Published online Aug 28, 2013. doi: 10.3748/wjg.v19.i32.5314
Revised: July 1, 2013
Accepted: July 12, 2013
Published online: August 28, 2013
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 °C and aerated with a mixture of 5% CO2 in oxygen (Carbogen). The tension and amplitude of the smooth muscle strips were recorded after adding HEF-19 (10-6, 10-5 and 10-4 mol/L). After cumulative administration of four antispasmodic agents, including acetylcholine chloride (Ach) (10-4 mol/L), histamine (10-4 mol/L), high-K+ (60 mmol/L) and BaCl2 (8.2 mmol/L), HEF-19 (3 × 10-7-3 × 10-4 mol/L) was added to investigate the relaxant effect of HEF-19. CaCl2 (10-4-2.5 × 10-3 mol/L) was added cumulatively to the smooth muscle preparations pretreated with and without HEF-19 (1 × 10-6 or 3 × 10-6 mol/L) and verapamil (1 × 10-7 mol/L) to study the mechanisms involved. Finally, phasic contraction was induced with ACh (15 × 10-6 mol/L), and CaCl2 (4 × 10-3 mol/L) was added to the smooth muscle preparations pretreated with and without HEF-19 (3 × 10-6 mol/L or 1 × 10-5 mol/L) and verapamil (1 × 10-7 mol/L) in calcium-free medium to further study the underlying mechanisms.
RESULTS: HEF-19 (1 × 10-6, 1 × 10-5 and 1 × 10-4 mol/L) suppressed spontaneous contraction of rabbit colonic smooth muscles. HEF-19 (3 × 10-7-3 × 10-4 mol/L) relaxed in a concentration-dependent manner colonic smooth muscle preparations pre-contracted with BaCl2, high-K+ solution, Ach or histamine with respective EC50 values of 5.15 ± 0.05, 5.12 ± 0.08, 5.58 ± 0.16 and 5.25 ± 0.24, thus showing a spasmolytic activity. HEF-19 (1 × 10-6 mol/L and 3 × 10-6 mol/L) shifted the concentration-response curves of CaCl2 to the right and depressed the maximum response to CaCl2. The two components contracted by Ach were attenuated with HEF-19 (3 × 10-6 mol/L or 10-5 mol/L) in calcium-free medium.
CONCLUSION: HEF-19 inhibited rabbit colonic smooth muscle contraction, probably through inhibiting opening of voltage-dependent Ca2+ channels. HEF-19 reduced inflow and intracellular release of Ca2+ ions.
Core tip: This is a good descriptive study in which authors found a new L-calcium-antagonist relaxing rabbit colonic smooth muscles and analyzed its possible mechanism. It provides an opportunity to search for a new drug highly selective to the gastrointestinal tract, effectively relieving pain, diarrhea and intestinal discomfort, but without significant adverse effects on irritable bowel syndrome patients.