The P2Y12 receptor regulates microglial activation by extracellular nucleotides

Microglia are primary immune sentinels of the CNS. Following injury, these cells migrate or extend processes toward sites of tissue damage. CNS injury is accompanied by release of nucleotides, serving as signals for microglial activation or chemotaxis. Microglia express several purinoceptors, including a G(i)-coupled subtype that has been implicated in ATP- and ADP-mediated migration in vitro. Here we show that microglia from mice lacking G(i)-coupled P2Y(12) receptors exhibit normal baseline motility but are unable to polarize, migrate or extend processes toward nucleotides in vitro or in vivo. Microglia in P2ry(12)(-/-) mice show significantly diminished directional branch extension toward sites of cortical damage in the living mouse. Moreover, P2Y(12) expression is robust in the 'resting' state, but dramatically reduced after microglial activation. These results imply that P2Y(12) is a primary site at which nucleotides act to induce microglial chemotaxis at early stages of the response to local CNS injury.

Platelet-collagen interaction: is GPVI the central receptor?

At sites of vascular injury, platelets come into contact with subendothelial collagen, which triggers their activation and the formation of a hemostatic plug. Besides glycoprotein Ib (GPIb) and alphaIIbbeta3 integrin, which indirectly interact with collagen via von Willebrand factor (VWF), several collagen receptors have been identified on platelets, most notably alpha2beta1 integrin and the immunoglobulin (Ig) superfamily member GPVI. Within the last few years, major advances have been made in understanding platelet-collagen interactions including the molecular cloning of GPVI, the generation of mouse strains lacking individual collagen receptors, and the development of collagen receptor-specific antibodies and synthetic peptides. It is now recognized that platelet adhesion to collagen requires prior activation of integrins through "inside-out" signals generated by GPVI and reinforced by released second-wave mediators adenosine diphosphate (ADP) and thromboxane A2. These developments have led to revision of the original "2-site, 2-step" model, which now places GPVI in a central position in the complex processes of platelet tethering, activation, adhesion, aggregation, degranulation, and procoagulant activity on collagen. This review discusses these recent developments and proposes possible mechanisms for how GPVI acts in concert with other receptors and signaling pathways to initiate hemostasis and arterial thrombosis.

Membrane potential of mitochondria measured with an electrode sensitive to tetraphenyl phosphonium and relationship between proton electrochemical potential and phosphorylation potential in steady state

The membrane potential of mitochondria was estimated from the accumulation of tetraphenyl phosphonium (TPP+), which was determined with the TPP+-selective electrode developed in the present study. The preparation and some operational parameters of the electrode were described. The kinetics for uptake by mitochondria of TPP+ and DDA+ (dibenzyldimethyl ammonium) were analyzed, and it was found that TPP+ permeated the mitochondrial membrane about 15 times faster than DDA+. The final amounts of accumulation of TPP+ and DDA+ by mitochondria were approximately equal. For the state-4 mitochondria, the membrane potential was about 180 mV (interior negative). Simultaneous measurements of TPP+-uptake and oxygen consumption showed that the transition between states 3 and 4 was detectable by use of the TPP+-electrode. After the TPP+-electrode showed that state-4 was reached, the extra-mitochondrial phosphorylation potential was measured. The difference in pH across the membrane was measured from the distribution of permeant anion, acetate, so as to calculate the proton electrochemical potential. The ratio of extra-mitochondrial phosphorylation potential to proton electro-chemical potential, n was close to 3. This value of n was also found to be 3 when ATP was hydrolyzed under the condition that the respiratory chain was arrested. The implication that n = 3 was discussed.

Purinergic signalling: pathophysiological roles

In this review, after a summary of the history and current status of the receptors involved in purinergic signalling, we focus on the distribution and physiological roles of purines and pyrimidines in both short-term events such as neurotransmission, exocrine and endocrine secretion and regulation of immune cell function, and long-term events such as cell growth, differentiation and proliferation in development and regeneration. Finally, the protective roles of nucleosides and nucleotides in events such as cancer, ischemia, wound healing, drug toxicity, inflammation and pain are explored and some suggestions made for future developments in this rapidly expanding field, with particular emphasis on the involvement of selective agonists and antagonists for purinergic receptor subtypes in therapeutic strategies.

