Multiple action sites of flufenamate on ion transport across the rat distal colon

The antisecretory effects of flufenamate in the rat distal colon were investigated with the Ussing-chamber and the patch-clamp method as well as by measurements of the intracellular Ca(2+) concentration using fura-2-loaded isolated crypts. Flufenamate (5.10(-4) mol l(-1)) suppressed the short-circuit current (Isc) induced by carbachol (5.10(-5) mol l(-1)), forskolin (5.10(-6) mol l(-1)) and the Isc induced by the membrane-permeable analogue of cyclic AMP, CPT - cyclic AMP (10(-4) mol l(-1)). Indomethacin (10(-6) - 10(-4) mol l(-1)) did not mimic the effect of flufenamate, indicating that the antisecretory effect of flufenamate is not related to the inhibition of the cyclo-oxygenase. When the basolateral membrane was depolarized by a high K(+) concentration and a Cl(-) current was induced by a mucosally directed Cl(-) gradient, the forskolin-stimulated Cl(-) current was blocked by flufenamate, indicating an inhibition of the cyclic AMP-stimulated apical Cl(-) conductance. When the apical membrane was permeabilized by the ionophore, nystatin, flufenamate decreased the basolateral K(+) conductance and inhibited the Na(+) - K(+)-ATPase. Patch-clamp experiments revealed a variable effect of flufenamate on membrane currents. In seven out of 11 crypt cells the drug induced an increase of the K(+) current, whereas in the remaining four cells an inhibition was observed. Experiments with fura-2-loaded isolated crypts indicated that flufenamate increased the basal as well as the carbachol-stimulated intracellular Ca(2+) concentration. These results demonstrate that flufenamate possesses multiple action sites in the rat colon: The apical Cl(-) conductance, basolateral K(+) conductances and the Na(+) - K(+)-ATPase.

Accelerated resequestration of cytosolic calcium and suppression of the pro-inflammatory activities of human neutrophils by CGS 21680 in vitro

We have investigated the effects of the adenosine A(2A) receptor agonist CGS 21680 (0.01 - 1 microM) on reactive oxidant production by, and elastase release from FMLP-activated human neutrophils, as well as on cytosolic Ca(2+) fluxes and intracellular concentrations of cyclic AMP. Oxidant production, elastase release and cyclic AMP were assayed using lucigenin-enhanced chemiluminescence, colourimetric and radioimmunoassay procedures respectively, while cytosolic Ca(2+) fluxes were measured by fura-2 spectrofluorimetry in combination with radiometric procedures which distinguish between net efflux and influx of the cation. Treatment of neutrophils with CGS 21680 did not affect the FMLP-activated release of Ca(2+) from intracellular stores, but resulted in dose-related acceleration of the rate of decline in fura-2 fluorescence, as well as decreases in both efflux and store-operated influx of Ca(2+), compatible with enhancement of resequestration of the cation by the endo-membrane Ca(2+)-ATPase. These effects on neutrophil Ca(2+) handling were associated with increased intracellular cyclic AMP and with inhibition of oxidant production and release of elastase. In contrast, treatment of neutrophils with the selective A(2A) receptor antagonist, ZM 241385 (2.5 microM), prevented the transient increase in cyclic AMP in FMLP-activated neutrophils which was associated with delayed sequestration of incoming Ca(2+) during store-operated influx. The CGS 21680-mediated reduction of Ca(2+) efflux from FMLP-activated neutrophils was also antagonized by pretreatment of the cells with ZM 241385 (2.5 microM), as well as by thapsigargin (1 microM), an inhibitor of the endo-membrane Ca(2+)-ATPase. ZM 241385 also neutralized the cyclic AMP-elevating and anti-inflammatory interactions of CGS 21680 with neutrophils. We conclude that A(2A) receptors regulate the pro-inflammatory activities of human neutrophils by promoting cyclic AMP-dependent sequestration of cytosolic Ca(2+).

