hemolymph Na⁺, Cl⁻, and K⁺ levels, hemolymph pH, body water content, and whole body Na⁺/K⁺-ATPase and V-type H⁺-ATPase activity) were examined 1, 3, 5, 12 and 24 h following BW transfer. Larvae transferred from FW to FW served as a control. Hemolymph Na⁺ and Cl⁻ levels increased following BW transfer. Hemolymph pH was initially regulated, but significantly decreased after 24 h in BW. Changes in hemolymph ions were not caused by osmotic loss of water from the hemolymph, since larvae tightly regulated total body moisture content. Furthermore, salinity did not affect hemolymph K⁺. When larvae were transferred to BW, Na⁺/K⁺-ATPase (NKA) activity did not significantly alter relative to FW control animals. In contrast, V-type H⁺-ATPase (VA) activity in C. riparius significantly decreased in BW. In FW-reared C. riparius, whole body NKA and VA activities were equivalent. However, in the isolated gut with intact Malpighian tubules of FW-reared C. riparius, VA activity was significantly greater than whole body while NKA activity was equivalent. This suggested that gut and/or Malpighian tubule VA activity contributes significantly to whole body VA activity and that a decline in whole body VA activity in BW may be closely linked to alterations in the physiology of gut and Malpighian tubule tissue. Taken together, data indicate that VA is important for ion uptake in FW and that the NKA does not play a major role in regulating ion homeostasis when larvae are acutely exposed to BW.
当幼虫直接从淡水（FW）转移到半咸水（BW；20%海水）时，研究了摇蚊幼虫的生理反应。检查了水盐状态（血淋巴 Na+、Cl-和 K+水平、血淋巴 pH 值、身体水分含量以及整个身体 Na+/K+-ATP 酶和 V 型 H+-ATP 酶活性）的终点，在 BW 转移后 1、3、5、12 和 24 小时。从 FW 转移到 FW 的幼虫作为对照。BW 转移后，血淋巴 Na+和 Cl-水平增加。血淋巴 pH 值最初得到调节，但在 BW 后 24 小时显着降低。血淋巴离子的变化不是由于水从血淋巴中渗透损失引起的，因为幼虫严格调节总身体水分含量。此外，盐度不会影响血淋巴 K+。当幼虫转移到 BW 时，与 FW 对照动物相比，Na+/K+-ATP 酶（NKA）活性没有显着改变。相比之下，V 型 H+-ATP 酶（VA）在 C. riparius 中的活性在 BW 中显着降低。在 FW 培养的 C. riparius 中，整个身体的 NKA 和 VA 活性相等。然而，在 FW 培养的 C. riparius 的完整肠道和完整的马氏管中，VA 活性明显大于整个身体，而 NKA 活性相等。这表明肠道和/或马氏管 VA 活性对整个身体 VA 活性有重要贡献，BW 中整个身体 VA 活性的下降可能与肠道和马氏管组织的生理学改变密切相关。综上所述，数据表明 VA 对 FW 中的离子吸收很重要，并且当幼虫急性暴露于 BW 时，NKA 不会在调节离子动态平衡中发挥主要作用。
