Adenylyl cyclase 6 mediates the action of cyclic AMP-dependent secretagogues in mouse pancreatic exocrine cells via protein kinase A pathway activation

Aquaporin-2 in the early stages of the adenine-induced chronic kidney disease model

Chronic kidney disease (CKD) is one of the leading health problems in the world. It is silent in the early stages and gradually progresses, inducing renal physiological and structural alterations. Moreover, CKD is associated with impaired life quality, increased risk for cardiovascular diseases, and reduced life expectancy. Different CKD animal models differ in underlying etiology, time of onset, and associated diseases. The 0.25% adenine diet induces progressive kidney damage, constituting an adequate model mimicking human CKD. Vasopressin (VP) was postulated as a mediator of CKD, mainly acting through its V2 receptors. However, the molecular mechanisms involved in the pathogenesis of this condition and its progression still are not entirely understood. This study aimed to evaluate if AQP2 expression is altered in an adenine-induced model of CKD in rats at early stages of development (two weeks) and to assess a potential beneficial effect of Tolvaptan (a V2 receptor antagonist) treatment. We showed an increased renal medullary AQP2 expression at two weeks of adenine administration. This increase was mainly cytoplasmic, explaining the increased urinary volume of CKD rats and suggesting a possible non-canonical role for AQP2. In addition, Tolvaptan effectively inhibited the V2 receptor in both control and CKD rats, decreasing AQP2 expression and increasing diuresis. Moreover, Tolvaptan slightly reduced BUN and plasma creatinine. On the other hand, the renal alterations induced by adenine in CKD rats were not prevented by Tolvaptan.

Physiological roles of mammalian transmembrane adenylyl cyclase isoforms

Adenylyl cyclases (ACs) catalyze the conversion of ATP to the ubiquitous second messenger cAMP. Mammals possess nine isoforms of transmembrane ACs, dubbed AC1-9, that serve as major effector enzymes of G protein-coupled receptors (GPCRs). The transmembrane ACs display varying expression patterns across tissues, giving the potential for them to have a wide array of physiological roles. Cells express multiple AC isoforms, implying that ACs have redundant functions. Furthermore, all transmembrane ACs are activated by Gαs, so it was long assumed that all ACs are activated by Gαs-coupled GPCRs. AC isoforms partition to different microdomains of the plasma membrane and form prearranged signaling complexes with specific GPCRs that contribute to cAMP signaling compartments. This compartmentation allows for a diversity of cellular and physiological responses by enabling unique signaling events to be triggered by different pools of cAMP. Isoform-specific pharmacological activators or inhibitors are lacking for most ACs, making knockdown and overexpression the primary tools for examining the physiological roles of a given isoform. Much progress has been made in understanding the physiological effects mediated through individual transmembrane ACs. GPCR-AC-cAMP signaling pathways play significant roles in regulating functions of every cell and tissue, so understanding each AC isoform's role holds potential for uncovering new approaches for treating a vast array of pathophysiological conditions.

Therapeutic potentials of agonist and antagonist of adenosine receptors in type 2 diabetes

Type 2 diabetes has been a global health challenge over the decades and is among the leading causes of death. Several treatment approaches have been developed, but more effective and new therapies are still needed. The role of adenosine in glucose and lipid homeostasis has offered a different therapeutic approach. Adenosine mediates its physiological role through the activation of adenosine receptors. These adenosine receptors have been implicated in glucose and lipid homeostasis. The ability of agonists and antagonists of adenosine receptors to activate or inhibit the adenosine signalling cascade and thereby affecting the balance of glucose and lipid homeostasis has challenged the studies of agonists and antagonists of adenosine receptors, both preclinical and clinical, as potential anti-diabetic drugs. This review provides a background on different anti-diabetic therapeutic approaches, outlining the role of adenosine receptors in glucose and lipid homeostasis, and mechanisms underlying the action of agonists/antagonists of adenosine receptors as a therapeutic potential towards type 2 diabetes.

