Review article: in vitro studies of gall-bladder smooth muscle function. Relevance in cholesterol gallstone disease

Single Cell RNA-Sequencing Reveals a Murine Gallbladder Cell Transcriptome Atlas During the Process of Cholesterol Gallstone Formation

Gallstone disease is a worldwide common disease. However, the knowledge concerning the gallbladder in the pathogenesis of cholesterol gallstone formation remains limited. In this study, using single-cell RNA sequencing (scRNA-seq) to obtain the transcriptome of gallbladder cells, we showed cellular heterogeneity and transcriptomic dynamics in murine gallbladder cells during the process of lithogenesis. Our results indicated gallbladder walls were subjected to remodeling during the process of lithogenesis. The major molecular events that happened included proliferation of epithelial cells, infiltration of immune-cells, activation of angiogenesis, and extracellular matrix modulation. Furthermore, we observed partial reversal of gallbladder cell transcriptomes by ursodeoxycholic acid treatment. This work thus provides novel and integral knowledges on the cellular changes during lithogenesis, which is of great significance to the understanding of pathogenesis and treatment of cholesterol gallstone.

Effect of Fructus Psoraleae on motility of gallbladder isolated smooth muscle strips from guinea pigs

AIM: To observe the effect of Fructus Psoraleae on motility of isolated gallbladder muscle strips of guinea pigs and its mechanism.

METHODS: Guinea pigs were hit to lose consciousness and the whole gallbladder was removed quickly. Two or three smooth muscle strips (8 mm × 3 mm) were cut along a longitudinal direction. The mucosa was gently removed. Every longitudinal muscle strip was suspended in a tissue chamber which was continuously perfused with 5 mL Krebs solution (37°C), pH 7.4, and aerated with 950 mL/L O₂ and 50 mL /L CO₂. The isometric response was recorded with an ink-writing recorder. After 2 h equilibration under 1 g-load, 50 μL Fructus Psoraleae (10, 20, 70, 200, 700, 1000 g/L) was added cumulatively into the tissue chamber in turn every 2 min to observe their effects on gallbladder muscle strips (cumulating final concentration of Fructus Psoraleae was 0.1, 0.3, 1.0, 3.0, 10.0, 20.0 g/L). The antagonists, including 4-DAMP, benzhydramine, hexamethonium, phentolamine, verapamil and idomethine were given 2 min before Fructus Psoraleae respectively to investigate the mechanisms involved.

RESULTS: Fructus Psoraleae dose-dependently increased the resting tension (r = 0.992, P < 0.001), decreased the mean contractile amplitude (r = 0.970, P < 0.001) and meanwhile increased the contractile frequency of the gallbladder muscle strip in vitro (r = 0.965, P < 0.001). The exciting action of Fructus Psoraleae on the resting tension could be partially blocked by 4-DAMP (the resting tension decreased from 1.37 ± 0.41 to 0.70 ± 0.35, P < 0.001), benzhydramine (from 1.37 ± 0.41 to 0.45 ± 0.38, P < 0.001), hexamethonium (from 1.37 ± 0.41 to 0.94 ± 0.23, P < 0.05), phentolamine ( from 1.37 ± 0.41 to 0.89 ± 0.22, P < 0.01) and verapamil (from 1.37 ± 0.41 to 0.94 ± 0.26, P < 0.05). But the above antagonists had no significant effect on the action of Fructus Psoraleae–induced mean contractile amplitude (P > 0.05). Moreover, the increase of the contractile frequency due to Fructus Psoraleae was inhibited by 4-DAMP (decreased from 8.3 ± 1.2 to 6.8 ± 0.5, P < 0.01) and hexamethonium (from 8.3 ± 1.2 to 7.0 ± 0.9, P < 0.05). Idomethine had no significant effect on the Fructus Psoraleae-induced responses (P > 0.05).

CONCLUSION: Fructus Psoraleae enhances the motility of isolated gallbladder muscle strips from guinea pigs, in a dose-dependent manner. The effect of Fructus Psoraleae is partly related to M₃, N receptor, α receptor, H₁ receptor, Ca²⁺ channel, but not related to prostaglandin.

Rho kinase expression and its central role in ovine gallbladder contractions elicited by a variety of excitatory stimuli

