Effect of arylazido aminopropionyl ATP (ANAPP3), on ATP responses of isolated guinea pig smooth muscle

Neuronal constitutive nitric oxide synthase is involved in murine enteric inhibitory neurotransmission

Mice lacking neuronal nitric oxide synthase gene (ncNOS) were used to determine the enzymatic source of nitric oxide (NO) and its relationship with other putative inhibitory neurotransmitters. Inhibitory junction potentials (IJP) of circular smooth muscle of gastric fundus were studied. The IJP in the wild-type mice consists of overlapping components, the fast and slow IJPs. NOS inhibitor L-NA or VIP receptor antagonist VIP(10-28), blocks the slow IJP but not the fast IJP. The fast UP is blocked by alpha-beta methylene ATP tachyphylaxis, by reactive blue 2, and by apamin. The IJP in the ncNOS-deficient [ncNOS(-)] mutant is of short duration and is abolished by blockers of the fast IJP, but is unaffected by blockers of the slow UP. Exogenous VIP produces membrane hyperpolarization in strips from wild-type but not ncNOS(-) mice. The hyperpolarizing action of VIP is resistant to nifedipine but is sensitive to omega-conotoxin GVIA.

IN CONCLUSION

(a) NO derived from ncNOS is an inhibitory neurotransmitter rather than a postjunctional mediator; (b) VIP is a prejunctional neurotransmitter that causes release of evanescent NO; and (c) ATP acts in parallel with the VIP/NO pathway.

Role of adenine compounds in autonomic neurotransmission

Clearly adenine compounds exert numerous effects throughout the autonomic nervous system. The responses of various peripheral tissues to purines are summarized in Table 2. The evidence supporting a possible excitatory neurotransmitter function for ATP is very good in the vas deferens and good in both the bladder detrusor and certain blood vessels. ATP may also be an excitatory neurotransmitter in the colon, hepatocytes and frog atrium. These responses appear to be mediated by P2x-purinoceptors. There is good evidence supporting a role for ATP as an inhibitory neurotransmitter in the taenia coli and duodenum, and some support in the anal sphincter and possibly the rabbit portal vein; these responses appear to be mediated by P2y-purinoceptors. There is good evidence against ATP being an inhibitory neurotransmitter in the stomach fundic muscle and ileum. ATP (or more likely its metabolite adenosine) may act as an inhibitory neurotransmitter by interacting with postsynaptic P1-purinoceptors in cultured sympathetic neurones and also in the parasympathetic vesicle ganglion of the cat. It seems likely that ATP released from heart, platelets or vascular endothelium could be an endogenous relaxant of blood vessels through its actions on the endothelium. Although the addition of exogenous adenosine affects many tissues, evidence supporting modulatory functions for endogenous extracellular adenosine has only been clearly demonstrated in the ileum, gallbladder, vas deferens, fallopian tubes, kidney, blood vessels, carotid sinus, heart and adipose tissue. Both ATP and adenosine, released during periods of hypoxia or ischemia, could exert negative inotropic, chronotropic and dromotropic actions in the heart. In many cases, the potential sources of extracellular purines have not been established. This is particularly important when attempting to establish a neurotransmitter function for ATP in a tissue. For instance, the one outstanding piece of evidence required to confirm that ATP is an excitatory neurotransmitter released from sympathetic nerves in blood vessels is the unequivocal demonstration that it is, in fact, released from the sympathetic nerves when they are stimulated. To date, only the release of radiolabeled metabolites of ATP, possibly from post- rather than presynaptic sites, has been detected. Studies of the release of ATP are complicated by its rapid degradation extracellularly by ecto-ATPase. Unfortunately, there are no specific inhibitors of ecto-ATPase available at present, but one hopes that a suitable inhibitor will be developed shortly.(ABSTRACT TRUNCATED AT 400 WORDS)

Neuroeffector transmission in the guinea-pig internal anal sphincter: an electrical and mechanical study

