Isolated human bladder: evidence for an adenine dinucleotide acting on P2X-purinoceptors and for purinergic transmission

Pre- and postjunctional effects of diadenosine polyphosphates in the guinea-pig vas deferens

The pre- and postjunctional activities of a number of diadenosine polyphosphates were examined in the guinea-pig isolated vas deferens at the level of the membrane potential, using a modified sucrose-gap technique. P1,P3-Di(adenosine 5')triphosphate (Ap3A), P1,P4-di(adenosine 5')tetraphosphate (Ap4A) and P1,P5-di(adenosine 5')pentaphosphate (Ap5A) all caused concentration-dependent depolarization of the smooth muscle membrane. The potency order was: Ap5A > Ap4A > or = Ap3A. P1,P2-Di(adenosine 5')pyrophosphate (Ap2A) did not evoke depolarization even at the highest concentration tested (1 mM). All the dinucleotides caused a reduction in the amplitude of evoked excitatory junction potentials (e.j.ps). The potency order was: Ap5A = Ap4A > Ap3A > Ap2A. The depolarizations evoked by the dinucleotides were markedly reduced by the selective P2X-purinoceptor antagonist, pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS, 10 microM), as was the amplitude of the fully facilitated e.j.p. The inhibition of the e.j.p. evoked by Ap3A and Ap2A was reduced by the P1-purinoceptor antagonist, 8-p-sulphophenyltheophylline (8-pSPT, 50 microM), but that evoked by Ap5A and Ap4A was not. Thus, Ap3A, Ap4A and Ap5A evoke depolarization of the guinea-pig vas deferens via P2X-purinoceptors, and additionally Ap2A and Ap3A exert a prejunctional effect via P1-purinoceptors. The prejunctional activity of Ap4A and Ap5A is mediated via an undefined purinoceptor, which is neither P1 nor P2X.

Effects of diadenosine polyphosphates, ATP and angiotensin II on cytosolic Ca2+ activity and contraction of rat mesangial cells

Diadenosine polyphosphates (Apn A) are known to influence cellular Ca2+ activity ([Ca2+]i) in several cells. Their vasoactive potency has been described in various systems including the kidney. We examined the effects of diadenosine polyphosphates, adenosine 5'-triphosphate (ATP) and angiotensin II (Ang II) on cytosolic Ca2+ activity of mesangial cells (MC) in culture obtained from normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats. [Ca2+]i was measured as a fluorescence ratio F340/F380 with the fura-2 technique using three excitation wavelengths (340 nm, 360 nm and 380 nm) and a photon counting tube. Resting [Ca2+]i was not significantly different in MC from WKY and SHR rats and was measured as 132 +/- 9 nmol/l (n = 65) and 114 +/- 12 nmol/l (n = 36), respectively. Diadenosine polyphosphates (Ap3A-Ap6A) increased [Ca2+]i transiently with an initial peak and a secondary plateau phase comparable to the effects of ATP or Ang II. Increases in [Ca2+]i induced by all these agonists were not significantly different between MC of WKY and SHR rats. ATP, Ap3A, Ap4A, Ap5A, Ap6A (each 5 micromol/l) increased the fura-2 fluorescence ratio initially by 0.66 +/- 0.09 (n = 33), 0.52 +/- 0.08 (n = 18), 0.25 +/- 0.05 (n = 16), 0.09 +/- 0.06 (n = 7), 0.09 +/- 0.04 (n = 11), respectively. A half-maximal initial increase in the fura-2 fluorescence ratio was reached at 22 nmol/l, 0.9 micromol/l, 2.0 micromol/l and 4.0 micromol/l with Ang II, Ap3A, ATP and Ap4A, respectively. Ap4A (100 micromol/l, n = 18) led to a reversible contraction of MC. Diadenosine polyphosphates increase [Ca2+]i in rat MC, in a similar manner to ATP or Ang II and lead to a contraction of MC, suggesting that these nucleotides are also involved in the control of glomerular haemodynamics.

Cytosolic free Ca2+ oscillations induced by diadenosine 5',5"'-P1,P3-triphosphate and diadenosine 5',5"'-P1,P4-tetraphosphate in single rat hepatocytes are indistinguishable from those induced by ADP and ATP respectively

Diadenosine 5',5"'-P1,P3-triphosphate (Ap3A) and diadenosine 5',5"'-P1,P4-tetraphosphate (Ap4A) induce distinctive patterns of [Ca2+]i oscillations in single rat hepatocytes. We show here that [Ca2+]i oscillations induced by Ap3A and ADP are indistinguishable and that [Ca2+]i oscillations induced by Ap4A closely resemble those induced by ATP. These similarities embrace the following: (1) ADP and Ap3A invariably induce [Ca2+]i transients of short duration (approx. 9 s). Ap4A, like ATP, can induce, depending upon the individual cell, either transients of short duration (approx. 9 s), transients of much longer duration or a mixture of short and long transients within a single response. We show here that the pattern of oscillations induced by Ap4A is similar to that induced by ATP in the same hepatocyte. (2) Elevated intracellular cyclic AMP concentration modulates Ap3A-induced transients, like ADP-induced transients, through an increase in both the peak [Ca2+]i and the frequency of the transients. In contrast, Ap4A-induced transients, like ATP-induced transients, develop an increased duration or a sustained rise in [Ca2+]i, with no rise in peak [Ca2+]i. (3) Ap3A-induced transients, like ADP-induced transients, are abolished by low concentrations of the phorbol ester 4 beta-phorbol 12,13-dibutyrate (PDB; 5-10 nM), whereas long Ap4A-induced transients, like long ATP-induced transients, are refractory to high concentrations of PDB (100 nM). We propose that the [Ca2+]i oscillations induced in rat hepatocytes by Ap3A are mediated by the same purinoceptor that mediates the effects of ADP, whereas the oscillations induced by Ap4A are mediated by the same purinoceptor(s) that mediate the effects of ATP.

Characterization and autoradiographic localization of [3H] alpha, beta-methylene adenosine 5'-triphosphate binding sites in human urinary bladder

OBJECTIVES

To characterize [3H] alpha, beta-methylene adenosine 5'-triphosphate ([3H] alpha, beta-MeATP, a radioligand for P2x-purinoceptors) binding sites in the washed homogenates and membrane preparations of human urinary bladder and, using autoradiography, to localize [3H] alpha, beta-MeATP binding sites in human bladder.

