Effect And Mechanism Of Rhein Inhibited Contraction Of Airway Smooth Muscle

Aims:this study was to investigate substances that inhibit airway smooth muscle contraction from plants and the underlying mechanism.Methods:The effects of Rhein on 80 mM K⁺?High-K⁺?-and 100?M acetylcholine?ACh?-induced precontractions on mouse tracheal rings were observed by muscle tension test.Whole-cell patch clamp technique and single cell calcium imaging were used to detect L-type voltage-dependent Ca²⁺channels?LVDCC?and store-operated Ca²⁺channels?SOCC?mediated currents,and the effect on Ca²⁺influx in airway smooth muscle cells?ASMCs?.Results:We found that ethyl alcohol extract of Cassia ang ustif olia Vahl?ECVV?inhibited the precontraction of mouse airway smooth muscle?ASM?.ECVV contained the monomeric Rhein,which had the same inhibitory effect.Therefore,we investigated the mechanism of Rhein-induced inhibition.Rhein?177.8?M?inhibited precontraction in tracheal rings caused by acetylcholine?ACh?or High-K⁺.ACh-induced precontraction can also be partially inhibited by nifedipine?a selective blocker of L-type voltage-dependent calcium channel,LVDCC?and YM-58483?specific inhibitor of store-operated calcium channel,SOCC?.In addition,nifedipine and YM-58483 inhibited currents mediated by LVDCC and SOCC.These channel currents were also inhibited by Rhein;Moreover,Rhein reduced intracellular calcium influx caused by ACh or High-K⁺.Finally,in the absence of external calcium,ACh induced a transient contractile response,High-K⁺failed,when 2 mM calcium was added,a strong contractile response was observed,however,it was significantly inhibited by Rhein.Conclusion:Rhein inhibits LVDCC and SOCC,reducing intracellular calcium,eventually relaxing precontracted airway smooth muscle.Rhein in Cassia ang ustif olia Vahl could be used to develop a bronchodilator.