Ticlopidine and clopidogrel

The thienopyridines ticlopidine and clopidogrel are inhibitors of platelet function in vivo. Their mode of action has not been defined, but it appears that they require conversion to as yet unidentified metabolites that are noncompetitive antagonists of the platelet ADP receptor. Inhibition of platelet aggregation with these compounds is delayed until 24 to 48 hours after administration. Maximum inhibition occurs after 3 to 5 days, and recovery is slow after drug withdrawal. Ticlopidine is effective in preventing cardiovascular events in cerebrovascular, cardiovascular, and peripheral vascular disease, with an efficacy that is similar to aspirin. However, its use is associated with significant and sometimes fatal adverse reactions, specifically neutropenia and bone marrow aplasia. Gastrointestinal side effects and skin rashes are common and result in discontinuation of therapy in up to 10% of patients. Clopidogrel is at least as effective as aspirin in preventing cardiovascular events in patients with a history of vascular disease. It appears to be safer than ticlopidine, although its efficacy in acute coronary syndromes or post-coronary-stent insertion has not been reported. Important outstanding issues are whether clopidogrel adds to the benefit of aspirin and whether the combination of these agents is safe. If so, this combination may become the standard for antithrombotic therapy in cardiovascular disease.

Purinergic signaling and vascular cell proliferation and death

Evidence for the role of purinergic signaling (via P1 and P2Y receptors) in the proliferation of vascular smooth muscle and endothelial cells is reviewed. The involvement of the mitogen-activated protein kinase second-messenger cascade in this action is clearly implicated, although details of the precise intracellular pathways involved still remain to be determined. Synergistic actions of purines and pyrimidines with growth factors occur in promoting cell proliferation. Interaction between purinergic signaling for vascular cell proliferation and cell death mediated by P2X7 receptors is discussed. There is evidence of the release of ATP from endothelial cells, platelets, and sympathetic nerves as well as from damaged cells in atherosclerosis, hypertension, restenosis, and ischemia; furthermore, there is evidence that vascular smooth muscle and endothelial cells proliferate in these pathological conditions. Thus, the involvement of ATP and its breakdown product, adenosine, is implicated; it is hoped that with the development of selective P1 (A2) and P2Y receptor agonists and antagonists, new therapeutic strategies will be explored.

A dual function for adenosine 5'-triphosphate in the regulation of vascular tone. Excitatory cotransmitter with noradrenaline from perivascular nerves and locally released inhibitory intravascular agent

A dual function for adenosine 5'-triphosphate in the regulation of vascular tone is considered. Adenosine 5'-triphosphate can cause vasodilation, acting via P2-purinoceptors located on vascular endothelial cells to release an endothelium-derived relaxing factor which diffuses to the vascular smooth muscle and induces vasodilation. The main source of intraluminal adenosine 5'-triphosphate is likely to be endothelial cells, and its release can be measured during pathophysiological conditions such as ischemia and hypoxia, in amounts likely to be sufficient to activate endothelial P2-purinoceptors. Adenosine 5'-triphosphate can also be released during intravascular platelet aggregation and from intact and damaged vascular smooth muscle cells, and so may play a role in the complex physiological mechanisms controlling local vascular tone under normoxic conditions and during vessel injury. Evidence is also presented for adenosine 5'-triphosphate acting as an excitatory cotransmitter with noradrenaline from sympathetic perivascular nerves, to cause vasoconstriction via excitatory P2-purinoceptors located on vascular smooth muscle. The postjunctional mechanical and electrical responses of a number of blood vessels following perivascular nerve stimulation contain a component that is resistant to blockade of the alpha-adrenoceptor. This nonadrenergic response is mimicked by adenosine 5'-triphosphate and can be blocked by selective desensitization of the P2-purinoceptor by alpha,beta-methylene adenosine 5'-triphosphate. Vesicular storage of adenosine 5'-triphosphate and its release from sympathetic perivascular nerves has also been demonstrated. The functional significance of adenosine 5'-triphosphate acting intraluminally as a vasodilator and extraluminally as a vasoconstrictor neuronal agent in the control of vascular tone is discussed.

