Abstract
Excessive contraction of airway smooth muscle cells (ASMCs) is a hallmark feature of asthma. Intriguing, the activation of bitter taste receptor (TAS2R) in ASMCs can relax ASMCs. However, there is a lack of potent TAS2R agonists that can be used in asthma therapies since those tested agonists cannot relax ASMCs at the dose below a few hundred micromolar. Considering that sanguinarine (SA) is a bitter substance often used in small doses for the treatment of asthma in folk medicine, the present study was to determine the rapid relaxation effect of SA on ASMCs and to reveal the underlying mechanisms associated with TAS2R signaling. Here, cell stiffness, traction force, calcium signaling, cAMP levels, and the mRNA expression were evaluated by using optical magnetic twisting cytometry, traction force microscopy, Fluo-4/AM labeling, enzyme-linked immunosorbent assay (ELISA), and quantitative (q)RT-PCR, respectively. We found that 0.5 µM SA immediately decreased cell stiffness and traction force, which is comparable with the effect of 5 µM isoproterenol. In addition, 0.5 µM SA immediately increased intracellular free calcium concentration ([Ca2+]i) and decreased the mRNA expression of contractile proteins such as calponin and α-smooth muscle actin after the treatment for 24 h. Furthermore, SA-mediated decrease in cell stiffness/traction force and increase in [Ca2+]i were significantly blunted by inhibiting the TAS2Rs signaling. These findings establish the rapid relaxation effect of SA at low concentration (<1 µM) on cultured ASMCs depending on TAS2R signaling, indicating that SA might be developed as a useful bronchodilator in asthma therapy.