MATERIALS AND METHODS

Specimens were obtained from the fundus of the urinary bladder of male patients aged 56-79 years. The washed homogenates or membrane preparations of the bladder specimens were incubated with [3H] alpha, beta-MeATP and the bound and free radioligand separated by filtration. For autoradiography, cryostat sections were incubated with 10 nM [3H] alpha, beta-MeATP, washed, dried and exposed for 2 weeks to emulsion-coated coverslips. In both experiments, 100 microM beta, gamma-methylene ATP was used to determine non-specific binding.

RESULTS

Six of 16 specimens in the binding assay and three of seven specimens in the localization study showed specific [3H] alpha, beta-MeATP binding. The binding process was saturable and the specific binding sites were composed of a high- and low-affinity component. The specific binding to membrane preparations was reduced in the presence of Mg2+ in the incubation medium. Competitive displacement experiments showed that the order of potency of the unlabelled ligands to displace the [3H] alpha, beta-MeATP binding was alpha, beta-methylene ATP > beta, gamma-methylene ATP > suramin > 2-methylthio ATP > ATP > ADP >> adenosine, which indicates that the binding sites are, or are linked to, P2x-purinoceptors. Autoradiography showed that the specific [3H] alpha, beta-MeATP binding sites were located only over the smooth muscle of the bladder.

CONCLUSIONS

The results suggest that P2x-purinoceptors exist in human urinary bladder, although at a lower density than reported for rodent urinary bladder.

A novel receptor for diadenosine polyphosphates coupled to calcium increase in rat midbrain synaptosomes

1. Diadenosine polyphosphates, Ap4A and Ap5A, as well as ATP, alpha,beta-MeATP and ADP-beta-S, were able to elicit variable intrasynaptosomal Ca2+ increases in rat midbrain synaptic terminals. The origin of the Ca2+ increment was the extra synaptosomal space since the elimination of extracellular Ca2+ abolished the effect of all the agonists. 2. The P2-purinoceptor antagonist, suramin, did not affect the Ca(2+)-increase evoked by diadenosine polyphosphates but dramatically blocked the Ca2+ entry induced by ATP and its synthetic analogues. 3. The actions of Ap5A and ATP on the intrasynaptosomal Ca2+ increase did not cross-desensitize. 4. Concentration-response studies for diadenosine polyphosphates showed pD2 values of 54.5 +/- 4.2 microM and 55.6 +/- 3.8 microM for Ap4A and Ap5A, respectively. 5. The entry of calcium induced by diadenosine polyphosphates could be separated into two components. The first represented a selective voltage-independent Ca2+ entry; the second, a sustained phase which was voltage-dependent. 6. Studies on the voltage-dependent Ca(2+)-channels involved in the effects of the diadenosine polyphosphates, demonstrated that omega-conotoxin G-VI-A inhibited the sustained Ca(2+)-entry, suggesting the participation of an N-type Ca(2+)-channel. This toxin was unable to abolish the initial cation entry induced by Ap4A or Ap5A. omega-Agatoxin IV-A, tetrodotoxin, or nifedipine did not inhibit the effects of the diadenosine polyphosphates. 7. The effect of ATP on Ca(2+)-entry was abolished by nifedipine and omega-conotoxin G-VI-A, suggesting the participation of L- and N-type Ca(2+)-channels in the response to ATP. 8. These data suggest that Ap4A, Ap5A and ATP activate the same intracellular Ca2+ signal through different receptors and different mechanisms. Ap4A and Ap5A induce a more selective Ca2+-entry in a voltage-independent process. This is the first time that a selective action of diadenosine polyphosphate through receptors other than P1 and P2-purinoceptors has been described.

Regulation of rat mesangial cell growth by diadenosine phosphates

The newly recognized human endogenous vasoconstrictive dinucleotides, diadenosine pentaphosphate (AP5A) and diadenosine hexaphosphate (AP6A), were tested for growth stimulatory effects in rat mesangial cells (MC). Both AP5A and AP6A stimulated growth in micromolar concentrations. The growth stimulatory effect exceeded that of ATP, alpha,beta-methylene ATP, adenosine 5'-O-(3-thio)triphosphate and UTP. Both diadenosine phosphates potentiated the growth response to platelet-derived growth factor, but not to insulin-like growth factor-1. To further elucidate the site of action in the cell cycle, RNA and protein synthesis were assessed. AP5 and AP6A stimulated protein synthesis, but not RNA formation. Furthermore, both agents increased cytosolic free Ca2+ concentration. It is concluded that AP5A and AP6A may play a regulatory role in MC growth as progression factors and possibly modify MC proliferation in glomerular disease.

Diadenosine polyphosphates: their biological and pharmacological significance

Diadenosine polyphosphates are members of a group of dinucleoside polyphosphates that are ubiquitous in bacteria to mammals. In recent years, the diadenosine polyphosphates have received considerable attention in view of their multiple biological activities and potential pharmacological activities. Diadenosine polyphosphates have been identified as modulators of cardiovascular and neurotransmitter-like activities in recent years, besides their previously described role in cell proliferation and as signal molecules when cells are undergoing stress. Diadenosine polyphosphates and their synthetic analogues are being evaluated for their potential as pharmacological agents. This article discusses the various biological functions and physiological significance of the diadenosine polyphosphates.

Effects of purinoceptor agonists on smooth muscle from hypertrophied rat urinary bladder

Tension responses induced by the purinoceptor agonists ATP and the stable ATP analogue alpha, beta-methylene ATP were investigated in isolated muscle strips from normal and hypertrophic urinary bladders from the rat. Hypertrophy was induced by a partial ligation of the urethra giving an increase in mean bladder weight from 65 mg to 300 mg. Activation with ATP and alpha, beta-methylene ATP caused phasic, concentration-dependent, contractions. The sensitivity to ATP was about 100-fold lower than that for alpha, beta-methylene ATP. The force of the contractions induced by the purinoceptor agonists was significantly lower in the hypertrophied bladder compared to the controls. The kinetics of the ATP-induced responses was studied by photolytic release of ATP from caged-ATP in intact fibre bundles. The rate of contraction following photolytic release of ATP was slower, and the force amplitude lower, in the hypertrophic preparations compared to the controls. The results suggest changes in the purinoceptor function or in the responses of the contractile system to transient increases in intracellular Ca2+ in the hypertrophic bladder.