Rho kinase has contractile activity, which induces Ca2+ sensitization in various cells. Several receptors are linked to the Rho/Rho-kinase pathway. Therefore, in this study we aimed to demonstrate the central importance of this novel pathway for diverse excitatory stimuli in the smooth muscle of the sheep gallbladder. Accordingly, the effects of a Rho kinase inhibitor, (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide dihydrochloride monohydrate (Y-27632, 10(-8)-3 x 10(-5) M), were investigated on cholecystokinin-8 (CCK-8, 10(-8) M), endothelin-1 (10(-8) M), carbachol (10(-6)-10(-5) M), 5-hydroxytryptamine (5-HT, 10(-6)-10(-5) M), histamine (10(-6)-10(-5) M), phenylephrine (10(-5)-10(-4) M), neurokinin A (10(-7)-10(-6) M), electrical field stimulation (40 V, 0.5 ms, 2, 4, 8, 16, 32 Hz, 15 s, 3 min intervals) and potassium chloride (KCl, 25-50 mM)-induced contractions as well as spontaneous contractile activity. Electrical field stimulation evoked tetrodotoxin (3 x 10(-6) M)-sensitive reproducible contractions, which were inhibited by atropine (2 x 10(-6) M) and potentiated by eserine (5 x 10(-7) M). EFS-induced contraction was significantly inhibited by Y-27632 (10(-5) M). In addition, spontaneous contractile activity was suppressed in the presence of the compound (10(-6)-10(-5) M). This Rho kinase inhibitor also dramatically decreased the contractions elicited by 5-HT, neurokinin A and carbachol. KCl-induced contraction, which was not atropine-sensitive, was also conspicuously attenuated by Y-27632. Moreover, Y-27632 (10(-8)-3 x 10(-5) M) relaxed gallbladder strips that were contracted by histamine, endothelin-1, CCK-8 and phenylephrine in a concentration-dependent manner. pEC50 values for Y-27632 were 6.25+/-0.10, 5.79+/-0.12, 5.83+/-0.09 and 5.70+/-0.13 for the contraction elicited by histamine, CCK-8, endothelin-1 and phenylephrine, respectively. Furthermore, we also demonstrated Rho kinase protein expression (ROCK-1 and ROCK-2) by Western blot analysis. In conclusion, ROCK is expressed in the smooth muscle of the ovine gallbladder, and it has a central role in the contractile activity induced by diverse excitatory stimuli.

Smooth muscle function and dysfunction in gallbladder disease

The gallbladder epithelium and smooth muscle layer are exposed to concentrated biliary solutes, including cholesterol and potentially toxic hydrophobic bile salts, which are able to influence muscle contraction. Physiologically, gallbladder tone is regulated by spontaneous muscle activity, hormones, and neurotransmitters released into the muscle from intrinsic neurons and extrinsic sympathetic nerves. Methods to explore gallbladder smooth muscle function in vitro include cholecystokinin (CCK) receptor-binding studies and contractility studies. In human and animal models, studies have focused on cellular and molecular events in health and disease, and in vitro findings mirror in vivo events. The interplay between contraction and relaxation of the gallbladder muscularis leads in vivo to appropriate gallbladder emptying and refilling during fasting and postprandially. Defective smooth muscle contractility and/or relaxation are found in cholesterol stone-containing gallbladders, featuring a type of gallbladder leiomyopathy; defects of CCKA receptors and signal transduction may coexist with abnormal responses to oxidative stress and inflammatory mediators. Abnormal smooth musculature contractility, impaired gallbladder motility, and increased stasis are key factors in the pathogenesis of cholesterol gallstones.

Investigation of the mechanism of nicotine-induced relaxation in guinea pig gallbladder

BACKGROUND

Muscular contraction of the gallbladder is the primary determinant of bile delivery into duedonum. Gallbladder filling and emptying are influenced by both inhibitory and excitatory stimuli, and NO plays a key role in normal relaxation. In this study, to determine whether nicotine acts on the gallbladder muscle, the mechanism of its effect on strips of guinea pig gallbladder was studied in vitro.

MATERIALS AND METHODS

Guinea pig gallbladder muscle strips were mounted in organ bath with modified Krebs-Henseleit solution and aerated with Carbogen. Tension was measured with isometric force transducers, and muscle relaxation was expressed as percent decrease of precontraction induced by carbachol.

RESULTS

Nicotine produced concentration dependent relaxation when preparations were precontracted by carbachol (10(-6) M). Nicotine-induced relaxation was 51.6 +/- 3.2% of phenylephrine contraction and was not affected by guanethidine (10(-5) M), propranolol (10(-6) M), hexamethonium (10(-4) M), indomethacin (10(-5) M), N(w)-nitro L-arginine methyl ester (L-NAME) (3 x 10(-5) M), methylene blue (10(-5) M), glibenclamide (10(-5) M), clotrimazole (10(-6) M), tetraethylammonium (3 x 10(-4) M), or 4-aminopyridine (10(-3) M). Nicotine did not exhibit a calcium antagonizing effect.

CONCLUSIONS

From these results, we concluded that nicotine-induced relaxation of the guinea pig gallbladder is not mediated by the release of noradrenaline, nitric oxide (NO), prostaglandins, or a related substance, or by the activation of potassium channels, or by the stimulation of nicotinic cholinoceptors. Further work is needed to determine the cellular mechanism(s) of action by which nicotine acts on gallbladder smooth muscle.

Cholesterol gallstones

Cholesterol cholelithiasis is common in Western populations and represents a consequence of altered cholesterol homeostasis. Gallstones form because of a complex and incompletely understood series of metabolic and physicochemical events that promote cholesterol crystallization in bile. In the context of current paradigms, this article reviews recent progress in research on biliary lipid metabolism and the pathogenesis of cholesterol gallstones.