NADPH oxidase 1 mediates caerulein-induced pancreatic fibrosis in chronic pancreatitis

Inflammatory disorders of the pancreas are divided into acute (AP) and chronic (CP) forms. Both states of pancreatitis are a result of pro-inflammatory mediators, including reactive oxygen species (ROS). One of the sources of ROS is NADPH oxidase (Nox). The rodent genome encodes Nox1-4, Duox1 and Duox2. Our purpose was to assess the extent to which Nox enzymes contribute to the pathogenesis of both AP and CP using Nox-deficient mice. Using RT-PCR, Nox1 was found in both isolated mouse pancreatic acini and pancreatic stellate cells (PaSCs). Subsequently, mice with genetically deleted Nox1 were further studied and showed that the histo-morphologic characteristics of caerulein-induced CP, but not caerulein-induced AP, was ameliorated in Nox1 KO mice. We also found that the lack of Nox1 impaired caerulein-induced ROS generation in PaSCs. Using Western blotting, we found that AKT mediates the fibrotic effect of Nox1 in a mouse model of CP. We also found a decrease in phospho-ERK and p38MAPK levels in Nox1 KO mice with CP, but not with AP. Both CP-induced TGF-β up-regulation and NF-ĸB activation were impaired in pancreas from Nox1 KO mice. Western blotting indicated increases in proteins involved in fibrosis and acinar-to-ductal metaplasia in WT mice with CP. No change in those proteins were observed in Nox1 KO mice. The lack of Nox1 lowered mRNA levels of CP-induced matrix metalloproteinase MMP-9 and E-cadherin repressor Twist in PaSCs. CONCLUSION: Nox1-derived ROS in PaSCs mediate the fibrotic process of CP by activating the downstream redox-sensitive signaling pathways AKT and NF-ĸB, up-regulating MMP-9 and Twist, and producing α-smooth muscle actin and collagen I and III.

Expression of Adenosine Receptors in Rodent Pancreas

Adenosine regulates exocrine and endocrine secretions in the pancreas. Adenosine is considered to play a role in acini-to-duct signaling in the exocrine pancreas. To identify the molecular basis of functional adenosine receptors in the exocrine pancreas, immunohistochemical analysis was performed in the rat, mouse, and guinea pig pancreas, and the secretory rate and concentration of HCO₃⁻ in pancreatic juice from the rat pancreas were measured. The A_2A adenosine receptor colocalized with ezrin, an A-kinase anchoring protein, in the luminal membrane of duct cells in the mouse and guinea pig pancreas. However, a strong signal ascribed to A_2B adenosine receptors was detected in insulin-positive β cells in islets of Langerhans. The A_2A adenosine receptor agonist 4-[2-[[6-Amino-9-(N-ethyl-β-D-ribofuranuronamidosyl)-9H-purin-2-yl]amino]ethyl]benzenepropanoic acid (CGS 21680) stimulated HCO₃⁻-rich fluid secretion from the rat pancreas. These results indicate that A_2A adenosine receptors may be, at least in part, involved in the exocrine secretion of pancreatic duct cells via acini-to-duct signaling. The adenosine receptors may be a potential therapeutic target for cancer as well as exocrine dysfunctions of the pancreas.

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.

Cystic Fibrosis of the Pancreas: The Role of CFTR Channel in the Regulation of Intracellular Ca2+ Signaling and Mitochondrial Function in the Exocrine Pancreas

Cystic fibrosis (CF) is the most common genetic disorder that causes a significant damage in secretory epithelial cells due to the defective ion flux across the cystic fibrosis transmembrane conductance regulator (CFTR) Cl^- channel. Pancreas is one of the organs most frequently damaged by the disease leading to pancreatic insufficiency, abdominal pain and an increased risk of acute pancreatitis in CF patients causing a significant decrease in the quality of life. CFTR plays a central role in the pancreatic ductal secretory functions by carrying Cl^- and HCO₃ ^- ions across the apical membrane. Therefore pathophysiological studies in CF mostly focused on the effects of impaired ion secretion by pancreatic ductal epithelial cells leading to exocrine pancreatic damage. However, several studies indicated that CFTR has a central role in the regulation of intracellular signaling processes and is now more widely considered as a signaling hub in epithelial cells. In contrast, elevated intracellular Ca²⁺ level was observed in the lack of functional CFTR in different cell types including airway epithelial cells. In addition, impaired CFTR expression has been correlated with damaged mitochondrial function in epithelial cells. These alterations of intracellular signaling in CF are not well characterized in the exocrine pancreas yet. Therefore in this review we would like to summarize the complex role of CFTR in the exocrine pancreas with a special focus on the intracellular signaling and mitochondrial function.