Smooth muscle layer-dependent distribution of 5-hydroxytryptamine(7) receptor in the porcine myometrium

1. To analyse the mechanisms of muscle layer-dependent inhibition of porcine myometrial contractility by 5-hydroxytryptamine (5-HT), the effects of 5-HT, 5-carboxamidotryptamine(5-CT), 5-methoxytryptamine (5-MeOT), forskolin and cyclic adenosine 3', 5'-monophosphate (cyclic AMP) analogues on spontaneous and stimulant-induced contractions were examined in longitudinal (LM) and circular muscles (CM). In addition, accumulation of cyclic AMP by 5-HT and distribution of 5-HT(7) receptors in LM and CM layers were compared using biochemical and molecular approaches. 2. 5-HT receptor agonists inhibited the spontaneous contractions of LM and CM (5-CT>5-HT>5-MeOT), but CM was more sensitive than was LM. The inhibition by the agonists was antagonized by methiothepin (100 nM). 3. Carbachol-, high-K(+)-, histamine- and Ca(2+)-induced contractions were inhibited by 5-HT with different responses (CM>LM). Even in the presence of 3-isobutyl-1-methylxanthine (IBMX), the inhibition by 5-HT in the CM was still more conspicuous than that in the LM. 4. Compared with the CM, the inhibition of spontaneous contraction by forskolin, dibutyryl-cyclic AMP and 8-bromo-cyclic AMP was marked in the LM. 5. 5-HT (1 nM - 1 microM) increased the cyclic AMP in both muscle layers, but the increment in the CM was higher than that in the LM whether IBMX was present or not. 6. LM and CM layers contained a single class of [(3)H]-5-CT binding sites with a similar K(d) value (0.21 - 0.24 nM). However, B(max) (5-HT(7) receptor concentration) in the CM (120.6 fmol mg(-1) protein) was higher than that in the LM (30.4 fmol mg(-1) protein). 7. The molecular study (reverse transcription polymerase chain reaction) demonstrated the expression of 5-HT(7) receptor mRNA in the CM was higher than that in the LM. 8. These results suggest that the muscle layer-dependent difference in inhibition by 5-HT is not restricted to spontaneous contraction but applies to various contractions in the porcine myometrium. Different inhibition of the contractility by 5-HT is caused by muscle layer-related accumulation of cyclic AMP (CM>LM), due to smooth muscle-layer dependent distribution (CM>LM) of 5-HT(7) receptors.

Suppression of arterial intimal hyperplasia by cilostamide, a cyclic nucleotide phosphodiesterase 3 inhibitor, in a rat balloon double-injury model

The effects of cilostamide, a cyclic nucleotide phosphodiesterase 3 (PDE3) selective inhibitor, on vascular intimal hyperplasia were evaluated using a single-balloon injury model and a double-injury model in which the rat common carotid artery was subjected to a second injury at a site injured 14 days previously. In the double-injury model, the second balloon injury caused more severe intimal hyperplasia (intima/media (IM) ratio, 1.88+/-0.10) than in the single-injury model (1.09+/-0.08). Histopathological study revealed that vascular smooth muscle cells (VSMC) were the predominant cell-type in the affected neointimal area. Oral administration of cilostamide for 2 weeks after the second injury suppressed intimal hyperplasia in the double-injury model (30 mg kg(-1) bid, 83% inhibition in terms of the IM ratio, P<0.05; 100 mg kg(-1) bid, 69% inhibition, P<0.05). Similar effects were also observed in the single-injury model with oral administration of cilostamide for 2 weeks (100 mg kg(-1) bid, 36% inhibition, P<0.01). Cilostamide inhibited DNA synthesis of cultured VSMC stimulated by foetal calf serum or different kinds of growth factors, but did not affect their migration stimulated by platelet-derived growth factor (PDGF)-BB. Cilostamide significantly increased the cyclic AMP concentration of VSMC dose-dependently. These results indicate that cilostamide suppresses intimal hyperplasia both in the single- and double-injury models of rat, presumably by inhibiting proliferation rather than migration of VSMC. It is suggested that PDE3 inhibitors might find application in preventing intimal hyperplasia following angioplasty such as percutaneous transluminal coronary angioplasty (PTCA) or stent.

