The Potential Involvement of an ATP-Dependent Potassium Channel-Opening Mechanism in the Smooth Muscle Relaxant Properties of Tamarix dioica Roxb

Abstract

Background: Tamarix dioica is traditionally used to manage various disorders related to smooth muscle in the gastrointestinal, respiratory, and cardiovascular systems. This study was planned to establish a pharmacological basis for the uses of Tamarix dioica in certain medical conditions related to the digestive, respiratory, and cardiovascular systems, and to explore the underlying mechanisms. Methods: A phytochemical study was performed by preliminary methods, followed by HPLC-DAD and spectrometric methods. In vivo evaluation of a crude hydromethanolic extract of T.dioica (TdCr) was done with a castor-oil-provoked diarrheal model in rats to determine its antidiarrheal effect. Ex vivo experiments were done by using isolated tissues to determine the effects on smooth and cardiac muscles and explore the possible mechanisms. Results: TdCr tested positive for flavonoids, saponins, phenols, and tannins as methanolic solvable constituents in a preliminary study. The maximum quantity of gallic acid equivalent (GAE), phenolic, and quercetin equivalent (QE) flavonoid content found was 146 ± 0.001 μg GAE/mg extract and 36.17 ± 2.35 μg QE/mg extract. Quantification based on HPLC-DAD (reverse phase) exposed the presence of rutin at the highest concentration, followed by catechin, gallic acid, myricetin, kaempferol, and apigenin in TdCr. In vivo experiments showed the significant antidiarrheal effect of TdCr (100, 200, and 400 mg/kg) in the diarrheal (castor-oil-provoked) model. Ex vivo experiments revealed spasmolytic, bronchodilatory, and vasorelaxant activities as well as partial cardiac depressant activity, which may be potentiated by a potassium channel opener mechanism, similar to that of cromakalim. The potassium channel (K_ATP channel)-opening activity was further confirmed by repeating the experiments in glibenclamide-pretreated tissues. Conclusions: In vivo and ex vivo studies of T.dioica provided evidence of the antidiarrheal, spasmolytic, bronchodilator, vasorelaxant, and partial cardiodepressant properties facilitated through the opening of the K_ATP channel.

Keywords: HPLC-DAD; KATP channel opener; Tamarix dioica; antidiarrheal; bronchodilator; spasmolytic; vasodilator.

Figure 1

HPLC-DAD chromatograms of (a) Standard at 257, 279, 325, and 368 nm; (b) Methanolic extract of TdCr extract at 257, 279, 325, and 368 nm.

Figure 2

Bar graph representing the antidiarrheal activity of TdCr by a castor-oil-provoked method in rats. Bars express mean ± SEM with n = 6, analyzed by using ANOVA (one-way) and multiple comparison by Dunnett’s test (*p < 0.05, **p < 0.01, ***p < 0.005 when compared to the control).

Figure 3

Tracing showing (a) Spontaneous contraction (Control) (b) The effect of methanolic extract of TdCr in comparison to the control on spontaneous contractions of isolated rabbit jejunum preparations.

Figure 3

Tracing showing (a) Spontaneous contraction (Control) (b) The effect of methanolic extract of TdCr in comparison to the control on spontaneous contractions of isolated rabbit jejunum preparations.

Figure 4

Concentration-response graphical presentation of (A) TdCr, (B) TdDcm, and (C) TdAq on natural and K+ (25 mmol/L) provoked contractions of isolated jejunal preparation. Values shown as mean ± SEM, n = 5.

Figure 5

Tracings showing the effect of a methanolic extract of TdCr plant on (a) high K⁺ (80 mmol/L) and (b) low K⁺ (25 mmol/L)-induced contractions in isolated rabbit jejunum preparations.

Figure 6

Concentration‒response graphical presentation of (A) TdCr compared with (B) cromakalim against K+ (80 mmol/L) in the absence or presence of glibenclamide (GB; 3 μmol) in isolated jejunal preparation. Values shown as mean ± SEM, n = 5.

Figure 7

Concentration‒response graphical presentation of (A) TdCr compared with (B) cromakalim (1 µmol/L) on K+ (80 mmol/L) and K+ (25 mmol/L)-provoked contractions in the absence or presence of glibenclamide (3 μM) isolated rabbit tracheal preparations. Values shown as mean ± SEM, n = 5.

Figure 8

Concentration‒response graphical presentation of (A) TdDcm and (B) TdAq on contractions provoked by CCh (1 µmol/L) and K⁺ (25 mmol/L) in isolated rabbit tracheal preparations. Values shown as mean ± SEM, n = 5.

Figure 9

Concentration‒response graphical presentation of (A) (TdCr), (B) TdDcm, and (C) TdAq on K+ (25 mmol/L) and phenylephrine (1 µmol/L) provoked contractions of isolated aortic ring preparations. Values shown as mean ± SEM, n = 5.

Figure 9

Concentration‒response graphical presentation of (A) (TdCr), (B) TdDcm, and (C) TdAq on K+ (25 mmol/L) and phenylephrine (1 µmol/L) provoked contractions of isolated aortic ring preparations. Values shown as mean ± SEM, n = 5.

Figure 10

Concentration‒response graphical presentation of (A) TdCr in comparison to (B) cromakalim against contractions provoked by K⁺ (80 mmol/L) and K⁺ (25 mmol/L) in the absence or presence of glibenclamide (GB; 3 μM) in isolated aortic ring preparations. Values shown as mean ± SEM, n = 5.

Figure 11

Tracings indicating the effect of (a) TdCr and (b) cromakalim on spontaneous contractions of paired atrial preparation of a rabbit.

Figure 12

Concentration-response curve presentation the inotropic and chronotropic effects of (A) TdCr and (B) cromakalim on spontaneous contractions of paired atrial preparation of a rabbit. Values shown as mean ± SEM, n = 5.

Figure 13

The schematic diagram of proposed mechanism of smooth muscle relaxation by K⁺ channel openers.