ATP and acetylcholine, equal brethren

María Teresa Miras Portugal: a pioneer for vesicular nucleotide storage

Chromaffin granules are secretory granules present in adrenal medulla chromaffin cells. They contain high contents of catecholamines and nucleotides and have been regarded as a model system for the study of vesicular transmitter uptake and release. In 1988, Dr. María Teresa Miras Portugal, when studying catecholamine biosynthesis, detected a novel group of nucleotides, the diadenosine polyphosphates, in the adrenal chromaffin granules. Based on this finding, she unraveled the existence of diadenosine polyphosphate-mediated chemical transmission, leading to a paradigm shift in the field of purinergic signaling. She is also a pioneer in the studies on vesicular nucleotide storage. First, María Teresa and her group characterized nucleotide transport in chromaffin granules and synaptic vesicles using fluorescent nucleotide derivatives such as 1, N6-ethenoadenosine triphosphates. Then, they revealed the presence of a hypothetical vesicular nucleotide transporter with unique properties in terms of substrate specificity. In this article, we will describe her contributions to vesicular nucleotide storage and the foundations she laid for future studies.

Inhibition of prejunctional parasympathetic pathways by β3-adrenoceptor agonists in the isolated pig detrusor: comparison with human detrusor studies

Adrenergic receptors of the β₃-subtype (β₃-ADRs) seem to represent a new target for a more effective pharmacological treatment of overactive bladder (OAB), a wide spread urinary disorder. A promising opportunity for OAB therapy might rely on the development of selective β₃-ADR agonists, but an appropriate preclinical screening, as well as investigation of their pharmacological mechanism(s), is limited by poor availability of human bladder samples and of translational animal models. In this study, we used the porcine urinary bladder as experimental tool to ascertain the functions of β₃-ADRs in the control the parasympathetic motor drive. Tritiated acetylcholine ([³H]-ACh), mainly originated from neural stores, was released by electrical field stimulation (EFS) in epithelium-deprived detrusor strips from pigs bred without estrogens. EFS produced simultaneously [³H]-ACh release and smooth muscle contraction allowing to asses neural (pre-junctional) and myogenic (postjunctional) effects in the same experiment. Isoprenaline and mirabegron produced on the EFS-evoked effects a concentration-dependent inhibition antagonized by L-748,337, a high selective β₃-ADR antagonist. The analysis of the resultant pharmacodynamic parameters supports the notion that in pig detrusors, as well as in previously described human detrusors, the activation of inhibitory β₃-ADRs can modulate neural parasympathetic pathways. In such inhibitory control, the involvement of membrane K⁺ channels, mainly of the SK type, seems to play a pivotal role similarly to what previously described in humans. Therefore, the isolated porcine detrusor can provide a suitable experimental tool to study the mechanisms underlying the clinical efficacy of selective β₃-ADR compounds for human use.

The simultaneous action of acute paradoxical sleep deprivation and hypothyroidism modulates synaptosomal ATPases and acetylcholinesterase activities in rat brain

BACKGROUND

Thyroid dysfunctions as well as sleep abnormalities are usually followed by neurological, psychiatric and/or behavioral disorders. On the other hand, changes in the brain adenosine triphosphatases (ATPases) and acetylcholinesterase (AChE) activities show significant importance in pathogenetic pathways in the evolution of numerous neuropsychiatric diseases.

METHODS

This study aimed to evaluate the in vivo simultaneous effects of hypothyroidism and paradoxical sleep deprivation for 72 h on synaptosomalATPases and AChE activities of whole rat brains. In order to induce hypothyroidism, 6-n-propyl-2-thiouracil was administrated in drinking water during 21 days. The modified multiple platform method was used to induce paradoxical sleep deprivation. The AChE and ATPases activities were measured using spectrophotometric methods.

RESULTS

Hypothyroidism significantly increased the activity of Na⁺/K⁺-ATPase compared to other groups, while at the same time significantly decreased AChE activity compared to the CT and SD groups. Paradoxical sleep deprivation significantly increased AChE activity compared to other groups. The simultaneous effect of hypothyroidism and sleep deprivation reduced the activity of all three enzymes (for Na⁺/K⁺-ATPase between HT/SD and HT group p < 0.0001, SD group p < 0.001,CT group p = 0.013; for ecto-ATPases between HT/SD and HT group p = 0.0034, SD group p = 0.0001, CT group p = 0.0007; for AChE between HT/SD and HT group p < 0.05, SD group p < 0.0001, CT group p < 0.0001).

CONCLUSIONS

The effect of simultaneous existence of hypothyroidism and paradoxical sleep deprivation reduces the activity of the Na⁺/K⁺-ATPase, ecto-ATPases, and AChE, what is different from individual effect of hypothyroidism and paradoxical sleep deprivation itself. This knowledge could help in the choice of appropriate therapy in such condition.

Is the vesicular nucleotide transporter a molecular target of eicosapentaenoic acid?

Vesicular nucleotide transporter (VNUT), an active transporter for nucleotides in secretory vesicles, is responsible for the vesicular storage of ATP and plays an essential role in purinergic chemical transmission. Inhibition of VNUT decreases the concentration of ATP in the luminal space of secretory vesicles, followed by decreased vesicular ATP release, resulting in the blockade of purinergic chemical transmission. Very recently, Miyaji and colleagues reported that eicosapentaenoic acid (EPA) is a potent VNUT inhibitor and effective in treating neuropathic and inflammatory pain and insulin resistance through inhibition of vesicular storage and release of ATP. However, our validation study indicated that, in bovine adrenal chromaffin granule membrane vesicles, EPA inhibited the formation of an electrochemical gradient of protons across the membrane with the concentration of 50% inhibition (IC50) being 1.0 μM without affecting concanamycin B-sensitive ATPase activity. Essentially, similar results were obtained with proteoliposomes containing purified vacuolar H⁺-ATPase. Consistent with these observations, EPA inhibited the ATP-dependent uptakes of ATP and dopamine by chromaffin granule membrane vesicles, with ID50 being 1.2 and 1.0 μM, respectively. Furthermore, EPA inhibited ATP-dependent uptake of L-glutamate by mouse brain synaptic vesicles with ID50 being 0.35 μM. These results indicate that EPA at sub-μM acts as a proton conductor and increases proton permeability across the membrane, regardless of the presence or absence of VNUT, thereby inhibiting non-specifically the vesicular storage of neurotransmitters. Thus, EPA may affect a broader range of chemical transmission than proposed.

Nucleoside transporters and immunosuppressive adenosine signaling in the tumor microenvironment: Potential therapeutic opportunities

Adenosine compartmentalization has a profound impact on immune cell function by regulating adenosine localization and, therefore, extracellular signaling capabilities, which suppresses immune cell function in the tumor microenvironment. Nucleoside transporters, responsible for the translocation and cellular compartmentalization of hydrophilic adenosine, represent an understudied yet crucial component of adenosine disposition in the tumor microenvironment. In this review article, we will summarize what is known regarding nucleoside transporter's function within the purinome in relation to currently devised points of intervention (i.e., ectonucleotidases, adenosine receptors) for cancer immunotherapy, alterations in nucleoside transporter expression reported in cancer, and potential avenues for targeting of nucleoside transporters for the desired modulation of adenosine compartmentalization and action. Further, we put forward that nucleoside transporters are an unexplored therapeutic opportunity, and modulation of nucleoside transport processes could attenuate the pathogenic buildup of immunosuppressive adenosine in solid tumors, particularly those enriched with nucleoside transport proteins.

