G protein-coupled receptors in gastrointestinal physiology. I. CCK receptors: an exemplary family

Synthesis, Molecular Docking, and Biological Evaluation of Novel Anthranilic Acid Hybrid and Its Diamides as Antispasmodics

The present article focuses on the synthesis and biological evaluation of a novel anthranilic acid hybrid and its diamides as antispasmodics. Methods: Due to the predicted in silico methods spasmolytic activity, we synthesized a hybrid molecule of anthranilic acid and 2-(3-chlorophenyl)ethylamine. The obtained hybrid was then applied in acylation with different acyl chlorides. Using in silico analysis, pharmacodynamic profiles of the compounds were predicted. A thorough biological evaluation of the compounds was conducted assessing their in vitro antimicrobial, cytotoxic, anti-inflammatory activity, and ex vivo spasmolytic activity. Density functional theory (DFT) calculation, including geometry optimization, molecular electrostatic potential (MEP) surface, and HOMO-LUMO analysis for the synthesized compounds was conducted using the B3LYP/6-311G(d,p) method to explore the electronic behavior, reactive regions, and stability and chemical reactivity of the compounds. Furthermore, molecular docking simulation along with viscosity measurement indicated that the newly synthesized compounds interact with DNA via groove binding mode. The obtained results from all the experiments demonstrate that the hybrid molecule and its diamides inherit spasmolytic, antimicrobial, and anti-inflammatory capabilities, making them excellent candidates for future medications.

In silico studies of interactions of peptide-conjugated cholesterol metabolites and betulinic acid with EGFR, LDR, and N-terminal fragment of CCKA receptors

In this work, we designed three new ligands by conjugating cholesterol metabolites 3-hydroxy-5-cholestenoic acid (3-HC) and 3-oxo-4-cholestenoic acid (3-OC) and the natural tri-terpenoid betulinic acid with the tumor-targeting peptide YHWYGYTPQNVI. Molecular interactions with the unconjugated peptide and the conjugates were examined with three receptors that are commonly overexpressed in pancreatic adenocarcinoma cells using ligand docking and molecular dynamics. This study demonstrated the utility of the designed conjugates as a valuable scaffold for potentially targeting EGFR and LDLR receptors. Our results indicate that the conjugates showed strong binding affinities and formation of stable complexes with EGFR, while the unconjugated peptide, BT-peptide conjugate, an 3-HC-peptide conjugate showed the formation of fairly stable complexes with LDLR receptor. For EGFR, two receptor kinase domains were explored. Interactions with the N-terminal domain of CCKA-R were relatively weaker. For LDLR, binding occurred in the beta-propeller region. For the N-terminal fragment of CCKA-R, the conjugates induced significant conformational changes in the receptor. The molecular dynamic simulations for 100 ns demonstrate that BT-peptide conjugates and the unconjugated peptide had the highest binding and formed the most stable complexes with EGFR. RMSD and trajectory analyses indicate that these molecules transit to a dynamically stable configuration in most cases within 60 ns. NMA analysis indicated that amongst the conjugates that showed relatively higher interactions with the respective receptors, the highest potential for deformability was seen for the N-terminal-47 amino acid region of the CCKA-R receptor with and the lowest for the LDLR-receptor. Thus, the newly designed compounds may be evaluated in the future toward developing drug delivery materials for targeting tumor cells overexpressing LDLR or EGFR.

Contributing mechanisms underlying desensitization of cholecystokinin-induced activation of primary nodose ganglia neurons

Cholecystokinin (CCK) is a gut-derived peptide that potently promotes satiety and facilitates gastric function in part by activating G protein-coupled CCK1 receptors on primary vagal afferent neurons. CCK signaling is dynamic and rapidly desensitizes, due to decreases in either receptor function and the resulting signal cascade, ion channel effectors, or both. Here we report a decay-time analytical approach using fluorescent calcium imaging that relates peak and steady-state calcium responses in dissociated vagal afferent neurons, enabling discrimination between receptor and ion channel effector functions. We found desensitization of CCK-induced activation was predictable, consistent across cells, and strongly concentration dependent. The decay-time constant (tau) was inversely proportional to CCK concentration, apparently reflecting the extent of receptor activation. To test this possibility, we directly manipulated the ion channel effector(s) with either decreased bath calcium or the broad-spectrum pore blocker ruthenium red. Conductance inhibition diminished the magnitude of the CCK responses without altering decay kinetics, confirming changes in tau reflect changes in receptor function selectively. Next, we investigated the contributions of the PKC and PKA signaling cascades on the magnitude and decay-time constants of CCK calcium responses. While inhibition of either PKC or PKA increased CCK calcium response magnitude, only general PKC inhibition significantly decreased the decay-time constant. These findings suggest that PKC alters CCK receptor signaling dynamics, while PKA alters the ion channel effector of the CCK response. This analytical approach should prove useful in understanding receptor/effector changes underlying acute desensitization of G-protein coupled signaling and provide insight into CCK receptor dynamics.

Cholecystokinin (CCK) Regulation of Pancreatic Acinar Cells: Physiological Actions and Signal Transduction Mechanisms

Pancreatic acinar cells synthesize and secrete about 20 digestive enzymes and ancillary proteins with the processes that match the supply of these enzymes to their need in digestion being regulated by a number of hormones (CCK, secretin and insulin), neurotransmitters (acetylcholine and VIP) and growth factors (EGF and IGF). Of these regulators, one of the most important and best studied is the gastrointestinal hormone, cholecystokinin (CCK). Furthermore, the acinar cell has become a model for seven transmembrane, heterotrimeric G protein coupled receptors to regulate multiple processes by distinct signal transduction cascades. In this review, we briefly describe the chemistry and physiology of CCK and then consider the major physiological effects of CCK on pancreatic acinar cells. The majority of the review is devoted to the physiologic signaling pathways activated by CCK receptors and heterotrimeric G proteins and the functions they affect. The pathways covered include the traditional second messenger pathways PLC-IP3-Ca²⁺ , DAG-PKC, and AC-cAMP-PKA/EPAC that primarily relate to secretion. Then there are the protein-protein interaction pathways Akt-mTOR-S6K, the three major MAPK pathways (ERK, JNK, and p38 MAPK), and Ca²⁺ -calcineurin-NFAT pathways that primarily regulate non-secretory processes including biosynthesis and growth, and several miscellaneous pathways that include the Rho family small G proteins, PKD, FAK, and Src that may regulate both secretory and nonsecretory processes but are not as well understood. © 2019 American Physiological Society. Compr Physiol 9:535-564, 2019.

Evidence That Calcium Entry Into Calcium-Transporting Dental Enamel Cells Is Regulated by Cholecystokinin, Acetylcholine and ATP

Dental enamel is formed by specialized epithelial cells which handle large quantities of Ca²⁺ while producing the most highly mineralized tissue. However, the mechanisms used by enamel cells to handle bulk Ca²⁺ safely remain unclear. Our previous work contradicted the dogma that Ca²⁺ is ferried through the cytosol of Ca²⁺-transporting cells and instead suggested an organelle-based route across enamel cells. This new paradigm involves endoplasmic reticulum (ER)-associated Ca²⁺ stores and their concomitant refilling by store-operated Ca²⁺ entry (SOCE) mediated by Ca²⁺ release activated Ca²⁺ (CRAC) channels. Given that Ca²⁺ handling is maximal during the enamel-mineralization stage (maturation), we anticipated that SOCE would also be elevated then. Confirmation was obtained here using single-cell recordings of cytosolic Ca²⁺ concentration ([Ca²⁺]_cyt) in rat ameloblasts. A candidate SOCE agonist, cholecystokinin (CCK), was found to be upregulated during maturation, with Cck transcript abundance reaching 30% of that in brain. CCK-receptor transcripts were also detected and Ca²⁺ imaging showed that CCK stimulation increased [Ca²⁺]_cyt in a dose-responsive manner that was sensitive to CRAC-channel inhibitors. Similar effects were observed with two other SOCE activators, acetylcholine and ATP, whose receptors were also found in enamel cells. These results provide the first evidence of a potential regulatory system for SOCE in enamel cells and so strengthen the Ca²⁺ transcytosis paradigm for ER-based transport of bulk Ca²⁺. Our findings also implicate enamel cells as a new physiological target of CCK and raise the possibility of an auto/paracrine system for regulating Ca²⁺ transport.

Gastrin stimulates pancreatic cancer cell directional migration by activating the Gα12/13-RhoA-ROCK signaling pathway

The mechanism by which gastrin promotes pancreatic cancer cell metastasis is unclear. The process of directing polarized cancer cells toward the extracellular matrix is principally required for invasion and distant metastasis; however, whether gastrin can induce this process and its underlying mechanism remain to be elucidated. In this study, we found that gastrin-induced phosphorylation of paxillin at tyrosine 31/118 and RhoA activation as well as promoted the metastasis of PANC-1 cancer cells. Depletion of Gα12 and Gα13 inhibited the phosphorylation of paxillin and downstream activation of GTP-RhoA, blocked the formation and aggregation of focal adhesions and facilitated polarization of actin filaments induced by gastrin. Suppression of RhoA and ROCK also exhibited identical results. Selective inhibition of the CCKBR–Gα12/13–RhoA–ROCK signaling pathway blocked the reoriented localization of the Golgi apparatus at the leading edge of migrated cancer cells. YM022 and Y-27632 significantly suppressed hepatic metastasis of orthotic pancreatic tumors induced by gastrin in vivo. Collectively, we demonstrate that gastrin promotes Golgi reorientation and directional polarization of pancreatic cancer cells by activation of paxillin via the CCKBR–Gα12/13–RhoA–ROCK signal pathway.