Involvement of the cyclic AMP system in the switch from tolerance into supersensitivity to the antinociceptive effect of the opioid sufentanil

1. We have previously demonstrated that chronic and simultaneous treatment of rats with the mu-opioid receptor agonist sufentanil and the Ca(2+) channel blocker nimodipine, not only prevented tolerance development, but the animals became supersensitive to the antinociceptive effect of the opioid. The focus of the present work was to determine the possible involvement of cross interactions between the adenylyl cyclase pathway and L-type voltage-sensitive Ca(2+)-channels, in modulating the switch from opioid tolerance into supersensitivity. 2. The modulatory effect of sufentanil on adenylyl cyclase activity was determined by measuring cyclic AMP production in slices from the cortex of rats rendered tolerant or supersensitive to the antinociceptive effect of the opioid. Tolerance was induced by chronic infusion of sufentanil, at a rate of 2 microg h(-1), for 7 days. Supersensitivity was induced by concurrent infusion of sufentanil (2 microg h(-1)) and nimodipine (1 microg h(-1)) for 7 days. Antinociception was evaluated by the tail-flick test. 3. Tolerance to the analgesic effect of sufentanil was associated with a significant reduction in the response of adenylyl cyclase to forskolin. Furthermore, the effect of the opioid on forskolin-induced cyclic AMP accumulation was abolished. On the other hand, supersensitivity to the analgesic effect of the opioid was associated with an increase in both, the adenylyl cyclase response to forskolin, and the opioid inhibition of cyclic AMP production. 4. We suggest that sustained L-type Ca(2+) channel blockade may result in changes in the adenylyl cyclase effector system triggered by mu-opioid receptor activation, leading to the switch from opioid tolerance into supersensitivity.

Utilization of spectral absorption for measurement of adenylate cyclase activity

The purpose of this study was to improve our previously described enzymatic fluorometric assay of the adenylate cyclase activity. Using physicochemical characteristics of NADPH, of which a 0.1 mmol/L solution would have an optical density of 0.627, we measured the adenylate cyclase activity by the spectral absorption of NADPH. The assay consists of two parts: pharmacological modulation of adenylate cyclase and measurement of newly synthesized cyclic AMP. The latter part involves four steps: enzymatic destruction of noncyclic adenine nucleotides and phosphorylated metabolites, conversion of cyclic AMP to ATP, amplification of ATP by enzymatic cycling, and measurement of NADPH with spectral absorption, which is generated in proportion to initial cyclic AMP levels. This new assay was tested in membrane preparations made from rat hearts in comparison with the previously described fluorometric assay. We obtained identical results by spectrophotometry and fluorometry with high reproducibility. Because the fluorometric assay possesses a high sensitivity while the spectrophotometric method is advantageous because of its wide analytical range of cyclic AMP measurement, combination of fluorometric and spectrophotometric methods may offer a convenient way to measure the adenylate cyclase activities in various samples.

Diadenosine polyphosphates as antagonists of the endogenous P2Y(1) receptor in rat brain capillary endothelial cells of the B7 and B10 clones

1. Diadenosine polyphosphates (Ap(n)As, n=2 - 7) are considered as stress mediators in the cardiovascular system. They act both via identified P2 purinoceptors and via yet to be characterized receptors. This study analyses the actions of Ap(n)As in clones of rat brain capillary endothelial cells that express P2Y(1) receptors (B10 cells) or both P2Y(1) and P2Y(2) receptors (B7 cells). 2. B10 cells responded to Ap(3)A with rises in intracellular Ca(2+) concentration ([Ca(2+)](i)). This response was prevented by adenosine-3'-phosphate-5'-phosphate, an antagonist of P2Y(1) receptors. It was largely suppressed by a treatment with apyrase VII or with creatine phosphokinase/creatine phosphate to degrade contaminating ADP. 3. Ap(n)As inhibited ADP induced increases in [Ca(2+)](i) mediated by P2Y(1) receptors by shifting ADP concentration-response curves to larger concentrations. Apparent K(i) values were estimated to be 6 microM for Ap(4)A, 10 microM for Ap(5)A and 47 microM for Ap(6)A. Ap(2)A and Ap(3)A were much less active. 4. Ap(n)As were neither agonists nor antagonists of the endogenous P2Y(2) receptor in B7 cells. 5. Ap(n)As are neither agonists nor antagonists of the G(i)-coupled, ADP receptor in B10 cells. 6. The results suggest that most actions of Ap(n)As in B7 and B10 cells can be accounted for by endogenous P2Y(1) receptors. Ap(4)A, Ap(5)A and Ap(6)A are specific antagonists of endogenous Ca(2+)-coupled P2Y(1) receptors.