Induction of aggression and anxiety-like responses by perfluorooctanoic acid is accompanied by modulation of cholinergic- and purinergic signaling-related parameters in adult zebrafish

Perfluorooctanoic acid (PFOA) is a contaminant of global concern owing to its prevalent occurrence in aquatic and terrestrial environments with potential hazardous impact on living organisms. Here, we investigated the influence of realistic environmental concentrations of PFOA (0, 0.25, 0.5, or 1.0 mg/L) on relevant behaviors of adult zebrafish (Danio rerio) (e.g., exploration to novelty, social preference, and aggression) and the possible role of PFOA in modulating cholinergic and purinergic signaling in the brain after exposure for 7 consecutive days. PFOA significantly increased geotaxis as well as reduced vertical exploration (a behavioral endpoint for anxiety), and increased the frequency and duration of aggressive episodes without affecting their social preference. Exposure to PFOA did not affect ADP hydrolysis, whereas ATP and AMP hydrolysis were significantly increased at the highest concentration tested. However, AChE activity was markedly decreased in all PFOA-exposed groups when compared with control. In conclusion, PFOA induces aggression and anxiety-like behavior in adult zebrafish and modulates both cholinergic and purinergic signaling biomarkers. These novel data can provide valuable insights into possible health threats related to human activities, demonstrating the utility of adult zebrafish to elucidate how PFOA affects neurobehavioral responses in aquatic organisms.

Targeting purinergic receptors to suppress the cytokine storm induced by SARS-CoV-2 infection in pulmonary tissue

The etiological agent of coronavirus disease (COVID-19) is the new member of the Coronaviridae family, a severe acute respiratory syndrome coronavirus 2 virus (SARS-CoV-2), responsible for the pandemic that is plaguing the world. The single-stranded RNA virus is capable of infecting the respiratory tract, by binding the spike (S) protein on its viral surface to receptors for the angiotensin II-converting enzyme (ACE2), highly expressed in the pulmonary tissue, enabling the interaction of the virus with alveolar epithelial cells promoting endocytosis and replication of viral material. The infection triggers the activation of the immune system, increased purinergic signaling, and the release of cytokines as a defense mechanism, but the response can become exaggerated and prompt the so-called “cytokine storm”, developing cases such as severe acute respiratory syndrome (SARS). This is characterized by fever, cough, and difficulty breathing, which can progress to pneumonia, failure of different organs and death. Thus, the present review aims to compile and correlate the mechanisms involved between the immune and purinergic systems with COVID-19, since the modulation of purinergic receptors, such as A2A, A2B, and P2X7 expressed by immune cells, seems to be effective as a promising therapy, to reduce the severity of the disease, as well as aid in the treatment of acute lung diseases and other cases of generalized inflammation.

Assessment of sexual behavior and neuromodulation of Cyperus esculentus L. and Tetracarpidium conophorum Müll. Arg dietary supplementation regulating the purinergic system in the cerebral cortex of L-NAME-challenged rats

This study examined the behavioral responses, purinergic receptor densities, ectonucleotidases (E-NTPDase), adenosine deaminase (ADA) activity, and nitric oxide (NO) levels along with the parameters of oxidative stress-related to erectile function in the cerebral cortex (CC) of L-NAME-challenged rats pretreated with tigernut (TN) and walnut (WN) dietary supplementation. Wistar rats (male) of 70 total animals (250-300 g) were used in this research and hence separated into seven groups (n = 10): Group I: normal control-fed basal diet; Group II: positive control-fed basal diet/L-NAME/Sildenafil citrate (5 mg kg-1  day-1 ); Group III: ED-induced (placed on a basal diet/L-NAME); Group IV: diet supplemented with processed TN (20%)/L-NAME; Group V: diet supplemented with raw TN (20%)/L-NAME; Group VI: diet supplemented with processed WN (20%)/L-NAME; and Group VII placed on a diet supplemented with raw WN (20%)/L-NAME. The rats were pretreated for 2 weeks before the L-NAME (40 mg kg-1  day-1 ) challenge on their respective diet. L-NAME brought about a decrease in the sexual behaviors evaluated while the effect was significantly reversed by supplemented diets containing TN and WN. L-NAME increased the levels of reactive oxygen species and malondialdehyde, E-NTPDase as well as ADA activities, and caused the level of NO in the CC as well as the purinoreceptor densities to be downregulated. Treatments with enriched diets, however, greatly reverse these effects. The behavioral responses and neuromodulatory capacity of the nuts displayed on the CC can, therefore, further support their aphrodisiac property. PRACTICAL APPLICATIONS: The results revealed the ability of tigernut (TN; Cyperus esculentus L.) and walnut (WN; Tetracarpidium conophorum Müll. Arg.) to enhance behavioral responses; modulate purinergic receptor densities, E-NTPDase, and ADA activities; increase NO levels; and prevent oxidative stress related to erectile function in the CC of L-NAME-challenged Wistar rats. The results show that these nuts are useful feeds for both animal and human nutrition.

Neurotransmitters responsible for purinergic motor neurotransmission and regulation of GI motility

Classical concepts of peripheral neurotransmission were insufficient to explain enteric inhibitory neurotransmission. Geoffrey Burnstock and colleagues developed the idea that ATP or a related purine satisfies the criteria for a neurotransmitter and serves as an enteric inhibitory neurotransmitter in GI muscles. Cloning of purinergic receptors and development of specific drugs and transgenic mice have shown that enteric inhibitory responses depend upon P2Y₁ receptors in post-junctional cells. The post-junctional cells that transduce purinergic neurotransmitters in the GI tract are PDGFRα⁺ cells and not smooth muscle cells (SMCs). PDGFRα⁺ cells express P2Y₁ receptors, are activated by enteric inhibitory nerve stimulation and generate Ca²⁺ oscillations, express small-conductance Ca²⁺-activated K⁺ channels (SK3), and generate outward currents when exposed to P2Y₁ agonists. These properties are consistent with post-junctional purinergic responses, and similar responses and effectors are not functional in SMCs. Refinements in methodologies to measure purines in tissue superfusates, such as high-performance liquid chromatography (HPLC) coupled with etheno-derivatization of purines and fluorescence detection, revealed that multiple purines are released during stimulation of intrinsic nerves. β-NAD⁺ and other purines, better satisfy criteria for the purinergic neurotransmitter than ATP. HPLC has also allowed better detection of purine metabolites, and coupled with isolation of specific types of post-junctional cells, has provided new concepts about deactivation of purine neurotransmitters. In spite of steady progress, many unknowns about purinergic neurotransmission remain and require additional investigation to understand this important regulatory mechanism in GI motility.

Ectonucleoside triphosphate diphosphohydrolases and ecto-5'-nucleotidase in purinergic signaling: how the field developed and where we are now

Geoffrey Burnstock will be remembered as the scientist who set up an entirely new field of intercellular communication, signaling via nucleotides. The signaling cascades involved in purinergic signaling include intracellular storage of nucleotides, nucleotide release, extracellular hydrolysis, and the effect of the released compounds or their hydrolysis products on target tissues via specific receptor systems. In this context ectonucleotidases play several roles. They inactivate released and physiologically active nucleotides, produce physiologically active hydrolysis products, and facilitate nucleoside recycling. This review briefly highlights the development of our knowledge of two types of enzymes involved in extracellular nucleotide hydrolysis and thus purinergic signaling, the ectonucleoside triphosphate diphosphohydrolases, and ecto-5'-nucleotidase.

