A large-conductance (BK) potassium channel subtype affects both growth and mineralization of human osteoblasts

Abstract

The pharmacology of the large-conductance K(+) (BK) channel in human osteoblasts is not well defined, and its role in bone is speculative. Here we assess BK channel properties in MG63 cells and primary human osteoblasts and determine whether pharmacological modulation affects cell function. We used RT-PCR and patch-clamp methods to determine the expression of BK channel subunits and cell number assays in the absence and presence of BK channel modulators. RT-PCR showed the presence of KCNMA1, KCNMB1, KCNMB2, KCNMB3, and KCNMB4 subunits. The BK channel was voltage dependent, with a mean unitary conductance of 228.8 pS (n = 10) in cell-attached patches (140 mM K(+)/140 mM K(+)) and a conductance of 142.5 pS (n = 16) in excised outside-out and 155 pS (n = 6) in inside-out patches in 3 mM K(+)/140 mM K(+). The selectivity ratio (ratio of K(+) to Na(+) permeability) was 15:1. The channel was blocked by tetraethylammonium (TEA, 0.3 mM), iberiotoxin (5-60 nM), tetrandrine (5-30 microM), and paxilline (10 microM) and activated by isopimaric acid (20 microM). BK channel modulators affected MG63 cell numbers: TEA and tetrandrine significantly increased cell numbers at low concentrations (3 mM and 3 microM, respectively) and reduced cell numbers at higher concentrations (>10 mM and >10 microM, respectively). Neither iberiotoxin (20-300 nM) nor slotoxin (300 nM) affected cell numbers. The increase in cell numbers by TEA was blocked by isopimaric acid. TEA (0.1-3.0 mM) significantly increased mineralization in primary osteoblasts. In conclusion, the BK channel has a distinctive pharmacology and is thus a target for therapeutic strategies aimed at modulating osteoblast proliferation and function.

Noradrenaline stimulates cell proliferation by suppressing potassium channels via Gi/o‐protein‐coupled α1B‐adrenoceptors in human osteoblasts

“…Zhou et al, (2008) demonstrated that BK channels were inhibited by Gbg-protein and we previously reported that BK channels were expressed in SaM-1 cells (Hirukawa et al, 2008). However, BK channels are inhibited by TEA and activated by [Ca 2+ ]i elevation (Henney et al, 2009;Lee and Cui, 2010). The inhibition of the current by noradrenaline was seen at cell potentials below -60 mV, and further inhibition was seen over 0 mV ( Figure 1C).…”

“…A number of studies have demonstrated that membrane potential and cell proliferation capacity were regulated by activities of potassium channels in several types of cells including osteoblasts (Pardo et al, 2005;Liebau et al, 2006;Henney et al, 2009;Jang et al, 2011). Adequate inhibition of potassium channels is thought to cause membrane depolarization and activate voltage-dependent calcium channels, leading to cell proliferation (Burg et al, 2008).…”

“…We previously demonstrated that noradrenaline suppressed Cs-sensitive and tetraethylammonium-insensitive (TEA-insensitive) potassium channels via a1B-adrenoceptors in human osteoblasts, SaM-1 cells, by using whole-cell patch clamp recordings (Kodama and Togari, 2010). Several types of potassium channel had been found to regulate membrane potential and cell proliferation (Pardo et al, 2005;Liebau et al, 2006;Henney et al, 2009;Jang et al, 2011). In osteoblasts, blockade of large conductance Ca-activated potassium (BK) channels, ERG channels and TREK-1 channels promoted cell proliferation (Hughes et al, 2006;Hernandez et al, 2007), while a high dose of TEA, a potassium channel inhibitor, impaired cell proliferation (Hernandez et al, 2007;Henney et al, 2009).…”

“…Several types of potassium channel had been found to regulate membrane potential and cell proliferation (Pardo et al, 2005;Liebau et al, 2006;Henney et al, 2009;Jang et al, 2011). In osteoblasts, blockade of large conductance Ca-activated potassium (BK) channels, ERG channels and TREK-1 channels promoted cell proliferation (Hughes et al, 2006;Hernandez et al, 2007), while a high dose of TEA, a potassium channel inhibitor, impaired cell proliferation (Hernandez et al, 2007;Henney et al, 2009). The physiological roles of the inhibitory effects of noradrenaline on potassium channels in human osteoblasts have not yet been defined.…”

Synthesis and Bioactivity Evaluation of Acylthiourea Derivatives Based on Isopimaric Acid

“…关于异海松酸的生物活性研究 报道较多的是其活化大型钙离子激活的钾离子(BK)通 道的活性 [1,2] . 进一步研究表明, 异海松酸作为 BK 通道 的活化剂可以调控初级成骨细胞的生长和矿化 [3] , 并降 低小鼠听觉神经网络自发活动的多动症和改善患阿尔 茨海默病小鼠的认知功能, 从而对神经活性多动症和阿 尔茨海默病具有潜在的治疗效果 [4,5] . 其次, 异海松酸对 结核病毒具有显著的疗效 [6] , 并对爱博斯坦巴尔病毒 也显示出抑制效果 [7] .…”