Enhanced relaxation of porcine coronary arteries after acute exposure to a physiological level of 17beta-estradiol involves non-genomic mechanisms and the cyclic AMP cascade

The present study extends our previous finding that the endothelium-independent relaxation in porcine coronary artery rings is enhanced after short-term (20 min) exposure to a physiological concentration (1 nM) of 17beta-estradiol and demonstrates that this effect may be attributable to activation of the cyclic AMP pathway. Isometric tension was recorded in isolated rings of porcine coronary arteries. Relaxation by levcromakalim and sodium nitroprusside, but not bradykinin and calcium ionophore A23187, were significantly potentiated following 20 min treatment with 1 nM 17beta-estradiol. This enhancing effect was insensitive to the transcriptional and translational inhibitors, actinomycin D and cycloheximide respectively and absent following repeated washing of the rings prior to construction of relaxation-response curves. The potentiating actions of 1 nM 17beta-estradiol on endothelium-independent relaxation were mimicked by the cyclic AMP analogue 8-Bromo-cyclic AMP and the protein kinase A activator Sp-cyclic AMPS but not by the cyclic GMP analogue 8-Bromo-cyclic GMP. The modulatory effect of 17beta-estradiol was increased in the presence of the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine. The cyclic AMP-dependent protein kinase A inhibitor Rp-cyclic AMPS, but not the cyclic GMP antagonist Rp-8-Bromo-cyclic GMPS, effectively inhibited the enhancing effects 1 M 17beta-estradiol had on the relaxation responses of levcromakalim and sodium nitroprusside. These data support our earlier findings that physiologically relevant concentrations of 17beta-estradiol can acutely modify vasorelaxation in vitro. Furthermore, we report that this short-term effect of 17beta-estradiol on vasorelaxation appears to be mediated via non-genomic pathways and involves the cyclic AMP cascade.

Characterization of a novel nonpeptide vasopressin V(2)-agonist, OPC-51803, in cells transfected human vasopressin receptor subtypes

We discovered the first nonpeptide arginine-vasopressin (AVP) V(2)-receptor agonist, OPC-51803. Pharmacological properties of OPC-51803 were elucidated using HeLa cells expressing human AVP receptor subtypes (V(2), V(1a) and V(1b)) and compared with those of 1-desamino-8-D-arginine vasopressin (dDAVP), a peptide V(2)-receptor agonist. OPC-51803 and dDAVP displaced [(3)H]-AVP binding to human V(2)- and V(1a)-receptors with K(i) values of 91.9+/-10.8 nM (n = 6) and 3.12+/-0.38 nM (n = 6) for V(2)-receptors, and 819+/-39 nM (n = 6) and 41.5+/-9.9 nM (n = 6) for V(1a)-receptors, indicating that OPC-51803 was about nine times more selective for V(2)-receptors, similar to the selectivity of dDAVP. OPC-51803 scarcely displaced [(3)H]-AVP binding to human V(1b)-receptors even at 10(-4) M, while dDAVP showed potent affinity to human V(1b)-receptors with the K(i) value of 13.7+/-3.2 nM (n = 4). OPC-51803 concentration-dependently increased cyclic adenosine 3', 5'-monophosphate (cyclic AMP) production in HeLa cells expressing human V(2)-receptors with an EC(50) value of 189+/-14 nM (n = 6). The concentration-response curve for cyclic AMP production induced by OPC-51803 was shifted to the right in the presence of a V(2)-antagonist, OPC-31260. At 10(-5) M, OPC-51803 did not increase the intracellular Ca(2+) concentration ([Ca(2+)](i)) in HeLa cells expressing human V(1a)-receptors. On the other hand, dDAVP increased [Ca(2+)](i) in HeLa cells expressing human V(1a)- and V(1b)-receptors in a concentration-dependent fashion. From these results, OPC-51803 has been confirmed to be the first nonpeptide agonist for human AVP V(2)-receptors without agonistic activities for V(1a)- and V(1b)-receptors. OPC-51803 may be useful for the treatment of AVP-deficient pathophysiological states and as a tool for AVP researches.

