Mechanism of cholecystokinin-induced contraction of the opossum gallbladder

Genetic Identification of Vagal Sensory Neurons That Control Feeding

Energy homeostasis requires precise measurement of the quantity and quality of ingested food. The vagus nerve innervates the gut and can detect diverse interoceptive cues, but the identity of the key sensory neurons and corresponding signals that regulate food intake remains unknown. Here, we use an approach for target-specific, single-cell RNA sequencing to generate a map of the vagal cell types that innervate the gastrointestinal tract. We show that unique molecular markers identify vagal neurons with distinct innervation patterns, sensory endings, and function. Surprisingly, we find that food intake is most sensitive to stimulation of mechanoreceptors in the intestine, whereas nutrient-activated mucosal afferents have no effect. Peripheral manipulations combined with central recordings reveal that intestinal mechanoreceptors, but not other cell types, potently and durably inhibit hunger-promoting AgRP neurons in the hypothalamus. These findings identify a key role for intestinal mechanoreceptors in the regulation of feeding.

Genetics of gallstone disease

Gallstone disease (GSD) is one of the most common biliary tract disorders worldwide. The prevalence, however, varies from 5.9-21.9% in Western society to 3.1-10.7% in Asia. Most gallstones (75%) are silent. Approximately half of symptomatic gallstone carriers experience a second episode of biliary pain within 1 year. These individuals are at increased risk of developing acute cholecystitis, acute cholangitis, and biliary pancreatitis. As can be expected, these complications burden health care systems because of their invasive nature and surgical cost. Factors that contribute to gallstone formation include supersaturation of cholesterol in bile, gallbladder hypomotility, destabilization of bile by kinetic protein factors, and abnormal mucins. Epidemiologic studies have implicated multiple environmental factors and some common genetic elements in gallstone formation. Genetic factors that influence gallstone formation have been elaborated from linkage studies of twins, families, and ethnicities. Accumulating evidence suggests that genetic factors play a role in GSD.

Somatostatin receptor subtypes 2 and 5 mediate inhibition of egg yolk-induced gall bladder emptying in mice

BACKGROUND

Somatostatin inhibits gall bladder contraction. Impaired gall bladder emptying is associated with gall bladder stone formation. The incidence of cholecystolithiasis is high in patients treated with a somatostatin agonist octreotide, which predominantly interacts with somatostatin receptor subtype 2 (SSTR2). Therefore, it is believed that SSTR2 regulates gall bladder contraction; however, evidence has not been provided. Here, we evaluate the effects of SSTR1-SSTR5-selective agonists on egg yolk-induced gall bladder contraction in mice.

METHODS

Homozygous deletion of SSTR2 and SSTR5 was generated by cross-mating of SSTR2(-/-) with SSTR5(-/-) mice. Mice of different genotypes were injected with SSTR1-5-selective agonists or octreotide 15 min before induction of gall bladder emptying by egg yolk. One hour later, gall bladders were removed and weighed.

KEY RESULTS

Egg yolk-reduced gall bladder weights in all mice, irrespective of their genotype. Octreotide was the most potent inhibitor of gall bladder emptying in wild-type mice. In contrast, agonists with high selectivity for SSTR2 or SSTR5 inhibited gall bladder emptying by approximately 50-60%, whereas SSTR1-, SSTR3- and SSTR4-selective agonists failed to influence gall bladder contraction. In SSTR2(-/-) mice, octreotide and an SSTR5-selective agonist inhibited gall bladder emptying by approximately 50%, whereas SSTR2-selective agonists were inactive. Octreotide inhibited gall bladder emptying in SSTR5(-/-) mice by approximately 50%, without any effect in SSTR2(-/-)/SSTR5(-/-) mice.

CONCLUSIONS & INFERENCES

Our study provides evidence for the role of SSTR2 and SSTR5 in regulating gall bladder emptying in mice.

Diminished gallbladder motility in Rotund leptin-resistant obese mice

BACKGROUND

Obesity is a risk factor for cholesterol gallstone formation, but the pathogenesis of this phenomenon remains unclear. Most human obesity is associated with diabetes and leptin-resistance. Previous studies from this laboratory have demonstrated that diabetic leptin-resistant (Lep(db)) obese mice have low biliary cholesterol saturation indices, enlarged gallbladders and diminished gallbladder response to neurotransmitters. Recently, a novel leptin-resistant mouse strain Lepr(db-rtnd) (Rotund) has been discovered. Rotund mice are also obese, diabetic, and have an abnormal leptin receptor. Therefore, we tested the hypothesis that leptin-resistant obese Rotund mice would have large gallbladders and reduced biliary motility.

METHODS

Eight-week-old control (C57BL/6J, N=12) and Rotund leptin-resistant (Lepr(db-rnd), N=9) mice were fed a non- lithogenic diet for four weeks. Animals were fasted and underwent cholecystectomy. Gallbladder volumes were recorded, and contractile responses (N/cm(2)) to acetylcholine (10(-5) M), Neuropeptide Y (10(-8,-7,-6) M), and cholecystokinin (10(-10,-9,-8,-7) M) were measured. Results were analyzed using the Mann-Whitney Rank Sum Test.