A hormone found in high levels in pancreatic cancer sufferers helps the disease spread by co-ordinating cellular migration. Pancreatic cancer is one of the most deadly forms of cancer, being highly aggressive and likely to metastasize. Honggang Yu at Renmin Hospital of Wuhan University and scientists across China have demonstrated that gastrin, a hormone expressed at higher levels in patients with pancreatic cancer, helps to co-ordinate directional cell migration and ensure the disease spreads effectively. By activating two key molecules via a specific signalling pathway, gastrin ensures the correct orientation of the Golgi apparatus, a cellular organelle tasked with packaging proteins for transportation. This in turn activates directional migration of the cancer cells. The results explain why gastrin is over-expressed in both tumors and blood in cancer patients, and may inform future therapies.

The role of Gαq/Gα11 signaling in intestinal epithelial cells

Intestinal homeostasis and the coordinated actions of digestion, absorption and excretion are tightly regulated by a number of gastrointestinal hormones. Most of them exert their actions through G-protein-coupled receptors. Recently, we showed that the absence of Gαq/Gα11 signaling impaired the maturation of Paneth cells, induced their differentiation toward goblet cells, and affected the regeneration of the colonic mucosa in an experimental model of colitis. Although an immunohistochemical study showed that Gαq/Gα11 were highly expressed in enterocytes, it seemed that enterocytes were not affected in Int-Gq/G11 double knock-out intestine. Thus, we used an intestinal epithelial cell line to examine the role of signaling through Gαq/Gα11 in enterocytes and manipulated the expression level of Gαq and/or Gα11. The proliferation was inhibited in IEC-6 cells that overexpressed Gαq/Gα11 and enhanced in IEC-6 cells in which Gαq/Gα11 was downregulated. The expression of T-cell factor 1 was increased according to the overexpression of Gαq/Gα11. The expression of Notch1 intracellular cytoplasmic domain was decreased by the overexpression of Gαq/Gα11 and increased by the downregulation of Gαq/Gα11. The relative mRNA expression of Muc2, a goblet cell marker, was elevated in a Gαq/Gα11 knock-down experiment. Our findings suggest that Gαq/Gα11-mediated signaling inhibits proliferation and may support a physiological function, such as absorption or secretion, in terminally differentiated enterocytes.

Exploiting cancer's phenotypic guise against itself: targeting ectopically expressed peptide G-protein coupled receptors for lung cancer therapy

Lung cancer, claiming millions of lives annually, has the highest mortality rate worldwide. This advocates the development of novel cancer therapies that are highly toxic for cancer cells but negligibly toxic for healthy cells. One of the effective treatments is targeting overexpressed surface receptors of cancer cells with receptor-specific drugs. The receptors-in-focus in the current review are the G-protein coupled receptors (GPCRs), which are often overexpressed in various types of tumors. The peptide subfamily of GPCRs is the pivot of the current article owing to the high affinity and specificity to and of their cognate peptide ligands, and the proven efficacy of peptide-based therapeutics. The article summarizes various ectopically expressed peptide GPCRs in lung cancer, namely, Cholecystokinin-B/Gastrin receptor, the Bombesin receptor family, Bradykinin B1 and B2 receptors, Arginine vasopressin receptors 1a, 1b and 2, and the Somatostatin receptor type 2. The autocrine growth and pro-proliferative pathways they mediate, and the distinct tumor-inhibitory effects of somatostatin receptors are then discussed. The next section covers how these pathways may be influenced or 'corrected' through therapeutics (involving agonists and antagonists) targeting the overexpressed peptide GPCRs. The review proceeds on to Nano-scaled delivery platforms, which enclose chemotherapeutic agents and are decorated with peptide ligands on their external surface, as an effective means of targeting cancer cells. We conclude that targeting these overexpressed peptide GPCRs is potentially evolving as a highly promising form of lung cancer therapy.

The Effect of Salt Intake and Potassium Supplementation on Serum Gastrin Levels in Chinese Adults: A Randomized Trial

Excess dietary salt is strongly correlated with cardiovascular disease, morbidity, and mortality. Conversely, potassium likely elicits favorable effects against cardiovascular disorders. Gastrin, which is produced by the G-cells of the stomach and duodenum, can increase renal sodium excretion and regulate blood pressure by acting on the cholecystokinin B receptor. The aim of our study was to assess the effects of altered salt and potassium supplementation on serum gastrin levels in humans. A total of 44 subjects (38–65 years old) were selected from a rural community in northern China. All subjects were sequentially maintained on a relatively low-salt diet for 7 days (3.0 g/day of NaCl), a high-salt diet for 7 days (18.0 g/day of NaCl), and then a high-salt diet supplemented with potassium for another 7 days (18.0 g/day of NaCl + 4.5 g/day of KCl). The high-salt intake significantly increased serum gastrin levels (15.3 ± 0.3 vs. 17.6 ± 0.3 pmol/L). This phenomenon was alleviated through potassium supplementation (17.6 ± 0.3 vs. 16.5 ± 0.4 pmol/L). Further analyses revealed that serum gastrin was positively correlated with 24 h urinary sodium excretion (r = 0.476, p < 0.001). By contrast, gastrin level was negatively correlated with blood pressure in all dietary interventions (r = −0.188, p = 0.031). The present study indicated that variations in dietary salt and potassium supplementation affected the serum gastrin concentrations in the Chinese subjects.

Requirement of Gαq/Gα11 Signaling in the Preservation of Mouse Intestinal Epithelial Homeostasis

BACKGROUND & AIMS

Proliferation, differentiation, and morphogenesis of the intestinal epithelium are tightly regulated by a number of molecular pathways. Coordinated action of intestine is achieved by gastrointestinal hormones, most of which exert these actions through G-protein-coupled receptors. We herein investigated the role of Gα_q/11-mediated signaling in intestinal homeostasis.

METHODS

Intestinal tissues from control (Gnaq^flox/floxGna11^+/+ ), Int-G_q knock-out (KO) (VilCre^+/-Gnaq^flox/floxGna11^+/+ ), G₁₁ KO (Gnaq^flox/floxGna11^-/- ), and Int-G_q/G₁₁ double knock-out (DKO) (VilCre^+/-Gnaq^flox/floxGna11^-/- ) mice were examined by microscopy, transmission electron microscopy, and immunohistochemistry. The effect of Gα_q/11-mediated signaling was studied in the cell lineage, proliferation, and apoptosis. Dextran sodium sulfate (DSS) colitis was induced to study the role of Gα_q/11 in colon.

RESULTS

Paneth cells were enlarged, increased in number, and mislocalized in Int-Gq/G11 DKO small intestine. Paneth cells also reacted with PAS and Muc2 antibody, indicating an intermediate character of Paneth and goblet cells. The nuclear β-catenin, T-cell factor 1, and Sox9 expression were reduced severely in the crypt base of Int-Gq/G11 DKO intestine. Proliferation was activated in the crypt base and apoptosis was enhanced along the crypt. Int-Gq/G11 DKO mice were susceptible to DSS colitis. Proliferation was inhibited in the crypt of unaffected and regenerative areas. Cystic crypts, periodic acid-Schiff-positive cells, and Muc2-positive cells were unusually observed in the ulcerative region.

CONCLUSIONS

The Gα_q/11-mediated pathway plays a pivotal role in the preservation of intestinal homeostasis, especially in Paneth cell maturation and positioning. Wnt/β-catenin signaling was reduced significantly in the crypt base in Gα_q/G₁₁-deficient mice, resulting in the defective maturation of Paneth cells, induction of differentiation toward goblet cells, and susceptibility to DSS colitis.

A Transcriptome-Led Exploration of Molecular Mechanisms Regulating Somatostatin-Producing D-Cells in the Gastric Epithelium

The stomach epithelium contains a myriad of enteroendocrine cells that modulate a range of physiological functions, including postprandial secretion of regulatory peptides, gastric motility, and nutrient absorption. Somatostatin (SST)-producing D-cells are present in the oxyntic and pyloric regions of the stomach, and provide a tonic inhibitory tone that regulates activity of neighboring enteroendocrine cells and gastric acid secretion. Cellular mechanisms underlying the effects of regulatory factors on gastric D-cells are poorly defined due to problems in identifying primary D-cells, and uncertainty remains about which stimuli influence D-cells directly. In this study, we introduce a transgenic mouse line, SST-Cre, which upon crossing with Cre reporter strains, facilitates the identification and purification of gastric D-cells, or cell-specific expression of genetically encoded calcium indicators. Populations of D-cells from the gastric antrum and corpus were isolated and analyzed by RNA sequencing and quantitative RT-PCR. The expression of hormones, hormone receptors, neurotransmitter receptors, and nutrient receptors was quantified. Pyy, Gipr, Chrm4, Calcrl, Taar1, and Casr were identified as genes that are highly enriched in D-cells compared with SST-negative cells. Hormone secretion assays performed in mixed gastric epithelial cultures confirmed that SST secretion is regulated by incretin hormones, cholecystokinin, acetylcholine, vasoactive intestinal polypeptide, calcitonin gene-related polypeptide, oligopetides, and trace amines. Cholecystokinin and oligopeptides elicited increases in intracellular calcium in single-cell imaging experiments performed using cultured D-cells. Our data provide the first transcriptomic analysis and functional characterization of gastric D-cells, and identify regulatory pathways that underlie the direct detection of stimuli by this cell type.