ATP (10(-7)-10(-4) M), ADP (10(-7)-10(-4) M), AMP (10(-7)-10(-4) M) and adenosine (10(-6)-10(-4) M) each hyperpolarized the membrane, inhibited spontaneous spike discharge and relaxed the guinea-pig internal anal sphincter. All experiments were carried out using intracellular microelectrode and simultaneous tension recording techniques in the presence of phentolamine (10(-6) M) and atropine (10(-6) M). ATP was the most effective and produced a concentration-dependent membrane potential change comparable in amplitude to that produced by field stimulation of non-adrenergic non-cholinergic (NANC) nerves. Inhibitory junction potentials, the accompanying relaxations and the responses to ATP (5 X 10(-6)-5 X 10(-5) M) were additive and were increased in K+-deficient and decreased in K+-rich solutions and inhibited by apamin (10(-7) M). A proteolytic enzyme, alpha-chymotrypsin (0.5 U/ml) preferentially antagonized the ability of vasoactive intestinal polypeptide (10(-7) M) to hyperpolarize the membrane and relax the sphincter. The electrical and mechanical responses to ATP (10(-5) M) and inhibitory nerve stimulation were only slightly reduced. The results are consistent with the view that ATP or a related adenine nucleotide may have a transmitter role in the guinea-pig internal anal sphincter.

An electrophysiological analysis of the effect of reactive blue 2, a putative P2-purinoceptor antagonist, on inhibitory junction potentials of rat caecum

The electrophysiological effects of the putative P2-purinoceptor antagonist reactive blue 2 (RB2) were investigated in strips of circular muscle of rat caecum with the sucrose gap technique. RB2 (0.1-1 mM) antagonized in a concentration-dependent manner, the amplitude, rate of rise and speed of onset of the inhibitory junction potentials elicited either with single pulse or with train of field stimulation at 10 Hz. A fully effective concentration of RB2 (0.5 mM) decreased the membrane response to high strength hyperpolarizing constant current pulses, thus indicating an increase in membrane conductance. At this concentration RB2 inhibited the hyperpolarization induced by the stable ATP analogue alpha,beta-methylene ATP, but did not significantly inhibit noradrenaline-induced hyperpolarization. RB2 (0.5 mM) also abolished the ability of carbachol to elicit spikes, while the carbachol-induced depolarization and the amplitude of accompanying mechanical responses were largely unaffected. The possible mechanisms responsible for the RB2-induced effects are discussed.

Arylazido aminopropionyl ATP (ANAPP3): interaction with adenosine receptors in longitudinal smooth muscle of the guinea-pig ileum

Arylazido aminopropionyl ATP (ANAPP3), an ATP-receptor antagonist containing a photosensitive arylazido moiety coupled to the 3' hydroxyl of ATP, inhibited the twitch response of electrically stimulated ileal longitudinal muscle strips in a dose-dependent manner. These agonist responses to ANAPP3 were attenuated by the enzyme adenosine deaminase and antagonized by the adenosine receptor antagonist 8-phenyltheophylline. Schild analysis yielded similar pA2 values for ANAPP3 and adenosine suggesting a common receptor site. Several 3'-ribose-modified adenosine analogs were tested for agonist activity and found to be inactive. Results suggest that ANAPP3 interacts at the presynaptic adenosine receptor of the ileum following its metabolism to adenosine, which explains the lack of antagonism at adenosine receptors of ileal smooth muscle following photolysis of ANAPP3.

Apamin distinguishes two types of relaxation mediated by enteric nerves in the guinea-pig gastrointestinal tract

Eight smooth muscle preparations from the stomach, small intestine and large intestine of the guinea-pig were used to compare apamin's actions in reducing the effectiveness of transmission from enteric inhibitory nerves and in reducing responses to inhibitory agonists alpha, beta-methylene ATP, VIP and isoprenaline. The effects of apamin on inhibitory reflexes in the ileum and colon were also evaluated. Apamin had little or no effect on responses to VIP and isoprenaline in any region, but consistently and substantially reduced responses to alpha, beta-methylene ATP. Responses to stimulation of enteric inhibitory neurons were substantially reduced by apamin in the antrum circular muscle, ileum longitudinal and circular muscle, taenia coli and distal colon longitudinal muscle, but it was ineffective in the fundus circular muscle, proximal colon longitudinal muscle and distal colon circular muscle. It caused a small reduction of the relaxation of the ileal circular muscle caused reflexly by distension, but did not modify the similar descending inhibitory reflex in the circular muscle of the colon. It is concluded that apamin can be used to distinguish two types of non-noradrenergic transmission from enteric inhibitory nerves to gastrointestinal muscle. Furthermore, neither VIP nor ATP can be the sole transmitter chemical released from enteric inhibitory neurons throughout the gastrointestinal tract.