RESULTS

Compared to control mice, Rotund mice had larger body weights, higher serum glucose levels, and greater gallbladder volumes (p<0.05). Rotund gallbladders had less contractility (p<0.05)) to acetylcholine and cholecystokinin than control mice. Responses to Neuropeptide Y were also less, but not statistically significant, in the Rotund mice.

CONCLUSIONS

These data suggest that leptin-resistant Rotund mice have (1) enlarged gallbladders with (2) diminished contractility compared to lean control mice. Therefore, this study confirms that leptin-resistance is associated with abnormal biliary motility and may lead to gallstone formation in leptin-resistant obesity.

Nonobese diabetic mice have diminished gallbladder motility and shortened crystal observation time

Diabetes and obesity are strongly associated and are risk factors for cholesterol gallstone disease. Leptin-deficient and leptin-resistant diabetic obese mice have enlarged, hypomotile gallbladders. In addition, bile from gallbladders of leptin-deficient mice has enhanced cholesterol crystal formation, whereas bile from gallbladders of leptin-resistant mice has delayed crystal observation time. To determine the effect of diabetes alone, we hypothesized that leptin-normal, nonobese diabetic (NOD) mice would have reduced biliary motility and rapid crystal formation. Twenty control and 9 prediabetic and 11 diabetic NOD, 12- to 26-week-old mice underwent glucose measurement and cholecystectomy for muscle bath stimulation with neurotransmitters. An additional group of 200 control and 78 NOD 12-week-old mice underwent microscopic bile examination for cholesterol crystal formation. Compared with control mice, prediabetic NOD mice had similar glucose levels and gallbladder volumes. Diabetic NOD mice had higher sugar levels and larger gallbladder volumes (P < 0.001) than control mice. Prediabetic NOD gallbladders had less contractility (P < 0.01) than control gallbladders, and contractility worsened (P < 0.01) in diabetic NOD mice. NOD mice formed cholesterol crystals earlier than did control mice (P < 0.05). Nonobese diabetic NOD mice have (1) decreased gallbladder contraction to neurotransmitters, which worsens with development of diabetes, and (2) rapid crystal formation. We conclude that diabetes alone alters gallbladder motility and cholesterol crystal formation.

Gallbladder myocytes are short and cholecystokinin-resistant in obese diabetic mice

BACKGROUND

Obesity is associated with diabetes and gallstone formation. Obese leptin-deficient (Lepob) and leptin-resistant (Lepdb) mice are hyperglycemic and have enlarged gallbladders with diminished response in vitro to cholecystokinin (CCK) and acetylcholine (ACh). Whether this phenomenon is secondary to hyperosmolar myocytes and/or decreased neuromuscular transmission remains unclear. We hypothesize that myocytes from Lepob and Lepdb obese mice would not respond normally to neurotransmitters.

METHODS

Cholecystectomy was performed on 39 lean, 19 Lepob, and 20 Lepdb 12-week-old female mice. The gallbladder was divided and enzymatically digested. Half of each gallbladder's myocytes had contraction induced by CCK (10(-8) mol/L, n = 38) or ACh (10(-5) mol/L, n = 40).

RESULTS

Body weights, gallbladder volumes, and serum glucoses were greater for Lep(ob) and Lepdb mice compared to controls (P < .001). Resting myocyte lengths from Lepob and Lepdb mice were 93% and 91% of the length of controls (P < .001). In response to CCK, lean myocytes shortened 6% (P < .01), while myocytes from obese mice demonstrated no shortening. None of the myocytes demonstrated significant shortening with ACh.

CONCLUSIONS

These data suggest that gallbladder myocytes from obese mice are (1) foreshortened and (2) have a diminished response to cholecystokinin. We conclude that altered leptin and/or increased glucose may foreshorten myocytes and decrease response to cholecystokinin.

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.

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Characteristics and cholinergic control of the 'minute rhythm' in ovine antrum, small bowel and gallbladder

Eight adult conscious rams were used to characterize further the minute rhythm and to determine the role of cholinergic receptors in nervous control of this event. In chronic experiments, the myoelectrical and motor activity of the gastrointestinal tract and gallbladder were recorded. Physiological experiments were performed in fasted or non-fasted rams before, during and after feeding, and the occurrence of minute rhythm during various phases of the migrating motor myoelectric complex was observed. The pattern occurred most frequently in the small intestine, where it exhibited mostly the propagating character. It was also detectable in the ileum. In the gallbladder, the minute rhythm arrived systematically and its character was irregular, propagating, retropropagating or stationary. In all episodes observed, it was well correlated with that in the small intestine. In the pyloric antrum, the minute rhythm was identified occasionally. During pharmacological experiments, 0.15 M NaCl or graded doses of hexamethonium, atropine and pirenzepine were administered intravenously during various phases of the migrating motor myoelectric complex, in fasted and non-fasted animals, before and during feeding. The drugs inhibited the minute rhythm in the small bowel for a longer period than in the gallbladder. However, the smallest dose of pirenzepine (0.02 mg/kg) exerted a non-significant effect both in the small intestine and in the gallbladder. It is concluded, that in normal conditions the minute rhythm occurs regularly in the entire small intestine and in the gallbladder. In the small intestine the pattern is organized more precisely. The minute rhythm is controlled by nicotinic receptors and by muscarinic receptor subtypes.

