aDepartment of Pharmacology, College of Medicine, Wuhan University, Wuhan 430071, China

bDepartment of Pharmacy, Hubei Cancer Hospital, Wuhan 430079, China

Received 5 August 2007; 

Abstract

Licorice root is used to treat asthma as a component of Shaoyao-Gancao-tang, a traditional Chinese medicine formula.

In this study, we investigated the tracheal relaxation effects of  isoliquiritigenin, a flavonoid isolated from the roots of Glycyrrhiza glabra (a kind of Licorice), on guinea-pig tracheal smooth muscle in vitro and in vivo.

The tension changes of isolated tracheal rings were isometrically recorded on a polygraph. The large-conductance Ca2+-activated K+ channels (BKCa) were measured by inside-out patch-clamp techniques and intracellular Ca2+ concentrations ([Ca2+]i) were tested by microfluorometric method in guinea-pig tracheal smooth muscle cells (TSMCs).

Isoliquiritigenin produced concentration-dependent relaxation in isolated guinea-pig tracheal rings precontracted with acetylcholine, KCl, and histamine.

Pretreatments with charybdotoxin, ODQ and KT5823 attenuated the relaxation induced by isoliquiritigenin. Isoliquiritigenin significantly increased intracellular cGMP level in cultured TSMCs and inhibited the activity of phosphodiesterase (PDE) 5 in human platelets. Moreover, isoliquiritigenin increased by 9-fold the probability of BKCa channel openings of TSMCs in inside-out patches and markedly reduced [Ca2+]i rise induced by acetylcholine in TSMCs, pretreatment with KT5823 attenuated above two responses to isoliquiritigenin. In vivo experiment isoliquiritigenin significantly prolonged the latency time of histamine–acetylcholine aerosol-induced collapse and inhibited the increase of lung overflow induced by intravenously administered histamine dose-dependently.

These data indicate that isoliquiritigenin relaxes guinea-pig trachea through a multiple of intracellular actions, including sGC activation, inhibition of PDEs, and associated activation of the cGMP/PKG signaling cascade, leading to the opening of BKCa channels and [Ca2+]i decrease through PKG-dependent mechanism and thus to tracheal relaxation.

Keywords: Isoliquiritigenin; Tracheal smooth muscle cell; cGMP; K+ channel; Intracellular Ca2+ concentration

Article Outline

1. Introduction

2. Methods

2.1. Animals

2.2. Drugs and chemicals

2.3. Isolated tracheal preparation and measurement of tension

2.4. Dispersal and culture of guinea-pig tracheal smooth muscle cells

2.5. Phosphodiesterase assay

2.6. Measurement of cAMP and cGMP

2.7. Patch-clamp studies

2.8. Ca2+ measurement in guinea-pig tracheal smooth muscle cells

2.9. In vivo experiments

2.10. Statistical evaluation of data

3. Results

3.1. Effect of isoliquiritigenin on isometric contraction of tracheal rings

3.2. Epithelium-, NO- and prostaglandin-independent effects

3.3. Involvement of sGC and PKG

3.4. Inhibition of phosphodiesterase

3.5. Measurement of cAMP and cGMP in cultured TSMCs

3.6. Effect of isoliquiritigenin on BKCa channels of tracheal smooth muscle

3.7. Inhibition by isoliquiritigenin of agonist-induced [Ca2+]i elevation in TSMCs

3.8. In vivo experiments

4. Discussion

Acknowledgements

References