Nitric oxide-dependent vasodilatation of rabbit femoral artery by beta(2)-adrenergic stimulation or cyclic AMP elevation in vivo

Some studies suggest that beta-adrenoceptor-mediated vasorelaxation is in part mediated through nitric oxide (NO) release. We wished to determine the contribution of the L-arginine / NO system to vasodilatation in response to beta-adrenoceptor stimulation with isoprenaline or cyclic adenosine-3',5'-monophosphate (cyclic AMP) elevation with forskolin and dibutyryl cyclic AMP in vivo, using a rabbit femoral artery constant perfusion model. Baseline femoral artery pressure was similar in rabbits receiving isoprenaline, forskolin or dibutyryl cyclic AMP. Isoprenaline, forskolin and dibutyryl cyclic AMP each decreased femoral artery pressure in a dose-dependent manner. The doses (mol kg(-1)) of isoprenaline, forskolin and dibutyryl cyclic AMP which decreased pressure by 10% from baseline, expressed as a negative logarithm (-log ED(10)) were: 10.0+/-0.2, 9.5+/-0.1 and 4.9+/-0.1 respectively (P<0.0001 for each). Use of beta-adrenoceptor subtype-selective antagonists showed that the vascular response to isoprenaline was purely due to stimulation of the beta(2)-adrenoceptor subtype. Injection of 1 micromol kg(-1) N(G)-nitro-L-arginine methyl ester (L-NAME) did not alter baseline pressure. However, it abolished the pressure response to isoprenaline (P<0.0001), and significantly attenuated the pressure responses to forskolin and dibutyryl cyclic AMP: -log ED(10) values for forskolin and dibutyryl cyclic AMP, in the presence of L-NAME, were 7.9+/-0.1 and 3.5+/-0.3 respectively (P<0.0001 for each, as compared with values in the absence of L-NAME). These results indicate that beta(2)-adrenergic stimulation and cylic AMP elevation activate the L-arginine/NO system in rabbit femoral artery in vivo, and that NO generation contributes importantly to the changes in vascular tone induced by agents which modulate beta-adrenoceptors or cyclic AMP.

Pharmacological characterization of human recombinant melatonin mt(1) and MT(2) receptors

We have pharmacologically characterized recombinant human mt(1) and MT(2) receptors, stably expressed in Chinese hamster ovary cells (CHO-mt(1) and CHO-MT(2)), by measurement of [(3)H]-melatonin binding and forskolin-stimulated cyclic AMP (cAMP) production. [3H]-melatonin bound to mt(1) and MT(2) receptors with pK(D) values of 9.89 and 9.56 and B(max) values of 1.20 and 0.82 pmol mg(-1) protein, respectively. Whilst most melatonin receptor agonists had similar affinities for mt(1) and MT(2) receptors, a number of putative antagonists had substantially higher affinities for MT(2) receptors, including luzindole (11 fold), GR128107 (23 fold) and 4-P-PDOT (61 fold). In both CHO-mt(1) and CHO-MT(2) cells, melatonin inhibited forskolin-stimulated accumulation of cyclic AMP in a concentration-dependent manner (pIC(50) 9.53 and 9.74, respectively) causing 83 and 64% inhibition of cyclic AMP production at 100 nM, respectively. The potencies of a range of melatonin receptor agonists were determined. At MT(2) receptors, melatonin, 2-iodomelatonin and 6-chloromelatonin were essentially equipotent, whilst at the mt(1) receptor these agonists gave the rank order of potency of 2-iodomelatonin>melatonin>6-chloromelatonin. In both CHO-mt(1) and CHO-MT(2) cells, melatonin-induced inhibition of forskolin-stimulated cyclic AMP production was antagonized in a concentration-dependent manner by the melatonin receptor antagonist luzindole, with pA(2) values of 5.75 and 7.64, respectively. Melatonin-mediated responses were abolished by pre-treatment of cells with pertussis toxin, consistent with activation of G(i)/G(o) G-proteins. This is the first report of the use of [(3)H]-melatonin for the characterization of recombinant mt(1) and MT(2) receptors. Our results demonstrate that these receptor subtypes have distinct pharmacological profiles.