CI-988 Inhibits EGFR Transactivation and Proliferation Caused by Addition of CCK/Gastrin to Lung Cancer Cells

Cholecystokinin (CCK) receptors are G-protein coupled receptors (GPCR) which are present on lung cancer cells. CCK-8 stimulates the proliferation of lung cancer cells, whereas the CCK2R receptor antagonist CI-988 inhibits proliferation. GPCR for some gastrointestinal hormones/neurotransmitters mediate lung cancer growth by causing epidermal growth factor receptor (EGFR) transactivation. Here, the role of CCK/gastrin and CI-988 on EGFR transactivation and lung cancer proliferation was investigated. Addition of CCK-8 or gastrin-17 (100 nM) to NCI-H727 human lung cancer cells increased EGFR Tyr(1068) phosphorylation after 2 min. The ability of CCK-8 to cause EGFR tyrosine phosphorylation was blocked by CI-988, gefitinib (EGFR tyrosine kinase inhibitor), PP2 (Src inhibitor), GM6001 (matrix metalloprotease inhibitor), and tiron (superoxide scavenger). CCK-8 nonsulfated and gastrin-17 caused EGFR transactivation and bound with high affinity to NCI-H727 cells, suggesting that the CCK2R is present. CI-988 inhibited the ability of CCK-8 to cause ERK phosphorylation and elevate cytosolic Ca(2+). CI-988 or gefitinib inhibited the basal growth of NCI-H727 cells or that stimulated by CCK-8. The results indicate that CCK/gastrin may increase lung cancer proliferation in an EGFR-dependent manner.

Gene expression profiling of gastric mucosa in mice lacking CCK and gastrin receptors

The stomach produces acid, which may play an important role in the regulation of bone homeostasis. The aim of this study was to reveal signaling pathways in the gastric mucosa that involve the acid secretion and possibly the bone metabolism in CCK1 and/or CCK2 receptor knockout (KO) mice. Gastric acid secretion was impaired and the ECL cell signaling pathway was inhibited in CCK2 receptor KO mice but not in CCK1 receptor KO mice. However, in CCK1+2 receptor double KO mice the acid secretion in response to pylorus ligation-induced vagal stimulation and the ECL cell pathway were partially normalized, which was associated with an up-regulated pituitary adenylate cyclase-activating polypeptide (PACAP) type 1 receptor (PAC1). The basal part of the gastric mucosa expressed parathyroid hormone-like hormone (PTHLH) in a subpopulation of likely ECL cells (and possibly other cells) and vitamin D3 1α hydroxylase probably in trefoil peptide2-immunoreactive cells. In conclusion, mice lacking CCK receptors exhibited a functional shift from the gastrin-CCK pathways to the neuronal pathway in control of the ECL cells and eventually the acid secretion. Taking the present data together with previous findings, we suggest a possible link between gastric PTHLH and vitamin D and bone metabolism.

Mercaptoacetate and fatty acids exert direct and antagonistic effects on nodose neurons via GPR40 fatty acid receptors

β-mercaptoacetate (MA) is a drug known to block mitochondrial oxidation of medium- and long-chain fatty acids (FAs) and to stimulate feeding. Because MA-induced feeding is vagally dependent, it has been assumed that the feeding response is mediated by MA's antimetabolic action at a peripheral, vagally innervated site. However, MA's site of action has not yet been identified. Therefore, we used fluorescent calcium measurements in isolated neurons from rat nodose ganglia to determine whether MA has direct effects on vagal sensory neurons. We found that MA alone did not alter cytosolic calcium concentrations in nodose neurons. However, MA (60 μM to 6 mM) significantly decreased calcium responses to both linoleic acid (LA; 10 μM) and caprylic acid (C8; 10 μM) in all neurons responsive to LA and C8. GW9508 (40 μM), an agonist of the FA receptor, G protein-coupled receptor 40 (GPR40), also increased calcium levels almost exclusively in FA-responsive neurons. MA significantly inhibited this response to GW9508. MA did not inhibit calcium responses to serotonin, high K(+), or capsaicin, which do not utilize GPRs, or to CCK, which acts on a different GPR. GPR40 was detected in nodose ganglia by RT-PCR. Results suggest that FAs directly activate vagal sensory neurons via GPR40 and that MA antagonizes this effect. Thus, we propose that MA's nonmetabolic actions on GPR40 membrane receptors, expressed by multiple peripheral tissues in addition to the vagus nerve, may contribute to or mediate MA-induced stimulation of feeding.

Cholecystokinin and pancreatic cancer: the chicken or the egg?

The gastrointestinal peptide cholecystokinin (CCK) causes the release of pancreatic digestive enzymes and growth of the normal pancreas. Exogenous CCK administration has been used in animal models to study pancreatitis and also as a promoter of carcinogen-induced or Kras-driven pancreatic cancer. Defining CCK receptors in normal human pancreas has been problematic because of its retroperitoneal location, high concentrations of pancreatic proteases, and endogenous RNase. Most studies indicate that the predominant receptor in human pancreas is the CCK-B type, and CCK-A is the predominant form in rodent pancreas. In pancreatic cancer cells and tumors, the role of CCK is better established because receptors are often overexpressed by these cancer cells and stimulation of such receptors promotes growth. Furthermore, in established cancer, endogenous production of CCK and/or gastrin occurs and their actions stimulate the synthesis of more receptors plus growth by an autocrine mechanism. Initially it was thought that the mechanism by which CCK served to potentiate carcinogenesis was by interplay with inflammation in the pancreatic microenvironment. But with the recent findings of CCK receptors on early PanIN (pancreatic intraepithelial neoplasia) lesions and on stellate cells, the question has been raised that perhaps CCK actions are not the result of cancer but an early driving promoter of cancer. This review will summarize what is known regarding CCK, its receptors, and pancreatic cancer, and also what is unknown and requires further investigation to determine which comes first, the chicken or the egg, "CCK or the cancer."

Gastrin and D1 dopamine receptor interact to induce natriuresis and diuresis

Oral NaCl produces a greater natriuresis and diuresis than the intravenous infusion of the same amount of NaCl. Gastrin is the major gastrointestinal hormone taken up by renal proximal tubule (RPT) cells. We hypothesized that renal gastrin and dopamine receptors interact to synergistically increase sodium excretion, an impaired interaction of which may be involved in the pathogenesis of hypertension. In Wistar-Kyoto rats, infusion of gastrin induced natriuresis and diuresis, which was abrogated in the presence of a gastrin (cholecystokinin B receptor [CCKBR]; CI-988) or a D1-like receptor antagonist (SCH23390). Similarly, the natriuretic and diuretic effects of fenoldopam, a D1-like receptor agonist, were blocked by SCH23390, as well as by CI-988. However, the natriuretic effects of gastrin and fenoldopam were not observed in spontaneously hypertensive rats. The gastrin/D1-like receptor interaction was also confirmed in RPT cells. In RPT cells from Wistar-Kyoto but not spontaneously hypertensive rats, stimulation of either D1-like receptor or gastrin receptor inhibited Na(+)-K(+)-ATPase activity, an effect that was blocked in the presence of SCH23390 or CI-988. In RPT cells from Wistar-Kyoto and spontaneously hypertensive rats, CCKBR and D1 receptor coimmunoprecipitated, which was increased after stimulation of either D1 receptor or CCKBR in RPT cells from Wistar-Kyoto rats; stimulation of one receptor increased the RPT cell membrane expression of the other receptor, effects that were not observed in spontaneously hypertensive rats. These data suggest that there is a synergism between CCKBR and D1-like receptors to increase sodium excretion. An aberrant interaction between the renal CCK BR and D1-like receptors (eg, D1 receptor) may play a role in the pathogenesis of hypertension.

Cholecystokinin: an excitatory modulator of mitral/tufted cells in the mouse olfactory bulb

Cholecystokinin (CCK) is widely distributed in the brain as a sulfated octapeptide (CCK-8S). In the olfactory bulb, CCK-8S is concentrated in two laminae: an infraglomerular band in the external plexiform layer, and an inframitral band in the internal plexiform layer (IPL), corresponding to somata and terminals of superficial tufted cells with intrabulbar projections linking duplicate glomerular maps of olfactory receptors. The physiological role of CCK in this circuit is unknown. We made patch clamp recordings of CCK effects on mitral cell spike activity in mouse olfactory bulb slices, and applied immunohistochemistry to localize CCK_B receptors. In cell-attached recordings, mitral cells responded to 300 nM –1 µM CCK-8S by spike excitation, suppression, or mixed excitation-suppression. Antagonists of GABA_A and ionotropic glutamate receptors blocked suppression, but excitation persisted. Whole-cell recordings revealed that excitation was mediated by a slow inward current, and suppression by spike inactivation or inhibitory synaptic input. Similar responses were elicited by the CCK_B receptor-selective agonist CCK-4 (1 µM). Excitation was less frequent but still occurred when CCK_B receptors were blocked by LY225910, or disrupted in CCK_B knockout mice, and was also observed in CCK_A knockouts. CCK_B receptor immunoreactivity was detected on mitral and superficial tufted cells, colocalized with Tbx21, and was absent from granule cells and the IPL. Our data indicate that CCK excites mitral cells postsynaptically, via both CCK_A and CCK_B receptors. We hypothesize that extrasynaptic CCK released from tufted cell terminals in the IPL may diffuse to and directly excite mitral cell bodies, creating a positive feedback loop that can amplify output from pairs of glomeruli receiving sensory inputs encoded by the same olfactory receptor. Dynamic plasticity of intrabulbar projections suggests that this could be an experience-dependent amplification mechanism for tuning and optimizing olfactory bulb signal processing in different odor environments.

Cholecystokinin but not ghrelin stimulates mucosal bicarbonate secretion in rat duodenum: independence of feeding status and cholinergic stimuli

Cholecystokinin (CCK) is an important regulator of food digestion but its influence on small intestinal secretion has received little attention. We characterized effects of CCK-8, ghrelin and some related peptides on duodenal HCO3(-) secretion in vivo and demonstrated CCK-induced calcium signaling in acutely isolated enterocytes. A segment of proximal duodenum with intact blood supply was cannulated in situ in anaesthetized rats. Mucosal HCO3(-) secretion was continuously recorded (pH-stat). Peptides were administrated to the duodenum by close intra-arterial infusion. Clusters of duodenal enterocytes were attached to the bottom of a perfusion chamber. The intracellular calcium concentration ([Ca(2+)]i) was examined by dual-wavelength imaging. CCK-8 (3.0, 15 and 60 pmol/kg,h) caused dose-dependent increases (p<0.01) in duodenal alkaline secretion in both overnight fasted and continuously fed animals. The CCK1R-antagonist devazepide but neither the CCK2R-antagonist YMM022 nor the melatonin MT2-selective antagonist luzindole inhibited the rise in secretion. Atropine decreased sensitivity to CCK-8. The appetite-related peptide ghrelin was without effect on the duodenal secretion in fasted as well as fed animals. Superfusion with CCK-8 (1.0-50 nM) induced [Ca(2+)]i signaling in acutely isolated duodenal enterocytes. After an initial peak response, [Ca(2+)]i returned to near basal values within 3-5min. Devazepide but not YMM022 inhibited this [Ca(2+)]i response. Low doses of CCK-8 stimulate duodenal alkaline secretion and induce enterocyte [Ca(2+)]i signaling by an action at CCK1 receptors. The results point to importance of CCK in the rapid postprandial rise in mucosa-protective duodenal secretion.

