β(2)-adrenoreceptor Inverse Agonist Down-regulates Muscarine Cholinergic Subtype-3 Receptor and Its Downstream Signal Pathways in Airway Smooth Muscle Cells in vitro

Mechanisms underlying β(2)-adrenoreceptor (β(2)AR) inverse agonist mediated bronchoprotectiveness remain unknown. We incubated ICI118,551, formoterol, budesonide, and formoterol plus budesonide, as well as ICI118,551 or pindolol plus formoterol, ICI118,551 plus forskolin, SQ22,536 or H89 plus formoterol in ASMCs to detect expressions of M(3)R, PLCβ(1) and IP(3). The level of M(3)R in the presence of 10(−5) mmol/L ICI118,551 were significantly decreased at 12 h, 24 h and 48 h (P < 0.05), and at 24 h were significantly reduced in ICI118,551 with concentration of 10(−5 )mmol/L, 10(−6 )mmol/L, 10(−7 )mmol/L, and 10(−8 )mmol/L (P < 0.05). The level of IP(3) in 10(−5 )mmol/L ICI118,551 was significantly diminished at 24 h (P < 0.01), except for that at 1 h, neither was in the level of PLCβ(1). A concentration of 10(−5 )mmol/L ICI118,551 at 24 h showed a significant reduction of M(3)R level compared to formoterol (P < 0.01), budesonide (P < 0.01), and formoterol + budesonide (P < 0.05), but significant reduction of PLCβ(1) and IP(3) was only found between 10(−5 )mmol/L ICI118,551 and formoterol at 24 h, but not in the comparison of budesonide or formoterol + budesonide. Pindolol and H89 could not inhibit the formoterol-induced expression of M(3)R (P > 0.05), but SQ22,536 significantly antagonized the formoterol-induced M(3)R expression (P < 0.05). In conclusions, β(2)AR inverse agonist, ICI118,551, exerts similar bronchoprotective effects to corticosteroids via decreasing the expression of M(3)R and inhibiting the production of IP(3).