Effects of lorglumide and atropine on MgSO(4)-induced gallbladder emptying in conscious dogs

The aim of the study was to examine the possible involvement of cholecystokinin (by lorglumide) and cholinergic mechanisms (by atropine) in magnesium sulphate (MgSO(4))-induced gallbladder contraction of conscious dogs. The gallbladder (GB) volume was determined by ultrasonography. The optimal dose of 80 mg kg(-1)of MgSO(4)was determined from a MgSO(4)dose-response curve using doses of 10, 20,40, 80, 120 mg kg(-1). The largest dose of MgSO(4)was less effective than the optimal dose. Peak gallbladder contraction (32 per cent) was achieved at 30 minutes. Atropine (50 microg kg(-1)s.c.) or lorglumide (1 mg kg(-1)p.o.) fully prevented GB contraction. In conclusion, supraoptimal doses of MgSO(4)have a diminishing effect. The sustained contraction of the gallbladder in response to the optimal dose of MgSO(4)can be explained by an additive effect of the cholecystokinin release and a cholinergic trigger mechanism. Ultrasonography and MgSO(4)stimulation proved to be a valuable technique for examination of gallbladder motility.

Effect of acalculous cholecystitis on gallbladder neuromuscular transmission and contractility

BACKGROUND

Impaired smooth muscle contractility is important in the pathophysiology of acalculous cholecystitis. Common bile duct ligation (CBDL) is a model of acalculous cholecystitis, producing acute inflammatory changes and decrease in gallbladder smooth muscle contractility. The aim of this study was to determine whether there is coexistent dysfunction of neural efferent motor pathways of the gallbladder after CBDL.

MATERIALS AND METHODS

Gallbladder muscle contractility was studied in vitro in normal, CBDL, and sham-operated guinea pigs. Electric field stimulation (EFS; 2-16 Hz) was used to activate intrinsic nerves and exogenous acetylcholine (ACh) was used to directly stimulate the muscle. H&E-stained slides of muscle strips were scored for inflammatory changes.

RESULTS

After CBDL, there was a progressive increase in the inflammation score and decrease in gallbladder muscle contractility to ACh. There was also a progressive decline in EFS-induced contractility when expressed as absolute force or normalized to the maximal muscle contractile response to ACh. The nitric oxide synthase inhibitor l-NNA (10 microM) increased EFS-induced contractions by 50 +/- 25% (P = 0.05) in CBDL animals but had no effect in sham surgical controls.

CONCLUSIONS

CBDL with its acute gallbladder inflammation affects gallbladder contractility by two mechanisms: (1) decreased smooth muscle contractility, and (2) decreased neurally mediated contractions. The neurally mediated alterations result from dysfunction of cholinergic excitatory nerves and upregulation of nitric-oxide-mediated inhibition of smooth muscle contractility.

Effect of somatostatin on human gallbladder motility: an in vitro study

In vivo studies have demonstrated that somatostatin induces human gallbladder relaxation. To determine whether this polypeptide acts directly on the gallbladder muscle, its effect on strips of human gallbladder was studied in vitro. Strips of gallbladder were set up isometrically in an organ bath containing oxygenated Krebs' solution. Dose-response curves to cholecystokinin-octapeptide and carbachol were first established. The ability of somatostatin to cause relaxation under basal conditions and during 50% maximal stimulation by cholecystokinin-octapeptide (7.2 x 10(-8) M) and carbachol (3.5 x 10(-6) M) was assessed in 32 strips at 4.3 x 10(-6) M concentration which mimics the plasma concentrations found in patients with somatostatinoma and in 12 additional strips at 4.3 x 10(-8) M concentration. Somatostatin action on the intrinsic innervation by using electrical field stimulation (EFS) (200 mA 5 msec in duration, 30 Hz; 400 mA, 1 msec in duration, 10 Hz) was also evaluated in 39 strips. Somatostatin had no effect on the basal or carbachol-generated tensions. On the contrary, somatostatin (4.3 x 10(-6) M) reduced cholecystokinin-octapeptide-generated tensions by 8% (P < 0.001) and reduced EFS-generated tensions at 30 Hz by 7.7% (P < 0.01) and those at 10 Hz by 41.2% (P < 0.01). All responses to cholecystokinin-octapeptide and carbachol were abolished by dibutyryl-guanosine 3', 5'-cyclic monophosphate (5 x 10(-3) M) and atropine (10(-5) M), respectively (P < 0.0002 and P < 0.0002). All responses to electrical field stimulation were reduced or abolished by tetrodotoxin (2 x 10(-6) M) (P < 0.001 and P < 0.0001, respectively). Our findings show that somatostatin exerts its inhibitory action on the response to cholecystokinin-octapeptide and on the intrinsic innervation of the gallbladder smooth muscle. The probable neurotransmitter is the acetylcholine.

