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OBJECTIVE To research two novel I1R isoforms and explore its function, so as find its role in the pharmacological function of I1R.METHODS Based on the bioinformatics, combined with previous investigation in our group, two new isoforms with Gen-Bank number AK036043 (named Nischarin472 in this project) and AK086880 (named Nischarin334 in this project) were cloned through RT-PCR.CHO cell models with stable expression of Nischarin/IRAS, Nischarin/IRAS1-826, Nischarin472 and Nischarin334 genes were constructed through retroviral vector method.Structure and function of isoforms was thoroughly investigated from the following 3 aspects: Influences on ERK phosphorylation of above cell models after I1 R agonist (Rilmenidine) stimulation; combination properties of above cell models to I1R ligand ([3 H-Clonidine) ; and influences on cell cycles.RESULTS We gained two new isoforms of Nishcrin/IRAS with 1420 bp and 1005 bp cDNA fragment (AK034063.1 and AK086880.1) which expressed in the eukarya cell.Using bioinformatics Nischarin472 and Nischarin334 is mapped to chromosomes 14B, and Nischarin472 protein contains two important domains including the PX_domain superfamily and LRR-RI Superfamily, and Nischarin334 contains the PX_domain superfamily and paryly LRRRI superfamily.Molecular weight of Nischarin472 and Nischarin334 are about 52000 and 40000 respectively, and are the same as the predicted ones.Splicing manners of Nischarin472 is intron retain, and Nischarin334 is extron skipping.Subcellular localization of the two isoforms are a cytosolic staining.Nischarin472 is expressed in multiple tissues in rat, and the expressed in peripheral tissues is higher than in brain.In cell models expressing Nischarin/IRAS, Nischarin/IRAS1-826, I1R agonist (Rilmenidine) time and dose dependently increased ERK phosphorylation, but no apparent changes in ERK phosphorylation were observed in cell models expressing Nischarin472 and Nischarin334 ; CHO cell models expressing Nischarin/IRAS, Nischarin/IRAS1-826 can specificly combine I1 R ligand ([3H]-Clonidine) with saturability and reversibility, but CHO cell models expressing Nischarin472 and Nischarin334 could not combine [3H]-Clonidine; Nischarin/IRAS, Nischarin/IRAS1-826 proteins might promote cell proliferation, but Nischarin472 and Nischarin334 inhibit ones.CONCLUSION We have obtained two new isoforms of I1R based on the above results.According to its molecular weight, subcellular location, characteristics and function, the pharmacological functions of two isoforms maybe be not the same as pharmacological function of I1 R known.These results pave the way for study the new biological function of I1R, providing information for clarifying the role of I1 R spliced variant in its pharmacological function.