Voltage-Sensitive Oxonol Dyes Are Novel Large-Conductance Ca2+-Activated K+ Channel Activators Selective for β1 and β4 but Not for β2 Subunits

• Published in: Molecular pharmacology Vol. 71; no. 4; p. 1075
• Main Authors: Takashi Morimoto, Kazuho Sakamoto, Hiroko Sade, Susumu Ohya, Katsuhiko Muraki, Yuji Imaizumi
• Format: Journal Article
• Language: English
• Published: American Society for Pharmacology and Experimental Therapeutics 01.04.2007
• ISSN: 0026-895X; 1521-0111
• DOI: 10.1124/mol.106.031146

The large-conductance Ca 2+ -activated K + (BK) channel is activated by both the increase of intracellular Ca 2+ concentration and membrane depolarization. The BK channel plays crucial roles as a key molecule in the negative feedback mechanism regulating membrane excitability and cellular Ca 2+ in various cell types. Here, we report that a widely used slow-response voltage-sensitive fluorescent dye, bis(1,3-dibutylbarbituric acid)trimethine oxonol [DiBAC 4 (3)], is a potent BK channel activator. The application of DiBAC 4 (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 DiBAC 4 (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. DiBAC 4 (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 DiBAC 4 (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 DiBAC 4 (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.