Development of a polarized pancreatic ductular cell epithelium for physiological studies

Pancreatic ductular epithelial cells comprise the majority of duct cells in pancreas, control cystic fibrosis transmembrane conductance regulator (CFTR)-dependent bicarbonate ([Formula: see text]) secretion, but are difficult to grow as a polarized monolayer. Using NIH-3T3-J2 fibroblast feeder cells and a Rho-associated kinase inhibitor, we produced well-differentiated and polarized porcine pancreatic ductular epithelial cells. Cells grown on semipermeable filters at the air-liquid interface developed typical epithelial cell morphology and stable transepithelial resistance and expressed epithelial cell markers (zona occludens-1 and β-catenin), duct cell markers (SOX-9 and CFTR), but no acinar (amylase) or islet cell (chromogranin) markers. Polarized cells were studied in Ussing chambers bathed in Krebs-Ringer [Formula: see text] solution at 37°C gassed with 5% CO2 to measure short-circuit currents ( Isc). Ratiometric measurement of extracellular pH was performed with fluorescent SNARF-conjugated dextran at 5% CO2. Cells demonstrated a baseline Isc (12.2 ± 3.2 μA/cm2) that increased significantly in response to apical forskolin-IBMX (∆ Isc: 35.4 ± 3.8 μA/cm2, P < 0.001) or basolateral secretin (∆ Isc: 31.4 ± 2.5 μA/cm2, P < 0.001), both of which increase cellular levels of cAMP. Subsequent addition of apical GlyH-101, a CFTR inhibitor, decreased the current (∆ Isc: 20.4 ± 3.8 μA/cm2, P < 0.01). Extracellular pH and [Formula: see text] concentration increased significantly after forskolin-IBMX (pH: 7.18 ± 0.23 vs. 7.53 ± 0.19; [Formula: see text] concentration, 14.5 ± 5.9 vs. 31.8 ± 13.4 mM; P < 0.05 for both). We demonstrate the development of a polarized pancreatic ductular epithelial cell epithelium with CFTR-dependent [Formula: see text] secretion in response to secretin and cAMP. This model is highly relevant, as porcine pancreas physiology is very similar to humans and pancreatic damage in the cystic fibrosis pig model recapitulates that of humans. NEW & NOTEWORTHY Pancreas ductular epithelial cells control cystic fibrosis transmembrane conductance regulator (CFTR)-dependent bicarbonate secretion. Their function is critical because when CFTR is deficient in cystic fibrosis bicarbonate secretion is lost and the pancreas is damaged. Mechanisms that control pancreatic bicarbonate secretion are incompletely understood. We generated well-differentiated and polarized porcine pancreatic ductular epithelial cells and demonstrated feasibility of bicarbonate secretion. This novel method will advance our understanding of pancreas physiology and mechanisms of bicarbonate secretion.

AC6 is the major adenylate cyclase forming a diarrheagenic protein complex with cystic fibrosis transmembrane conductance regulator in cholera

The World Health Organization(WHO) has reported a worldwide surge in cases of cholera caused by the intestinal pathogen Vibrio cholerae, and, combined, such surges have claimed several million lives, mostly in early childhood. Elevated cAMP production in intestinal epithelial cells challenged with cholera toxin (CTX) results in diarrhea due to chloride transport by a cAMP-activated channel, the cystic fibrosis transmembrane conductance regulator (CFTR). However, the identity of the main cAMP-producing proteins that regulate CFTR in the intestine and may be relevant for secretory diarrhea is unclear. Here, using RNA-Seq to identify the predominant AC isoform in mouse and human cells and extensive biochemical analyses for further characterization, we found that the cAMP-generating enzyme adenylate cyclase 6 (AC6) physically and functionally associates with CFTR at the apical surface of intestinal epithelial cells. We generated epithelium-specific AC6 knockout mice and demonstrated that CFTR-dependent fluid secretion is nearly abolished in AC6 knockout mice upon CTX challenge in ligated ileal loops. Furthermore, loss of AC6 function dramatically impaired CTX-induced CFTR activation in human and mouse intestinal spheroids. Our finding that the CFTR-AC6 protein complex is the key mediator of CTX-associated diarrhea may facilitate development of antidiarrheal agents to manage cholera symptoms and improve outcomes.