History of ectonucleotidases and their role in purinergic signaling

Ectonucleotidases are key for purinergic signaling. They control the duration of activity of purinergic receptor agonists. At the same time, they produce hydrolysis products as additional ligands of purinergic receptors. Due to the considerable diversity of enzymes, purinergic receptor ligands and purinergic receptors, deciphering the impact of extracellular purinergic receptor control has become a challenge. The first group of enzymes described were the alkaline phosphatases - at the time not as nucleotide-metabolizing but as nonspecific phosphatases. Enzymes now referred to as nucleoside triphosphate diphosphohydrolases and ecto-5'-nucleotidase were the first and only nucleotide-specific ectonucleotidases identified. And they were the first group of enzymes related to purinergic signaling. Additional research brought to light a surprising number of ectoenzymes with broad substrate specificity, which can also hydrolyze nucleotides. This short overview traces the development of the field and briefly highlights important results and benefits for therapies of human diseases achieved within nearly a century of investigations.

Autonomic regulation of T-lymphocytes: Implications in cardiovascular disease

The nervous and immune systems both serve as essential assessors and regulators of physiological function. Recently, there has been a great interest in how the nervous and immune systems interact to modulate both physiological and pathological states. In particular, the autonomic nervous system has a direct line of communication with immune cells anatomically, and moreover, immune cells possess receptors for autonomic neurotransmitters. This circumstantial evidence is suggestive of a functional interplay between the two systems, and extensive research over the past few decades has demonstrated neurotransmitters such as the catecholamines (i.e. dopamine, norepinephrine, and epinephrine) and acetylcholine have potent immunomodulating properties. Furthermore, immune cells, particularly T-lymphocytes, have now been found to express the cellular machinery for both the synthesis and degradation of neurotransmitters, which suggests the ability for both autocrine and paracrine signaling from these cells independent of the nervous system. The details underlying the functional interplay of this complex network of neuroimmune communication are still unclear, but this crosstalk is suggestive of significant implications on the pathogenesis of a number of autonomic-dysregulated and inflammation-mediated diseases. In particular, it is widely accepted that numerous forms of cardiovascular diseases possess imbalanced autonomic tone as well as altered T-lymphocyte function, but a paucity of literature exists discussing the direct role of neurotransmitters in shaping the inflammatory microenvironment during the progression or therapeutic management of these diseases. This review seeks to provide a fundamental framework for this autonomic neuroimmune interaction within T-lymphocytes, as well as the implications this may have in cardiovascular diseases.

Effect of Essential Oils from Ginger (Zingiber officinale) and Turmeric (Curcuma longa) Rhizomes on Some Inflammatory Biomarkers in Cadmium Induced Neurotoxicity in Rats

Studies have revealed that anti-inflammatory agents could provide beneficial effect in lowering the incidence/progression of neurological diseases. Hence, this study sought to investigate the effect of essential oils from Nigeria ginger and turmeric rhizomes on some cytokines in cadmium induced neurotoxicity. The result revealed that essential oil from ginger and turmeric rhizomes exerts anti-inflammatory effect by preventing alterations of some cytokines/inflammatory biomarkers (IL-6, IL-10 and TNF-Alpha) levels and inhibits both hippocampus and prefrontal cortex acetylcholinesterase (AChE) and adenosine deaminase (ADA) activities (important enzymes relevant in the management/prevention of neurodegenerative diseases) in Cd treated rats. In conclusion, essential oil from ginger and turmeric rhizomes exerts anti-inflammatory properties in Cd induced neurotoxicity. The observed effect could be due to the volatile compounds as revealed by GC-MS analysis.

A Role of Intestinal Alkaline Phosphatase 3 (Akp3) in Inorganic Phosphate Homeostasis

BACKGROUND/AIMS

Hyperphosphatemia is a serious complication of late-stage chronic kidney disease (CKD). Intestinal inorganic phosphate (Pi) handling plays an important role in Pi homeostasis in CKD. We investigated whether intestinal alkaline phosphatase 3 (Akp3), the enzyme that hydrolyzes dietary Pi compounds, is a target for the treatment of hyperphosphatemia in CKD.

METHODS

We investigated Pi homeostasis in Akp3 knockout mice (Akp3-/-). We also studied the progression of renal failure in an Akp3-/- mouse adenine treated renal failure model. Plasma, fecal, and urinary Pi and Ca concentration were measured with commercially available kit, and plasma fibroblast growth factor 23, parathyroid hormone, and 1,25(OH)2D3 concentration were measured with ELISA. Brush border membrane vesicles were prepared from mouse intestine using the Ca2+ precipitation method and used for Pi transport activity and alkaline phosphatase activity. In vivo intestinal Pi absorption was measured with oral 32P administration.

RESULTS

Akp3-/- mice exhibited reduced intestinal type II sodium-dependent Pi transporter (Npt2b) protein levels and Na-dependent Pi co-transport activity. In addition, plasma active vitamin D levels were significantly increased in Akp3-/- mice compared with wild-type animals. In the adenine-induced renal failure model, Akp3 gene deletion suppressed hyperphosphatemia.

CONCLUSION

The present findings indicate that intestinal Akp3 deletion affects Na+-dependent Pi transport in the small intestine. In the adenine-induced renal failure model, Akp3 is predicted to be a factor contributing to suppression of the plasma Pi concentration.

A bio-image sensor for simultaneous detection of multi-neurotransmitters

We report here a new bio-image sensor for simultaneous detection of spatial and temporal distribution of multi-neurotransmitters. It consists of multiple enzyme-immobilized membranes on a 128 × 128 pixel array with read-out circuit. Apyrase and acetylcholinesterase (AChE), as selective elements, are used to recognize adenosine 5'-triphosphate (ATP) and acetylcholine (ACh), respectively. To enhance the spatial resolution, hydrogen ion (H⁺) diffusion barrier layers are deposited on top of the bio-image sensor and demonstrated their prevention capability. The results are used to design the space among enzyme-immobilized pixels and the null H⁺ sensor to minimize the undesired signal overlap by H⁺ diffusion. Using this bio-image sensor, we can obtain H⁺ diffusion-independent imaging of concentration gradients of ATP and ACh in real-time. The sensing characteristics, such as sensitivity and detection of limit, are determined experimentally. With the proposed bio-image sensor the possibility exists for customizable monitoring of the activities of various neurochemicals by using different kinds of proton-consuming or generating enzymes.

Characterization of ectonucleoside triphosphate diphosphohydrolase (E-NTPDase; EC 3.6.1.5) activity in mouse peritoneal cavity cells

This study aimed to characterize the activity of ectonucleoside triphosphate diphosphohydrolase (E-NTPDase; EC 3.6.1.5) in peritoneal cavity cells from BALB/c mice. E-NTPDase was activated in the presence of both calcium (1.5mM) and magnesium (1.5mM) ions. However, the activity was higher in the presence of Ca²⁺ . A pH of 8.5 and temperature of 37°C were the optimum conditions for catalysis. The apparent Km values were 0.51mM and 0.66mM for the hydrolysis of adenosine triphosphate (ATP) and adenosine diphosphate (ADP), respectively. The Vmax values were 136.4 and 120.8 nmol Pi/min/mg of protein for ATPase and ADPase activity, respectively. Nucleotide hydrolysis was inhibited in the presence of sodium azide (20mM, ATP: P < .05; ADP: P < .001), sodium fluoride (20mM; ATP and ADP: P < .001), and suramin (0.3mM; ATP: P < .01; ADP: P < .05), which is a known profile for NTPDase inhibition. Although all of the diphosphate and triphosphate nucleotides that were tested were hydrolyzed, enzyme activity was increased when adenine nucleotides were used as substrates. Finally, we stress that knowledge of the E-NTPDase catalytic biochemical properties in mouse peritoneal cavity cells is indispensable for properly determining its activity, as well as to fully understand the immune response profile in both healthy and sick cells.