The insulinotropic mechanism of the novel hypoglycaemic agent JTT-608: direct enhancement of Ca(2+) efficacy and increase of Ca(2+) influx by phosphodiesterase inhibition

We examined the effects of the novel hypoglycaemic agent JTT-608 [trans-4-(4-methylcyclohexyl)-4-oxobutyric acid] on insulin secretion using rat pancreatic islets, and analysed the mechanism of its effect. JTT-608 augmented 8.3 mM glucose-induced insulin secretion dose-dependently, and there was a stimulatory effect of 100 microM JTT-608 at both moderate and high concentrations (8.3, 11. 1 and 16.7 mM) of glucose, but not at low concentrations (3.3 and 5. 5 mM). In perifusion experiments, both phases of insulin release were enhanced, and the effect was eliminated 10 min after withdrawal of the agent. In the presence of 200 microM diazoxide and a depolarizing concentration (30 mM) of K(+), there was an augmentation of insulin secretion by 100 microM JTT-608, not only under high levels of glucose but also under low levels, and the effects were abolished by 10 microM nitrendipine. JTT-608 augmented insulin secretion from electrically permeabilized islets in the presence of stimulatory concentrations (0.3 and 1.0 microM) of Ca(2+), and the intracellular Ca(2+) concentration ([Ca(2+)](i)) response under 16.7 mM glucose, 200 microM diazoxide, and 30 mM K(+) was also increased. The cyclic AMP content in the islets was increased by 100 microM JTT-608, and an additive effect to 1 microM forskolin was observed, but not to 50 microM 3-isobutyl-1-methylxanthine (IBMX). JTT-608 inhibited phosphodiesterase (PDE) activity dose-dependently. We conclude that JTT-608 augments insulin secretion by enhancing Ca(2+) efficacy and by increasing Ca(2+) influx. This appears to be a result of the increased intracellular cyclic AMP concentration due to PDE inhibition.

Regional modulation of cyclic nucleotides by endothelin-1 in rat pulmonary arteries: direct activation of G(i)2-protein in the main pulmonary artery

The ability of endothelin-1 (ET-1) to modulate the cyclic nucleotides, guanosine 3' 5' cyclic monophosphate (cyclic GMP) and adenosine 3' 5' cyclic monophosphate (cyclic AMP) was assessed in the main elastic pulmonary elastic artery (4 - 5 mm i.d.) and the small muscular pulmonary arteries (150 - 200 micrometer i.d.) of the rat. ET-1 caused an increase in cyclic GMP in the larger vessels but had no effect in the smaller arteries. The increase in cyclic GMP was not dependent on an intact endothelium and was inhibited by the ET(A)-receptor antagonist FR139137 (1 microM). ET-1 caused a decrease in cyclic AMP in the main pulmonary arteries, an effect that was partially blocked by FR139317 but not influenced by the ET(B)-receptor antagonist BQ-788 (1 microM) or removal of the vascular endothelium. In contrast, ET-1 caused an increase in cyclic AMP in the small vessels, an effect that was blocked by BQ-788 but unaffected by FR139317. In the main pulmonary arteries, ET-1 caused enhanced incorporation of radiolabelled ADP-ribose by cholera toxin into G(i)2 in the main pulmonary artery, an indicator of its receptor-mediated activation. In summary, we have shown that in the small muscular pulmonary artery of the rat, (where ET(B) mediated vasoconstriction prevails), there is an ET(B)-mediated increase in cyclic AMP with no net effect on cyclic GMP levels. In the large arteries, (where vasoconstriction is mediated via the ET(A) receptor), there is an ET(A)-mediated increase in cyclic GMP (endothelium independent) and an ET(A)-mediated (endothelium independent) decrease in cyclic AMP.