Di-N-octylphthalate acts as a proliferative agent in murine cell hepatocytes by regulating the levels of TGF-β and pro-apoptotic proteins

Di-n-octylphthalate (DNOP) is a phthalate used in the manufacturing of a wide variety of polyvinyl chloride-containing medical and consumer products. A study on chronic exposure to DNOP in rodents showed the development of pre-neoplastic hepatic lesions following exposure to a tumor initiator. The objective of this study was to identify the mechanisms by which DNOP leads to pre-neoplastic hepatic lesions. Mouse hepatocyte AML-12 and FL83B cells were treated with DNOP. The rate of cell proliferation was increased in treated cells in a concentration-dependent manner. DNOP increased the expression of transforming growth factor-β (tgf-β) in both cell lines, and primary culture mouse hepatocytes. The TGF-β receptor inhibitor LY2109761 impaired the effect of DNOP. The presence of pro-apoptotic proteins decreased in the presence of DNOP. Our observation indicates that DNOP, through an increase in the expression of tgf-β and a decrease in the levels of pro-apoptotic proteins, acts as a proliferative agent in normal mouse hepatocytes. We also studied the morphological and functional changes of the mouse liver upon a short-term treatment of DNOP. Mice exposed to DNOP displayed an epithelial-to-mesenchymal transition and cholestasis, which was reflected in an increase in hepatic bile acids and glutathione levels.

International Union of Basic and Clinical Pharmacology. CI. Structures and Small Molecule Modulators of Mammalian Adenylyl Cyclases

Adenylyl cyclases (ACs) generate the second messenger cAMP from ATP. Mammalian cells express nine transmembrane AC (mAC) isoforms (AC1-9) and a soluble AC (sAC, also referred to as AC10). This review will largely focus on mACs. mACs are activated by the G-protein Gαs and regulated by multiple mechanisms. mACs are differentially expressed in tissues and regulate numerous and diverse cell functions. mACs localize in distinct membrane compartments and form signaling complexes. sAC is activated by bicarbonate with physiologic roles first described in testis. Crystal structures of the catalytic core of a hybrid mAC and sAC are available. These structures provide detailed insights into the catalytic mechanism and constitute the basis for the development of isoform-selective activators and inhibitors. Although potent competitive and noncompetitive mAC inhibitors are available, it is challenging to obtain compounds with high isoform selectivity due to the conservation of the catalytic core. Accordingly, caution must be exerted with the interpretation of intact-cell studies. The development of isoform-selective activators, the plant diterpene forskolin being the starting compound, has been equally challenging. There is no known endogenous ligand for the forskolin binding site. Recently, development of selective sAC inhibitors was reported. An emerging field is the association of AC gene polymorphisms with human diseases. For example, mutations in the AC5 gene (ADCY5) cause hyperkinetic extrapyramidal motor disorders. Overall, in contrast to the guanylyl cyclase field, our understanding of the (patho)physiology of AC isoforms and the development of clinically useful drugs targeting ACs is still in its infancy.