Evidence for the presence of both pre- and postjunctional P2-purinoceptor subtypes in human isolated urinary bladder

1. In order to characterize P2-purinoceptor(s) in human urinary bladder the contractile effects of ATP and its slowly-hydrolyzable analogues alpha, beta-methylene ATP (alpha, beta-MeATP) and beta, gamma-methylene ATP (beta, gamma-MeATP) were investigated on human detrusor strips taken from patients undergoing cystectomy for bladder carcinoma. 2. Serial concentration-response curves (SCRC) for ATP, alpha, beta-MeATP and beta, gamma-MeATP were constructed with an interval of 25 min between two successive doses to avoid tachyphylaxis. ATP (10 microM-10 mM) induced a phasic contraction, which was very rapid in onset. The dose-response curve to ATP appeared not to be monophasic: at the lower concentrations (10-300 microM) the curve was shallow, whilst at high concentrations (1-10 mM) the curve was steeper. The magnitude of the response obtained at the highest concentration tested (10 mM) was only 21.1 +/- 2.8% (mean +/- s.e. mean; n = 4) of the KCl (100 mM)-induced contraction. 3. alpha, beta-MeATP (0.3 microM-1 mM) and beta, gamma-MeATP (10 microM-1 mM) elicited a phasic contraction with a time course similar to that exhibited by ATP. The magnitude of the response obtained at the highest concentration tested (1 mM) was 70.3 +/- 6.3% for alpha, beta-MeATP (n = 10) and 27.9 +/- 4.5% for beta, gamma-MeATP (n = 8) of KCl (100 mM)-induced contraction. The rank order of potency was alpha, beta-MeATP > beta, gamma-MeATP > ATP. A plateau of response could not be achieved by any of these agonists. 4. The P2-purinoceptor antagonist, suramin (10-300 microM), dose-dependently antagonized only the lower part of alpha,beta-MeATP dose-response curve. Data were analysed in terms of dose-ratio estimated at two levels of response (10% and 35% of KC1 100 mM-induced contraction). At 10% of KCl response the Schild plot slope was 0.98 and the estimated pKB was 5.85, whereas using the dose-ratio at the 35% level of the KCl response, the Schild plot was not linear suggesting an interaction of alpha,beta-MeATP with a heterogeneous receptor population.5. The putative P2-purinoceptor antagonist, Coomassie Brilliant Blue G (CB-G) at 0.3 and 1 l micro M(n = 5), shifted to the left the alpha,beta-MeATP SCRC. The response at the highest concentration of agonist was potentiated, being equal to 78.8 +/- 11.7% of the KCl (100 mM) response (n = 5). CB-G at 0.3 microM also shifted to the left the beta,upsilon-MeATP SCRC and significantly potentiated the response at 1 mM up to 46.3 +/- 5.6% of KCl 100 mM response (n = 4).6. Pretreatment with terodotoxin (TTX) at 1 microM shifted to the left the alpha,beta-MeATP SCRC but the response to the highest concentration of the agonist was not potentiated, being 73.6 +/- 9.9% of the KCl(100 mM) response (n = 5). TTX (1 micro M) shifted to the left the beta,upsilon-MeATP SCRC and significantly potentiated the response at 1 mM (61.6 +/- 3.1% of KCl response; n = 4).7. The NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) at 100 micro M did not modify the SCRC to either alpha, beta or beta,upsilon-MeATP.8. We conclude that in human detrusor muscle there is a heterogeneity of purinoceptors. The complex antagonism exhibited by suramin suggests the presence not only of Ph-purinoceptors but also of another contractile P2-purinoceptor subtype insensitive to suramin. Moreover, the activity of CB-G and TTX seems to support the existence of a prejunctional P2-purinoceptor subtype inducing the release of one or more inhibitor neurotransmitters.

Comparative studies on the affinities of ATP derivatives for P2x-purinoceptors in rat urinary bladder

1. Radioligand binding assays have been used to determine the affinities of a series of ATP derivatives with modifications of the polyphosphate chain, adenine and ribose moieties of the ATP molecule for [H]-alpha,beta-methylene ATP ([3H]-alpha,beta-MeATP) binding sites in rat urinary bladder. 2. The replacement of the bridging oxygen in the triphosphate chain of ATP (pIC50 = 5.58) with a methylene or imido group markedly increased the affinity (691 fold in IC50 values for beta,gamma-imidoATP, 15 fold for beta,gamma-methylene ATP), and the replacement of an ionized oxygen on the gamma-phosphate with a sulphur (ATP gamma S) also led to increased affinity (5623 fold in IC50 values). 3. Modifications at N6, N1, and C-8 positions on the purine base usually reduced the affinity of ATP (a decrease of 2.8 fold in IC50 values for N6-methylATP and 8.9 fold for 8-bromo ATP), while the attachment of an alkylthio group to the C-2 position greatly increased the affinity for P2x-purinoceptors (from 3.5 to 98 fold increase in IC50 values). 4. Replacement of the 3'-hydroxyl group on the ribose with substituted amino or acylamino groups produced more potent P2x-purinoceptor agonists (an increase of 447 fold in IC50 values for 3'-deoxy-3'-benzylamino ATP and 28 fold for 3'-deoxy-3'-(4-hydroxyphenylpropionyl)amino ATP. 5. Diadenosine polyphosphates (Ap[n]A) were also shown to displace the [3H]-alpha,beta-MeATP binding. The rank order of potency was Ap6A > Ap5A > Ap4A >> Ap3A >> Ap2A. 6. Suramin, PPADS, and reactive blue 2 could competitively displace the binding of [3H]-alpha,beta-MeATP toP2X-purinoceptors, with pIC50 values of 6.26, 5.35, and 6.22, respectively.

Purinoceptors: are there families of P2X and P2Y purinoceptors?