Effects of chlorogenic acid on adenine nucleotides hydrolyzing enzyme activities and expression in platelets of rats experimentally demyelinated with ethidium bromide

BACKGROUND

The effects of chlorogenic acid (one of the major phenolic acid found in human diets) were investigated on the adenine nucleotides hydrolyzing enzymes; ecto-nucleotide pyrophosphatase/phophodiesterase (E-NPP), ecto-nucleoside triphosphate diphosphohydrolase (E-NTPDase), E-5'- nucleotidase and ecto-adenosine deaminase (E-ADA) activities and expression in platelets of rats experimentally demyelinated with ethidium bromide.

METHODS

Rats were divided into four groups of eight animals each. Group I rats were control rats; injected with saline (CT), group II rats were injected with saline and treated with chlorogenic acid (AC), group III rats were injected with 0.1% ethidium bromide (EB) and group IV rats were injected with 0.1% EB and treated with chlorogenic acid (EB+AC). The activities of the enzymes were analyzed using colorimetric methods, and the gene expression of NTPDase 1, 2 and 3 were analyzed using the polymerase chain reaction (PCR).

RESULTS

The results revealed that there was a significant (P<0.01) reduction in E-NPP activity in EB group (1.63±0.10nmol p-nitrophenol released/min/mg protein) when compared to CT group (2.33±0.14nmol p-nitrophenol released/min/mg protein). However, treatment with chlorogenic acid significantly (P<0.05) increased E-NPP activity in EB group. Furthermore, no significant (P>0.05) change was observed in the E-NPP activity of EB+AC group (2.19±0.08nmol p-nitrophenol released/min/mg protein) when compared to CT group (2.33±0.14nmol p-nitrophenol released/min/mg protein). In addition, there was a significant (P<0.05) increase in AMP hydrolysis in EB rat group when compared to CT group. No significant (P>0.05) difference was observed in AMP hydrolysis between AC, AC+EB and CT groups. Conversely, there were no significant (P>0.05) differences in ATP and ADP hydrolyses between all the groups (AC, EB, AC+EB and CT groups). Likewise, there were no significant (P>0.05) changes in E-ADA activity and percentage platelet aggregation among all groups studied. Similarly, no significant (P>0.05) change was observed in the expression of E-NTPDase 1, 2 and 3 in all the groups tested.

CONCLUSIONS

Our study revealed that chlorogenic acid may modulate the hydrolysis of adenine nucleotides in platelets of rats demyelinated and treated with chlorogenic acid via alteration of E-NPP and ecto-5'-nucleotidase activities.

Purinergic signaling and energy homeostasis in psychiatric disorders

Purinergic signaling regulates numerous vital biological processes in the central nervous system (CNS). The two principle purines, ATP and adenosine act as excitatory and inhibitory neurotransmitters, respectively. Compared to other classical neurotransmitters, the role of purinergic signaling in psychiatric disorders is not well understood or appreciated. Because ATP exerts its main effect on energy homeostasis, neuronal function of ATP has been underestimated. Similarly, adenosine is primarily appreciated as a precursor of nucleotide synthesis during active cell growth and division. However, recent findings suggest that purinergic signaling may explain how neuronal activity is associated neuronal energy charge and energy homeostasis, especially in mental disorders. In this review, we provide an overview of the synaptic function of mitochondria and purines in neuromodulation, synaptic plasticity, and neuron-glia interactions. We summarize how mitochondrial and purinergic dysfunction contribute to mental illnesses such as schizophrenia, bipolar disorder, autism spectrum disorder (ASD), depression, and addiction. Finally, we discuss future implications regarding the pharmacological targeting of mitochondrial and purinergic function for the treatment of psychiatric disorders.

Hyperglycemia alters E-NTPDases, ecto-5'-nucleotidase, and ectosolic and cytosolic adenosine deaminase activities and expression from encephala of adult zebrafish (Danio rerio)

Hyperglycemia is the main feature for the diagnosis of diabetes mellitus (DM). Some studies have demonstrated the relationship between DM and dysfunction on neurotransmission systems, such as the purinergic system. In this study, we evaluated the extracellular nucleotide hydrolysis and adenosine deamination activities from encephalic membranes of hyperglycemic zebrafish. A significant decrease in ATP, ADP, and AMP hydrolyses was observed at 111-mM glucose-treated group, which returned to normal levels after 7 days of glucose withdrawal. A significant increase in ecto-adenosine deaminase activity was observed in 111-mM glucose group, which remain elevated after 7 days of glucose withdrawal. The soluble-adenosine deaminase activity was significantly increased just after 7 days of glucose withdrawal. We also evaluated the gene expressions of ecto-nucleoside triphosphate diphosphohydrolases (E-NTPDases), ecto-5'-nucleotidase, ADA, and adenosine receptors from encephala of adult zebrafish. The entpd 2a.1, entpd 2a.2, entpd 3, and entpd 8 mRNA levels from encephala of adult zebrafish were decreased in 111-mM glucose-treated and glucose withdrawal groups. The gene expressions of adenosine receptors (adora 1 , adora 2aa , adora 2ab , and adora 2b ) were decreased in 111-mM glucose-treated and glucose withdrawal groups. The gene expression of ADA (ada 2a.1) was decreased in glucose withdrawal group. Maltodextrin, used as a control, did not affect the expression of adenosine receptors, ADA and E-NTPDases 2, 3, and 8, while the expression of ecto-5'-nucleotidase was slightly increased and the E-NTPDases 1 decreased. These findings demonstrated that hyperglycemia might affect the ecto-nucleotidase and adenosine deaminase activities and gene expression in zebrafish, probably through a mechanism involving the osmotic effect, suggesting that the modifications caused on purinergic system may also contribute to the diabetes-induced progressive cognitive impairment.

Extracellular levels of ATP and acetylcholine during lithium-pilocarpine induced status epilepticus in rats

Acetylcholine (ACh) and ATP are rapidly acting neurotransmitters with a putative role in epileptic seizures. In the present study we investigated extracellular concentrations of both neurotransmitters in parallel by microdialysis in rat hippocampus. We found that infusion of neostigmine increases, while calcium-free perfusion and infusion of tetrodotoxin (TTX) decreases, ACh levels. Calcium-free perfusion also decreased ATP levels which were, however, not affected by neostigmine or TTX. During status epilepticus, ACh levels were increased threefold but returned to baseline after the termination of seizures by diazepam. ATP levels were unchanged during status epilepticus but a several-fold increase was seen when AOPCP, an inhibitor of 5'-endonucleotidase, was infused. The results demonstrate an increase of ATP levels during epileptic seizures which, however, was not of neuronal origin.

Emerging role of P2X7 receptors in CNS health and disease

Purinergic signalling in the brain is becoming an important focus in the study of CNS health and disease. Various purinergic receptors are found to be present in different brain cells in varying extent, which get activated upon binding of ATP or its analogues. Conventionally, ATP was considered only as a major metabolic fuel of the cell but its recognition as a neurotransmitter in early 1970s, brought meaningful insights in neuron glia crosstalk, participating in various physiological functions in the brain. P2X7R, a member of ligand gated purinergic receptor (P2X) family, is gaining attention in the field of neuroscience because of its emerging role in broad spectrum of ageing and age related neurological disorders. The aim of this review is to provide an overview about the structure and function of P2X7R highlighting its unique features which distinguish it from the other members of its family. This review critically analyzes the literature mentioning the details about the agonist and antagonist of the P2X7R. It also emphasizes the advancements in understanding the dual role of P2X7R in brain development and disorders inviting meaningful insights about its involvement in Alzheimer's disease, Huntington's disease, Multiple Sclerosis, Neuropathic pain, Spinal Cord Injury and NeuroAIDS. Exploring the roles of P2X7R in detail is critical to identify its therapeutic potential in the treatment of acute and chronic neurodegenerative diseases. Moreover, this review also helps to raise more interest in the neurobiology of the purinergic receptors and thus providing new avenues for future research.