Adenylyl cyclase 3/adenylyl cyclase-associated protein 1 (CAP1) complex mediates the anti-migratory effect of forskolin in pancreatic cancer cells

Pancreatic cancer is one of the most lethal human malignancies. A better understanding of the intracellular mechanism of migration and invasion is urgently needed to develop treatment that will suppress metastases and improve overall survival. Cyclic adenosine monophosphate (cyclic AMP) is a second messenger that has shown to regulate migration and invasion of pancreatic cancer cells. The rise of cyclic AMP suppressed migration and invasion of pancreatic ductal adenocarcinoma cells. Cyclic AMP is formed from cytosolic ATP by the enzyme adenylyl cyclase (AC). There are ten isoforms of ACs; nine are anchored in the plasma membrane and one is soluble. What remains unknown is the extent to which the expression of transmembrane AC isoforms is both modified in pancreatic cancer and mediates the inhibitory effect of forskolin on cell motility. Using real-time PCR analysis, ADCY3 was found to be highly expressed in pancreatic tumor tissues, resulting in a constitutive increase in cyclic AMP levels. On the other hand, ADCY2 was down-regulated. Migration, invasion, and filopodia formation in two different pancreatic adenocarcinoma cell lines, HPAC and PANC-1 deficient in AC1 or AC3, were studied. We found that AC3, upon stimulation with forskolin, enhanced cyclic AMP levels and inhibited cell migration and invasion. Unlikely to be due to a cytotoxic effect, the inhibitory effects of forskolin involved the quick formation of AC3/adenylyl cyclase-associated protein 1 (CAP1)/G-actin complex, which inhibited filopodia formation and cell motility. Using Western blotting analysis, forskolin, through AC3 activation, caused phosphorylation of CREB, but not ERK. The effect of CREB phosphorylation is likely to be associated with long-term signaling changes. © 2016 Wiley Periodicals, Inc.

The adenosine A2B receptor is involved in anion secretion in human pancreatic duct Capan-1 epithelial cells

Adenosine modulates a wide variety of biological processes via adenosine receptors. In the exocrine pancreas, adenosine regulates transepithelial anion secretion in duct cells and is considered to play a role in acini-to-duct signaling. To identify the functional adenosine receptors and Cl⁻ channels important for anion secretion, we herein performed experiments on Capan-1, a human pancreatic duct cell line, using open-circuit Ussing chamber and gramicidin-perforated patch-clamp techniques. The luminal addition of adenosine increased the negative transepithelial potential difference (V_te) in Capan-1 monolayers with a half-maximal effective concentration value of approximately 10 μM, which corresponded to the value obtained on whole-cell Cl⁻ currents in Capan-1 single cells. The effects of adenosine on V_te, an equivalent short-circuit current (I_sc), and whole-cell Cl⁻ currents were inhibited by CFTRinh-172, a cystic fibrosis transmembrane conductance regulator (CFTR) Cl⁻ channel inhibitor. The adenosine A_2B receptor agonist, BAY 60-6583, increased I_sc and whole-cell Cl⁻ currents through CFTR Cl⁻ channels, whereas the A_2A receptor agonist, CGS 21680, had negligible effects. The A_2B receptor antagonist, PSB 603, inhibited the response of I_sc to adenosine. Immunohistochemical analysis showed that the A_2A and A_2B receptors colocalized with Ezrin in the luminal membranes of Capan-1 monolayers and in rat pancreatic ducts. Adenosine elicited the whole-cell Cl⁻ currents in guinea pig duct cells. These results demonstrate that luminal adenosine regulates anion secretion by activating CFTR Cl⁻ channels via adenosine A_2B receptors on the luminal membranes of Capan-1 cells. The present study endorses that purinergic signaling is important in the regulation of pancreatic secretion.

Glucagon-like peptide-1 receptor is present in pancreatic acinar cells and regulates amylase secretion through cAMP

Glucagon-like peptide-1 (GLP-1) is a glucoincretin hormone that can act through its receptor (GLP-1R) on pancreatic β-cells and increase insulin secretion and production. GLP-1R agonists are used clinically to treat type 2 diabetes. GLP-1 may also regulate the exocrine pancreas at multiple levels, including inhibition through the central nervous system, stimulation indirectly through insulin, and stimulation directly on acinar cells. However, it has been unclear whether GLP-1R is present in pancreatic acini and what physiological functions these receptors regulate. In the current study we utilized GLP-1R knockout (KO) mice to study the role of GLP-1R in acinar cells. RNA expression of GLP-1R was detected in acutely isolated pancreatic acini. Acinar cell morphology and expression of digestive enzymes were not affected by loss of GLP-1R. GLP-1 induced amylase secretion in wild-type (WT) acini. In GLP-1R KO mice, this effect was abolished, whereas vasoactive intestinal peptide-induced amylase release in KO acini showed a pattern similar to that in WT acini. GLP-1 stimulated cAMP production and increased protein kinase A-mediated protein phosphorylation in WT acini, and these effects were absent in KO acini. These data show that GLP-1R is present in pancreatic acinar cells and that GLP-1 can regulate secretion through its receptor and cAMP signaling pathway.

