Mechanisms mediating cholinergic antral circular smooth muscle contraction in rats

Figure 1 Effect of bethanechol on smooth muscle contraction. Antrum circular smooth muscle strips were incubated with increasing concentrations of bethanechol (10^-4 mol/L to 10^-7 mol/L). The vertical axis represents the developed tension (in grams per mm²). Bethanechol significantly increased circular muscle tension (P < 0.05; paired t-test). Each data point represents mean ± SE, n = 4.

Figure 2 Effect of depletion of Ca²⁺ from medium on the contraction of antral circular smooth muscle strips to bethanechol (10^-4 mol/L). Ca²⁺ depletion caused a significant decrease in the muscle tension; after 5 min incubation (P < 0.06, paired t-test); and after 10 min incubation (P < 0.005, paired t-test) compared to the base contraction induced by bethanechol before Ca²⁺ depletion. Each data point represents mean ± SE, n = 3.

Figure 3 Effect of PTX on antrum circular smooth muscle strips contraction to bethanechol (10^-4 mol/L to 10^-6 mol/L). PTX significantly inhibited the contractile activity of the smooth muscle (P ≤ 0.01; paired t-test) compared to control rats. Each point represents mean ± SE, n = 7; dotted bars represent control animals; solid bars-PTX-pretreated animals.

Figure 4 Effect of PTX on dispersed antral circular smooth muscle myocytes from PTX-pretreated rats contraction to bethanechol (10^-7 mol/L and 10^-8 mol/L). Myocytes from PTX-treated rats contracted less than myocytes from control rats. Each point represents mean ± SE; of the percentage of the control cells diastolic length (no bethanechol). At least 50 myocytes per point were calculated, P < 0.005; n = 7 and 11. Dotted bars represent control animals; solid bars PTX-pretreated animals.

Figure 5 Concentration-response curves for the contractile effect of (+)-cis-Dioxolane alone and in combination with different concentrations of M1 antagonist, pirenzepine (10^-8 mol/L to 10^-5 mol/L) on the rat antral circular smooth muscle strips. Each point represents the mean ± SE, n = 6, 6, 7 and 8 strips. Cumulative concentration-effect curve was constructed for each strip for (+)-cis-Dioxolane, (10^-8 to 3 × 10^-5 mol/L). After washing, strips were equilibrated in either the absence (control) or presence of pirenzepine for 90 min. Subsequently, the second concentration-effect curve for (+)-cis-Dioxolane was constructed for each strip. Pirenzepine caused a significant inhibition of the contractile muscle response to (+)-cis-dioxolane.

Figure 6 Concentration-response curves for the contractile effect of (+)-cis-Dioxolane alone and in combination with different concentrations of M₂ antagonist, methocramine (from 10^-8 mol/L to 10^-5 mol/L) on the rat antral circular smooth muscle strips. Each point represents the mean ± SE; n = 4, 9, 10 and 11 strips. First, cumulative concentration-effect curve was constructed for each strip for (+)-cis-Dioxolane, (10^-8 to 3 × 10^-5 mol/L). After washing, tissues were equilibrated in either the absence (control) or presence of methocramine for a 90 min. Subsequently, the second concentration-effect curve for (+)- cis-Dioxolane was constructed for each strip. Methocramine caused a significant inhibition of the contractile muscle response to (+)-cis-Dioxolane.

Figure 7 Concentration-response curves for the contractile effect of (+)-cis-Dioxolane alone and in combination with different concentrations of M₃ antagonist, darifenacin (from 10^-10 mol/L to 10^-6 mol/L) on the rat antral circular smooth muscle strips. Each point represents the mean ± SE; n = 4, 7, 11, 10 strips. First, cumulative concentration-effect curve was constructed for each strip for (+)-cis-Dioxolane, (10^-8 to 3 × 10^-5 mol/L). After wash, tissues were equilibrated in either the absence (control) or presence of darifenacin for a 90 min. Subsequently, the second concentration-effect curve for (+)-cis-Dioxolane was constructed for each strip. Darifenacin caused a significant inhibition of the contractile muscle response to (+)-cis-Dioxolane.

Figure 8 Comparison of the inhibition of the contractile response to cis-Dioxolane by 3 muscarinic receptor antagonists: M₃- darifenacin, M₂- methocramine, and M₁- pirenzepine. The M₃ antagonist, darifenacin, was the most potent inhibitor of the contraction induced by (+)-cis Dioxolane (10^-6 mol/L). The EC₅₀ values for each were: for darifenacin (M₃) -7.9; for methocramine (M₂) -7.2; and for pirenzepine (M₁) -6.8.