Ethacrynic Acid Inhibits Mouse Airway Smooth Muscle Contraction

Objective:The aim of this study was to investigate the inhibitory effect and the underlying mechanism of ethacrynic acid（EA） on the contraction of mouse airway smooth muscle.Methods:BL-420S force measuring system was used to measure the tension of mouse tracheal rings.The whole cell patch clamp technique was utilized to record the channel currents of airway smooth muscle（ASM） cells.The calcium imaging system was used to measure the level of intracellular Ca²⁺ in ASM cells.CCK8（cell counting kit-8） was used to analysis the cell activity of 16HBE.The Flexi Vent system was used to assess the respiratory resistance of mice in vivo.These experiments were used to define whether EA inhibits the contraction of mouse ASM and the underlying mechanism.Results:EA dose-dependently relaxed the contraction of mouse tracheal rings induced by high K⁺（80 mM K⁺） and acetylcholine（ACh,100μM）.The maximal relaxation percentages were（97.02±1.56）%and（85.21±0.03）%,and the median effective concentrations of EA were（40.28±2.20）μM and（56.22±7.62）μM,respectively.EA decreased intracellular Ca²⁺ elevations induced by high K⁺and ACh from（0.40±0.04）to（0.16±0.01）,（0.50±0.01）to（0.39±0.01）,respectively.EA inhibited L-type voltage-dependent calcium channel（L-VDCC）-and store-operated calcium channel（SOCC）-mediated currents,and Ca²⁺ influx in ASM cells.In addition,EA decreased the increase of mouse Rrs induced by ACh in vivo.Conclusion:These results indicate that EA inhibits L-VDCC and SOCC,which results in termination of Ca²⁺ influx to decrease intracellular Ca²⁺,leading to relaxation of airway smooth muscle.In addition,EA decreased mouse Rrs in vivo.Taken together,EA will be a potential bronchodilator.