Effects of AMP derivatives on cyclic AMP levels in NG108-15 cells

1. In NG108-15 neuroblastomaxglioma hybrid cells, ATP stimulates intracellular cyclic AMP formation, which is inhibited by both adenosine (P(1)) and P2 receptor antagonists. In the present study, we examined the effects of several AMP derivatives in NG108-15 cells and mouse neuroblastoma N18TG-2 cells. 2. Adenosine 2'-monophosphate (A2P), adenosine 3'-monophosphate (A3P) and adenosine 5'-phosphosulphate (A5PS) increased cyclic AMP levels with similar concentration-dependencies in NG108-15 cells. 3. Increases in cyclic AMP by AMP derivatives were inhibited by the P2 receptor antagonist PPADS, but not by suramin. Effects of AMP derivatives were also inhibited by P(1) receptor antagonists ZM241385, XAC, DPCPX and partially by alloxazine. The ecto-nucleotidase inhibitor alpha, beta-methyleneADP was without effect. 4. In contrast, AMP derivatives did not change cyclic AMP levels in N18TG-2 cells. Accumulation of cyclic AMP in N18TG-2 cells was stimulated by adenosine A(2) receptor agonists CGS21680 and NECA, but not by ATP or beta, gamma-methyleneATP, agonists for cyclic AMP production in NG108-15 cells. 5. Reverse transcription-coupled polymerase chain reaction (RT - PCR) analyses revealed that N18TG-2 cells express both A(2A) and A(2B) receptors, while NG108-15 cells express mainly A(2A) receptors. 6. AMP derivatives did not affect the P2X and P2Y receptors expressed in NG108-15 cells. 7. These results suggest that A2P, A3P and A5PS act as agonists for cyclic AMP production and that these compounds are valuable tools for determinating the mechanism of ATP-stimulated cyclic AMP response in NG108-15 cells.

Measurement of adenylate cyclase activity in the right ventricular endomyocardial biopsy samples from patients with chronic congestive heart failure

A highly sensitive fluorometric assay technique was adopted in order to examine the adenylate cyclase activity in the minute right ventricular endomyocardial biopsy samples from patients with chronic congestive heart failure (n = 10). Norepinephrine (10(-4) M) and adenosine (10(-3) M) were incubated for 30 min with 10 microl of membrane preparation (1-2 mg protein/mg) to analyze the extent of the receptor-coupled adenylate cyclase activity. Forskolin (10(-4) M) stimulation was used to estimate the maximum adenylate cyclase activity (pmol/mg protein/min, mean +/- SE). The new microanalytical cyclic AMP assay involves four steps: enzymatic destruction of noncyclic adenine nucleotides and phosphorylated metabolites, conversion of cyclic AMP to ATP, amplification of ATP by enzymatic cycling, and fluorometric measurement of NADPH, which is generated in proportion to initial cyclic AMP levels. Basal and forskolin-stimulated maximum adenylate cyclase activities were 75 +/- 8 and 123 +/- 15, respectively. Norepinephrine increased the adenylate cyclase activity to 107 +/- 14, while adenosine tended to decrease it to 65 +/- 7. In addition, elimination of adenosine by adenosine deaminase (10 U/ml) slightly increased the adenylate cyclase activity to 82 +/- 9. These results indicate that the adenylate cyclase activity can be measured in minute endomyocardial biopsy samples. Use of this new approach shows promise of becoming a new and potentially important way to predict the efficacy of pharmacological treatment.

Effects of P(1) and P2 receptor antagonists on beta, gamma-methyleneATP- and CGS21680-induced cyclic AMP formation in NG108-15 cells

1. We have previously shown that ATP increased cyclic AMP in NG108-15 cells, which was inhibited by P(1) receptor antagonist methylxanthines. In the present study, we examined the effects of P(1) and P2 receptor antagonists on cyclic AMP formation induced by beta,gamma-methyleneATP (beta,gamma-MeATP) and CGS21680, an A(2A) adenosine receptor agonist, in NG108-15 cells. 2. beta,gamma-MeATP and CGS21680 increased intracellular cyclic AMP with EC(50) values of 8. 0+/-0.98 microM (n=4) and 42+/-7.5 nM (n=4), respectively. 3. Several P(1) receptor antagonists inhibited both beta,gamma-MeATP- and CGS21680-induced cyclic AMP increase with a similar rank order of potency; ZM241385>CGS15943>XAC>DPCPX. However, the pK(i) values of these antagonists for beta,gamma-MeATP were larger than those for CGS21680. 4. Alloxazine, a P(1) receptor antagonist, and several P2 receptor antagonists (PPADS, iPPADS, reactive blue-2) inhibited beta, gamma-MeATP-induced response, while these antagonists little affected CGS21680-induced one. Suramin was effective only for beta, gamma-MeATP-induced response at 1 mM. 5. 2-chloroadenosine (2CADO) and 2-chloroATP (2ClATP) increased cyclic AMP with similar potencies. The effects of these agonists were both inhibited by ZM241385, but only 2ClATP-induced response was inhibited by PPADS. 6. ATP- and beta, gamma-MeATP-induced responses were little affected by alpha, beta-methyleneADP, a 5'-nucleotidase inhibitor. 7. These results clearly demonstrate that ATP-stimulated cyclic AMP formation can be distinguished from the A(2A) receptor agonist-induced one by using the several P(1) and P2 receptor antagonists.