Humoral mechanisms and clinical aspects of biliary tract motility

This review is intended to summarize current information on neurohumoral regulation of the gallbladder and sphincter of Oddi motility under both physiological and pathological circumstances with emphasis on Hungarian contributions to today's knowledge. The mechanism of action of neurohumoral agents that interact on these segments of the biliary tract, and the explored details of the stimulation-contraction/relaxation coupling process of these substances, will be discussed. A modified classification of biliary tract motility disorders with new diagnostic and therapeutic approaches will also be provided. This information will aid understanding of the pathogenesis of motor disorders of the gallbladder and sphincter of Oddi, and will indicate possibilities for pharmacological exploitation in the treatment of diseases resulting from biliary tract motility abnormalities.

Signal transduction pathways mediating CCK-induced gallbladder muscle contraction

The signal transduction that mediates CCK-induced contraction of gallbladder muscle was investigated in the cat. Contraction was measured by scanning micrometry in single muscle cells isolated enzymatically with collagenase. Production of D-myo-inositol 1,4, 5-trisphosphate (IP3) and sn-1,2-diacylglycerol (DAG) was quantitated using HPLC and TLC, respectively. Protein kinase C (PKC) activity was determined by measuring the phosphorylation of a specific substrate peptide from myelin basic protein, Ac-MBP-(4-14). CCK-induced contraction was blocked by incubation in strontium medium, pertussis toxin (PTx), and antibodies against Gialpha3 or betagamma-subunits but was not blocked by Ca2+-free medium or by antibodies against Gq/11alpha, Gialpha1-2, or Goalpha. The contraction induced by CCK was inhibited by the phospholipase C (PLC) inhibitor U-73122, anti-PLC-beta3 antibody, and the IP3 receptor antagonist heparin but was not inhibited by the the phospholipase D inhibitor propranolol or antibodies against PLC-beta1 or PLC-beta2. Western blot analysis of gallbladder muscle revealed the presence of PLC-beta2 and PLC-beta3 but not PLC-beta1. CCK caused a 94% increase in IP3 generation and an 86% increase in DAG generation. A low dose of CCK caused PKC translocation, and CCK-induced contraction was blocked by the PKC inhibitor H-7. A high dose of CCK, however, caused no PKC translocation, and its contraction was blocked by the calmodulin antagonist CGS9343B. In conclusion, CCK contracts cat gallbladder muscle by stimulating PTx-sensitive Gi 3 protein coupled with PLC-beta3, producing IP3 and DAG. Low doses activate PKC, whereas high doses activate calmodulin.

Nerves and Hormones Interact to Control Gallbladder Function

Ganglia are the target of several regulatory inputs to the gallbladder. Hormonal cholecystokinin and sympathetic nerves can up- or downregulate neurotransmission in the gallbladder, respectively, by altering the rate of acetylcholine release from vagal preganglionic terminals. Peptides released from sensory axons act directly on gallbladder neurons to increase their excitability.

Innervation of the gallbladder: structure, neurochemical coding, and physiological properties of guinea pig gallbladder ganglia

The muscle and epithelial tissues of the gallbladder are regulated by a ganglionated plexus that lies within the wall of the organ. Although these ganglia are derived from the same set of precursor neural crest cells that colonize the gut, they exhibit structural, neurochemical and physiological characteristics that are distinct from the myenteric and submucous plexuses of the enteric nervous system. Structurally, the ganglionated plexus of the guinea pig gallbladder is comprised of small clusters of neurons that are located in the outer wall of the organ, between the serosa and underlying smooth muscle. The ganglia are encapsulated by a shell of fibroblasts and a basal lamina, and are devoid of collagen. Gallbladder neurons are rather simple in structure, consisting of a soma, a few short dendritic processes and one or two long axons. Results reported here indicate that all gallbladder neurons are probably cholinergic since they all express immunoreactivity for choline acetyltransferase. The majority of these neurons also express substance P, neuropeptide Y, and somatostatin, and a small remaining population of neurons express vasoactive intestinal peptide (VIP) immunoreactivity and NADPH-diaphorase enzymatic activity. We report here that NADPH-diaphorase activity, nitric oxide synthase immunoreactivity, and VIP immunoreactivity are expressed by the same neurons in the gallbladder. Physiological studies indicate that the ganglia of the gallbladder are the site of action of the following neurohumoral inputs: 1) all neurons receive nicotinic input from vagal preganglionic fibers; 2) norepinephrine released from sympathetic postganglionic fibers acts presynaptically on vagal terminals within gallbladder ganglia to decrease the release of acetylcholine from vagal terminals; 3) substance P and calcitonin gene-related peptide, which are co-expressed in sensory fibers, cause prolonged depolarizations of gallbladder neurons that resemble slow EPSPs; and 4) cholecystokinin (CCK) acts presynaptically within gallbladder ganglia to increase the release of acetylcholine from vagal terminals. Results reported here indicate that hormonal CCK can readily access gallbladder ganglia, since there is no evidence for a blood-ganglionic barrier in the gallbladder. Taken together, these results indicate that gallbladder ganglia are not simple relay stations, but rather sites of complex modulatory interactions that ultimately influence the functions of muscle and epithelial cells in the organ.

