Soluble adenylyl cyclase (sAC) is a $\text{HC}{\text{O}}_3^{\hspace{0.17em}-}$-stimulated enzyme that produces the ubiquitous signalling molecule cAMP, and deemed an evolutionarily conserved acid–base sensor. However, its presence is not yet confirmed in bony fishes, the most abundant and diverse of vertebrates. Here, we identified sAC genes in various cartilaginous, ray-finned and lobe-finned fish species. Next, we focused on rainbow trout sAC (rtsAC) and identified 20 potential alternative spliced mRNAs coding for protein isoforms ranging in size from 28 to 186 kDa. Biochemical and kinetic analyses on purified recombinant rtsAC protein determined stimulation by $\text{HC}{\text{O}}_3^{\hspace{0.17em}-}$ at physiologically relevant levels for fish internal fluids (EC₅₀ ∼ 7 mM). rtsAC activity was sensitive to KH7, LRE1, and DIDS (established inhibitors of sAC from other organisms), and insensitive to forskolin and 2,5-dideoxyadenosine (modulators of transmembrane adenylyl cyclases). Western blot and immunocytochemistry revealed high rtsAC expression in gill ion-transporting cells, hepatocytes, red blood cells, myocytes and cardiomyocytes. Analyses in the cell line RTgill-W1 suggested that some of the longer rtsAC isoforms may be preferentially localized in the nucleus, the Golgi apparatus and podosomes. These results indicate that sAC is poised to mediate multiple acid–base homeostatic responses in bony fishes, and provide cues about potential novel functions in mammals.

可溶性腺苷酸环化酶 (sAC)$\text{HC}{\text{○}}_3^{\hspace{0.17em}-}$- 产生普遍存在的信号分子 cAMP 的刺激酶，被认为是进化上保守的酸碱传感器。然而，它的存在尚未在硬骨鱼中得到证实，硬骨鱼是脊椎动物中最丰富和多样的。在这里，我们在各种软骨、射线鳍和叶鳍鱼类中鉴定了 sAC 基因。接下来，我们专注于虹鳟鱼 sAC (rtsAC)，并确定了 20 个潜在的可变剪接 mRNA，它们编码的蛋白质异构体的大小范围从 28 到 186 kDa。纯化重组 rtsAC 蛋白的生化和动力学分析确定刺激$\text{HC}{\text{○}}_3^{\hspace{0.17em}-}$鱼体内液体的生理相关水平（EC ₅₀ ∼ 7 mM）。rtsAC 活性对 KH7、LRE1 和 DIDS（已确定的来自其他生物体的 sAC 抑制剂）敏感，对毛喉素和 2,5-二脱氧腺苷（跨膜腺苷酸环化酶的调节剂）不敏感。Western印迹和免疫细胞化学显示在鳃离子转运细胞、肝细胞、红细胞、肌细胞和心肌细胞中高表达rtsAC。对细胞系 RTgill-W1 的分析表明，一些较长的 rtsAC 同种型可能优先定位于细胞核、高尔基体和足体。这些结果表明，sAC 有望介导硬骨鱼类的多种酸碱平衡反应，并为哺乳动物的潜在新功能提供线索。