The Physiology and Pathophysiology of Pancreatic Ductal Secretion: The Background for Clinicians

The human exocrine pancreas consists of 2 main cell types: acinar and ductal cells. These exocrine cells interact closely to contribute to the secretion of pancreatic juice. The most important ion in terms of the pancreatic ductal secretion is HCO3. In fact, duct cells produce an alkaline fluid that may contain up to 140 mM NaHCO3, which is essential for normal digestion. This article provides an overview of the basics of pancreatic ductal physiology and pathophysiology. In the first part of the article, we discuss the ductal electrolyte and fluid transporters and their regulation. The central role of cystic fibrosis transmembrane conductance regulator (CFTR) is highlighted, which is much more than just a Cl channel. We also review the role of pancreatic ducts in severe debilitating diseases such as cystic fibrosis (caused by various genetic defects of cftr), pancreatitis, and diabetes mellitus. Stimulation of ductal secretion in cystic fibrosis and pancreatitis may have beneficial effects in their treatment.

Recent advances in the regulation of pancreatic secretion

PURPOSE OF REVIEW

This review highlights recent progress made in the field of pancreatic secretion.

RECENT FINDINGS

This review summarizes a number of recent studies demonstrating the intracellular pathways by which hormones and neural inputs regulate pancreatic exocrine and endocrine secretion. In particular, the effects of vasoactive intestinal peptide and secretin on intra-acinar cell adenosine 3',5'-cyclic monophosphate are explored. Considerable attention is paid to regulation of β-cell function and includes studies detailing the mechanisms of regulation of insulin by somatostatin, serotonin, and melanocortins. These studies emphasize the critical role that hormonal, paracrine, and neural factors play in glucose homeostasis.

SUMMARY

Exocrine and endocrine pancreatic secretions are regulated by hormonal and neural mechanisms, and understanding these pathways will enable the discovery and design of new and improved therapies for prevention and control of diabetes and perhaps exocrine insufficiency.

Calcium signaling in pancreatic ductal epithelial cells: an old friend and a nasty enemy

Ductal epithelial cells of the exocrine pancreas secrete HCO3(-) rich, alkaline pancreatic juice, which maintains the intraluminal pH and washes the digestive enzymes out from the ductal system. Importantly, damage of this secretory process can lead to pancreatic diseases such as acute and chronic pancreatitis. Intracellular Ca(2+) signaling plays a central role in the physiological regulation of HCO3(-) secretion, however uncontrolled Ca(2+) release can lead to intracellular Ca(2+) overload and toxicity, including mitochondrial damage and impaired ATP production. Recent findings suggest that the most common pathogenic factors leading to acute pancreatitis, such as bile acids, or ethanol and ethanol metabolites can evoke different types of intracellular Ca(2+) signals, which can stimulate or inhibit ductal HCO3(-) secretion. Therefore, understanding the intracellular Ca(2+) pathways and the mechanisms which can switch a good signal to a bad signal in pancreatic ductal epithelial cells are crucially important. This review summarizes the variety of Ca(2+) signals both in physiological and pathophysiological aspects and highlight molecular targets which may strengthen our old friend or release our nasty enemy.

Adenylyl cyclases in the digestive system

Adenylyl cyclases (ACs) are a group of widely distributed enzymes whose functions are very diverse. There are nine known transmembrane AC isoforms activated by Gαs. Each has its own pattern of expression in the digestive system and differential regulation of function by Ca(2+) and other intracellular signals. In addition to the transmembrane isoforms, one AC is soluble and exhibits distinct regulation. In this review, the basic structure, regulation and physiological roles of ACs in the digestive system are discussed.