PT - JOURNAL ARTICLE AU - Takashi Morimoto AU - Kazuho Sakamoto AU - Hiroko Sade AU - Susumu Ohya AU - Katsuhiko Muraki AU - Yuji Imaizumi TI - Voltage-Sensitive Oxonol Dyes Are Novel Large-Conductance Ca<sup>2+</sup>-Activated K<sup>+</sup> Channel Activators Selective for β1 and β4 but Not for β2 Subunits AID - 10.1124/mol.106.031146 DP - 2007 Apr 01 TA - Molecular Pharmacology PG - 1075--1088 VI - 71 IP - 4 4099 - http://molpharm.aspetjournals.org/content/71/4/1075.short 4100 - http://molpharm.aspetjournals.org/content/71/4/1075.full SO - Mol Pharmacol2007 Apr 01; 71 AB - The large-conductance Ca2+-activated K+ (BK) channel is activated by both the increase of intracellular Ca2+ concentration and membrane depolarization. The BK channel plays crucial roles as a key molecule in the negative feedback mechanism regulating membrane excitability and cellular Ca2+ in various cell types. Here, we report that a widely used slow-response voltage-sensitive fluorescent dye, bis(1,3-dibutylbarbituric acid)trimethine oxonol [DiBAC4(3)], is a potent BK channel activator. The application of DiBAC4(3) at concentrations of 10 nM and higher significantly increased whole-cell BK channel currents in human embryonic kidney 293 cells expressing rat BK channel α and β1 subunits (rBKαβ1). In the presence of 300 nM DiBAC4(3), the activation voltage of the BK channel current shifted to the negative direction by approximately 30 mV, but the single-channel conductance was not affected. DiBAC4(3) activated whole-cell rBKαβ1 and rBKαβ4 currents in the same concentration range but partially blocked rBKαβ2 currents. The BK channel α subunit alone and some other types of K+ channels examined were not markedly affected by 1 μM DiBAC4(3). Structure-activity relationship analyses revealed that a set of oxo- and oxoanion-moieties in two 1,3-dialkylbarbituric acids, which are conjugated by oligomethine, is the novel skeleton for the β-subunit-selective BK channel-opening property of DiBAC4(3) and related oxonol compounds. This conjugated structure may be located stereochemically in one plane. These findings provide a molecular and structural basis for understanding the regulatory mechanism of BK channel activity by an auxiliary β subunit and will be fundamental to the development of β-selective BK channel openers. The American Society for Pharmacology and Experimental Therapeutics