Characteristics of P2 (nucleotide) receptors mediating contraction and relaxation of rat aortic strips: possible physiological relevance

ATP and ADP relaxed rat aortic strips precontracted with noradrenaline by an endothelium-dependent mechanism. 5'-AMP was much less potent and adenosine was essentially without effect. The metabolically stable analogues alpha,beta-methylene ATP and beta,gamma-methylene ATP further contracted precontracted aorta. Aortic strips, which had not been precontracted with noradrenaline, contracted when exposed to either ATP or alpha,beta-methylene ATP, the latter nucleotide being much more potent than the former. Removal of the endothelium increased the contractions to ATP. ANAPP3 had no effect on the endothelium-dependent relaxations produced by ATP but it antagonized contractions produced by alpha,beta-methylene ATP. These results provide evidence for the possible existence of two subtypes of P2 receptors in rat aorta; a P2 receptor mediating contraction residing on smooth muscle which can be antagonized by ANAPP3 and where alpha,beta-methylene ATP is more potent than ATP, and a P2 receptor mediating relaxation located on the endothelium which cannot be antagonized by ANAPP3 and where ATP is much more potent than alpha,beta-methylene ATP.

Actions of adenine dinucleotides in the guinea-pig taenia coli: NAD acts indirectly on P1-purinoceptors; NADP acts like a P2-purinoceptor agonist

The actions of the adenine dinucleotides beta-nicotinamide adenine dinucleotide (NAD) and beta-nicotinamide adenine dinucleotide phosphate (NADP) were examined on the carbachol-contracted taenia coli of the guinea-pig. Both were capable of inducing full relaxations in a concentration-dependent manner; NADP was 21.4 times more effective than NAD at EC50; the threshold for NADP was approximately 0.1 microM and for NAD approximately 1.0 microM. The P1-purinoceptor antagonist, 8-phenyltheophylline (10 microM), produced a large parallel rightward shift in the NAD concentration-response curve; in contrast it produced a small parallel leftward shift in the NADP concentration-response curve. Dipyridamole (0.2 microM), a purine nucleoside uptake inhbitor, markedly potentiated responses to NAD and slightly potentiated NADP. 8-Phenyltheophylline antagonized the dipyridamole potentiation of both NAD and NADP. By use of high performance liquid chromatography it was shown that the action of NAD involves a breakdown to adenosine. Apamin, a K+ channel blocker, which antagonizes P2-purinoceptor activation in the intestine, abolished responses to NADP but not to NAD. The alpha-and beta-adrenoceptor antagonists, phentolamine (1 microM) and propranolol (1 microM), did not affect responses to NAD or NADP. Tetrodotoxin, a neurotoxin, did not abolish responses to either NAD or NADP. It is concluded that NAD acts largely indirectly as a P1-purinoceptor agonist following its breakdown to adenosine by ectoenzymes, while NADP acts in a similar manner to a P2-purinoceptor agonist.

Interaction of [3H]arylazido aminopropionyl ATP ([3H]ANAPP3) with P2-purinergic receptors in the smooth muscle of the isolated guinea-pig vas deferens

Following its photolysis in the presence of the isolated guinea-pig vas deferens, the ATP photoaffinity label ANAPP3 produces a specific antagonism of adenine nucleotide-induced contractile responses which are mediated by P2-purinergic receptors. To characterize the site of covalent photoincorporation of ANAPP3, intact vasa deferentia were treated with [3H]ANAPP3 and samples of homogenate, cytosol and a crude membrane fraction were analyzed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Photolysis of [3H]ANAPP3 (10(-5) M; 3.0 mu Ci/ml) resulted in the incorporation of radioactivity into cellular components with apparent molecular weights of 54-66 and 43-57 kilodaltons. The photoincorporation of [3H]ANAPP3 was associated with the crude membrane fraction and not the cytosol, was reduced in the presence of ATP in an ATP-concentration-dependent manner, was lessened following pretreatment of the tissues with photolyzed nonradiolabeled ANAPP3, and was unaffected by the nucleoside transport inhibitor, dipyridamole. In tension studies on the same tissues the presence of ATP resulted in a concentration-dependent reduction in the initial contractile response to [3H]ANAPP3 the response to 3H was antagonized in tissues which had been pretreated with nonradiolabeled ANAPP3, and dipyridamole had no effect on the contractile response to [3H]ANAPP3. According to several criteria these findings indicate that the antagonism by photolyzed ANAPP3 of adenine nucleotide-induced responses is a direct result of the covalent insertion at or near the recognition site of cell-surface P2-purinergic receptors.

Is there a basis for distinguishing two types of P2-purinoceptor?