There has been an exponential growth in interest in purinoceptors since the potent effects of purines were first reported in 1929 and purinoceptors defined in 1978. A distinction between P1 (adenosine) and P2 (ATP/ADP) purinoceptors was recognized at that time and later, A1 and A2, as well as P2x and P2y subclasses of P1 and P2 purinoceptors were also defined. However, in recent years, many new subclasses have been claimed, particularly for the receptors to nucleotides, including P2t, P2z, P2u(n) and P2D, and there is some confusion now about how to incorporate additional discoveries concerning the responses of different tissues to purines. The studies beginning to appear defining the molecular structure of P2-purinoceptor subtypes are clearly going to be important in resolving this problem, as well as the introduction of new compounds that can discriminate pharmacologically between subtypes. Thus, in this review, on the basis of this new data and after a detailed analysis of the literature, we propose that: (1) P2X(ligand-gated) and P2Y(G-protein-coupled) purinoceptor families are established; (2) four subclasses of P2X-purinoceptor can be identified (P2X1-P2X4) to date; (3) the variously named P2-purinoceptors that are G-protein-coupled should be incorporated into numbered subclasses of the P2Y family. Thus: P2Y1 represents the recently cloned P2Y receptor (clone 803) from chick brain; P2Y2 represents the recently cloned P2u (or P2n) receptor from neuroblastoma, human epithelial and rat heart cells; P2Y3 represents the recently cloned P2Y receptor (clone 103) from chick brain that resembles the former P2t receptor; P2Y4-P2Y6 represent subclasses based on agonist potencies of newly synthesised analogues; P2Y7 represents the former P2D receptor for dinucleotides. This new framework for P2 purinoceptors would be fully consistent with what is emerging for the receptors to other major transmitters, such as acetylcholine, gamma-aminobutyric acid, glutamate and serotonin, where two main receptor families have been recognised, one mediating fast receptor responses directly linked to an ion channel, the other mediating slower responses through G-proteins. We fully expect discussion on the numbering of the different receptor subtypes within the P2X and P2Y families, but believe that this new way of defining receptors for nucleotides, based on agonist potency order, transduction mechanisms and molecular structure, will give a more ordered and logical approach to accommodating new findings. Moreover, based on the extensive literature analysis that led to this proposal, we suggest that the development of selective antagonists for the different P2-purinoceptor subtypes is now highly desirable, particularly for therapeutic purposes.

Evidence for purinergic neurotransmission in human urinary bladder affected by interstitial cystitis

Detrusor specimens were obtained from 5 patients affected by interstitial cystitis (IC) and 5 patients with bladder carcinoma (controls). Muscle strips were prepared for in vitro pharmacological studies. In all detrusor strips taken from IC patients, an important portion of the electrically-induced contraction was atropine-resistant. In contrast, atropine-resistance was never observed in control detrusors. H1 and H2 antagonists did not affect noncholinergic contractile response which, conversely, was abolished following desensitization to alpha, beta methylene ATP (APCPP). Detrusor muscle from patients affected by IC exhibited an increase in sensitivity to APCPP and a decrease in sensitivity to acetylcholine with respect to control detrusor. Taken together these results are consistent with the presence of a purinergic neurotransmission in parasympathetic nerve terminals of the urinary bladder affected by IC, probably as a consequence of alterations in the innervation and/or electrical coupling between smooth muscle cells. The sensitivity of IC detrusor muscle to histamine was much lower than that of control detrusor, suggesting a desensitization of histamine receptors present in the bladder wall of IC patients.

PPADS selectively antagonizes P2X-purinoceptor-mediated responses in the rabbit urinary bladder

1. Pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS), an inhibitor of P2X-purinoceptor-mediated responses in rabbit vas deferens, was investigated for its ability to antagonize contractions evoked by alpha,beta-methylene ATP (alpha,beta-MeATP), carbachol and electrical field stimulation in the rabbit urinary bladder detrusor muscle. 2. PPADS. (1-30 microM) caused concentration-dependent inhibition of contractions to the stable P2X-purinoceptor agonist, alpha,beta-MeATP, decreasing the maximum response to alpha,beta-MeATP (30 microM) at concentrations of 3-30 microM. The pD2 value for alpha,beta-MeATP in the absence of PPADS was 6.52 +/- 0.10 (8). In the presence of PPADS at concentrations of 1, 3, 10 and 30 microM the negative log concentrations of alpha,beta-MeATP that cause the same contractile response as the pD2 value were significantly different from control, being respectively 6.17 +/- 0.09 (8), 5.64 +/- 0.12 (7), 5.15 +/- 0.23 (7) and 4.78 +/- 0.22 (5). 3. PPADS (1-30 microM) caused concentration-dependent inhibition of contractions to stimulation of intramural purinergic nerves (1-32 Hz). There was a greater inhibition at lower frequencies (1-8 Hz) than at higher frequencies (16-32 Hz). PPADS, 30 microM, did not produce significantly greater antagonism than 10 microM. 4. PPADS (30 microM) had no significant influence on the contractile potency of carbachol: the pD2 values of carbachol in the absence and presence of PPADS were not significantly different being 6.42 +/- 0.16 (5) and 6.33 +/- 0.18 (5), respectively. However, PPADS caused a small, but significant, suppression of the maximal response of carbachol, reducing it by approximately 9%. 5. Radioligand binding studies carried out on rabbit bladder membranes with [3H]-alpha,beta-methylene ATP([3H]-alpha,beta-MeATP) showed that PPADS concentration-dependently inhibited the binding of [3H]-alpha,beta-MeATP to P2X-purinoceptors, while the binding of [3H]-quinuclidinyl benzilate to muscarinic cholinoceptors was not affected.6. Thus, PPADS (1-30 microM) antagonized responses mediated via P2X-purinoceptors in the rabbit urinary bladder. It was selective for P2-purinoceptor-mediated contractions rather than those mediated via muscarinic receptors. Binding studies demonstrated that the antagonistic effect of PPADS is via a direct interaction with P2x-purinoceptors.