Switch-based mechanism of kinesin motors

Kinesin motors are specialized enzymes that use hydrolysis of ATP to generate force and movement along their cellular tracks, the microtubules. Although numerous biochemical and biophysical studies have accumulated much data that link microtubule-assisted ATP hydrolysis to kinesin motion, the structural view of kinesin movement remains unclear. This study of the monomeric kinesin motor KIF1A combines X-ray crystallography and cryo-electron microscopy, and allows analysis of force-generating conformational changes at atomic resolution. The motor is revealed in its two functionally critical states-complexed with ADP and with a non-hydrolysable analogue of ATP. The conformational change observed between the ADP-bound and the ATP-like structures of the KIF1A catalytic core is modular, extends to all kinesins and is similar to the conformational change used by myosin motors and G proteins. Docking of the ADP-bound and ATP-like crystallographic models of KIF1A into the corresponding cryo-electron microscopy maps suggests a rationale for the plus-end directional bias associated with the kinesin catalytic core.

Residual arachidonic acid-induced platelet activation via an adenosine diphosphate-dependent but cyclooxygenase-1- and cyclooxygenase-2-independent pathway: a 700-patient study of aspirin resistance

BACKGROUND

Thrombotic events still occur in aspirin-treated patients with coronary artery disease.

METHODS AND RESULTS

To better understand aspirin "resistance," serum thromboxane B2 (TXB2) and flow cytometric measures of arachidonic acid-induced platelet activation (before and after the ex vivo addition of aspirin and indomethacin) were analyzed in 700 consecutive aspirin-treated patients undergoing cardiac catheterization. In 680 of 682 evaluable patients, serum TXB2 concentrations were reduced compared with nonaspirinated healthy donors. Twelve patients had serum TXB2 that was lower than nonaspirinated healthy donors but >10 ng/mL. Arachidonic acid stimulated greater platelet activation in patients with high serum TXB2 (>10 ng/mL) than in patients with low serum TXB2. Addition of ex vivo aspirin reduced arachidonic acid-induced platelet activation to similar levels regardless of serum TXB2 concentrations, which suggests that patients with high residual serum TXB2 concentrations were either noncompliant or underdosed with aspirin. Among the remaining 98% of patients, ex vivo administration of either aspirin or indomethacin failed to prevent platelet activation across all degrees of arachidonic acid-induced platelet activation and aspirin doses. Although the patients were not randomized with respect to clopidogrel treatment, multivariate analysis showed that arachidonic acid-induced platelet activation was less in patients receiving clopidogrel.

CONCLUSIONS

There is a residual arachidonic acid-induced platelet activation in aspirin-treated patients that (1) is caused by underdosing and/or noncompliance in only approximately 2% of patients and (2) in the remaining patients, occurs via a cyclooxygenase-1 and cyclooxygenase-2 independent pathway, in direct proportion to the degree of baseline platelet activation, and is mediated in part by adenosine diphosphate-induced platelet activation.

Oxidant, mitochondria and calcium: an overview

Mitochondria are active in the continuous generation of reactive oxygen species (ROS), (e.g., superoxide), thereby favouring a situation of mitochondrial oxidative stress. Under oxidative stress--for example, ischaemia-reoxygenation injury to cells--mitochondria form superoxide, which in turn is converted to hydrogen peroxide and the potent reactive species, hydroxyl radical. Alternatively, mitochondrial superoxide may react with nitric oxide to form potent oxidant peroxynitrite and as a consequence, mitochondrial function is altered. An increase in the release of calcium from mitochondria by oxidants stimulates calcium-dependent enzymes such as calcium-dependent proteases, nucleases, and phospholipases, which subsequently trigger apoptosis of the cells. In principle, calcium can leave mitochondria by different ways: by non-specific leakage through the inner membrane by "pore formation," by changes in the membrane lipid phase, by reversal of the uniport influx carrier, by the specific calcium/hydrogen (or sodium) antiport system, by channel-mediated release pathways, or by a combination of two or more of these pathways. Additionally, the release of calcium from mitochondria can also occur either by oxidation of internal nicotinamide adenine nucleotides to ADP ribose and nicotinamide or by oxidation of thiols in membrane proteins. Once calcium efflux has been triggered, a series of common pathways of apoptosis are initiated, each of which may be sufficient to destroy the cell. Apoptosis requires the active participation of cellular components, and several genes have been suggested to control apoptosis. The proto-oncogene bcl-2 suppresses apoptosis through mitochondrial effects. Overexpression of bcl-2 in the mitochondrial membrane inhibits calcium efflux, but the underlying mechanisms are not clearly known. Further studies are needed to explore the nature of the apoptosis-inducing pathways, the precise mechanisms of calcium efflux, the molecular partners of bcl-2 oncoproteins at the level of the outer-inner membrane contact sites, the molecular biology of the apoptosis-inducing factor formation and release, and the essential molecular targets of apoptosis-inducing proteases. Clarification of these issues might facilitate the understanding of mitochondrial response on cellular calcium dynamics under oxidant stress.