It is suggested that the P2-purinoceptor may be separated into two subtypes largely on the basis of the rank order of agonist potency of structural analogues of ATP and also on the activity of antagonists at the P2-purinoceptor: Subtype 1 (designated P2X), potency order: alpha, beta-methyleneATP, beta, gamma-methyleneATP greater than ATP = 2 methylthioATP; antagonism by ANAPP3 and selectively desensitisation following administration of alpha, beta-methyleneATP; present in the vas deferens and urinary bladder of guinea-pig and rat, frog and rat ventricle, and also in the smooth muscle of the rat femoral artery and rabbit central ear artery, where they mediate excitation. Subtype 2 (designated P2Y), potency order: 2-methylthioATP much greater than ATP greater than alpha, beta-methyleneATP, beta, gamma-methyleneATP; weak antagonism by ANAPP3 and desensitisation following administration of alpha, beta-methyleneATP; present in the guinea-pig taenia coli and the longitudinal muscle layer of the rabbit portal vein, where they mediate relaxation and also on the vascular endothelial cells of the rat femoral artery and pig aorta (where occupation leads to the production of endothelium-derived relaxing factor). Differences in the structure of the P2-purinoceptor in various tissues may be useful in the development of drugs for the treatment of vascular, gastrointestinal and urinoglenital disorders.

Comparison of the effects of apamin, a Ca2+-dependent K+ channel blocker, and arylazido aminopropionyl ATP (ANAPP3), a P2-purinergic receptor antagonist, in the guinea-pig vas deferens

Apamin, which blocks Ca2+-dependent increases in K+ permeability, antagonizes ATP-induced relaxation of several smooth muscles. The ATP photoaffinity label arylazido aminopropionyl ATP (ANAPP3), following its photolysis in the presence of the guinea-pig vas deferens, antagonizes contractile responses to ATP. This study was conducted to determine whether apamin antagonizes ATP-induced responses in the guinea-pig vas deferens, and also to evaluate whether ANAPP3 antagonizes responses to ATP by interfering with Ca2+-dependent K+ permeability changes. Apamin (10(-6) M) potentiated ATP-induced contractions. This potentiation was nonspecific in that responses to norepinephrine, histamine and acetylcholine also were enhanced; responses to KCl were unaffected. To evaluate the possible interactions between the two agents at the same cellular site, the effect of apamin was examined in ANAPP3-treated tissues. In such tissues apamin did not potentiate the residual responses to ATP; however, apamin was nevertheless able to potentiate responses of ANAPP3-treated tissues to norepinephrine, histamine and acetylcholine, and responses to KCl remained unaffected. These studies provide additional support for the view that ANAPP3 antagonizes ATP-induced responses of the guinea-pig vas deferens by blocking P2-purinergic receptors. The antagonism by ANAPP3 is not attributable to a blockade of Ca2+-dependent K+ permeability changes.

A study of the atropine-resistant component of the neurogenic response of the rabbit urinary bladder

Rabbit bladder body was stimulated to contract by a number of agonists, of which bradykinin was the most potent, and ATP one of the least potent substances tested. The atropine-resistant component of the neurogenic response was unaffected by 2 X 10(-5) M chlorpheniramine or 10(-6) M methysergide, doses which suppressed responses to histamine or 5HT. Indomethacin 10(-5) M, or 10(-5) M capsaicin both reduced the atropine-resistant component. Following treatment with 10(-6) M atropine and 10(-5) M prazosin, 10(-4) M ANAPP3 produced a further suppression of the response, but did not antagonize the response to ATP. In the bladder body, the transmitter(s) responsible for the neurogenic response may be acetylcholine and prostaglandins and possibly ATP and substance P.

Purine receptors in the rat anococcygeus muscle

Adenosine triphosphate (ATP) caused contraction of the resting isolated rat anococcygeus muscle. Non-phosphorylated purines did not cause contraction of the resting muscle but did so in muscles in which the tone was raised by carbachol or guanethidine. Adenosine, (-)N6-phenylisopropyladenosine (PIA) and 5'-N-ethyl-carboxamide adenosine (NECA) were approximately equipotent, and these responses were not prevented by theophylline, quinidine, 2,2'-pyridylisatogen tosylate, phentolamine, methysergide, dipyridamole, hexobendine or indomethacin. The contractions became smaller as muscle tone progressively declined, and it is suggested that this effect may explain the apparent blockade of ATP responses by indomethacin reported previously. Adenosine, 2-chloroadenosine, ATP, PIA and NECA inhibited contractile responses of the anococcygeus to field stimulation of the excitatory adrenergic innervation. This inhibitory action was blocked by theophylline, and as PIA was easily the most potent purine tested, it may involve activation of an A1/Ri receptor. It is also argued, however, that the A/R scheme of classification may be inappropriate for the description of responses of intact tissues. As response to noradrenaline were not changed by the purines, the inhibitory effect on stimulation-evoked contractions is probably mediated at a presynaptic site. None of the purines tested had any effect on the neurally mediated inhibition of the anococcygeus which is seen when intrinsic tone is raised and the excitatory adrenergic nerves are blocked.