Occupancy of P2 purinoceptors with unique properties modulates the function of human platelets

This report demonstrates that platelets possess P2 purinoceptors with unique properties that distinguish them from the ADP (P2T) receptor. Extracellular ATP, and its poorly hydrolyzable analogues, inhibit collagen- and U46619 (a thromboxane mimetic)-induced platelet aggregations. Adenosine deaminase was without effect on ATP action while reversing the inhibitory effect of adenosine. A unique aspect of the P2 receptor is the sensitivity to UTP and CTP and insensitivity to GTP. The rank order of inhibition by beta gamma-methylene ATP, alpha beta-methylene ATP > ATP indicates that a P2x-like receptor is present on the platelet membrane. This conclusion is further supported by the nearly complete desensitization to ATP by pre-exposure of platelets to alpha beta-methylene-ATP. However, unlike previously described P2x purinoceptors, the inhibition of platelet aggregation by extracellular ATP appears to result, at least in part, from the ATP-induced increase of intracellular cyclic AMP levels apparently coupled through a Gs protein. The combined addition of iloprost (0.14 to 1.39 nM) and ATP (18 microM) or ATP (20-40 microM) and the phosphodiesterase inhibitor theophylline (0.5 to 1 mM) synergistically inhibited platelet aggregation implying a common interactive site with adenylate cyclase. This is further substantiated by the ability of the adenylate cyclase inhibitor, 2',5'-dideoxyadenosine, to abrogate the inhibitory effects of ATP. The protein kinase A (PKA) inhibitor H1004 blocks ATP inhibition of platelet aggregation while the protein kinase C inhibitor H7 did not. This implies that the generation of cyclic AMP, with the subsequent activation of PKA and phosphorylation of selected proteins is required, in part, for the action of ATP.

Functional importance of cholinergic and purinergic neurotransmission for micturition contraction in the normal, unanaesthetized rat

1. The cholinergic and purinergic neurotransmission involved in micturition in the normal, unanaesthetized rat was investigated by means of continuous cystometry. 2. ATP (1 and 5 mg kg-1), administered intra-arterially (i.a.) close to the bladder, produced rapid, phasic, dose-dependent increases in bladder pressure with micturition immediately after injection. The micturition pressure of the following spontaneous voidings increased, and bladder capacity, micturition volume, and residual volume decreased. Pretreatment with alpha,beta-methylene ATP (1 mg kg-1, i.a.) blocked the effects of ATP (5 mg kg-1). 3. alpha,beta-Methylene ATP (0.25, 0.5 and 1 mg kg-1, i.a.) produced rapid, phasic, increases in bladder pressure with micturition immediately after injection. The effects of alpha,beta-methylene ATP (0.25 mg kg-1, i.a.) were not affected by pretreatment with indomethacin (0.5-2 mg kg-1, i.a.). The micturition pressure of the subsequent spontaneous voidings decreased, and bladder capacity and residual volume increased. 4. Carbachol (5-50 micrograms kg-1, i.a.) produced rapid, sustained, dose-dependent increases in bladder pressure with micturition, and then increased basal pressure, threshold pressure, and micturition pressure, and decreased bladder capacity and micturition volume during the following spontaneous voidings. 5. Atropine (1 mg kg-1, i.a.) decreased micturition pressure and micturition volume, but did not induce dribbling incontinence. Micturition contractions still occurred after the injection, but changed in appearance and were of shorter duration than before. In the presence of atropine (1 mg kg-1, i.a.), alpha,beta-methylene ATP (1 mg kg-1, i.a.) produced initially a phasic increase in bladder pressure with micturition and then dribbling incontinence in all animals tested. 6. After blockade of the micturition reflex with morphine (10 microg intrathecally), ATP (5 mg kg-1, i.a.),alpha,beta-methylene ATP (0.25-1 mg kg-1 , i.a.), and carbachol (5-500 microg kg-1, i.a.) were unable to empty the bladder.7. The results suggest that drug-induced bladder emptying in the normal, unanaesthetized rat requires an intact micturition reflex and they support the view that the two physiologically important transmitters involved in micturition are acetylcholine and ATP.

Ap4A and ADP-beta-S binding to P2 purinoceptors present on rat brain synaptic terminals

1. Diadenosine tetraphosphate (Ap4A) a dinucleotide stored and released from rat brain synaptic terminals presents two types of affinity binding sites in synaptosomes. When [3H]-Ap4A was used for binding studies a Kd value of 0.10 +/- 0.014 nM and a Bmax value of 16.6 +/- 1.2 fmol mg-1 protein were obtained for the high affinity binding site from the Scatchard analysis. The second binding site, obtained by displacement studies, showed a Ki value of 0.57 +/- 0.09 microM. 2. Displacement of [3H]-Ap4A by non-labelled Ap4A and P2-purinoceptor ligands showed a displacement order of Ap4A > adenosine 5'-O-(2-thiodiphosphate) (ADP-beta-S) > 5'-adenylyl-imidodiphosphate (AMP-PNP) > alpha,beta-methylene adenosine 5'-triphosphate (alpha,beta-MeATP) in both sites revealed by the Ki values of 0.017 nM, 0.030 nM, 0.058 nM and 0.147 nM respectively for the high affinity binding site and values of 0.57 microM, 0.87 microM, 2.20 microM and 4.28 microM respectively for the second binding site. 3. Studies of the P2-purinoceptors present in synaptosomes were also performed with [35S]-ADP-beta-S. This radioligand showed two binding sites the first with Kd and Bmax values of 0.11 +/- 0.022 nM and 3.9 +/- 2.1 fmol mg-1 of protein respectively for the high affinity binding site obtained from the Scatchard plot. The second binding site showed a Ki of 0.018 +/- 0.0035 microM obtained from displacement curves. 4. Competition studies with diadenosine polyphosphates of [35S]-ADP-beta-S binding showed a displacement order of Ap4A > Ap5A > Ap6A in the high affinity binding site and Ki values of 0.023 nM, 0.081 nM and 5.72 nM respectively. The second binding site potency order was Ap5A> Ap4A > Ap6A,with Ki values of 0.28 microM, 0.53 microM and 5.32 microM respectively.5. Displacement studies of [35S]-ADP-beta-S with P2-purinoceptor agonists showed the following potency pattern: ADP-beta-S > AMP-PNP >alpha,beta-MeATP with Ki values of 0.021 nM, 0.029 nM 0.215 nM respectively in the high affinity binding site. 2-Methylthio-adenosine 5'-triphosphate (2MeSATP) was unable to displace [35S]-ADP-beta-S in this binding site. The second binding site showed a profile of ADP-beta-S> a,beta-MeATP> AMP-PNP > 2MeSATP and Ki values of 0.0 18 microM, 0.212 microM, 0.481 microM and 18.04 microM respectively.6. These studies suggest the presence of a new P2-purinoceptor in rat brain synaptosomes with high affinity for diadenosine polyphosphates which we tentatively designate as P2d.