Radiopharmaceutical development of radiolabelled peptides

Receptor targeting with radiolabelled peptides has become very important in nuclear medicine and oncology in the past few years. The overexpression of many peptide receptors in numerous cancers, compared to their relatively low density in physiological organs, represents the molecular basis for in vivo imaging and targeted radionuclide therapy with radiolabelled peptide-based probes. The prototypes are analogs of somatostatin which are routinely used in the clinic. More recent developments include somatostatin analogs with a broader receptor subtype profile or with antagonistic properties. Many other peptide families such as bombesin, cholecystokinin/gastrin, glucagon-like peptide-1 (GLP-1)/exendin, arginine-glycine-aspartic acid (RGD) etc. have been explored during the last few years and quite a number of potential radiolabelled probes have been derived from them. On the other hand, a variety of strategies and optimized protocols for efficient labelling of peptides with clinically relevant radionuclides such as (99m)Tc, M(3+) radiometals ((111)In, (86/90)Y, (177)Lu, (67/68)Ga), (64/67)Cu, (18)F or radioisotopes of iodine have been developed. The labelling approaches include direct labelling, the use of bifunctional chelators or prosthetic groups. The choice of the labelling approach is driven by the nature and the chemical properties of the radionuclide. Additionally, chemical strategies, including modification of the amino acid sequence and introduction of linkers/spacers with different characteristics, have been explored for the improvement of the overall performance of the radiopeptides, e.g. metabolic stability and pharmacokinetics. Herein, we discuss the development of peptides as radiopharmaceuticals starting from the choice of the labelling method and the conditions to the design and optimization of the peptide probe, as well as some recent developments, focusing on a selected list of peptide families, including somatostatin, bombesin, cholecystokinin/gastrin, GLP-1/exendin and RGD.

Comparative pharmacology of cholecystokinin induced activation of cultured vagal afferent neurons from rats and mice

Cholecystokinin (CCK) facilitates the process of satiation via activation of vagal afferent neurons innervating the upper gastrointestinal tract. Recent findings indicate CCK acts on these neurons via a ruthenium red (RuR) sensitive pathway that involves members of the vanilloid (V) subfamily of transient receptor potential (TRP) channels. To further test this mechanism, the mouse provides an ideal model in which genetic tools could be applied. However, whether CCK acts by similar mechanism(s) in mice has not been determined. In the present study we explored the actions of CCK on nodose neurons isolated from Sprague Dawley (SD) rat and two strains of mice; C57BL/6 and BalbC using fluorescence-based calcium imaging. With minor exceptions nodose neurons isolated from all species/strains behaved similarly. They all respond to brief depolarization with a large calcium transient. A significant subset of neurons responded to capsaicin (CAP), a TRPV1 agonist, although neurons from C57BL/6 were 10-fold more sensitive to CAP than SD rats or BalbC mice, and a significantly smaller fraction of neurons from BalbC mice responded to CAP. CCK-8 dose-dependently activated a subpopulation of neurons with similar dose dependency, percent responders, and overlap between CCK and CAP responsiveness. In all species/strains CCK-8 induced activation was significantly attenuated (but not completely blocked) by pretreatment with the TRPV channel blocker RuR. Surprisingly, the CCK analogue JMV-180, which is reported to have pure antagonistic properties in rat but mixed agonist/antagonist properties in mice, behaved as a pure antagonist to CCK in both rat and mouse neurons. The pure antagonistic action of JMV-180 in this in vitro preparation suggests that prior reported differential effects of JMV-180 on satiation in rats versus mouse must be mediated by a site other than vagal afferent activation.

A single nucleotide polymorphism of the cholecystokinin-B receptor predicts risk for pancreatic cancer

There currently are no tests available for early diagnosis or for the identification of patients at risk for development of pancreatic cancer. We report the discovery of single nucleotide polymorphism (SNP) in the cholecystokinin B receptor (CCKBR) gene predicts survival and risk of pancreatic cancer. Growth of human pancreatic cancer is stimulated by gastrin through the CCKBR and an alternatively spliced isoform of the CCKBR gene called CCKCR. One hundred and ten surgically resected benign and malignant pancreatic tissues as well as normal pancreas were prospectively evaluated for CCKBR genotype and protein expression. Analysis demonstrated the expression of the spliced isoform, CCKCR, was associated with a (SNP) (C > A) at position 32 of the intron 4 (IVS 4) of the CCKBR gene. Since the SNP is within an intron, it has not previously been identified in the GWAS studies. Only patients with the A/A or A/C genotypes, exhibited immunoreactivity to a selective CCKCR antibody. Survival among pancreatic cancer patients with the A-SNP was significantly shorter (p = 0.0001, hazard ratio = 3.63) compared with individuals with C/C genotype. Other variables such as surgical margins, lymph node status, histologic grade or adjuvant chemotherapy were not associated with survival. Furthermore, having one or two of the A-alleles was found to increase the risk of pancreatic adenocarcinoma by 174% (p = 0.0192) compared with the C/C wild type. Cancer cells transfected to overexpress the CCKCR demonstrated increased proliferation over controls. Genetic screening for this SNP may aid in early detection of pancreatic cancer in high risk subjects.

Role of AMP-18 in oral mucositis

Oral mucositis (OM) is a devasting toxicity associated with cytotoxic cancer therapy. Antrum mucosal protein (AMP)-18 and a synthetic peptide surrogate, exhibit cell protective and mitogenic properties in in vitro and in vivo models of gastrointestinal epithelial cell injury. The mucosal barrier-protective effects may be mediated by AMP-18's capacity to increase accumulation of specific tight junction (TJ) and adherens junction proteins, and also protect against their loss after injury. Here we asked if AMP peptide could protect the oral mucosa and speed healing from radiation-induced injury. We found AMP peptide prevented radiation-induced OM in a murine model. The peptide also stimulated HaCaT cell growth used to model the oral mucosa. Binding of recombinant human (rh) AMP-18 to the plasma membrane of keratinocytes in normal human oral mucosal tissue suggested that its effects may be receptor mediated. Using an immobilized His-tagged rhAMP-18 fusion protein the receptor was identified as the cholecystokinin-B/gastrin receptor (CCKBR) by affinity purification and mass spectrometry analysis. CCKBR was expressed and co-immunoprecipitated with exogenous rhAMP-18 in diverse epithelial cell lines. Immunofluorescence staining revealed that rhAMP-18 colocalized with CCKBR on the surface of CCKBR-transfected cells. Furthermore, rhAMP-18-stimulated signaling pathways were blocked by a CCKBR-specific antagonist, YM022. rhAMP-18 enhanced viability and growth of CCKBR-transfected, but not empty vector-transfected cells. These results suggest the importance of epithelial junctional integrity in the pathogenesis of OM and demonstrate that AMP-18, by targeting TJ proteins through the activation of CCKBR, could provide a novel strategy for the prevention and treatment of OM.

Effects of lorglumide on growth and invasion of human pancreatic cancer cell line Mia PaCa-2 in vitro through the cholecystokinin-cholecystokinin-1 receptor pathway

BACKGROUND

Cholecystokinin (CCK) has been found to be a growth stimulant through its special receptor pathway, especially for gastrointestinal malignancies. Although the CCK-1 receptor has been shown to be highly expressed in resected human pancreatic cancer samples, its role is less clear.

OBJECTIVE

The aim of this in vitro study was to investigate the CCK-1 receptor expression and the function of the CCK-CCK-1 receptor pathway in the human pancreatic adenocarcinoma cell line, Mia PaCa-2.

METHODS

The expression of the CCK-1 receptor in Mia PaCa-2 cells was detected by reverse-transcriptase polymerase chain reaction and flow cytometry. CCK-1 receptor agonist CCK-8S (the major transmitter form of CCK) and antagonist lorglumide were cultured respectively with Mia PaCa-2. Three groups were created for this study: CCK-8S group (Mia PaCa-2 cells treated with CCK-8S), lorglumide group (Mia PaCa-2 cells treated with lorglumide), and the control group (Mia PaCa-2 cells alone). Investigators were blinded to group designation. 3-[4,5-Dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) and flow cytometry were used to detect the cell growth, cell cycle, and apoptosis. Apoptosis index rate was measured by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling. Cell invasion ability was observed by invasion assay. Expression of matrix metalloproteinase-2 (MMP-2) was measured by Western blotting.

RESULTS

Mia PaCa-2 cells were found to express the CCK-1 receptor. Compared with the control group (70.2% [1.5%]), CCK-8S was associated with significant mean (SD) cell proliferation (85.1% [1.7%]; P = 0.039), and the ratio in the S stage of the cell cycle increased significantly (50.5% [1.7%] vs 42.2% [1.4%]; P = 0.021). CCK-8S was also associated with increased Mia PaCa-2 cell invasion ability (123.8 [1.7] vs 102.1 [5.8]; P = 0.005 vs control). Compared with the control group, lorglumide was associated with significantly inhibited cell growth (52.1% [1.8%]; P = 0.002) and cell invasion (77.6% [1.2%]; P = 0.003). Lorglumide also induced G0/G1 cell cycle arrest and apoptosis (27.1% [3-5%] vs 3-7% [0.6%]; P = 0.003 vs control). The change of invasion ability appeared to be mediated by MMP-2 expression, which was upregulated by CCK-8S and downregulated by lorglumide.