Comparison of photoaffinity labeling of P2-purinergic receptors of isolated guinea-pig vas deferens by arylazido aminopropionyl ATP and by arylazido aminobutyryl ATP

Two chemically related arylazido photoaffinity analogs of ATP (arylazido aminopropionyl ATP (ANAPP3) and arylazido aminobutyryl ATP (ANABP3)), which have been reported in the literature to differ in their ability to inhibit myosin ATPase, were compared for their ability to antagonize contractile responses of the isolated guinea-pig vas deferens to ATP. During photolysis in organ chambers the photoconversion (delta A260/delta t) of ANAPP3 occurred with greater than first order kinetics or was multiexponential and t1/2 = 7.5 min, while delta A260/delta t for ANABP3 was first order and t1/2 = 2.25 min. After photolysis of these compounds in the presence of the guinea-pig vas deferens, using irradiation periods which caused 80% consumption of the compounds, ANABP3 was 2-3 times more potent than ANAPP3 in antagonizing contractions to ATP, which are mediated by P2-purinergic receptors. A comparison of concentration-response curves obtained for nonphotolyzed ANAPP3 and ANABP3 used as agonists suggested that the greater antagonism produced by photolyzed ANABP3 is not attributable to a greater potency. The results suggest that the longer 3'-hydroxyl-arylazide bridge length of ANABP3 places the arylnitrene intermediate in a position at or near the P2-receptor which is more favorable for covalent insertion.

Direct evidence against a role of ATP as the nonadrenergic, noncholinergic inhibitory neurotransmitter in guinea pig tenia coli

Electrical field stimulation of the isolated guinea pig tenia coli in the presence of a muscarinic receptor antagonist (atropine) and an adrenergic neuron blocker (guanethidine) produces relaxation. A large amount of indirect evidence has suggested that the neurotransmitter that is released from these nonadrenergic, noncholinergic inhibitory neurons is ATP or a related nucleotide, and the nerves have been termed "purinergic." A photoaffinity analog of ATP, arylazido aminopropionyl ATP, which produces a specific pharmacological antagonism of P2 purinergic receptors in isolated guinea pig vas deferens and urinary bladder, was utilized in the present study to evaluate directly whether ATP is the nonadrenergic, noncholinergic inhibitory neurotransmitter in tenia coli. By blocking postjunctional P2 receptors, arylazido aminopropionyl ATP produced a pronounced antagonism of relaxations induced by exogenously added ATP. Responses produced by ADP, AMP, and adenosine also were antagonized by arylazido aminopropionyl ATP, but to a lesser extent. Inhibitory responses to isoproterenol were not antagonized. Under these conditions of established, specific P2-receptor blockade of responses to exogenously added ATP, relaxations induced by field stimulation of intrinsic inhibitory nerves in the presence of atropine (1 microM) and guanethidine (1 microM) were not antagonized. Though these results provide no indication of the actual substance involved, they suggest strongly that the nonadrenergic, noncholinergic inhibitory neurotransmitter in the guinea pig tenia coli is not ATP.

Evidence against ATP being the nonadrenergic, noncholinergic inhibitory transmitter in guinea pig stomach

THe adenosine-sensitive P1 purinoceptor antagonists 8-phenyl theophylline and 8-(p-bromophenyl)theophylline (4 microM) antagonized ATP-induced relaxation of spontaneous tone in guinea pig stomach, but caused no significant modification of relaxation to electrical field stimulation (0.2 - 10 Hz, 1 msec for 30 sec, atropine 1.5 microM, and guanethidine 4 microM treated). These results suggest that in fundic muscle ATP acts via hydrolysis to adenosine, with subsequent activation of P1 purinoceptors, and that ATP is not the nonadrenergic, noncholinergic inhibitory transmitter in stomach fundus.