Relationship between gallbladder bile concentration and motility in conscious dogs: role of cholecystokinin

The relationship between gallbladder (GB) bile concentration and motility was studied in conscious dogs. The 12-h GB bile concentrations between meals could be divided into three periods: diluting, minimum, and concentrating periods. During the diluting period, inhibition of GB contractions by a CCKA receptor antagonist, atropine or hexamethonium, resulted in concentration of GB bile, whereas during the concentrating period, CCK-8 shifted the concentration process back to dilution. The GB appears to absorb water continuously from GB bile, which is not regulated by cholinergic or CCKA receptors. The postprandial progressive dilution of GB bile is brought about by GB pumping controlled by cholecystokinin (CCK).

Coordination of biliary and upper gastrointestinal motility in the fasted conscious pig

A chronic pig model was developed which permits the simultaneous measurement of integrated biliary motility as resistance to flow (CBD inflow), gallbladder, duodenal and gastric motility in addition to collection of venous blood samples for gut hormones estimations. Animals displayed a duodenal interdigestive cycle of 55.4 +/- 3.4 min (mean +/- SEM, n = 6), consisting of phase I, II and III (21.2 +/- 2.1, 70.5 +/- 2.0, 8.7 +/- 0.5% of the cycle, respectively). A gastric interdigestive cycle of 60.2 +/- 6.5 min (n = 4) was similarly demonstrated consisting of three phases which corresponded to the three duodenal phases. The gastric phases I, II and III comprised 26.3 +/- 3.0, 71.2 +/- 2.7 and 2.5 +/- 0.8% of the cycle, respectively. The gastric phase III immediately preceded the onset of the duodenal phase III. The gallbladder likewise displayed an interdigestive cycle of 54.5 +/- 7.2 min (n = 6) consisting of a quiescent period (37.2 +/- 3.7% of the cycle) corresponding temporally to duodenal phase III and phase I. This quiescent phase was followed by a period of rhythmic contractions (64.5 +/- 4.1% of the cycle) which corresponded temporally to duodenal phase II. The onset of the gallbladder quiescent period coincided with the onset of duodenal phase III. The CBD inflow similarly demonstrated an interdigestive cycle of 53.4 +/- 9.6 min (n = 4) duration, consisting of three phases. The initial phase was evident as a period of rapid inflow, the onset of which coincided with the onset of duodenal phase III and the gallbladder quiescent period, and occupied 12.0 +/- 0.8% of the cycle. The second phase which occupied 18.0 +/- 7.4% of the cycle, was typified as a period of declining inflow which reached a relatively stable level at a time corresponding to the end of duodenal phase I. The third phase consisted of the maintenance of the inflow rate achieved at the end of the previous phase (60% of maximum inflow), corresponding in onset and duration with duodenal phase II and occupied 70.0 +/- 8.6% of the cycle. Plasma motilin levels fluctuated in relation to the duodenal interdigestive cycle, peaking during phase III relative to phase I (36.9 +/- 8.5 vs 25.4 +/- 7.7 pg mL-1, respectively, n = 5, P < 0.05). Cholecystokinin levels did not fluctuate, remaining low (2.3 +/- 2.1 pM cholecystokinin octapeptide equivalents, n = 5) throughout the duodenal interdigestive cycle, but increased about two fold after ingestion of solid food. Feeding disrupted the gastric, duodenal, gallbladder and CBD inflow cycles.

Control of gallbladder contractions by cholecystokinin through cholecystokinin-A receptors in the vagal pathway and gallbladder in the dog

The mechanism of CCK action on gallbladder contractions in the physiological condition is unclear. Gallbladder contractions were monitored by means of chronically implanted force transducers in conscious dogs. Postprandial gallbladder contractions were partially inhibited by atropine and hexamethonium, and completely inhibited by devazepide. In vitro contractile response of canine gallbladder muscle strips to CCK-8 was also studied. CCK-8-induced muscle strip contraction was atropine and tetrodotoxin resistant, but was completely eliminated by devazepide. The existence of CCK receptors in the vagal nerve and gallbladder was examined by means of autoradiography. Forty-eight hours after ligation of the abdominal vagus, CCK-8 binding sites were found to accumulate in the subdiaphragmatic vagal nerve immediately proximal to the ligature, and similar binding sites were also found in the gallbladder smooth muscle layer. These binding sites were displaced by the addition of 10(-7) mol/1 unlabeled CCK-8 and devazepide, but L-365,260 had no effect. In conclusion, it is considerable that postprandial CCK-induced gallbladder contractions are controlled through CCK-A receptors both on the vagal nerve in stimulating endogenous release of acetylcholine and on the gallbladder directly to stimulate muscle contraction in the dog.

