Kir Channel Blockages by Proflavine Derivatives via Multiple Modes of Interaction

Many compounds inhibit tetrameric and pseudo-tetrameric cation channels by associating with the central cavity located in the middle of the membrane plane. They traverse the ion conduction pathway from the intracellular side and through access to the cavity. Previously, we reported that the bacteriostatic agent, proflavine, preferentially blocked a subset of inward rectifier K⁺ (Kir) channels. However, the development of the inhibition of Kir1.1 by the compound was obviously different from that operating in Kir3.2 as a pore blocker. To gain mechanistic insights into the compound-channel interaction, we analyzed its chemical specificity, subunit selectivity, and voltage dependency using 13 different combinations of Kir-channel family members and 11 proflavine derivatives. The Kir-channel family members were classified into three groups: 1) Kir2.2, Kir3.x, Kir4.2, and Kir6.2Δ36, which exhibited Kir3.2-type inhibition (slow onset and recovery, irreversible, and voltage-dependent blockage); 2) Kir1.1 and Kir4.1/Kir5.1 (prompt onset and recovery, reversible, and voltage-independent blockage); and 3) Kir2.1, Kir2.3, Kir4.1, and Kir7.1 (no response). The degree of current inhibition depended on the combination of compounds and channels. Chimera between proflavine-sensitive Kir1.1 and -insensitive Kir4.1 revealed that the extracellular portion of Kir1.1 is crucial for the recognition of the proflavine derivative acrinol. In conclusion, preferential blockage of Kir-channel family members by proflavine derivatives is based on multiple modes of action. This raises the possibility of designing subunit-specific inhibitors.