A model of crossbridge action: the effects of ATP, ADP and Pi

We have explored a model of crossbridge kinetics that explains many of the effects on steady-state muscle contraction of ligands that bind to the nucleotide site on myosin. The mathematical model follows the basic framework for crossbridge function first established by A. F. Huxley. In the model, detached crossbridges initially bind in a weakly attached, A.M.D.Pi state (A, actin; M, myosin; D, ADP; Pi, orthophosphate) at the beginning of the region of positive force production. Pi release then results in transition to a strongly-bound A.M.D state, as has been suggested by other investigators from both biochemical and mechanical data. Mg2+ ADP release and subsequent crossbridge detachment due to Mg2+ ATP binding to the A.M state occur at the end of the region of positive force production. Work in a number of laboratories has now defined the effects on steady-state contraction of variations in the concentrations of Mg2+ ATP, Mg2+ ADP and Pi. These data provide valuable constraints that can be used to further refine current models. The maximum velocity of shortening (V max) and ATPase activity of muscle fibres exhibit classical saturation behaviour with respect to Mg2+ ATP concentration, with Mg2+ ADP acting as a competitive inhibitor. The model can reproduce this behaviour. The model also explains the observations that increasing [Mg2+ ATP] decreases isometric tension and increasing [Mg2+ ADP] increases tension. As the concentration of Pi increases, model predictions suggest that tension should decrease approximately as log[Pi], that ATPase activity should decrease less than tension and that V max should be almost unchanged, as has been found experimentally. The model also demonstrates that the connection between the parameters of contraction and the free energy of hydrolysis of Mg2+ ATP can be complex.

Respiratory control and the integration of heart high-energy phosphate metabolism by mitochondrial creatine kinase

This review has attempted to integrate three areas of cellular bioenergetics to present a novel and comprehensive view of heart high-energy phosphate metabolism. The goal has been to provide a rational view for the functions of phosphocreatine, creatine, and creatine kinase in the energy metabolism of muscle. The first point is that mitochondrial respiratory control is influenced by changes in the concentration of ADP, stimulating the adenine nucleotide translocase and oxidative phosphorylation. Secondly, as a consequence of the proximity of mitochondrial creatine kinase to the translocase, there appears to be a kinetic preference for ADP generated by the forward creatine kinase reaction. As a result, in heart, it can be viewed that the end product of oxidative phosphorylation is phosphocreatine. Finally, thermodynamic considerations suggest that phosphocreatine plays a major role to maintain or buffer the ATP content of the myocardium. Under conditions of increased ATP turnover, large-scale increases in the concentration of ADP, along with major decreases in ATP, are minimized by the creatine kinase equilibrium. The system responds to such a demand with substantial changes in phosphocreatine and creatine, which can kinetically increase the rate of mitochondrial creatine kinase and thus oxidative phosphorylation. Theoretical enzymologists have long argued whether enzymes are under kinetic or thermodynamic control. Heart creatine kinase may be a unique example where both types of control simultaneously operate in different microenvironments, with mitochondrial creatine kinase kinetically controlled, while the sarcoplasmic isozyme is influenced by equilibrium thermodynamics. Overall, heart creatine kinase may be a unique example of "kineto-dynamic" metabolic integration.

The ATP-sensitivity of K+ channels in rat pancreatic B-cells is modulated by ADP

ATP-sensitive K+ channels in inside-out membrane patches from dispersed rat pancreatic B-cells were studied using patch-clamp methods. The dose-response curve for ATP-induced channel inhibition was shifted to higher concentrations in the presence of ADP (2 mM). In glucose-free solution, the total intracellular concentration of ATP was 3.8 mM and of ADP 1.5 mM; glucose (20 mM) increased ATP and decreased ADP by approx. 40%. These results suggest that both ADP and ATP may be involved in regulating the activity of the glucose-sensitive K+ channel in intact B-cells.