ATP induced-relaxation in the mouse bladder smooth muscle

1. The effect of adenosine 5'-triphosphate (ATP) on the free cytosolic Ca2+ concentration ([Ca2+]i) as measured with the fluorescent Ca(2+)-indicator fura-2, and on force was investigated in the intact smooth muscle strips of the mouse urinary bladder. 2. ATP elicited, when exogenously applied, a large increase of [Ca2+]i with limited force development resulting in a marked Ca(2+)-force dissociation. 3. Release of endogenous neurotransmitters by transmural electrical stimulation (TES) for 30 s induced a steady increase of [Ca2+]i and a peak contraction, followed within 15 s by a relaxation. 4. In carbachol-prestimulated preparations, ATP elicited an initial rise of [Ca2+]i followed by a return to the initial precontraction Ca(2+)-level. Force in contrast presented a biphasic pattern, i.e. an initial contraction was followed by a sustained relaxation. 5. In the K(+)-depolarized precontracted preparation, ATP elicited a slight initial rise of [Ca2+]i. The partial relaxation of the force during depolarization was not preceded by a transient contraction. 6. The ATP-induced relaxation of the K(+)-prestimulated preparations was not inhibited by 8-phenyltheophylline, a potent P1-purinoceptor antagonist. 7. The order of potency for relaxation of the ATP analogues was 2-MeSATP > ATP > beta gamma Me-ATP, which is characteristic for P2y-purinoceptors. 8. These results indicate that, besides its activating effect, ATP also relaxes the mouse urinary bladder. It is suggested that the relaxant effect, mediated through P2y-purinoceptors, is mainly responsible for the low contractile potency of ATP in the bladder.

Adenine dinucleotide-mediated activation of glycogen phosphorylase in isolated liver cells

The ability of purine nucleotides (e.g. ATP) to cause a dose-dependent activation of glycogen phosphorylase in isolated liver cells is well known. These agents mediate their effects through interaction with specific P2-purinoceptors in the plasma membrane. We have investigated the ability of a range of synthetic and naturally occurring adenine dinucleotides to cause a similar stimulation of glycogen phosphorylase activity in isolated rat liver cells. Our results indicate that Ap3A and Ap4A, the most abundant naturally occurring adenine dinucleotides, cause a dose-dependent activation of glycogen phosphorylase similar to that observed with ATP. Similar responses were seen with Ap5A, Ap6A and a series of phosphorothioate analogues. In contrast, the response to phosphonate analogues depended on the position of the P-C-P bridge. The dinucleotides appear to exert their effects directly, rather than through hydrolytic products such as adenosine and/or ATP. The possibility that adenine dinucleotides are physiologically significant extracellular purinergic effectors is discussed in the light of these observations.

Loss of sensory neuropeptides in the obstructed human bladder

This is the first investigation of alterations in the innervation of the obstructed human bladder by nerves containing neuropeptides. The patient groups studied were those with stable detrusor function, those with unstable detrusor function, and those presenting with acute retention of urine. Specimens of bladder tissue were taken from the lateral wall of the bladder below the peritoneal reflection. A total of 23 patients was studied (control, n = 4; acute retention, n = 5; stable obstruction, n = 5; unstable obstruction, n = 9). Substance P, calcitonin gene-related peptide and vasoactive intestinal polypeptide levels in the bladder were quantified by immunoassay. The density of innervation of the bladder detrusor by nerves containing these neurotransmitters and by those containing neuropeptide Y and somatostatin was assessed using both semiquantitative and quantitative immunohistochemical techniques. A reduction in the density of innervation by vasoactive intestinal polypeptide, calcitonin gene-related peptide, substance P and somatostatin-immunoreactive but not neuropeptide Y-immunoreactive nerve fibres was shown in the obstructed bladder. These findings, combined with the significant reduction in substance P content of the obstructed bladder and in particular of the acute retention bladder, indicate that there may be an afferent nerve dysfunction resulting from prostatic bladder outflow obstruction.

Extracellular hydrolysis of diadenosine polyphosphates, ApnA, by bovine chromaffin cells in culture

An ectoenzyme hydrolyzing diadenosine polyphosphates (ApnA) to AMP and Ap(n-1) has been studied in cultured chromaffin cells from bovine adrenal medulla. The KM value for extracellular Ap4A hydrolysis was 2.90 +/- 0.72 microM, the V(max) value obtained was 11.59 +/- 0.92 pmol/min x 10(6) cells (116 pmol/min.mg total protein). Ap3A, Ap5A, Ap6A, and Gp4G were competitive inhibitors of Ap4A hydrolysis with K(i) values of 3.65, 1.10, 1.20, and 2.65 microM, respectively. Phosphatidylinositol-specific phospholipase C removes the ApnA hydrolase activity from cultured chromaffin cells, suggesting an anchorage of this protein to the plasma membrane through the phosphatidylinositol. The turnover time for this enzyme calculated in the presence of cycloheximide was 38.94 +/- 1.53 hr for cultured chromaffin cells.

Contractions induced by angiotensin I, angiotensin II and bradykinin in isolated smooth muscle from the human detrusor

In isolated human detrusor preparations angiotensin (At)II 10(-9)-10(-5) M caused concentration-dependent contractions. The contractile effect was immediate, and had an amplitude which at the highest concentration used, 10(-5) M, reached 103 +/- 16% of the mean contraction produced by K+ 124 mM (27.6 +/- 1.4 mN). The AtII effect was completely blocked by saralasin 10(-6) M, but was not affected by pre-treatment of the preparations with captopril or enalaprilate. There was a marked tachyphylaxis to the actions of the peptide. AtI (10(-8)-10(-5) M) also caused contractions which were rapidly developing, and subject to a marked tachyphylaxis. At a concentration of 10(-5) M, the mean amplitude was 66 +/- 9% of the K(+)-induced contraction. The contractions were blocked by saralasin 10(-6) M, but not by captopril or enalaprilate 10(-5) M. In contrast, contractions produced by AtI in rabbit mesenteric arteries were practically abolished by the angiotensin converting enzyme (ACE) inhibitors. The contractions induced by both AtI and AtII were practically abolished after pre-treatment in a nominally calcium-free Krebs solution. However, blockade of L-type calcium channels by nifedipine 10(-6) M reduced the responses to both AtI 10(-6) M (by 38 +/- 4%) and AtII 10(-6) M (by 39 +/- 7%), but never abolished the contractions. Bradykinin (Bk; 3 x 10(-8)-10(-5) M) had a contractile effect in detrusor preparations which varied widely between strips. At a concentration of 3 x 10(-6) M, a maximum was reached amounting to 30 +/- 10% of the K(+)-induced contraction.(ABSTRACT TRUNCATED AT 250 WORDS)

Antimuscarinic activity of telenzepine on isolated human urinary bladder: no role for M1-muscarinic receptors

1. The antimuscarinic activity of the selective M1-blocking drug, telenzepine, was investigated on the isolated human urinary bladder, contracted with exogenous muscarinic agonists and with field stimulation. 2. Telenzepine (3 x 10(-8)-10(-5) M) concentration-dependently shifted to the right the dose-response curves of bethanechol, acetylcholine and McN-A343, and partially depressed the electrically-evoked twitch responses. 3. pA2 values of telenzepine against bethanechol and McN-A343 were very close. 4. McN-A343 did not modify twitch responses elicited by field stimulation up to 10(-5) M. 5. The lack of muscarinic M1 receptors in human detrusor muscle is confirmed.

