HEF-19-induced relaxation of colonic smooth muscles and the underlying mechanisms

AIM:To investigate the relaxant effect of chromane HEF-19 on colonic smooth muscles isolated from rabbits,and the underlying mechanisms.METHODS:The relaxant effect and action mechanisms of HEF-19 were investigated using descending colon smooth muscle of the rabbits.Preparations 1 cm long were mounted in 15-mL tissue baths containing Tyrode’s solution,maintained at 37±0.5℃and aerated with a mixture of 5%CO2in oxygen(Carbogen).The tension and amplitude of the smooth muscle strips were recorded after adding HEF-19(10-6,10-5and 10-4mol/L).After cumulative administration of four antispasmodic agents,including acetylcholine chloride(Ach)(10-4mol/L),histamine(10-4mol/L),high-K+(60 mmol/L)and BaCl2(8.2 mmol/L),HEF-19(3×10-7-3×10-4mol/L)was added to investigate the relaxant effect of HEF-19.CaCl2(10-4-2.5×10-3mol/L)was added cumulatively to the smooth muscle preparations pretreated with and without HEF-19(1×10-6or 3×10-6mol/L)and verapamil(1×10-7mol/L)to study the mechanisms involved.Finally,phasic contraction was induced with ACh(15×10-6mol/L),and CaCl2(4×10-3mol/L)was added to the smooth muscle preparations pretreated with and without HEF-19(3×10-6mol/L or 1×10-5mol/L)and verapamil(1×10-7mol/L)in calcium-free medium to further study the underlying mechanisms.RESULTS:HEF-19(1×10-6,1×10-5and 1×10-4mol/L)suppressed spontaneous contraction of rabbit colonic smooth muscles.HEF-19(3×10-7-3×10-4mol/L)relaxed in a concentration-dependent manner colonic smooth muscle preparations pre-contracted with BaCl2,high-K+solution,Ach or histamine with respective EC50values of 5.15±0.05,5.12±0.08,5.58±0.16and 5.25±0.24,thus showing a spasmolytic activity.HEF-19(1×10-6mol/L and 3×10-6mol/L)shifted the concentration-response curves of CaCl2to the right and depressed the maximum response to CaCl2.The two components contracted by Ach were attenuated with HEF-19(3×10-6mol/L or 10-5mol/L)in calcium-free medium.CONCLUSION:HEF-19 inhibited rabbit colonic smooth muscle contraction,probably through inhibiting opening of