Abstract：
The zebrafish, Danio rerio, is a widely adopted in vivo model that conserves organs such as the liver, kidney, stomach, and brain, being, therefore, suitable for studying human diseases, drug discovery and toxicology. The brain aminergic systems are also conserved and the histamine H1, H2 and H3 receptors were previously cloned and identified in the zebrafish brain. Genome studies identified another putative H2 receptor (Hrh2) with ∼50% sequence identity with H2 receptor orthologs. In this study, we recombinantly expressed both zebrafish H2 receptor paralogs (hrh2a and hrh2b) and compared their pharmacology with the human H2 receptor ortholog. Our results showed that both zebrafish receptors conserve all the class A GPCR motifs. However, in contrast with the Hrh2a paralog, the Hrh2b does not possess all the amino acid residues shown to participate in histamine binding. The zebrafish Hrh2a receptor displays high affinity for [3H]-tiotidine with a binding profile for H2 receptor ligands similar to that of the human H2 receptor. The zebrafish Hrh2a receptor couples to GαS and Gαq/11 proteins, resulting in cAMP accumulation and activation of several reporter genes linked to the Gαq/11 pathway. Additionally, this receptor shows high constitutive activity, with histamine potency in the low nanomolar range for cAMP accumulation and the micromolar range for the activation of the NFAT response element. Moreover, dimaprit and amthamine seem to preferentially activate GαS over Gαq/11 proteins via the zebrafish Hrh2a receptor. These results can contribute to clarifying the functional roles of the H2 receptor in zebrafish.
摘要：
斑马鱼,DanioRerio,是一种广泛采用的体内模型，可以保护肝脏等器官，肾,胃,和大脑，being,因此,适合研究人类疾病，药物发现和毒理学。脑胺能系统也是保守的，并且先前在斑马鱼脑中克隆并鉴定了组胺H1，H2和H3受体。基因组研究确定了另一种推定的H2受体（Hrh2），与H2受体直系同源物具有〜50％的序列同一性。在这项研究中,我们重组表达了两种斑马鱼H2受体同源物（hrh2a和hrh2b），并将其药理学与人H2受体直系同源物进行了比较。我们的结果表明，两种斑马鱼受体都保留了所有A类GPCR基序。然而,与Hrh2a模拟相反，Hrh2b不具有显示参与组胺结合的所有氨基酸残基。斑马鱼Hrh2a受体对[3H]-tiotidine显示出高亲和力，对H2受体配体的结合谱与人H2受体相似。斑马鱼Hrh2a受体与GαS和Gαq/11蛋白偶联,导致cAMP积累和与Gαq/11途径相关的几个报告基因的激活。此外,这种受体显示出高的组成活性，对于cAMP积累，组胺的效力在低纳摩尔范围内，而对于NFAT反应元件的激活则在微摩尔范围内。此外，dimaprit和amthamine似乎通过斑马鱼Hrh2a受体优先激活GαS而不是Gαq/11蛋白。这些结果有助于阐明H2受体在斑马鱼中的功能作用。