Intradermal administration of ATP augments methacholine-induced cutaneous vasodilation but not sweating in young males and females

Acetylcholine released from cholinergic nerves is a key neurotransmitter contributing to heat stress-induced cutaneous vasodilation and sweating. Given that sympathetic cholinergic nerves also release ATP, ATP may play an important role in modulating cholinergic cutaneous vasodilation and sweating. However, the pattern of response may differ between males and females given reports of sex-related differences in the peripheral mechanisms governing these heat loss responses. Cutaneous vascular conductance (CVC, laser-Doppler perfusion units/mean arterial pressure) and sweat rate (ventilated capsule) were evaluated in 17 young adults (8 males, 9 females) at four intradermal microdialysis skin sites continuously perfused with: 1) lactated Ringer (Control), 2) 0.3 mM ATP, 3) 3 mM ATP, or 4) 30 mM ATP. At all skin sites, methacholine was coadministered in a concentration-dependent manner (0.0125, 0.25, 5, 100, 2,000 mM, each for 25 min). In both males and females, CVC was elevated with the lone infusion of 30 mM ATP (both P < 0.05), but not with 0.3 and 3 mM ATP compared with control (all P >0.27). However, 0.3 mM ATP induced a greater increase in CVC compared with control in response to 100 mM methacholine infusion in males (P < 0.05). In females, 0.3 mM ATP infusion resulted in a lower concentration of methacholine required to elicit a half-maximal response (EC50) (P < 0.05). In both males and females, methacholine-induced sweating was unaffected by any concentration of ATP (all P > 0.44). We demonstrate that ATP enhances cholinergic cutaneous vasodilation albeit the pattern of response differs between males and females. Furthermore, we show that ATP does not modulate cholinergic sweating.

Menthol inhibits detrusor contractility independently of TRPM8 activation

Agonists such as icilin and menthol can activate the cool temperature-sensitive ion channel TRPM8. However, biological responses to menthol may occur independently of TRPM8 activation. In the rodent urinary bladder, menthol facilitates the micturition reflex but inhibits muscarinic contractions of the detrusor smooth muscle. The site(s) of TRPM8 expression in the bladder are controversial. In this study we investigated the regulation of bladder contractility in vitro by menthol. Bladder strips from wild type and TRPM8 knockout male mice (25–30 g) were dissected free and mounted in organ baths. Isometric contractions to carbachol (1 nM–30 µM), CaCl₂ (1 µM to 100 mM) and electrical field stimulation (EFS; 8, 16, 32 Hz) were measured. Strips from both groups contracted similarly in response to both carbachol and EFS. Menthol (300 µM) or nifedipine (1 µM) inhibited carbachol and EFS-induced contractions in both wild type and TRPM8 knockout bladder strips. Incubation with the sodium channel blocker tetrodotoxin (1 µM), replacement of extracellular sodium with the impermeant cation N-Methyl-D-Glucamine, incubation with a cocktail of potassium channel inhibitors (100 nM charybdotoxin, 1 µM apamin, 10 µM glibenclamide and 1 µM tetraethylammonium) or removal of the urothelium did not affect the inhibitory actions of menthol. Contraction to CaCl₂ was markedly inhibited by either menthol or nifedipine. In cultured bladder smooth muscle cells, menthol or nifedipine abrogated the carbachol or KCl-induced increases in [Ca²⁺]_i. Intravesical administration of menthol increased voiding frequency while decreasing peak voiding pressure. We conclude that menthol inhibits muscarinic bladder contractions through blockade of L-type calcium channels, independently of TRPM8 activation.

Signal transduction: From the atomic age to the post-genomic era

We have come a long way in the 55 years since Edmond Fischer and the late Edwin Krebs discovered that the activity of glycogen phosphorylase is regulated by reversible protein phosphorylation. Many of the fundamental molecular mechanisms that operate in biological signaling have since been characterized and the vast web of interconnected pathways that make up the cellular signaling network has been mapped in considerable detail. Nonetheless, it is important to consider how fast this field is still moving and the issues at the current boundaries of our understanding. One must also appreciate what experimental strategies have allowed us to attain our present level of knowledge. We summarize here some key issues (both conceptual and methodological), raise unresolved questions, discuss potential pitfalls, and highlight areas in which our understanding is still rudimentary. We hope these wide-ranging ruminations will be useful to investigators who carry studies of signal transduction forward during the rest of the 21st century.

Self-built microdialysis probes with improved recoveries of ATP and neuropeptides

BACKGROUND

Microdialysis is an established technique for collecting small molecular weight substances (e.g. neurotransmitter and energy metabolites) from the extracellular space. The major element of microdialysis is the probe which contains a semi-permeable membrane and is exposed to the interstitial space. As the microdialysis technique has major advantages, e.g. versatility and use in awake animals, commercially produced probes are in great demand.

NEW METHOD

We here present the design of a probe assembly step by step which will enable researchers to build custom-made probes. Probe recoveries of substances with different molecular weight (ranging from 100 to 1600 Da) were compared for three different probes (CMA 12 Elite probe, custom-made 10 kDa and 30 kDa probes). Recoveries of glucose, lactate, acetylcholine, choline, ATP and the neuropeptides angiotensin II, substance P and somatostatin are presented.

RESULTS

We found that the 10 kDa probe is only useful for compounds up to 1000 Da while recoveries of the CMA-12 Elite Probe are variable and apparently dependent on ionic charges of analytes. The recovery of the custom-made 30 kDa probe is highest and evidently not influenced by physicochemical parameters of analytes. In a further optimization step, we describe the use of ZipTip(®) μC-18 collection tips to replace the outlet tubing when purifying the dialysate for MALDI-MS measurements of neuropeptides.

COMPARISON WITH EXISTING METHODS

The results show that self-built microdialysis probes can be equally or more effective than commercially available probes.

CONCLUSIONS

Self-built microdialysis probes with large pore-membranes are capable of dialyzing ATP and neuropeptides.

Signalling molecules in the urothelium

The urothelium was long considered to be a silent barrier protecting the body from the toxic effects of urine. However, today a number of dynamic abilities of the urothelium are well recognized, including its ability to act as a sensor of the intravesical environment. During recent years several pathways of these urothelial abilities have been proposed and a major part of these pathways includes release of signalling molecules. It is now evident that the urothelium represents only one part of the sensory web. Urinary bladder signalling is finely tuned machinery of signalling molecules, acting in autocrine and paracrine manner, and their receptors are specifically distributed among different types of cells in the urinary bladder. In the present review the current knowledge of the formation, release, and signalling effects of urothelial acetylcholine, ATP, adenosine, and nitric oxide in health and disease is discussed.

Two new adenosine receptor antagonists for the treatment of Parkinson's disease: istradefylline versus tozadenant

INTRODUCTION

Adenosine A2A receptors are localized in the brain, mainly within the caudate and putamen nuclei of the basal ganglia. Their activation leads to stimulation of the 'indirect' pathway. Conversely, administration of A2A receptor antagonists leads to inhibition of this pathway, which was translated into reduced hypomotility in several animal models of parkinsonism.