CONCLUSION

The findings of this in vitro study suggest that CCK may exert a trophic action on the Mia PaCa-2 cell line, while lorglumide inhibited the cell growth and invasion.

Radiolabeled CCK/gastrin peptides for imaging and therapy of CCK2 receptor-expressing tumors

Cholecystokinin (CCK) receptors are overexpressed in numerous human cancers, like medullary thyroid carcinomas, small cell lung cancers and stromal ovarian cancers. The specific receptor-binding property of the endogenous ligands for these receptors can be exploited by labeling peptides with a radionuclide and using these as carriers to guide the radioactivity to the tissues that express the receptors. In this way, tumors can be visualized using positron emission tomography and single photon emission computed tomography imaging. A variety of radiolabeled CCK/gastrin-related peptides has been synthesized and characterized for imaging. All peptides have the C-terminal CCK receptor-binding tetrapeptide sequence Trp-Met-Asp-Phe-NH₂ in common or derivatives thereof. This review focuses on the development and application of radiolabeled CCK/gastrin peptides for radionuclide imaging and radionuclide therapy of tumors expressing CCK receptors. We discuss both preclinical studies as well as clinical studies with CCK and gastrin peptides.

Progesterone receptor A mediates VIP inhibition of contraction

The slow transit time of the colon in females with constipation is due to impairment of agonist-induced contraction. The impairment is associated with downregulation of G proteins that mediate contraction and upregulation of Gs proteins that mediate relaxation. These changes are caused by overexpression of progesterone (P4) receptors in the colon, rendering its muscle cells sensitive to physiological P4 concentrations. Downregulation of Gq/11 is mediated by P4 receptor B (PR-B). We examined whether upregulation of Gs proteins increased the inhibition of contraction and whether the increase is mediated by the P4 receptor A (PR-A). These studies were conducted in colon-isolated colon muscle cells from human control and slow-transit constipation (STC) females and from guinea pigs. Muscle cell contraction was induced by CCK-8. Inhibition of contraction was induced by vasoactive intestinal polypeptide (VIP), and 8'bromo-c'AMP (8B-c'AMP) G protein levels were determined by Western blot. VIP-induced inhibition of contraction was greater in muscle cells from STC and P4-treated muscle cells. There were no differences in the inhibition induced by 8B-c'AMP between muscle cells from STC and P4-treated controls. The increased VIP-induced inhibition of muscle cells treated with P4 was blocked by pretreatment with PR-A antibodies and unaffected by PR-B antibodies. These antibodies had no effect on 8B-c'AMP induced-inhibition. The P4 upregulation of Gs proteins was blocked by PR-A antibodies and unaffected by PR-B antibodies. Similar results were obtained in muscle cells from guinea pig colons. We concluded that P4 upregulation of Gs proteins increases VIP-induced inhibition of contraction mediated by PR-A.

The production and role of gastrin-17 and gastrin-17-gly in gastrointestinal cancers

The gastrointestinal peptide hormone gastrin is responsible for initiating the release of gastric acid in the stomach in response to the presence of food and/or humoral factors such as gastrin releasing peptide. However, it has a role in the growth and maintenance of the gastric epithelium, and has been implicated in the formation and growth of gastric cancers. Hypergastrinemia resulting from atrophic gastritis and pernicious anemia leads to hyperplasia and carcinoid formation in rats, and contributes to tumor formation in humans. Additionally, gastrin has been suspected to play a role in the formation and growth of cancers of the colon, but recent studies have instead implicated gastrin processing intermediates, such as gastrin-17-Gly, acting upon a putative, non-cholecystokinin receptor. This review summarizes the production and chemical structures of gastrin and of the processing intermediate gastrin-17-Gly, as well as their activities in the gastrointestinal tract, particularly the promotion of colon cancers.

Modulation of inhibitory neurotransmission in brainstem vagal circuits by NPY and PYY is controlled by cAMP levels

Pancreatic polypeptides such as neuropeptide Y (NPY) and peptide YY (PYY) exert profound, vagally mediated effects on gastrointestinal (GI) motility. Vagal efferent outflow to the GI tract is determined principally by tonic GABAergic synaptic inputs onto dorsal motor nucleus of the vagus (DMV) neurons, yet neither peptide modulates GABAergic transmission. We showed recently that opioid peptides appear similarly ineffective because of the low resting cAMP levels. Using whole cell recordings from identified DMV neurons, we aimed to correlate the influence of brainstem cAMP levels with the ability of pancreatic polypeptides to modulate GABAergic synaptic transmission. Neither NPY, PYY, nor the Y1 or Y2 receptor selective agonists [Leu,Pro]NPY or NPY(3-36) respectively, inhibited evoked inhibitory postsynaptic current (eIPSC) amplitude unless cAMP levels were elevated by forskolin or 8-bromo-cAMP, by exposure to adenylate cyclase-coupled modulators such as cholecystokinin octapeptide (sulfated) (CCK-8s) or thyrotropin releasing hormone (TRH), or by vagal deafferentation. The inhibition of eIPSC amplitude by [Leu,Pro]NPY or NPY(3-36) was stable for approximately 30 min following the initial increase in cAMP levels. Thereafter, the inhibition declined gradually until the agonists were again ineffective after 60 min. Analysis of spontaneous and miniature currents revealed that such inhibitory effects were due to actions at presynaptic Y1 and Y2 receptors. These results suggest that, similar to opioid peptides, the effects of pancreatic polypeptides on GABAergic transmission depend upon the levels of cAMP within gastric inhibitory vagal circuits.

A high-fat diet attenuates the central response to within-meal satiation signals and modifies the receptor expression of vagal afferents in mice

During digestion, macronutrients are sensed within the small intestine. This sensory process is dependent upon the action of gut mediators, such as cholecystokinin (CCK) or serotonin (5-HT), on vagal afferents that, in turn, convey peripheral information to the brain to influence the control of food intake. Recent studies have suggested that dietary conditions alter vagal sensitivity to CCK and 5-HT. This phenomenon may be of importance to the onset of eating disorders. The aim of the present study was thus to investigate the effects of subjecting mice to 15 days of either an HF diet (30% fat, 54% carbohydrate) or an NF diet (10% fat, 74% carbohydrate) on 1) daily and short-term food intake, 2) vagal sensitivity to peripheral anorectic factors and macronutrient loads, and 3) vagal afferent neuron receptor expression. The results indicated that compared with an NF diet, and while increasing food intake and body weight gain, an HF diet altered the short-term response to CCK-8 and intragastric macronutrient loads, while decreasing vagal activation by CCK-8 and modifying the receptor expression of vagal neurons. These findings, therefore, suggest that dietary intervention effect on food intake could be linked to changes in vagal afferent receptor profiles.

Mechanisms of action of CCK to activate central vagal afferent terminals

Cholecystokinin [CCK] is a peptide released as a hormone by the proximal gut in response to the presence of peptones and fatty acid in the gut. Considerable evidence suggests that CCK inhibits feeding behavior and gastric function by acting as a paracrine modulator of vagal afferents in the periphery, especially in the duodenum. CCK is also widely distributed throughout the mammalian brain and appears to function as a neurotransmitter and neuromodulator. More recent studies have suggested that CCK may act directly within the CNS to activate central vagal afferent terminal inputs to the solitary nucleus. We have developed an in vitro calcium imaging method that reveals, for the first time, the direct effects of this peptide on vagal terminals in the solitary nucleus. In vitro imaging reveals that CCK provokes increases in intracellular calcium in vagal afferent terminals as a consequence of a complex interaction between protein kinase A [PKA] and phospholipase C [PLC] transduction mechanisms that open L-type calcium channels and causes endoplasmic reticular [ER] calcium release. The subsequent activation of PKC may be responsible for initiating calcium spiking which is dependent on a TTX-sensitive mechanism. Thus, imaging of the isolated but spatially intact hindbrain slice has allowed a more complete appreciation of the interdependent transduction mechanisms used by CCK to excite identified central vagal afferent fibers and varicosities.

Heterogeneity of acid secretion induced by carbachol and histamine along the gastric gland axis and its relationship to [Ca2+]i

The gastric glands of the mammalian fundic mucosa are constituted by different cell types. Gastric fluid is a mixture of acid, alkali, ions, enzymes, and mucins secreted by parietal, chief, and mucous cells. We studied activation of acid secretion using LysoSensor Yellow/Blue in conjunction with fluo 3 to measure changes in pH and Ca(2+) in isolated rabbit gastric glands. We evidenced a spatial heterogeneity in the amplitude of acid response along the gland axis under histamine and cholinergic stimulation. Carbachol induced a transitory pH increase before acidification. This relative alkalinization may be related to granule release from other cell types. Omeprazole inhibited the acid component but not the rise in pH. Histamine stimulated acid secretion without increase of lumen pH. We studied the relationship between Ca(2+) release and/or entry and H(+) secretion in glands stimulated by carbachol. Ca(2+) release was associated with a fast and transient components of H(+) secretion. We found a linear relationship between Ca(2+) release and H(+) secretion. Ca(2+) entry was associated with a second slow and larger component of acid secretion. The fast component may be the result of activation of Cl(-) and K(+) channels and hence H(+)/K(+) pumps already present in the membrane, whereas the slow component might be associated with translocation of H(+)/K(+) pumps to the canaliculi. In conclusion, with cholinergic stimulation, gastric glands secrete a mixture of acid and other product(s) with a pH above 4.2, both triggered by Ca(2+) release. Maintenance of acid secretion depends on Ca(2+) entry and perhaps membrane fusion.

