关键词: 昆虫, 内向整流钾离子通道, 氟啶虫酰胺, 杀虫剂靶标, 马氏管, 唾液分泌, Kir抑制剂

Abstract:  Inwardly-rectifying potassium channels (Kir) play important roles in various tissues of animals. Although the research on insect Kir channels is limited, some important findings about insect Kir had been achieved in the recent five years, which were reviewed in this article. Until now the studies on insect Kirs have been mainly focused on the insect orders Diptera and Hemiptera. The analysis on genomic data and gene cloning demonstrated that insects have much fewer Kir genes than mammals. The dipteran insects Aedes aegypti and Anopheles gambiae harbor five to six Kir genes, Drosophila melanogaster has only three Kir genes, and the hemipteran insects Nilaparvata lugens and Cimex lectularius also have only three Kir genes. The number of Kir genes in soybean aphid (Aphis glycines) reduced to only two, and the third one was lost, which conjecturally is related with the degeneration of Malpighian tubules during the evolution of aphids. Phylogenetic analysis reveals that insect Kirs belong to three subfamilies; however, they are not orthologous to the seven subfamilies of mammal Kirs. Even so, insect Kirs have similar structural characteristics with mammal Kirs: insect Kirs are tetramer channels composed by four Kir subunits, each subunit has two transmembrane domains (TM1 and TM2), and K⁺ selective filter sequence is present between TM1 and TM2. The Kir genes are highly expressed in salivary gland and Malpighian tubules of insects. Kir inhibitors, which block the inward potassium current of Kir in insects, suppress the secretion activities of salivary gland and Malpighian tubules, and therefore disrupt the processes of insect feeding and excretion, and finally lead to the death of insects. These results suggest that the secretion activities of salivary gland and Malpighian tubules are regulated by Kir, and the transmembrane transport of K⁺ mediated by Kir drives the secretion activities in these epithelial cells. The most important discovery is that flonicamid, an insecticide with long-sought-after mode of action, has high blocking activity on Kir in N. lugens, and disrupts the physiological function of salivary gland and renal tubes. These results demonstrate that Kir is the molecular target of flonicamid, suggesting that Kir is the excellent insecticidal target. Finally, the author analyzed the emerging scientific issues in insect Kir research remaining to be solved and highlighted the research prospects on the development of new insecticides targeting at Kir channels.

Key words: Insect, inwardly-rectifying potassium channel, flonicamid, insecticide target, Malpighian tubules, salivary secretion, Kir inhibitor