內皮素對斑馬魚適應酸性環境時排酸功能的急性調節

Abstract

環境污染及氣候變遷導致的水域酸化已嚴重威脅水生生物的生存。神經內分泌系統是感受體外環境變化並啟動體內生理反應的重要媒介，然而其在魚類酸鹼適應中的調節角色仍所知有限。過去研究證實內皮素藉由對於氫離子幫浦的轉譯後調控進行斑馬魚表皮排酸功能的調節，而本研究旨在探討內皮素在斑馬魚酸環境適應的短期調節中可能的角色。孵化後斑馬魚胚胎面臨酸性(pH4)環境時，表皮的排酸能力在6小時內即顯著增加，內皮素基因表現亦於酸處理後4小時內顯著上升，而此時氫離子幫浦表現量並無明顯變化，且表皮離子細胞分化基因表現量在酸處理12小時候才開始上升，而其他內分泌激素基因表現於酸處理較晚期才產生變化，暗示內皮激素可能參與短期排酸能力的調控，而長期的酸環境適應機制於面臨酸性壓力12小時候才開啟。又斑馬魚胚胎面臨較低強度的酸性刺激（pH 5.5）時氫離子幫浦和表皮離子細胞分化基因表現皆未產生變化，然而內皮素基因表現已顯著上升，暗示內皮素可能參與適應較低強度酸性刺激的調節功能。

Water area acidification caused by industrial pollution and climate change has threatened the survival of aquatic habitants. As a primary link between environmental changes and physiological responses, the role of neuroendocrine system in acid-base regulation under pH disturbance in fish remains unclear. Previous study indicated that Endothelin-1 (EDN1) was involved in regulation of skin acid secretion in zebrafish embryos. The aim of this study is to explore the role of EDN1 in acute regulation of acid secretion upon acidic challenge in fish. The results showed that skin acid secretion of zebrafish embryos was stimulated in 6hr after low pH (pH4) treatment, but no concomitant changes were observed on the expression of H+-ATPase (HA). Expression of EDN1was also increased in 4hr after treatment while the expression of other hormones increase at latter timepoints. Moreover, the expression of ionocyte differentiation factors increased in 12hr after treatment, implying the long-term regulatory mechanism to acidic stress may be turned on in a latter stage and the involvement of EDN1 in short-term regulation of acid secretion. During acclimation to moderate acid conditions (pH 5.5), expression of EDN1 was upregulated while no significant difference was observed in the transcription levels of H+-ATPase and ionocyte differentiation factor, implying that EDN1 may be involved in regulating moderate acid challenge.