Exploring the binding pocket for pyridopyrimidine ligands at the CCK1 receptor by molecular docking

Pyridopyrimidine-based analogues are among the most highly potent and selective antagonists of cholecystokinin receptor subtype-1 (CCK1R) described to date. To better understand the structural and chemical features responsible for the recognition mechanism, and to explore the binding pocket of these compounds, we performed automated molecular docking using GOLD2.2 software on some derivatives with structural diversity, and propose a putative binding conformation for each compound. The docking protocol was guided by the key role of the Asn333 residue, as revealed by site directed mutagenesis studies. The results suggest two putative binding modes located in the same pocket. Both are characterized by interaction with the main residues revealed by experiment, Asn333 and Arg336, and differ in the spatial position of the Boc-Trp moiety of these compounds. Hydrophobic contacts with residues Thr117, Phe107, Ile352 and Ile329 are also in agreement with experimental data. Despite the poor correlation obtained between the estimated binding energies and the experimental activity, the proposed models allow us to suggest a plausible explanation of the observed binding data in accordance with chemical characteristics of the compounds, and also to explain the observed diastereoselectivity of this family of antagonists towards CCK1R. The most reasonable selected binding conformations could be the starting point for future studies. Figure Superimposition of the two putative binding conformations revealed by molecular docking for pyridopyrimidine-based CCK1 antagonists.

Control of gastric acid secretion in somatostatin receptor 2 deficient mice: shift from endocrine/paracrine to neurocrine pathways

The gastrin-enterochromaffin-like (ECL) cell-parietal cell axis is known to play an important role in the regulation of gastric acid secretion. Somatostatin, acting on somatostatin receptor type 2 (SSTR(2)), interferes with this axis by suppressing the activity of the gastrin cells, ECL cells, and parietal cells. Surprisingly, however, freely fed SSTR(2) knockout mice seem to display normal circulating gastrin concentration and unchanged acid output. In the present study, we compared the control of acid secretion in these mutant mice with that in wild-type mice. In SSTR(2) knockout mice, the number of gastrin cells was unchanged; whereas the numbers of somatostatin cells were reduced in the antrum (-55%) and increased in the oxyntic mucosa (35%). The ECL cells displayed a reduced expression of histidine decarboxylase and vesicle monoamine transport type 2 (determined by immunohistochemistry), and an impaired transformation of the granules to secretory vesicles (determined by electron microscopic analysis), suggesting low activity of the ECL cells. These changes were accompanied by an increased expression of galanin receptor type 1 in the oxyntic mucosa. The parietal cells were found to respond to pentagastrin or to vagal stimulation (evoked by pylorus ligation) with increased acid production. In conclusion, the inhibitory galanin-galanin receptor type 1 pathway is up-regulated in the ECL cells, and the direct stimulatory action of gastrin and vagal excitation is enhanced on the parietal cells in SSTR(2) knockout mice. We suggest that there is a remodeling of the neuroendocrine mechanisms that regulate acid secretion in these mutant mice.

Further evidence for a C-terminal structural motif in CCK2 receptor active peptide hormones

A comparison of the conformational characteristics of the related hormones [Nle(15)] gastrin-17 and [Tyr(9)-SO(3)] cholecystokinin-15, in membrane-mimetic solutions of dodecylphosphocholine micelles and water, was undertaken using NMR spectroscopy to investigate the possibility of a structural motif responsible for the two hormones common ability to stimulate the CCK(2) receptor. Distance geometry calculations and NOE-restrained molecular dynamics simulations in biphasic solvent boxes of decane and water pointed to the two peptides adopting near identical helical C-terminal configurations, which extended one residue further than their shared pentapeptide sequence of Gly-Trp-Met-Asp-Phe-NH(2). The C-terminal conformation of [Nle(15)] gastrin-17 contained a short alpha-helix spanning the Ala(11)-Trp(14) sequence and an inverse gamma-turn centered on Nle(15) while that of [Tyr(9)-SO(3)] cholecystokinin-15 contained a short 3(10) helix spanning its Met(10) to Met(13) sequence and an inverse gamma-turn centered on Asp(14). Significantly, both the C-terminal helices were found to terminate in type I beta-turns spanning the homologous Gly-Trp-Met-Asp sequences. This finding supports the hypothesis that this structural motif is a necessary condition for CCK(2) receptor activation given that both gastrin and cholecystokinin have been established to follow a membrane-associated pathway to receptor recognition and activation. Comparison of the conformations for the non-homologous C-terminal tyrosyl residues of [Nle(15)] gastrin-17 and [Tyr(9)-SO(3)] cholecystokinin-15 found that they lie on opposite faces of the conserved C-terminal helices. The positioning of this tyrosyl residue is known to be essential for CCK(1) activity and non-essential for CCK(2) activity, pointing to it as a possible differentiator in CCK(1)/CCK(2) receptor selection. The different tyrosyl orientations were retained in molecular models for the [Nle(15)] gastrin-17/CCK(2) receptor and [Tyr(9)-SO(3)] cholecystokinin-15/CCK(1) receptor complexes, highlighting the role of this residue as a likely CCK(1)/CCK(2) receptor differentiator.

Cholecystokinin Down-Regulation by RNA Interference Impairs Ewing Tumor Growth

PURPOSE

Tumors of the Ewing family are characterized by chromosomal translocations that yield chimeric transcription factors, such as EWS/FLI1, which regulate the expression of specific genes that contribute to the malignant phenotype. In the present study, we show that cholecystokinin (CCK) is a new target of the EWS/FLI1 oncoprotein and assess its functional role in Ewing tumor pathogenesis.

EXPERIMENTAL DESIGN

Relevant EWS/FLI1 targets were identified using a combination of cell systems with inducible EWS/FLI1 expression, Ewing tumors and cell lines, microarrays, and RNA interference with doxycycline-inducible small hairpin RNA (shRNA) vectors. A doxycycline-inducible CCK-shRNA vector was stably transfected in A673 and SK-PN-DW Ewing cell lines to assess the role of CCK in cell proliferation and tumor growth.

RESULTS

Microarray analysis revealed that CCK was up-regulated by EWS/FLI1 in HeLa cells. CCK was overexpressed in Ewing tumors as compared with other pediatric malignancies such as rhabdomyosarcoma and neuroblastoma, with levels close to those detected in normal tissues expressing the highest levels of CCK. Furthermore, EWS/FLI1 knockdown in A673 and SK-PN-DW Ewing cells using two different doxycycline-inducible EWS/FLI1-specific shRNA vectors down-regulated CCK mRNA expression and diminished the levels of secreted CCK, showing that CCK is a EWS/FLI1 specific target gene in Ewing cells. A doxycycline-inducible CCK-specific shRNA vector successfully down-regulated CCK expression, reduced the levels of secreted CCK in Ewing cell lines, and inhibited cell growth and proliferation in vitro and in vivo. Finally, we show that Ewing cell lines and tumors express CCK receptors and that the growth inhibition produced by CCK silencing can be rescued by culturing the cells with medium containing CCK.

CONCLUSIONS

Our data support the hypothesis that CCK acts as an autocrine growth factor stimulating the proliferation of Ewing cells and suggest that therapies targeting CCK could be promising in the treatment of Ewing tumors.

How does cholecystokinin stimulate exocrine pancreatic secretion? From birds, rodents, to humans

The field of cholecystokinin (CCK) stimulation of exocrine pancreatic secretion has experienced major changes in the recent past. This review attempts to summarize the present status of the field. CCK production in the intestinal I cells, the molecular forms of CCK produced and subsequently circulated in the blood, the presence or absence of CCK receptors on the isolated pancreatic acinar cells and the associated signaling for acinar cell secretion, and the actual circuits and sites of action for CCK regulation of exocrine pancreatic secretion in vivo are reviewed in different animal species with an emphasis on birds, rodents, and humans. Clear differences in the relative importance of neural and direct modes of CCK action on pancreatic acinar cells were identified. Rodents seem to be endowed with both modes of action, whereas in humans the neural mode may predominate. In birds, such as duck, the direct mode needs further assistance from pituitary adenylate cyclase-activating peptide/VIP receptors. However, much further work needs to be directed to the neural mode to map out all sites of CCK action and details of the full circuits, and we foresee a major revival for this field of research in the near future.

Elevated cholecystokininergic tone constitutes an important molecular/neuronal mechanism for the expression of anxiety in the mouse

Cholecystokinin (CCK), one of the most abundant neuropeptides in the brain, plays an important role in anxiogenesis through the activation of CCK receptor-2 (CCKR-2). Accumulating evidence, however, has suggested this role depends on endogenous CCKergic "tone," which is largely determined by the expression level of the CCKR-2. Using the tTA/tetO-inducible transgenic (tg) approach, we show here that overexpression of the CCKR-2 in neurons of the forebrain significantly increases CCKR-2 binding capacity in tg mice compared with their littermate controls. Interestingly, these tg mice consistently exhibit increased fear responses, which are generally interpreted as anxiety-like behaviors in the rodent, in a battery of behavioral tests, which represented conflict situations or delivered stress to the subjects. The inhibition of transgene expression with doxycycline treatment completely diminished both increased receptor-binding activity and all behavioral phenotypes. Furthermore, treatment of tg mice with diazepam significantly attenuated these anxiety-like behaviors. Our results directly demonstrate that the elevated CCKergic tone via overexpression of the CCKR-2 in the brain may constitute an underlying molecular/neuronal mechanism for the expression of anxiety. In addition, our study has validated a robust genetic anxiety model in the mouse in terms of their face, constructive, and predictive validity.

