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

Abstract

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 Ca(2+) channels. HEF-19 reduced inflow and intracellular release of Ca(2+) ions.

Keywords: Ca2+ channels; Colonic smooth muscle; Smooth muscle relaxation.

Figure 1

3.4-dihydro-7-[3-(diethylamino) propoxy] chroman hydrochloride.

Figure 2

Effects of HEF-19 on spontaneous tension and amplitude of isolated rabbit descending colonic smooth muscle.

Figure 3

Relaxant effect of HEF-19 (3 × 10^-7-3 × 10^-4 mol/L) on isolated rabbit descending colonic smooth muscle pre-contracted with Ach, histamine, high-K⁺ solution or BaCl₂. Data are mean ± SE (n = 6).

Figure 4

Effect of HEF-19 and verapamil on the contraction-response curve of CaCl₂ in descending colonic smooth muscle isolated from rabbits. Data are mean ± SE (n = 6) and are expressed as percentage of maximum contraction.

Figure 5

Effects of HEF-19 (3 × 10^-6 and 10^-5 mol/L) and verapamil (1 × 10^-7 mol/L) on biphasic contraction induced by Ach in descending colonic smooth muscle isolated from rabbits. Data are mean ± SE (n = 6). ^aP < 0.05, ^bP < 0.01 vs the controls.