P2 receptor subtypes in the cardiovascular system

Extracellular nucleotides have been implicated in a number of physiological functions. Nucleotides act on cell-surface receptors known as P2 receptors, of which several subtypes have been cloned. Both ATP and ADP are stored in platelets and are released upon platelet activation. Furthermore, nucleotides are also released from damaged or broken cells. Thus during vascular injury nucleotides play an important role in haemostasis through activation of platelets, modulation of vascular tone, recruitment of neutrophils and monocytes to the site of injury, and facilitation of adhesion of leucocytes to the endothelium. Nucleotides also moderate these functions by generating nitric oxide and prostaglandin I2 through activation of endothelial cells, and by activating different receptor subtypes on vascular smooth muscle cells. In the heart, P2 receptors regulate contractility through modulation of L-type Ca2+ channels, although the molecular mechanisms involved are still under investigation. Classical pharmacological studies have identified several P2 receptor subtypes in the cardiovascular system. Molecular pharmacological studies have clarified the nature of some of these receptors, but have complicated the picture with others. In platelets, the classical P2T receptor has now been resolved into three P2 receptor subtypes: the P2Y1, P2X1 and P2TAC receptors (the last of these, which is coupled to the inhibition of adenylate cyclase, is yet to be cloned). In peripheral blood leucocytes, endothelial cells, vascular smooth muscle cells and cardiomyocytes, the effects of classical P2X, P2Y and P2U receptors have been found to be mediated by more than one P2 receptor subtype. However, the exact functions of these multiple receptor subtypes remain to be understood, as P2-receptor-selective agonists and antagonists are still under development.

Intracellular ADP activates K+ channels that are inhibited by ATP in an insulin-secreting cell line

The effect of ADP on ATP-sensitive K+ channels in the insulin-secreting RINm5F cell line has been investigated with the help of single-channel current recording from saponin-permeabilized cells. ADP (100-500 microM) markedly activates K+ channels when added to the bath solution in contact with the membrane inside. ADP-beta-S cannot mimick this effect. During sustained ATP (500 microM)-evoked inhibition of K+ channel opening, 500 microM ADP markedly and reversibly activates the channels. Conversely ATP markedly reduces the opening probability of ADP-activated channels. It is suggested that the physiological control of K+ channel opening in the insulin-secreting cells is mediated by changes in ATP/ADP ratio rather than being solely determined by the ATP concentration.

Factors affecting the rate of phosphocreatine resynthesis following intense exercise

Within the skeletal muscle cell at the onset of muscular contraction, phosphocreatine (PCr) represents the most immediate reserve for the rephosphorylation of adenosine triphosphate (ATP). As a result, its concentration can be reduced to less than 30% of resting levels during intense exercise. As a fall in the level of PCr appears to adversely affect muscle contraction, and therefore power output in a subsequent bout, maximising the rate of PCr resynthesis during a brief recovery period will be of benefit to an athlete involved in activities which demand intermittent exercise. Although this resynthesis process simply involves the rephosphorylation of creatine by aerobically produced ATP (with the release of protons), it has both a fast and slow component, each proceeding at a rate that is controlled by different components of the creatine kinase equilibrium. The initial fast phase appears to proceed at a rate independent of muscle pH. Instead, its rate appears to be controlled by adenosine diphosphate (ADP) levels; either directly through its free cytosolic concentration, or indirectly, through its effect on the free energy of ATP hydrolysis. Once this fast phase of recovery is complete, there is a secondary slower phase that appears almost certainly rate-dependent on the return of the muscle cell to homeostatic intracellular pH. Given the importance of oxidative phosphorylation in this resynthesis process, those individuals with an elevated aerobic power should be able to resynthesise PCr at a more rapid rate than their sedentary counterparts. However, results from studies that have used phosphorus nuclear magnetic resonance ((31)P-NMR) spectroscopy, have been somewhat inconsistent with respect to the relationship between aerobic power and PCr recovery following intense exercise. Because of the methodological constraints that appear to have limited a number of these studies, further research in this area is warranted.