Probing a model of a GPCR/ligand complex in an explicit membrane environment: the human cholecystokinin-1 receptor

A three-dimensional model structure of a complex formed by a G-protein-coupled receptor (GPCR) and an agonist ligand is probed and refined using molecular-dynamics simulations and free energy calculations in a realistic environment. The model of the human receptor of cholecystokinin associated to agonist ligand CCK9 was obtained from a synergistic procedure combining site-directed mutagenesis experiments and in silico modeling. The 31-ns molecular-dynamics simulation in an explicit membrane environment indicates that both the structure of the receptor and its interactions with the ligand are robust. Whereas the secondary structure of the alpha-helix bundle is well preserved, the region of the intracellular loops exhibits a significant flexibility likely to be ascribed to the absence of G-protein subunits in the model. New insight into the structural features of the binding pocket is gained, in particular, the interplay of the ligand with both the receptor and internal water molecules. Water-mediated interactions are shown to participate in the binding, hence, suggesting additional site-directed mutagenesis experiments. Accurate free energy calculations on mutated ligands provide differences in the receptor-ligand binding affinity, thus offering a direct, quantitative comparison to experiment. We propose that this detailed consistency-checking procedure be used as a routine refinement step of in vacuo GPCR models, before further investigation and application to structure-based drug design.

Gene expression profiling of gastrin target genes in parietal cells

Previous studies demonstrated that mice with a null mutation in the gene encoding the hormone gastrin have impaired gastric acid secretion. Hence, the aim of this study was to evaluate changes in the acid-secreting parietal cell in gastrin-deficient (GAS-KO) mice. Analysis of several transcripts encoding parietal cell proteins involved in gastric acid secretion showed reduced abundance in the GAS-KO stomach, including H+,K+-ATPase alpha- and beta-subunits, KCNQ1 potassium channel, aquaporin-4 water channel, and creatine kinase B, which were reversed by gastrin infusion for 1 wk. Although mRNA and protein levels of LIM and SH3 domain-containing protein-1 (LASP-1) were not greatly changed in the mutant, there was a marked reduction in phosphorylation, consistent with its proposed role as a cAMP signal adaptor protein associated with acid secretion. A more comprehensive analysis of parietal cell gene expression in GAS-KO mice was performed using the Affymetrix U74AV2 chip with RNA from parietal cells purified by flow cytometry to >90%. Comparison of gene expression in GAS-KO and wild-type mice identified 47 transcripts that differed by greater than or equal to twofold, suggesting that gastrin affects parietal cell gene expression in a specific manner. The differentially expressed genes included several genes in signaling pathways, with a substantial number (20%) known to be target genes for Wnt and Myc.

Qdot nanocrystal conjugates conjugated to bombesin or ANG II label the cognate G protein-coupled receptor in living cells

Quantum dots (Qdot Nanocrystal Conjugates; Quantum Dot, Hayward, CA) exhibit high fluorescence and low photobleaching compared with organic dyes, properties that should enhance their detection at low densities. In view of the properties of Qdots and the biological and pharmaceutical importance of G protein-coupled receptors (GPCRs), we attempted to use Qdots to label GPCRs in a variety of live cell types. An agonist consisting of biotinylated bombesin or ANG II was conjugated to Qdot Nanocrystal Conjugates coated with streptavidin through a biotin-streptavidin linkage (Qdot agonist). Herein we demonstrate that Qdot-bombesin conjugate can label the bombesin-preferring GPCR in living mouse Swiss 3T3 cells and in Rat-1 cells. Similarly, we used the Qdot-ANG II conjugate to label GPCR in intact rat intestinal epithelial cells (IEC)-18 and in a human pancreatic adenocarcinoma cell line of ductal origin, HPAF-II cells. We demonstrate that Qdot-ANG II is brighter and more photostable than agonist labeled with the organic dye Cy3. Our results demonstrate that Qdot technology can be adapted to monitor ligand binding to GPCRs. Combined with the narrow and symmetric emission profile of Qdot Nanocrystal Conjugates, this information suggests the potential for a new multiplex strategy to determine the effect of agonists and/or antagonists on agonist binding to several GPCRs simultaneously in living cells.

Fugetaxis: active movement of leukocytes away from a chemokinetic agent

Chemotaxis or active movement of leukocytes toward a stimulus has been shown to occur in response to chemokinetic agents including members of the recently identified superfamily of proteins called chemokines. Leukocyte chemotaxis is thought to play a central role in a wide range of physiological and pathological processes including the homing of immune cells to lymph nodes and the accumulation of these cells at sites of tissue injury and pathogen or antigen challenge. We have recently identified a novel biological mechanism, which we term fugetaxis (fugere, to flee from; taxis, movement) or chemorepulsion, which describes the active movement of leukocytes away from chemokinetic agents including the chemokine, stromal cell derived factor-1, and the HIV-1 envelope protein, gp120. In this article, we review the evidence that supports the observation that leukocyte fugetaxis occurs in vitro and in vivo and suggestions that this novel mechanism can be exploited to modulate the immune response. We propose that leukocyte fugetaxis plays a critical role in both physiological and pathological processes in which leukocytes are either excluded or actively repelled from specific sites in vivo including thymic emigration, the establishment of immune privileged sites and immune evasion by viruses and cancer. We believe that current data support the thesis that a greater understanding of leukocyte fugetaxis will lead to the development of novel therapeutic approaches for a wide range of human diseases.

Cholecystokinin octapeptide improves cardiac function by activating cholecystokinin octapeptide receptor in endotoxic shock rats

AIM: To explore the effect of sulfated cholecystokinin octapeptide (sCCK-8) on cardiac functions and its receptor mechanism in endotoxic shock (ES) rats.

METHODS: The changes of the mean arterial pressure (MAP), heart rate (HR), the left ventricular pressure (LVP) and the maximal/minimum rate of LVP (±LVdp/dt_max)) were measured by using physiological record instrument in eight groups of rats. The expression of cholecystokinin-A receptor (CCK-AR) and cholecystokinin-B receptor (CCK-BR) mRNA of myocardium in ES rats was examined by reverse transcription polymerase chain reaction (RT-PCR).

RESULTS: (1) Low doses of sCCK-8 (0.4 μg/kg) caused tachycardia (441±27, normal control 391±22 s/min) and slight increase in MAP, LVP and ±LVdp/dt_max (16.96±1.79, 18.21±1.69 and +768.85±31.28/-565.04±27.71 kPa, respectively, all P<0.01), while medium doses (4.0 μg/kg) and high doses of sCCK-8 (40 μg/kg) elicited bradycardia and marked increase in MAP, LVP and ±LVdp/dt_max (17.29±1.63, 19.46±2.57 and +831.46±22.57/-606.08 ±31.32; 17.46±1.08, 19.83±2.91 and +914.52±35.95/-639.15±30.23 kPa, respectively, all P<0.01). Proglumide (1.0 mg/kg), a nonselective antagonist of CCK-receptor (CCK-R), significantly inhibited the pressor effects of sCCK-8 (15.96±1.38, 17.36±0.66 and +748.18±19.29/-512.12±14.39 kPa, respectively, all P<0.01), whilst reversing the bradycardiac responses. (2) High doses of LPS (8 mg/kg) elicited marked decrease in MAP, LVP and ±LVdp/dt_max. (7.16±0.59, 7.6±0.68 and +298.01±25.52/-166.96±19.25 kPa, respectively, all P<0.01). Pretreatment with sCCK-8 (40 μg/kg) could reverse the decline of cardiac functions (10.71±0.45, 11.7±1.26 and +446.04±67.18/-347.90±36.98 kPa, respectively, all P<0.01), while proglumide could cause further decline of cardiac function in ES rats (4.71±0.67, 5.58±1.25 and +226.48±15.84/-142.83±20.23 kPa, respectively, all P<0.01). (3) CCK-A/BR mRNAs were expressed in myocardium of control rats. Gene expression of CCK-AR and CCK-BR significantly increased in myocardium of ES rats. The increase of CCK-AR mRNA induced by LPS began at 0.5 h, peaked at 2 h, kept a high level at 6 h and declined at 12 h, respectively. Similar to CCK-AR mRNA, the expression of CCK-BR mRNA peaked at 2 h and kept a high level at 6 h, but it did not change at the first 0.5 h and was stable at a high level at 12 h.

CONCLUSION: The above results indicate that endogenous and exogenous sCCK-8 may significantly improve cardiac function and intractable hypotension of ES rats, which was likely related to high expression of CCK-A/BR in myocardium induced by LPS.

Mu-opioid receptor trafficking on inhibitory synapses in the rat brainstem

Whole-cell recordings were made from identified gastric-projecting rat dorsal motor nucleus of the vagus (DMV) neurons. The amplitude of evoked IPSCs (eIPSCs) was unaffected by perfusion with met-enkephalin (ME) or by mu-, delta-, or kappa-opioid receptor selective agonists, namely D-Ala2-N-Me-Phe4-Glycol5-enkephalin (DAMGO), cyclic [D-Pen2-D-Pen5]-enkephalin, or trans-3,4-dichloro-N-methyl-N-[2-(1-pyrolytinil)-cyclohexyl]-benzeneacetamide methane sulfonate (U50,488), respectively. Brief incubation with the adenylate cyclase activator forskolin or the nonhydrolysable cAMP analog 8-bromo-cAMP, thyrotropin releasing hormone, or cholecystokinin revealed the ability of ME and DAMGO to inhibit IPSC amplitude; this inhibition was prevented by pretreatment with the mu-opioid receptor (MOR1) selective antagonist D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2. Conversely, incubation with the adenylate cyclase inhibitor dideoxyadenosine, with the protein kinase A (PKA) inhibitor N-[2-(p-Bromocinnamyl-amino)ethyl]-5-isoquinolinesulfonamide dihydrochloride (H89), or with the Golgi-disturbing agent brefeldin A, blocked the ability of forskolin to facilitate the inhibitory actions of ME. Immunocytochemical experiments revealed that under control conditions, MOR1 immunoreactivity (MOR1-IR) was colocalized with glutamic acid decarboxylase (GAD)-IR in profiles apposing DMV neurons only after stimulation of the cAMP-PKA pathway. Pretreatment with H89 or brefeldin A or incubation at 4 degrees C prevented the forskolin-mediated insertion of MOR1 on GAD-IR-positive profiles. These results suggest that the cAMP-PKA pathway regulates trafficking of mu-opioid receptors into the cell surface of GABAergic nerve terminals. By consequence, the inhibitory actions of opioid peptides in the dorsal vagal complex may depend on the state of activation of brainstem vagal circuits.

