Inwardly rectifying potassium channels: Critical insights for insect species and Apis mellifera

Kir (inwardly rectifying potassium) channels that play key roles in maintaining potassium homeostasis, neuronal excitability, and osmoregulation have been cloned and characterized in a variety of insects. In Drosophila melanogaster, three Kir channels (dKir1 dKir2, and dKir3) have been cloned and characterized, and share significant homology with mammalian Kir channels. The dKir channels are essential for various developmental processes, such as wing patterning, by modulating bone morphogenetic protein signaling pathways. Electrophysiological studies have confirmed that Drosophila Kir channels function in a way analogous to their mammalian counterparts, indicating that their roles in cellular and developmental signaling have been evolutionarily conserved. Several Kir channels have also been identified and characterized in mosquitoes (Aedes aegypti and Anopheles gambiae). Interestingly, insect Kir channel orthologs cluster into three gene "clades" or subfamilies (Kir1, Kir2, Kir3) that are distinct from mammal Kir channels based on sequence comparisons. Insect Kir channel paralogs range from two to eight Kir channel genes per species genome representing separate gene duplication events. These differences may be attributed to distinct physiological adaptations associated with their respective taxonomic groups. The honeybee Apis mellifera genome contains two Kir channel genes, AmKir1 and AmKir2, producing six Kir channel isoforms via alternative splicing, which have been cloned and expressed in heterologous systems to study their electrophysiological properties. This review provides a comprehensive overview of current knowledge about Kir channel structures, activities, and gating as well as of their roles in insects, including evolutionary genomic aspects, molecular biology, physiological roles, and pharmacological targeting.