AREAS COVERED

In this review, the effects of two A2A receptor antagonists, istradefylline and tozadenant, on parkinsonian symptoms in animal and humans will be discussed.

EXPERT OPINION

Animal studies have shown potent antiparkinsonian effects for several A2A receptor antagonists, including istradefylline. In clinical trials, istradefylline reduced OFF time when administered with levodopa, but results are inconclusive. Results with tozadenant are scarce. Modification of thalamic blood flow compatible with reduced inhibition was noted in one small trial, followed by a significant reduction in OFF time in a larger one. Therefore, both drugs show promising efficacy for the reduction of OFF time in levodopa-treated Parkinson's disease patients, but further research is needed in order to obtain definitive conclusions.

Alterations in the cholinesterase and adenosine deaminase activities and inflammation biomarker levels in patients with multiple sclerosis

Multiple sclerosis (MS) is one of the main chronic inflammatory diseases of the CNS that cause functional disability in young adults. It has unknown etiology characterized by the infiltration of lymphocytes and macrophages into the brain. The aim of this study was to evaluate the acetylcholinesterase (AChE) activity in lymphocytes and whole blood, as well as butyrylcholinesterase (BChE) and adenosine deaminase (ADA) activities in serum. We also checked the levels of nucleotides, nucleosides, biomarkers of inflammation such as cytokines (interleukin (IL)-1, IL-6, interferon (IFN)-γ, tumor necrosis factor-alpha (TNF-α) and IL-10) and C-reactive protein (CRP) in serum from 29 patients with the relapsing-remitting form of MS (RRMS) and 29 healthy subjects as the control group. Results showed that AChE in lymphocytes and whole blood as well as BChE, and ADA activities in serum were significantly increased in RRMS patients when compared to the control group (P<0.05). In addition, we observed a decrease in ATP levels and a significant increase in the levels of ADP, AMP, adenosine and inosine in serum from RRMS patients in relation to the healthy subjects (P<0.05). Results also demonstrated an increase in the IFN-γ, TNF-α, IL-1, IL-6 and CRP (P<0.05) and a significant decrease in the IL-10 (P<0.0001) in RRMS patients when compared to control. Our results suggest that alterations in the biomarkers of inflammation and hydrolysis of nucleotides and nucleosides may contribute to the understanding of the neurological dysfunction of RRMS patients.

Contractile responses of urinary bladder in an experimental model of chronic renal failure

Chronic kidney disease is a public health problem with increasing prevalence caused by diabetes, hypertension and glomerulonephritis. Number of publications investigate the lower urinary tract dysfunction due to CKD is limited. There is a high incidence of bladder dysfunction of different degrees in patients with renal failure. Mechanism of the lower urinary tract dysfunction in these patients is not well known. In this study, we aimed to investigate the effects of CKD on detrusor function in a rat model of CKD. In our study, 20 Wistar Albino rats have been divided into two groups as CKD and control groups. To the experiment group, left partial nephrectomy and right nephrectomy have been applied. CKD confirmation has done with the BUN and creatinin values from the blood of the rats. The bladder strips were prepared from the CKD and control groups and its contractile responses were evaluated in-vitro. There wasn't a considerable difference with the contractile responses caused by carbachol, KCL. There was a considerable increase in the contractile responses caused by ATP, ADP and electrical field stimulation on the behalf of the CKD group. The present study demonstrated that isolated DSM of CKD group showed significantly increased contraction responses to purinergic agonists ADP, ATP and atropine resistant component in electrical field stimulation-induced contractions as compared to those of the control group. Bladder overactivity and reduced bladder volume in CKD patients might be due to the change in purinergic system.

Ectoenzymes and cholinesterase activity and biomarkers of oxidative stress in patients with lung cancer

We aimed to examine the nucleoside triphosphate diphosphohydrolases (NTPDase) in lymphocytes; adenosine deaminase (ADA) and butyrylcholinesterase (BChE) in serum; and acetylcholinesterase (AChE), superoxide dismutase (SOD), and catalase (CAT) activity in whole blood; since these enzymes are involved in inflammation responses as well as in oxidative stress conditions. We also checked the levels of total thiols (T-SH), non-protein thiols (NPSH), and thiobarbituric acid reactive substances (TBARS) in serum of patients with lung cancer. We collected blood samples from patients (n = 31) previously treated for lung cancer with chemotherapy. Patients were classified as stage IIIb and IV according to the Union for International Cancer Control (UICC). The results showed a significant increase in the hydrolysis of ATP, ADP, and adenosine in patients when compared with the control group. The activity of AChE, SOD, and CAT as well as the T-SH and NPSH levels were higher in patients group and TBARS levels were lower in patients compared with the control group. These findings demonstrated that the enzymes activity involved in the control of inflammatory and immune processes as well as the oxidative stress parameters are altered in patients with lung cancer.

Arginine exposure alters ectonucleotidase activities and morphology of zebrafish larvae (Danio rerio)

Hyperargininemia is an inborn error of metabolism (IEM) characterized by tissue accumulation of arginine (Arg). Mental retardation and other neurological features are common symptoms in hyperargininemic patients. Considering purinergic signaling has a crucial role from the early stages of development and underlying mechanisms of this disease are poorly established, we investigated the effect of Arg administration on locomotor activity, morphological alterations, and extracellular nucleotide hydrolysis in larvae and adult zebrafish. We showed that 0.1 mM Arg was unable to promote changes in locomotor activity. In addition, 7-day-post-fertilization (dpf) larvae treated with Arg demonstrated a decreased body size. Arg exposure (0.1 mM) promoted an increase in ATP, ADP, and AMP hydrolysis when compared to control group. These findings demonstrated that Arg might affect morphological parameters and ectonucleotidase activities in zebrafish larvae, suggesting that purinergic system is a target for neurotoxic effects induced by Arg.

Cellular function and molecular structure of ecto-nucleotidases

Ecto-nucleotidases play a pivotal role in purinergic signal transmission. They hydrolyze extracellular nucleotides and thus can control their availability at purinergic P2 receptors. They generate extracellular nucleosides for cellular reuptake and salvage via nucleoside transporters of the plasma membrane. The extracellular adenosine formed acts as an agonist of purinergic P1 receptors. They also can produce and hydrolyze extracellular inorganic pyrophosphate that is of major relevance in the control of bone mineralization. This review discusses and compares four major groups of ecto-nucleotidases: the ecto-nucleoside triphosphate diphosphohydrolases, ecto-5'-nucleotidase, ecto-nucleotide pyrophosphatase/phosphodiesterases, and alkaline phosphatases. Only recently and based on crystal structures, detailed information regarding the spatial structures and catalytic mechanisms has become available for members of these four ecto-nucleotidase families. This permits detailed predictions of their catalytic mechanisms and a comparison between the individual enzyme groups. The review focuses on the principal biochemical, cell biological, catalytic, and structural properties of the enzymes and provides brief reference to tissue distribution, and physiological and pathophysiological functions.

Vesicular and conductive mechanisms of nucleotide release

Extracellular nucleotides and nucleosides promote a vast range of physiological responses, via activation of cell surface purinergic receptors. Virtually all tissues and cell types exhibit regulated release of ATP, which, in many cases, is accompanied by the release of uridine nucleotides. Given the relevance of extracellular nucleotide/nucleoside-evoked responses, understanding how ATP and other nucleotides are released from cells is an important physiological question. By facilitating the entry of cytosolic nucleotides into the secretory pathway, recently identified vesicular nucleotide and nucleotide-sugar transporters contribute to the exocytotic release of ATP and UDP-sugars not only from endocrine/exocrine tissues, but also from cell types in which secretory granules have not been biochemically characterized. In addition, plasma membrane connexin hemichannels, pannexin channels, and less-well molecularly defined ATP conducting anion channels have been shown to contribute to the release of ATP (and UTP) under a variety of conditions.