Involvement of endogenous CCK and CCK1 receptors in colonic motor function

Cholecystokinin (CCK) is a brain-gut peptide; it functions both as a neuropeptide and as a gut hormone. Although the pancreas and the gallbladder were long thought to be the principal peripheral targets of CCK, CCK receptors are found throughout the gut. It is likely that CCK has a physiological role not only in the stimulation of pancreatic and biliary secretions but also in the regulation of gastrointestinal motility. The motor effects of CCK include postprandial inhibition of gastric emptying and inhibition of colonic transit. It is now evident that at least two different receptors, CCK(1) and CCK(2) (formerly CCK-A and CCK-B, respectively), mediate the actions of CCK. Both localization and functional studies suggest that the motor effects of CCK are mediated by CCK(1) receptors in humans. Since CCK is involved in sensory and motor responses to distension in the intestinal tract, it may contribute to the symptoms of constipation, bloating and abdominal pain that are often characteristic of functional gastrointestinal disorders in general and irritable bowel syndrome (IBS), in particular. CCK(1) receptor antagonists are therefore currently under development for the treatment of constipation-predominant IBS. Clinical studies suggest that CCK(1) receptor antagonists are effective facilitators of gastric emptying and inhibitors of gallbladder contraction and can accelerate colonic transit time in healthy volunteers and patients with IBS. These drugs are therefore potentially of great value in the treatment of motility disorders such as constipation and constipation-predominant IBS.

Involvement of endogenous CCK and CCK1 receptors in colonic motor function

Cholecystokinin (CCK) is a brain-gut peptide; it functions both as a neuropeptide and as a gut hormone. Although the pancreas and the gallbladder were long thought to be the principal peripheral targets of CCK, CCK receptors are found throughout the gut. It is likely that CCK has a physiological role not only in the stimulation of pancreatic and biliary secretions but also in the regulation of gastrointestinal motility. The motor effects of CCK include postprandial inhibition of gastric emptying and inhibition of colonic transit. It is now evident that at least two different receptors, CCK(1) and CCK(2) (formerly CCK-A and CCK-B, respectively), mediate the actions of CCK. Both localization and functional studies suggest that the motor effects of CCK are mediated by CCK(1) receptors in humans. Since CCK is involved in sensory and motor responses to distension in the intestinal tract, it may contribute to the symptoms of constipation, bloating and abdominal pain that are often characteristic of functional gastrointestinal disorders in general and irritable bowel syndrome (IBS), in particular. CCK(1) receptor antagonists are therefore currently under development for the treatment of constipation-predominant IBS. Clinical studies suggest that CCK(1) receptor antagonists are effective facilitators of gastric emptying and inhibitors of gallbladder contraction and can accelerate colonic transit time in healthy volunteers and patients with IBS. These drugs are therefore potentially of great value in the treatment of motility disorders such as constipation and constipation-predominant IBS.

Cholecystokinin-1 receptor protein up-regulation during pancreatic regeneration after acute haemorrhagic pancreatitis in rats

BACKGROUND

Cholecystokinin (CCK) plays an important role in regeneration after acute pancreatitis in rats. The present study was aimed to elucidate the role of CCK-1 receptor (CCK-1R) in acute pancreatitis. We investigated the serial changes in CCK-1R mRNA and protein levels and their immunolocalization after acute haemorrhagic pancreatitis induced in male Wistar rats by retrograde intraductal infusion of 4% sodium taurocholate (100 micro L 100 g(-1) body weight).

METHODS

Histological changes were evaluated by haematoxylin and eosin staining. Pancreatic CCK-1R mRNA was determined by Northern blot analysis. Pancreatic CCK-1R protein was evaluated by immunoblot analysis and immunohistochemistry with a polyclonal antibody against rat CCK-1R protein.

RESULTS

Histological findings revealed that newly formed acinar cells were detected at the periphery of tubular complexes on day 14, and normal architecture of lobules was observed focally on day 21. Pancreatic CCK-1R mRNA peaked on day 3 and thereafter gradually decreased. Cholecystokinin-1R protein rapidly increased after induction of pancreatitits, reaching a maximal level on day 3. On day 3, intense immunoreactivity for CCK-1R protein was observed in both the cytoplasm of vacuolized acinar cells and the tubular complexes. In the regenerative process after acute haemorrhagic pancreatitis in rats, the expression of pancreatic CCK-1R mRNA and protein increased, and intense immunoreactivity for CCK-1R protein was observed in tubular complexes in the cytoplasm of regenerated acinar cells.

CONCLUSION

These results suggest that CCK-1R contributes to pancreatic regeneration after acute haemorrhagic pancreatitis and that tubular complexes are involved in the process of acinar cell regeneration following pancreatic injury.

High tumorigenic potential of a constitutively active mutant of the cholecystokinin 2 receptor

The cholecystokinin 2 receptor (CCK2R) increases proliferation of normal and neoplastic gastrointestinal cells and activates various mitogenic signaling pathways when stimulated by gastrin. To study the incidence of permanent activation of this receptor in tumorigenicity, a constitutively active mutant was generated by replacing residue Glu151 in the conserved E/DRY motif by Ala. Expression of the E151A-CCK2R mutant in NIH-3T3 cells causes ligand-independent activation of phospholipase C and ornithine decarboxylase, two enzymes critical for mitogenesis. Strikingly, the constitutive activity of this mutant was associated with dramatic alteration of NIH-3T3 cell morphology, enhanced cell proliferation and invasion. Moreover, injection of cells expressing E151A-CCK2R in nude mice resulted in the development of large and rapidly growing tumors. By contrast, none of these effects was observed with cells expressing the wild-type CCK2R, indicating that the tumorigenic properties of the E151A-CCK2R mutant is the result of its constitutive activation. To date, this is the first report that provides evidence for the high tumorigenic effect of a constitutively active CCK2R mutant, thus raising a potential role of the CCK2R in human cancer.

Expression and cell-specific localization of cholecystokinin receptors in rat lung

AIM: To elucidate whether CCK receptors exist in lung tissues and their precise cellular localization in the lung.

METHODS: CCK-AR and CCK-BR mRNA expression and cellular distribution in the rat lung were detected by highly sensitive method of in situ reverse transcription-polymerase chain reaction (RT-PCR) and conventional in situ hybridization.

RESULTS: CCK-AR and CCK-BR gene positive signals were observed in bronchial epithelial cells, alveolar epithelial cells, pulmonary macrophages and vascular endothelial cells of the rats lung by in situ RT-PCR. The hybridization signals of CCK-AR were relatively faint. By in situ hybridization, however, only the signals of CCK-BR but not CCK-AR were detected in the lung, and the positive staining was only found in vascular endothelial cells and macrophages.

CONCLUSION: CCK-AR and CCK-BR gene were present in pulmonary vascular endothelial cells, macrophages, bronchial epithelial cells and alveolar epithelial cells, which play an important role in mediating the regulatory actions of CCK-8 on these cells.

Effect of cholesterol liposomes on calcium mobilization in muscle cells from the rabbit sphincter of Oddi

AIM: To analyze the influence of cholesterol liposome on the Ca²⁺ mobilization of cultured muscle cells in rabbit sphincter of Oddi’s.

METHODS: New Zealand rabbit was sacrificed and the sphincter of Oddi (SO) segement was obtained aseptically. The SO segment was cut into pieces and cultured in DMEM solution. Then the smooth muscle cells were subcultured, and the 4th-7th passage cells were used for further investigation. The intracellular Ca²⁺ increase was measured under confocal microscope after the addition of 20 mmol·L^-1 KCl, 10^-7 mol·L^-1 acetylcholine and 10^-7 mol·L^-1 cholecystokinin, and different antagonists were added to analyze the Ca²⁺ mobilization pathway. After the cells were incubated with 1 g·L^-1 cholesterol liposome (CL)(molar ratio was-2:1), the intracellular Ca²⁺ increase was measured again to determine the effect of CL on cellular Ca²⁺ mobilization.

RESULTS: The resting cellular calcium concentration of cultured SO cell was 108 nmol·L^-1± 21 nmol·L^-1. The intracellular Ca²⁺ increases induced by 20 mmol·L^-1 KCl, 10^-7 mol·L^-1 ACh and 10^-7 mol·L^-1 CCK were 183% ± 56%, 161% ± 52% and 130% ± 43%, respectively. When the extracellular Ca²⁺ was eliminated by 2 mmol·L^-1 EGTA and 5 μmol·L^-1 verapamil, the intracellular Ca²⁺ increases induced by KCl, ACh and CCK were 20% ± 14%, 82% ± 21% and 104% ± 23%, respectively. After the preincubation with heparin, the Ca²⁺ increases were 62% ± 23% and 23% ± 19% induced by ACh and CCK, as for preincubation with procaine they were 72% ± 28% and 85% ± 37% induced by ACh and CCK, respectively. Pretreatment with CL for 18 h, the resting cellular Ca²⁺ concentration elevated to 152 nmol·L^-1± 26 nmol·L^-1, however, the cellular Ca²⁺ increase percentages in response to these agonists were 67% ± 32%, 56% ± 33% and 34% ± 15%.

CONCLUSION: KCl elicite the SO cellular Ca²⁺ increase depends on influx of extracellular Ca²⁺, ACh evoked the SO celllular Ca²⁺ increase is through the mobilization of intracellular Ca²⁺ pool and influx of extracellular Ca²⁺ as well, CCK excites the SO cells mainly through mobilization of intracellular IP3-sensitive Ca²⁺ store. After the incorporation with cholesterol liposome, KCl,ACh and CCK induced cellular Ca²⁺ increase percentages decreased.