Radioactive choline metabolism in guinea pig gallbladder. Is there measurable acetylcholine release?

Acetylcholine may be released from gallbladder intrinsic nerves in response to cholecystokinin stimulation. This study characterized metabolites of [14C]choline produced in the gallbladder and released during incubation, with or without cholecystokinin-octapeptide. Radiolabeled [14C]choline was applied to the mucosal or muscle surface of intact guinea pig gallbladders in an organ bath. After radiolabeling, gallbladders were incubated with or without the contractile agonist cholecystokinin-octapeptide. Metabolites of [14C]choline were identified in gallbladder tissue and incubation buffers using HPLC and thin-layer chromatography. The major metabolites of [14C]choline were betaine and phosphocholine. [14C]Phosphocholine was incorporated slowly into [14C]phosphatidylcholine. [14C]Choline was released into buffers during incubation. [14C]Acetylcholine constituted less than 1% of radiolabel in the gallbladder. There was no identifiable [14C]acetylcholine released in buffers. Cholecystokinin-octapeptide did not affect choline metabolism. These studies showed that choline in the gallbladder is metabolized along pathways similar to those in the liver. Gallbladders released mostly choline, rather than acetylcholine, even during hormonally induced contraction.

Effects of cisapride on gallbladder emptying and pancreatic polypeptide and cholecystokinin release in humans

We investigated the effects of cisapride on gallbladder motility and on the release of pancreatic polypeptide and cholecystokinin in the fasting and postprandial states. Cisapride (7.5 mg) and/or a test meal was administered intraduodenally to seven healthy volunteers with or without atropine pretreatment (0.5 mg, i.m.). In the fasting state, cisapride increased gallbladder volume to 154% of the basal level, and significantly elevated plasma pancreatic polypeptide levels. The effects of cisapride were inhibited by atropine. In the postprandial state, integrated pancreatic polypeptide and cholecystokinin responses were increased by cisapride to 180% and 192%, respectively, of control values. Atropine inhibited the integrated gallbladder and pancreatic polypeptide response to about 60% of the control value, but did not affect the cholecystokinin response. These observations suggest that: (1) fasting gallbladder tone is influenced by cholinergic inhibitory mechanisms, (2) acetylcholine (ACh) is the final mediator for about 40% of the postprandial gallbladder emptying and pancreatic polypeptide response, and (3) coordination between the ACh-independent cholecystokinin response and ACh-dependent pancreatic polypeptide response may be important in the regulation of postprandial gallbladder emptying.

Cholesterol gallstone formation in man and potential treatments of the gallbladder motility defect

Cholelithiasis affects 10-15% of the adult population in Western society, and about 75% of gallstones are of cholesterol type. Hepatic hypersecretion of cholesterol with the formation of instable cholesterol-rich vesicles in bile, an imbalance between nucleation-inhibiting and nucleation-promoting proteins with further aggregation of cholesterol crystals in a gallbladder with a motility defect (stasis), all play a role in the pathogenesis of cholesterol gallstones. Experimental animal models suggest that gallstone formation can be prevented by improving gallbladder emptying. Thus, a better understanding of the causes underlying the impaired gallbladder motor function in patients with gallstones might lead to the selection of therapeutic approaches for those individuals who are at increased risk for the formation or recurrence of gallstones. The present article focuses on current concepts and theories on the pathogenesis of cholesterol gallstones with emphasis on the gallbladder motility defect. Several treatment strategies for the correction of gallbladder hypomotility are also discussed.

Inflammation impairs neurally mediated responses to electrical field stimulation in isolated strips of human gallbladder muscle

Strips from human gallbladder removed at surgery were exposed to cholecystokinin octopeptide CCK-OP 15 nM and were subjected to electrical field stimulation (EFS) in vitro using parameters for selective stimulation of nerves (5- to 10-sec trains of 0.3-msec pulses at 10 Hz). An adjacent strip from the same specimen was processed for histological examination. These preparations were given a numerical score for inflammatory change. The strength of contraction in response to CCK-OP was inversely related to the severity of inflammation. Gallbladders with no response to EFS had a higher inflammation score (median 11, range 5-16) than those with a response (median 7, range 3-12). We conclude that inflammatory changes in human gallbladder impair responses to neural and hormonal stimulation, but we are unable to determine unequivocally in this study whether this is a result of damage to nerves or muscle cells. However, the observation that some strips were able to contract in response to CCK-OP but not to neural stimulation suggests the possibility of neural damage in gallbladder inflammation.