ATP synthesis and storage

Since 1929, when it was discovered that ATP is a substrate for muscle contraction, the knowledge about this purine nucleotide has been greatly expanded. Many aspects of cell metabolism revolve around ATP production and consumption. It is important to understand the concepts of glucose and oxygen consumption in aerobic and anaerobic life and to link bioenergetics with the vast amount of reactions occurring within cells. ATP is universally seen as the energy exchange factor that connects anabolism and catabolism but also fuels processes such as motile contraction, phosphorylations, and active transport. It is also a signalling molecule in the purinergic signalling mechanisms. In this review, we will discuss all the main mechanisms of ATP production linked to ADP phosphorylation as well the regulation of these mechanisms during stress conditions and in connection with calcium signalling events. Recent advances regarding ATP storage and its special significance for purinergic signalling will also be reviewed.

Release, neuronal effects and removal of extracellular β-nicotinamide adenine dinucleotide (β-NAD⁺) in the rat brain

Recent evidence supports an emerging role of β-nicotinamide adenine dinucleotide (β-NAD(+) ) as a novel neurotransmitter and neuromodulator in the peripheral nervous system -β-NAD(+) is released in nerve-smooth muscle preparations and adrenal chromaffin cells in a manner characteristic of a neurotransmitter. It is currently unclear whether this holds true for the CNS. Using a small-chamber superfusion assay and high-sensitivity high-pressure liquid chromatography techniques, we demonstrate that high-K(+) stimulation of rat forebrain synaptosomes evokes overflow of β-NAD(+) , adenosine 5'-triphosphate, and their metabolites adenosine 5'-diphosphate (ADP), adenosine 5'-monophosphate, adenosine, ADP-ribose (ADPR) and cyclic ADPR. The high-K(+) -evoked overflow of β-NAD(+) is attenuated by cleavage of SNAP-25 with botulinum neurotoxin A, by inhibition of N-type voltage-dependent Ca(2+) channels with ω-conotoxin GVIA, and by inhibition of the proton gradient of synaptic vesicles with bafilomycin A1, suggesting that β-NAD(+) is likely released via vesicle exocytosis. Western analysis demonstrates that CD38, a multifunctional protein that metabolizes β-NAD(+) , is present on synaptosomal membranes and in the cytosol. Intact synaptosomes degrade β-NAD(+) . 1,N (6) -etheno-NAD, a fluorescent analog of β-NAD(+) , is taken by synaptosomes and this uptake is attenuated by authentic β-NAD(+) , but not by the connexin 43 inhibitor Gap 27. In cortical neurons local applications of β-NAD(+) cause rapid Ca(2+) transients, likely due to influx of extracellular Ca(2+) . Therefore, rat brain synaptosomes can actively release, degrade and uptake β-NAD(+) , and β-NAD(+) can stimulate postsynaptic neurons, all criteria needed for a substance to be considered a candidate neurotransmitter in the brain.

The effect of curcumin in the ectonucleotidases and acetylcholinesterase activities in synaptosomes from the cerebral cortex of cigarette smoke-exposed rats

With the evidence that curcumin may be a potent neuroprotective agent and that cigarette smoke is associated with a decline in the cognitive performance as our bases, we investigated the activities of Ecto-Nucleoside Triphosphate Diphosphohydrolase (NTPDase), 5'-nucleotidase and acetylcholinesterase (AChE) in cerebral cortex synaptosomes from cigarette smoke-exposed rats treated with curcumin (Cur). The experimental procedures entailed two sets of experiments. In the first set, the groups were vehicle, Cur 12·5, 25 and 50 mg·kg(-1) ; those in the second set were vehicle, smoke, smoke and Cur 12·5, 25 and 50 mg·kg(-1) . Curcumin prevented the increased NTPDase, 5'-nucleotidase and AChE activities caused by smoke exposure. We suggest that treatment with Cur was protective because the decrease of ATP and acetylcholine (ACh) concentrations is responsible for cognitive impairment, and both ATP and ACh have key roles in neurotransmission.

Investigation of neurogenic excitatory and inhibitory motor responses and their control by 5-HT(4) receptors in circular smooth muscle of pig descending colon

The aim of this study was to investigate whether the pig colon descendens might be a good model for the responses mediated via the different locations of human colonic 5-HT(4) receptors. The intrinsic excitatory and inhibitory motor neurotransmission in pig colon descendens was therefore first characterized. In circular smooth muscle strips, electrical field stimulation (EFS) at basal tone induced only in the combined presence of the NO synthase inhibitor N(ω)-nitro-L-arginine methyl ester hydrochloride (L-NAME) and the SK channel blocker apamin voltage-dependent on-contractions. These on-contractions were largely reduced by the neuronal conductance blocker tetrodotoxin (TTX) and by the muscarinic receptor antagonist atropine, illustrating activation of cholinergic neurons. The 5-HT(4) receptor agonist prucalopride facilitated submaximal EFS-evoked cholinergic contractions and this effect was prevented by the 5-HT(4) receptor antagonist GR113808, supporting the presence of facilitating 5-HT(4) receptors on the cholinergic nerve endings innervating circular muscle in pig colon descendens. Relaxations were induced by EFS in strips pre-contracted with substance P in the presence of atropine. The responses at lower stimulation voltages were abolished by TTX. L-NAME or apamin alone did not influence or only moderately reduced the relaxations, but L-NAME plus apamin abolished the relaxations at lower stimulation voltages, suggesting that NO and ATP act as inhibitory neurotransmitters in a redundant way. Prucalopride did not influence the EFS-induced relaxations at lower stimulation voltage, nor did it per se relax contracted circular muscle strips. No evidence for relaxing 5-HT(4) receptors, either on inhibitory neurons or on the muscle cells was thus obtained in pig colon descendens circular muscle.

Purinergic signalling in epithelial ion transport: regulation of secretion and absorption

Intracellular ATP, the energy source for many reactions, is crucial for the activity of plasma membrane pumps and, thus, for the maintenance of transmembrane ion gradients. Nevertheless, ATP and other nucleotides/nucleosides are also extracellular molecules that regulate diverse cellular functions, including ion transport. In this review, I will first introduce the main components of the extracellular ATP signalling, which have become known as the purinergic signalling system. With more than 50 components or processes, just at cell membranes, it ranks as one of the most versatile signalling systems. This multitude of system components may enable differentiated regulation of diverse epithelial functions. As epithelia probably face the widest variety of potential ATP-releasing stimuli, a special attention will be given to stimuli and mechanisms of ATP release with a focus on exocytosis. Subsequently, I will consider membrane transport of major ions (Cl(-) , HCO(3)(-) , K(+) and Na(+) ) and integrate possible regulatory functions of P2Y2, P2Y4, P2Y6, P2Y11, P2X4, P2X7 and adenosine receptors in some selected epithelia at the cellular level. Some purinergic receptors have noteworthy roles. For example, many studies to date indicate that the P2Y2 receptor is one common denominator in regulating ion channels on both the luminal and basolateral membranes of both secretory and absorptive epithelia. In exocrine glands though, P2X4 and P2X7 receptors act as cation channels and, possibly, as co-regulators of secretion. On an organ level, both receptor types can exert physiological functions and together with other partners in the purinergic signalling, integrated models for epithelial secretion and absorption are emerging.

