Marine Biology Research Division, Scripps Institution of Oceanography, University of California, La Jolla, California, USA.
Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada.
Acta Physiol (Oxf). 2022 Oct;236(2):e13845. doi: 10.1111/apha.13845. Epub 2022 Jun 24.
Pacific hagfish are exceptionally tolerant to high environmental ammonia (HEA). Here, we elucidated a cellular mechanism that enables hagfish to actively excrete ammonia against steep ammonia gradients expected to be found inside a decomposing whale carcass.
Hagfish were exposed to varying concentrations of HEA in the presence or absence of environmental Na , while plasma ammonia levels were tracked. C-methylammonium was used as a proxy for NH to measure efflux in whole animals and in isolated gill pouches; the latter allowed us to assess the effects of amiloride specifically on Na /H exchangers (NHEs) in gill cells. Western blotting and immunohistochemistry were utilized to evaluate the abundance and sub-cellular localization of Rhesus glycoprotein (Rh) channels in the response to HEA.
Hagfish actively excreted NH against steep inwardly directed E (ΔE ~ 35 mV) and pNH (ΔpNH ~ 2000 μtorr) gradients. Active NH excretion and plasma ammonia hypo-regulation were contingent on the presence of environmental Na , indicating a Na /NH exchange mechanism. Active NH excretion across isolated gill pouches was amiloride-sensitive. Exposure to HEA resulted in decreased abundance of Rh channels in the apical membrane of gill ionocytes.
During HEA exposure, hagfish can actively excrete ammonia against a steep concentration gradient using apical NHEs energized by Na -K -ATPase in gill ionocytes. Additionally, apical Rh channels are removed from the apical membrane, presumably to reduce ammonia loading from the environment. We suggest that this mechanism allows hagfish to maintain tolerable ammonia levels while feeding inside decomposing carrion, allowing them to exploit nutrient-rich food-falls.
太平洋盲鳗对高环境氨（HEA）具有极强的耐受性。在这里，我们阐明了一种细胞机制，使盲鳗能够在预计在分解鲸鱼尸体内部存在的陡峭氨浓度梯度下主动排泄氨。
在存在或不存在环境 Na 的情况下，将盲鳗暴露于不同浓度的 HEA 中，同时跟踪血浆氨水平。使用 C-甲基铵作为 NH 的替代品，以测量整个动物和分离的鳃囊中氨的外排；后者使我们能够专门评估阿米洛利对鳃细胞中钠/氢交换器（NHE）的影响。利用 Western blot 和免疫组织化学技术评估 Rh 糖蛋白（Rh）通道在响应 HEA 时的丰度和亚细胞定位。
盲鳗主动排泄 NH ，以应对陡峭的内向 E （ΔE ~ 35 mV）和 pNH （ΔpNH ~ 2000 μtorr）梯度。主动 NH 排泄和血浆氨低调节取决于环境 Na 的存在，表明存在 Na / NH 交换机制。分离的鳃囊中主动 NH 排泄对阿米洛利敏感。暴露于 HEA 导致鳃离子细胞顶膜上 Rh 通道的丰度降低。
在 HEA 暴露期间，盲鳗可以通过鳃离子细胞中的顶膜 NHE 利用 Na -K -ATP 酶主动排泄氨，以应对陡峭的浓度梯度。此外，顶膜 Rh 通道从顶膜中去除，可能是为了减少来自环境的氨负荷。我们认为，这种机制使盲鳗能够在分解的腐肉中进食时保持可耐受的氨水平，从而能够利用富含营养的食物掉落。