Role of CCK in gallbladder function

Cholecystokinin may play a role in regulation of interdigestive motility, but this still remains to be investigated. CCK constitutes the major hormonal stimulus for postprandial gallbladder emptying. CCK exerts its contractile effects mainly through interaction directly with receptors on the gallbladder smooth muscle cells in the muscle layer, but also through interaction with cholinergic nerves extrinsic and/or intrinsic in nature. Furthermore, CCK can enhance ongoing nicotinic ganglionic transmission occurring in the serosal layer by release of acetylcholine. CCK interaction with the gallbladder smooth muscle CCKA receptor was studied in further detail. CCK contracts strips of gallbladder muscle in a concentration-dependent way with a potency in the nanomolar range in all tested species. The potency is 1,000-fold better than that of gastrin; thus, the receptor is of type CCKA. CCK binding to this receptor is specific and of high affinity, 1,000-fold better than that of gastrin with no differences between the tested species including bovine, porcine, and human. Also, CCK binding affinity was independent of age, gender, or weight of the person and pathology of the human gallbladder. The biochemistry of the CCKA receptor varies between the tested species (bovine and human). Both CCKA receptors are heavily glycosylated, but of different size and carbohydrate content. The bovine CCKA receptor is of apparent size M(r) = 70-85 kD with N-linked complex carbohydrates and sialic acids. The human CCKA receptor is of M(r) = 85-95 kD, with N-linked complex carbohydrates, but no sialic acids. They both have a protein core of apparent size M(r) = 43 kD, with almost identically sized fragments after enzymatic cleavage. Probably the protein cores contain the receptor binding region, which seems well preserved between species. CCK and the CCKA gallbladder muscularis receptor are main regulators of postprandial gallbladder emptying. The biochemistry of the CCKA gallbladder smooth muscle receptor is in accord with newly generated data of purification and cloning of the rat pancreatic CCKA receptor.

Cholecystokinin-coupled intracellular signaling in human gallbladder muscle

BACKGROUND/AIMS

It has been shown that cholecystokinin (CCK) contracts the gallbladder muscle by utilizing intracellular calcium, but the intracellular pathways have not been elucidated. The present study was designed to characterize the signal transduction pathways that mediate CCK-induced contraction of human gallbladder muscle.

METHODS

Single muscle cells were isolated from human gallbladders by enzymatic digestion with collagenase. Permeable cells were obtained by incubation with saponin. Protein kinase C (PKC) activity was determined by measuring the phosphorylation of a specific substrate peptide from myelin basic protein, Ac-MBP(4-14).

RESULTS

The inositol-1,4,5-trisphosphate (IP3) antagonist heparin blocked the contractions induced by CCK. The PKC inhibitor H-7 blocked the contractions caused by low, but not high, concentrations of CCK and IP3. In contrast, the calmodulin inhibitor CGS9343B blocked the contractions induced by high, but not low, doses of CCK and IP3. Furthermore, exogenously activated calmodulin blocked the PKC-mediated contraction induced by diacylglycerol. Direct measurements of PKC activity showed that low, but not high, CCK concentrations caused PKC translocation.

CONCLUSIONS

CCK contracts the gallbladder muscle via IP3-mediated calcium release. CCK activates the PKC pathway at low concentrations, whereas it activates the calmodulin pathway at high concentrations, which in turn inhibits the activation of PKC.

Noradrenaline as a presynaptic inhibitory neurotransmitter in ganglia of the guinea-pig gall-bladder

1. The effects of noradrenaline on guinea-pig gall-bladder ganglia were investigated with intracellular recording techniques. 2. Noradrenaline (0.01-100 microM) decreased the amplitude of the fast excitatory postsynaptic potential (EPSP) that was evoked by stimulation of interganglionic fibre tracts. High concentrations of noradrenaline (10-100 microM) caused an inhibition ranging from 93-100%. The noradrenaline concentration that resulted in half-maximal inhibition (EC50) of the EPSP was 280 nM. 3. Experiments with selective agonists and antagonists indicated that the alpha 2-adrenoreceptor was involved in the inhibition of the EPSP. Clonidine (0.001-100 microM) reduced the EPSP in a concentration-dependent manner with an EC50 of 30 nM. Yohimbine (100-300 nM) caused a rightward shift of the noradrenaline concentration-effect relationship, with a dissociation equilibrium constant of 1.4 nM. 4. Release of endogenous catecholamines by tyramine (100 microM) in the presence of desipramine (1.0 microM), caused a yohimbine-sensitive decrease in the amplitude of the EPSP. Treatment with tyramine did not affect the amplitude of the EPSP in tissue that had undergone prior chemical sympathectomy with 6-hydroxydopamine. 5. Electrical stimulation of the vascular plexus (1-3 s; 10-20 Hz; 10 mA) decreased the amplitude of the EPSP. In some cases suprathreshold responses were reduced to subthreshold EPSPs following stimulation of the vascular plexus. Yohimbine (300 nM) reversibly inhibited the effects of vascular plexus stimulation. 6. Noradrenaline did not modify the responses of gall-bladder neurones to exogenously applied acetylcholine. Also, application of noradrenaline, by superfusion (0.001-100 microM) or by pressure microejection (1.0 mM), had no effect on the resting membrane potential, membrane conductance, or action potential characteristics of gall-bladder neurones. 7. Immunoreactivity for type A monoamine oxidase (MAO-A) was found in the vascular plexus and the ganglionated plexus of the gall-bladder. 8. These results show that noradrenaline has an alpha 2-adrenoreceptor-mediated presynaptic inhibitory effect on fast synaptic transmission in the ganglia of the guinea-pig gall-bladder. It is proposed that vagal terminals may be an important target of this adrenergic inhibitory input to the gall-bladder.