Contractile effect of alpha,beta-methylene ATP on the guinea-pig isolated trachea

The effects of alpha,beta-methylene adenosine 5'-triphosphate (alpha,beta-methylene ATP), 2-chloroadenosine and R-PIA (N6-(L-2-phenylisopropyl)-adenosine) and their interaction with dipyridamole, indomethacin, 8-phenyl-theophylline, diazepam and other agonists of central or peripheral benzodiazepine receptors were studied on the guinea-pig isolated trachea. alpha,beta-methylene ATP exerted contractile effects on the guinea-pig isolated trachea; - log EC50 and E(max) values were 8.86 +/- 0.19 and 31.3 +/- 2.3 (n = 31) (% vs acetylcholine 10(-3) M) respectively. In comparison with other purinergic receptor agonists, the rank order of potency was: alpha,beta-methylene ATP greater than 2-chloroadenosine greater than R-PIA. alpha,beta-methylene ATP and 2-chloroadenosine had significantly (P less than 0.05) greater efficacy (E(max)) than R-PIA. Indomethacin (3 x 10(-6) M) and 8-phenyltheophylline (10(-7) to 10(-5) M) significantly reduced the contractile effect of 2-chloroadenosine and R-PIA but did not affect alpha,beta-methylene ATP-induced contraction. Conversely, dipyridamole significantly reduced (10(-7) M) or suppressed (10(-6) M) the contractile effects of alpha,beta-methylene ATP whereas it only partially reduced (10(-6) M) the contractile effects of high concentrations of 2-chloroadenosine or R-PIA. Diazepam potentiated the efficacy of alpha,beta-methylene ATP. The E(max) (% vs acetylcholine 10(-3) M) values were 26.1 +/- 2.0 (n = 10) in control conditions and 45.9 +/- 4.6 (n = 5; P less than 0.05) in the presence of diazepam 10(-5) M. Diazepam did not modify the contractile effects of 2-chloroadenosine or R-PIA. Ro5-4864 (10(-7) to 10(-5) M), an agonist of peripheral benzodiazepine receptors, potentiated the contractile effects of alpha,beta-methylene ATP to the same extent as diazepam. Clonazepam, an agonist of central benzodiazepine receptors, did not modify these effects. Antagonists of central (flumazenil) or peripheral (RP 52028) benzodiazepine receptors had no influence on the interaction between diazepam or Ro-4864 and alpha,beta-methylene ATP. In conclusion, alpha,beta-methylene ATP exerts on guinea-pig isolated trachea a contractile effect which is not modified by indomethacin and 8-phenyltheophylline, but is reduced by dipyridamole. It is suggested that this effect might involve P2 chi receptor stimulation.

Presence of diadenosine polyphosphates--Ap4A and Ap5A--in rat brain synaptic terminals. Ca2+ dependent release evoked by 4-aminopyridine and veratridine

The study of the adenine nucleotides in middle brain synaptosomes from rat showed the presence of two diadenosine polyphosphates, Ap4A and Ap5A. HPLC techniques and phosphodiesterase digestion were employed in order to characterize and quantify the dinucleotides. The Ap4A content per mg of protein was 169 +/- 25 pmol and 159 +/- 22 pmol for Ap5A. The study of the exocytotic release of these compounds was carried out with 100 microM 4-aminopyridine or 10 microM veratridine in the presence and in the absence of calcium. 4-Aminopyridine released 14.5 +/- 3.0 pmol/mg protein of Ap4A and 11.6 +/- 2.4 pmol/mg protein of Ap5A in a calcium dependent process. Veratridine in the presence of calcium released 19.9 +/- 3.0 and 16.6 +/- 2.8 pmol/mg of protein of Ap4A and Ap5A respectively. The ratios of exocytosis were close to 7-9% and 10-12% of the total synaptosomal content in the presence of 4-aminopyridine and veratridine, respectively.

Human, pig and guinea-pig bladder smooth muscle cells generate similar inward currents in response to purinoceptor activation

The contribution of purinergic neurotransmission to bladder excitation in pigs and man is small. Exogenously-applied adenosine-trisphosphate (ATP) however, elicits large inward currents in dispersed bladder smooth muscle cells in both species. The essential properties of the ATP-induced current in human and pig detrusor are similar and the current intensity is comparable to those in the guinea-pig, which has a powerful purinergic excitatory innervation. This suggests that other features of the tissue such as the closeness of the innervation and the degree of cell-to-cell coupling may be important in determining the effectiveness of purinergic transmission.

The effect of streptozotocin-induced diabetes on cholinergic motor transmission in the rat urinary bladder

1. The effect of streptozotocin (STZ)-induced diabetes on cholinergic motor transmission in the rat urinary bladder was investigated by recording contractile activity of detrusor strips in vitro. 2. The Ca(2+)-channel antagonist, nifedipine, was found to be more effective in blocking the noncholinergic motor transmission than P2-purinoceptor desensitization by alpha,beta-methylene ATP. 3. The neurogenic contractile responses to electrical field stimulation in the presence of nifedipine (cholinergic) were larger in the diabetic detrusor than in the non-diabetic controls. The potentiation of the cholinergic transmission was more evident at higher frequencies. 4. Concentration-response curves for acetylcholine were identical in detrusors from diabetic and non-diabetic animals, thus excluding a postsynaptic supersensitivity to acetylcholine being responsible for the potentiation of cholinergic motor transmission. 5. It is concluded that the potentiation of cholinergic motor transmission is due to enhanced release of acetylcholine in diabetic detrusor. Possible reasons for this enhancement are discussed in relation to diabetes.

