DiBAC4(3) hits a "sweet spot" for the activation of arterial large-conductance Ca²âº-activated potassium channels independently of the ß1-subunit.

The voltage-sensitive dye bis-(1,3-dibutylbarbituric acid)trimethine oxonol [DiBAC4(3)] has been reported as a novel large-conductance Ca²âº-activated K⁺ (BK) channel activator with selectivity for its ß1- or ß4-subunits. In arterial smooth muscle, BK channels are formed by a pore-forming α-subunit and a smooth muscle-abundant regulatory ß1-subunit. This tissue specificity has driven extensive pharmacological research aimed at regulating arterial tone. Using animals with a disruption of the gene for the ß1-subunit, we explored the effects of DiBAC4(3) in native channels from arterial smooth muscle. We tested the hypothesis that, in native BK channels, activation by DiBAC4(3) relies mostly on its α-subunit. We studied BK channels from wild-type and transgenic ß1-knockout mice in excised patches. BK channels from brain arteries, with or without the ß1-subunit, were similarly activated by DiBAC4(3). In addition, we found that saturating concentrations of DiBAC4(3) (~30 µM) promote an unprecedented persistent activation of the channel that negatively shifts its voltage dependence by as much as -300 mV. This "sweet spot" for persistent activation is independent of Ca²âº and/or the ß1₋4-subunits and is fully achieved when DiBAC4(3) is applied to the intracellular side of the channel. Arterial BK channel response to DiBAC4(3) varies across species and/or vascular beds. DiBAC4(3) unique effects can reveal details of BK channel gating mechanisms and help in the rational design of BK channel activators.