The role of cholecystokinin in ganglionic transmission in the guinea-pig gall-bladder

1. The effects of cholecystokinin (CCK) on intact guinea-pig gall-bladder ganglia were investigated with intracellular, single-electrode current- and voltage-clamp recording techniques. 2. Cholecystokinin octapeptide (CCK-8; 0.01-100 nM) increased the amplitude of the fast excitatory postsynaptic potential (EPSP) that was evoked by stimulation of interganglionic fibre tracts. In most cases, neurones that exhibited subthreshold EPSPs in normal Krebs solution fired action potentials in the presence of CCK-8. In a low Ca2+/high Mg2+ solution, CCK-8 caused a 3-fold increase in the amplitude of fast EPSPs. 3. The amplitude of the evoked excitatory postsynaptic current (EPSC) was increased by CCK-8 (0.01-100 nM) in a concentration-dependent manner. The effect was maximal at 1.0 nM. 4. Cholecystokinin octapeptide caused a 3-fold increase in the quantal content of the EPSP in a low Ca2+/high Mg2+ solution, but had no effect on the quantal size. 5. The specific CCK-A receptor antagonist, MK-329 (formerly L-364,718; 1.0 nM), reversibly blocked the facilitatory effect of CCK-8 on ganglionic transmission. However, the specific CCK-B receptor antagonist, L-365,260 (10 nM), did not alter the presynaptic facilitatory effect of CCK-8. 6. The response of gall-bladder neurones to exogenously applied ACh was not modified by CCK-8. 7. Application of CCK-8, by superfusion (0.001-100 nM) or by pressure microejection (100 microM), had no effect on the membrane potential, membrane conductance, action potential, or threshold of gall-bladder neurones. 8. Immunohistochemistry was employed to determine whether the actions of CCK could be elicited by release of the peptide from nerve terminals within the ganglionated plexus of the gall-bladder. Immunoreactivity for CCK was not detected in the ganglionated plexus of the gall-bladder, but CCK immunoreactivity was plentiful in control preparations of intestinal myenteric and submucosal plexuses. 9. These results show that CCK has a presynaptic facilitatory effect on fast synaptic transmission in guinea-pig gall-bladder ganglia, and that this effect is mediated by presynaptic CCK-A receptors. Furthermore, it appears that such an effect would normally occur in response to hormonal CCK, rather than CCK that is released from nerve terminals.

Cholecystokinin-induced contraction of opossum sphincter of Oddi. Mechanism of action

In this study, we evaluated the mechanism of action whereby cholecystokinin increases spike-burst rate of the opossum sphincter of Oddi (SO). Each spike burst corresponds to a peristaltic SO contraction. Two types of animal preparations were evaluated: (1) awake chronic animal preparations and (2) anesthetized animals. A total of 19 chronic animals were prepared by implantation of electrodes on the SO, gastric antrum, duodenum, and jejunum. SO spike-burst rate was stimulated by intravenous infusion of CCK-OP (10 ng/kg/min), feeding, or intraduodenal infusion of fat-containing nutrient. Each stimulus was begun 20 min after cessation of phase III duodenal MMC activity and caused an increase in SO spike-burst rate from about 2 to 6/min that lasted for less than or equal to 1 hr. Such increases were antagonized substantially by hexamethonium, atropine, or methysergide. The CCK antagonist, L364718, antagonized the excitatory SO response to CCK-OP infusion or intraduodenal infusion of fat-containing nutrient (Isocal) but did not antagonize the response to feeding; CR1409 had no antagonistic effect on SO response to any of the three types of stimuli. In the acute studies in anesthetized animals, an intravenous bolus dose of CCK-OP (800 ng/kg) caused a substantial increase in SO spike-burst rate that was antagonized by CR1409 but not by atropine, hexamethonium, methysergide, L364718, or TTX.(ABSTRACT TRUNCATED AT 250 WORDS)