High- and low-affinity binding sites for [3H]-alpha, beta-methylene ATP in rat urinary bladder membranes

1. The characteristics of [3H]-alpha, beta-methylene adenosine 5'triphosphate ([3H]-alpha, beta-MeATP) binding to membrane preparations of rat urinary bladder detrusor were studied. 2. The rat bladder membrane preparation was obtained by multiple centrifugation. [3H]-quinuclidinyl benzilate [( 3H]-QNB) binding to this preparation demonstrated that the muscarinic receptor density was 4.32 times higher than that in the homogenate. [3H]-alpha, beta-MeATP binding was increased 3.88 times. 3. Saturation analysis revealed that the rat bladder membrane contained a high density of [3H]-alpha, beta-MeATP binding sites, which could be divided into a high-affinity component (Kd = 8.1-8.9 nM) and a low-affinity component (Kd = 67.0-119.8 nM). 4. Magnesium ions inhibited the maximum binding in a concentration-dependent manner. The maximum high-affinity binding was reduced from 10.32 pmol mg-1 protein in magnesium-free buffer to 4.62 pmol mg-1 protein with 25 mM MgCl2, while the maximum low-affinity binding was reduced from 58.84 pmol mg-1 protein to 14.24 pmol mg-1 protein. Kd values were not greatly affected. 5. The binding was a rapid reversible process. The association rate constants were 7.64 x 10(7) M-1 min-1 for high-affinity binding, and 7.31 x 10(6) M-1 min-1 for low-affinity binding. The dissociation rate constants were 0.2896 min-1 for high-affinity binding, and 0.6348 min-1 for the low-affinity binding. 6. Displacement experiments with unlabelled purinoceptor ligands confirmed that [3H]-alpha, beta-MeATP mainly binds to P2X-purinoceptors. The potency order was: a,/i-methylene ATP > fy-methylene ATP > suramin > ATP > ADP > 2-methylthio ATP > adenosine. 7. The results indicate that [3H]-a,,B-MeATP is a radioligand for the P2x-purinoceptor, which satisfies the basic criteria for use in radioligand binding assay.

Inhibitory effect of streptozotocin-induced diabetes on non-cholinergic motor transmission in rat detrusor and its prevention by sorbinil

1. Non-cholinergic motor transmission in the urinary bladder of streptozotocin (STZ)-diabetic rats was studied by recording contractile activity of strips of detrusor in vitro. 2. The neurogenic contractile responses to electrical field stimulation (EFS) of atropine-treated detrusor strips were decreased in 4, 8 and 12 week STZ-diabetic rats. The decrease was most marked in 12 week diabetic rats and least in 4 week ones. 3. Concentration-response curves showed no change in sensitivity of the detrusor to acetylcholine (ACh) in diabetic rats. The maximum tension generated by ACh was similar in diabetic and non-diabetic animals. 4. The contractile responses to EFS at frequencies greater than or equal to 1 Hz were not maintained during stimulation. The 'fade' was significantly greater in detrusor strips of diabetic rats. 5. The contractile response of detrusor to EFS was significantly greater in 12 week diabetic rats treated with the aldose reductase inhibitor sorbinil, than in untreated 12 week diabetic rats. The sensitivity to ACh was similar in the two groups. 6. It is concluded that the reduction of the neurogenic non-cholinergic responses of detrusor to EFS in STZ-diabetic rats is probably caused by a reduction in the release of the non-cholinergic motor transmitter. The results are discussed in relation to bladder dysfunction in human diabetes mellitus.

Purinoceptor desensitization impairs but does not abolish the non-cholinergic motor transmission in rat isolated urinary bladder

In order to determine the effectiveness of purinoceptor desensitization in blocking the non-cholinergic motor transmission in rat detrusor, isolated preparations of urinary bladder, pretreated with atropine 3 microM + indomethacin 10 microM were contracted by alpha, beta-methylene-ATP, a stable analogue of ATP and by electrical stimulation at frequencies of 1, 2, 4, 8 and 16 Hz. The mean maximum tension generated by alpha, beta-methylene-ATP was 43% of that by electrical field stimulation. Desensitization to the contractile action of alpha, beta-methylene-ATP was achieved by administration of alpha, beta-methylene-ATP 10 microM, three times at 10 min intervals. Responses to electrical field stimulation were reduced following induction of alpha, beta-methylene-ATP desensitization but a sizeable proportion of the response persisted (51% at 1 Hz; 29% at 8 Hz). Tetrodotoxin 0.5 microM abolished the responses to electrical field stimulation, persisting after alpha, beta-methylene-ATP desensitization. It is concluded that ATP is unlikely to be the sole non-cholinergic motor transmitter in the rat detrusor.

Pharmacological activity of adenine dinucleotides in the periphery: possible receptor classes and transmitter function

1. The pharmacological actions of adenine dinucleotides, in particular beta-nicotinamide adenine dinucleotide (NAD), beta-nicotinamide adenine dinucleotide phosphate (NADP) and a homologous series of alpha,omega-adenine dinucleotide polyphosphates has been reviewed. 2. It is apparent that many actions of NAD can be explained in terms of activation of P1-purinoceptors, but actions of NADP cannot be explained in terms of activation of P1- or P2-purinoceptors. 3. Similarly, pharmacological activities of P1,P3-diadenosine triphosphate and P1,P4-diadenosine tetraphosphate are not in keeping with activation of P1- or P2-purinoceptors. 4. In the vas deferens and urinary bladder, P1,P4-diadenosine tetraphosphate, P1,P5-diadenosine pentaphosphate and P1,P6-diadenosine hexaphosphate act on P2x-purinoceptors and can cause desensitization of these receptors. 5. It is suggested that classes of receptors for adenine dinucleotides exist which are distinct from either P1- or P2-purinoceptors. 6. It is also suggested that in view of the finding of high concentrations of alpha,omega-adenine dinucleotide polyphosphates in adrenal medullary chromaffin cells, and of the involvement of the P2x-purinoceptor in the vas deferens and urinary bladder with purinergic neuromuscular transmission, that alpha,omega-adenine dinucleotide polyphosphates may yet be discovered in autonomic neurones and serve as neurotransmitters.