Chronic ethanol treatment alters purine nucleotide hydrolysis and nucleotidase gene expression pattern in zebrafish brain

Ethanol is a widely consumed drug that acts on the central nervous system (CNS), modifying several signal transduction pathways activated by hormones and neurotransmitters. The zebrafish is an experimental model for the study of human diseases and the use of this species in biochemical and behavioral studies on alcoholism and alcohol-dependence has increased recently. However, there are no data concerning the effects of chronic ethanol exposure on the purinergic system, where extracellular nucleotides act as signaling molecules. Purinergic signaling is controlled by a group of enzymes named ectonucleotidases, which include NTPDases and ecto-5'-nucleotidase already characterized in zebrafish brain. The aim of this study was to evaluate nucleotide hydrolysis by NTPDases and ecto-5'-nucleotidase after long-term ethanol exposure. Additionally, the gene expression patterns of NTPDases1-3 and 5'-nucleotidase were determined. Animals were exposed to 0.5% ethanol for 7, 14, and 28 days. There were no significant changes in ATP and GTP hydrolysis after all treatments. However, a decrease in ADP (46% and 34%) and GDP (48% and 36%) hydrolysis was verified after 7 and 14 days, respectively. After 7 and 14 days of ethanol exposure, a significant decrease in AMP hydrolysis (48% and 36%) was also observed, whereas GMP hydrolysis was inhibited only after 7 days (46%). NTPDase2_mv and NTPDase3 mRNA transcript levels decreased after 7 and 14 days, respectively. In contrast, ethanol increased NTPDase1, NTPDase2_mq, and NTPDase3 transcript levels after 28 days of exposure. NTPDase2_mg and 5'-nucleotidase gene expression was not altered. Therefore, the ectonucleotidase pathway may be a target of chronic ethanol toxicity and the regulation of purinergic system could play a key role in the neurochemical mechanisms underlying the effects of ethanol on the CNS.

Characterization of the urinary bladder dysfunction in renovascular hypertensive rats

AIMS

Association between arterial hypertension and urinary bladder dysfunction has been reported in humans and spontaneously hypertensive rats. However, no study exists evaluating the bladder dysfunction in conditions of renovascular hypertension. The purpose of this study was to characterize the bladder dysfunction in two kidney-one clip (2K-1C) hypertensive rats.

METHODS

A silver clip was placed around the renal artery of male Wistar rats. After 8 weeks, cystometric study, concentration-response curves to contractile and relaxant agents, frequency-dependent contractions, histomorphometry, muscarinic M(2) /M(3) mRNA expression and cyclic AMP measurements were performed.

RESULTS

2K-1C rats showed enhanced bladder volume, wall thickness and smooth muscle density. 2K-1C rats also exhibited increases in bladder capacity and non-void contractions, and decreases in the inter-contraction intervals. In isolated detrusor smooth muscle (DSM), contractions to carbachol and electrical-field stimulation (EFS) were significantly greater in 2K-1C rats. The Rho-kinase inhibitor Y27632 (10 µM) significantly reduced the carbachol-induced contractions in SHAM and 2K-1C rats, but DSM remained overactive in 2K-1C rats in presence of Y27632. Concentration-dependent contractions to the P2X receptor agonist α,β-methylene ATP, KCl and extracellular Ca(2+) did not change between SHAM and 2K-1C groups. In 2K-1C rats, isoproterenol, metaproterenol and BRL 37-344 (non-selective, β(2) - and β(3) -selective adrenoceptor agonists, respectively) produced significantly lower relaxations and decreased cAMP levels, whereas relaxant responses to sodium nitroprusside and BAY 41-2272 remained unchanged. Muscarinic M(3) mRNA expression receptors were higher in 2K-1C group.

CONCLUSIONS

Renovascular hypertensive rats exhibit bladder dysfunction that involves tissue remodeling and enhanced muscarinic M(3) -mediated contractions associated with reduced β-adrenoceptor-mediated signal transduction.

A method for isolation of rat lymphocyte-rich mononuclear cells from lung tissue useful for determination of nucleoside triphosphate diphosphohydrolase activity

Methods for the isolation of peripheral blood mononuclear cells (PBMCs) and human lung mononuclear cells (LMCs) have been proposed previously. This study describes a method that allows the separation of lymphocyte-rich LMCs from rats. Trypan blue was applied to determine cell viability. White blood cell and differential cell counts were also performed. Relationships between nucleoside triphosphate diphosphohydrolase (NTPDase, EC 3.6.1.5) activities expressed in milligrams of protein, millions of cells, and millions of viable cells were examined as linear correlations. The lung tissue yielded 82.46% lymphocytes, 8.6% macrophages, 2.20% monocytes, and 1.27% polymorphonuclear cells (PMNs). In LMCs, a very strong correlation was observed as follows: between NTPDase activity, as determined using ATP or ADP as a substrate, expressed in milligrams of protein and that expressed in millions of cells (r ≥ 0.91), between that expressed in milligrams of protein and that expressed in millions of viable cells (r ≥ 0.91), and between that expressed in millions of cells and that expressed in millions of viable cells (r ≥ 0.98). Based on our results, we affirm that NTPDase activity could be expressed in millions of viable cells, millions of cells, or milligrams of protein.

Beyond the wiring diagram: signalling through complex neuromodulator networks

During the computations performed by the nervous system, its 'wiring diagram'--the map of its neurons and synaptic connections--is dynamically modified and supplemented by multiple actions of neuromodulators that can be so complex that they can be thought of as constituting a biochemical network that combines with the neuronal network to perform the computation. Thus, the neuronal wiring diagram alone is not sufficient to specify, and permit us to understand, the computation that underlies behaviour. Here I review how such modulatory networks operate, the problems that their existence poses for the experimental study and conceptual understanding of the computations performed by the nervous system, and how these problems may perhaps be solved and the computations understood by considering the structural and functional 'logic' of the modulatory networks.

Excitatory cholinergic and purinergic signaling in bladder are equally susceptible to botulinum neurotoxin a consistent with co-release of transmitters from efferent fibers

Mediators of neuromuscular transmission in rat bladder strips were dissected pharmacologically to examine their susceptibilities to inhibition by botulinum neurotoxins (BoNTs) and elucidate a basis for the clinical effectiveness of BoNT/A in alleviating smooth muscle spasms associated with overactive bladder. BoNT/A, BoNT/C1, or BoNT/E reduced peak and average force of muscle contractions induced by electric field stimulation (EFS) in dose-dependent manners by acting only on neurogenic, tetrodotoxin-sensitive responses. BoNTs that cleaved vesicle-associated membrane protein proved to be much less effective. Acetylcholine (ACh) and ATP were found to provide virtually all excitatory input, because EFS-evoked contractions were abolished by the muscarinic receptor antagonist, atropine, combined with either a desensitizing agonist of P2X(1) and P2X(3) or a nonselective ATP receptor antagonist. Both transmitters were released in the innervated muscle layer and, thus, persisted after removal of urothelium. Atropine or a desensitizer of the P2X(1) or P2X(3) receptors did not alter the rate at which muscle contractions were weakened by BoNT/A. Moreover, although cholinergic and purinergic signaling could be partially delineated by using high-frequency EFS (which intensified a transient, largely atropine-resistant spike in muscle contractions that was reduced after P2X receptor desensitization), they proved equally susceptible to BoNT/A. Thus, equi-potent blockade of ATP co-released with ACh from muscle efferents probably contributes to the effectiveness of BoNT/A in treating bladder overactivity, including nonresponders to anticholinergic drugs. Because purinergic receptors are known mediators of sensory afferent excitation, inhibition of efferent ATP release by BoNT/A could also help to ameliorate acute pain and urgency sensation reported by some recipients.