Identification of a 2-stage platelet aggregation process mediating shear-dependent thrombus formation

Disturbances of blood flow at sites of atherosclerotic plaque rupture are one of the key pathogenic events promoting platelet activation and arterial thrombus formation. Shear effects of platelets have been extensively investigated in vitro; however, the mechanisms by which shear promotes platelet aggregation in vivo remain incompletely understood. By employing high-resolution imaging techniques to in vitro and in vivo thrombosis models, we demonstrate a unique mechanism initiating shear-dependent platelet aggregation involving aggregate formation between discoid platelets. These discoid platelet aggregates are initially unstable and result from the development of membrane tethers between coadhering platelets. Tether formation involves the adhesive function of GPIb/V/IX and integrin alphaIIbbeta3, and conversion of discoid platelet aggregates into stable aggregates requires released ADP. The efficiency of this process is regulated by 3 independent variables, including the reactivity of the adhesive substrate, the level of shear flow, and the platelet density at the adhesive surface. These studies identify a new mechanism initiating platelet aggregation that is critically influenced by shear, physical proximity between translocating platelets, and membrane tether formation. Moreover, they provide a model to explain how the discoid morphology of platelets facilitates the maintenance of adhesive interactions with thrombogenic surfaces under high shear stress conditions.

Role of adenine nucleotides, adenosine, and inorganic phosphate in the regulation of skeletal muscle blood flow

Experiments were performed on isolated frog sartorius muscle and in situ dog skeletal muscle to determine whether adenine nucleotides and their degradation products are released during contraction in concentrations capable of producing arteriolar dilation ATP was not detectable (>10 -8 M) in the bathing solution of the resting or contracting frog sartorius muscle. Inorganic phosphate (P 1 ) in the muscle bath increased from 9 x 10 -5 M to 28 x 10 -5 M with 30 minutes of contraction (2 Hz) or with rest. With the dog hindlirnb preparation, ATP, ADP, and AMP were not detectable (>5 x 10 ⊟8 M in the venous blood collected after 5 minutes of ischemic contraction whereas P 1 was present at a concentration of 3.7 x 10 x8 M. Arterial blood levels required to elicit detectable vasodilation for ATP, ADP, AMP, and P 1 were 28.7 x 10 -8 M, 27.1 x 10 -8 M 31.4 x 10 -8 M and 7.2 ⊠ 10 -4 M respectively. The adenosine concentration in dog muscle increased from 0.7 to 1.5 nmole/g with ischemic contraction, and hypoxanthine and inosine increased from 4.5 to 8.5 nmole/g and 2.0 to 5.5 nmole/g, respectively. The adenosine concentration in venous plasma collected from the hiodlimb immediately after termination of the irchemic contraction period was 2.2 x 10 -7 MM as compared to 0.4 x 10 -7 M in control venous and arterial blood samples. Hypoxanthine and inosine concentrations in venous blood increased 22- and 270-fold, respectively, foflowing ischemic contraction. The calculated interstitial fluid adenosine concentration was twice the arterial concentration of adenosine required to elicit maximal arteriolar dilation. These findings suggest that adenosine may play a role in the metabolic regulation of skeletal muscle blood flow, whereas ATP, ADP, AMP, and P 1 may not.

Adenosine triphosphate: established and potential clinical applications

Adenosine 5'-triphosphate (ATP) is a purine nucleotide found in every cell of the human body. In addition to its well established role in cellular metabolism, extracellular ATP and its breakdown product adenosine, exert pronounced effects in a variety of biological processes including neurotransmission, muscle contraction, cardiac function, platelet function, vasodilatation and liver glycogen metabolism. These effects are mediated by both P1 and P2 receptors. A cascade of ectonucleotidases plays a role in the effective regulation of these processes and may also have a protective function by keeping extracellular ATP and adenosine levels within physiological limits. In recent years several clinical applications of ATP and adenosine have been reported. In anaesthesia, low dose adenosine reduced neuropathic pain, hyperalgesia and ischaemic pain to a similar degree as morphine or ketamine. Postoperative opioid use was reduced. During surgery, ATP and adenosine have been used to induce hypotension. In patients with haemorrhagic shock, increased survival was observed after ATP treatment. In cardiology, ATP has been shown to be a well tolerated and effective pulmonary vasodilator in patients with pulmonary hypertension. Bolus injections of ATP and adenosine are useful in the diagnosis and treatment of paroxysmal supraventricular tachycardias. Adenosine also allowed highly accurate diagnosis of coronary artery disease. In pulmonology, nucleotides in combination with a sodium channel blocker improved mucociliary clearance from the airways to near normal in patients with cystic fibrosis. In oncology, there are indications that ATP may inhibit weight loss and tumour growth in patients with advanced lung cancer. There are also indications of potentiating effects of cytostatics and protective effects against radiation tissue damage. Further controlled clinical trials are warranted to determine the full beneficial potential of ATP, adenosine and uridine 5'-triphosphate.