Involvement of cyclic AMP - PKA pathway in VIP-induced, charybdotoxin-sensitive relaxation of longitudinal muscle of the distal colon of Wistar-ST rats

The intracellular mechanism of vasoactive intestinal peptide (VIP)-induced, charybdotoxin (ChTx)-sensitive relaxation of longitudinal muscle of the distal colon of Wistar-ST rats was studied. A single pulse or 100 pulses at 10 Hz of electrical field stimulation (EFS) induced rapid transient relaxation or that with a subsequent contraction of the longitudinal muscle in the presence of atropine and guanethidine, respectively. Rp-8 bromo cAMPS, an inhibitor of cyclic AMP dependent protein kinase (PKA), at 30 microM inhibited the relaxations induced by EFS with a single or 100 pulses maximally by about 80 or 60%, respectively. It also inhibited VIP (300 nM)-induced relaxation by 82%. VIP (100 nM - 1 microM) increased the cyclic AMP content of longitudinal muscle myenteric plexus preparations obtained from the distal colon. ChTx at 100 nM almost completely inhibited 8 bromo cyclic AMP-induced relaxation of the distal segments. EFS with two or three pulses at 10 Hz induced inhibitory junction potentials consisting of two phases, rapid and subsequent slow hyperpolarization in the membrane potential of longitudinal smooth muscle cells. Rp-cAMPS, another inhibitor of PKA, inhibited the delayed slow hyperpolarization. It also inhibited the exogenously added VIP-induced hyperpolarization of the cell membrane. Thus, the present study suggests that activation of PKA via activation of VIP receptors is associated with activation of ChTx-sensitive K(+) channels in relaxation of longitudinal muscle of the distal colon of Wistar-ST rats. British Journal of Pharmacology (2000) 129, 140 - 146

alpha(2)-adrenoceptor and NPY receptor-mediated contractions of porcine isolated blood vessels: evidence for involvement of the vascular endothelium

1. Enhanced contractions to the alpha(2)-adrenoceptor agonist UK14304 and neuropeptide Y (NPY) in the porcine ear artery can be uncovered by pharmacological manipulation. The aim of this study was to determine whether similar pharmacological manipulation can uncover enhanced contractions in the porcine splenic artery, and to determine whether the endothelium modulates these responses. 2. UK14304 (0.3 microM) and NPY (0.1 microM) produced small contractions of the porcine splenic artery. After pre-contraction of the tissue with U46619, followed by relaxation with forskolin, the responses to both UK14304 and NPY were enhanced. Enhanced contractions to both UK14304 and NPY were also obtained after relaxation with SNP. These results demonstrate that, as in the porcine ear artery, alpha(2)-adrenoceptors and NPY receptors are able to produce enhanced contractile responses through both adenylyl cyclase-dependent and -independent signal transduction pathways. 3. Removal of the endothelium had no significant effect on responses to UK14304 either alone or in the presence of U46619 and forskolin in the porcine splenic artery. On the other hand, responses to UK14304 after relaxation with SNP were reduced after endothelium-denudation in both the porcine splenic artery and ear artery. Similar results were obtained with NPY in the porcine ear artery. 4. In conclusion, enhanced contractile responses to UK14304 and NPY in the porcine splenic artery can be uncovered using methods similar to those employed in the porcine ear artery. Under certain conditions the responses to both agents are modulated by the endothelium. These data highlight further the similarities in the signal transduction pathways used by both alpha(2)-adrenoceptors and NPY receptors to induce vasoconstriction.

Pharmacological characterization of the human P2Y11 receptor

1 The human P2Y11 receptor is coupled to both the phosphoinositide and the cyclic AMP pathways. A pharmacological characterization of the recombinant human P2Y11 receptor has been conducted following stable expression in two different cell lines: the 1321N1 astrocytoma cells for inositol trisphosphate measurements and the CHO-K1 cells for cyclic AMP assays. The rank order of potency of a series of nucleotides was almost identical for the two pathways: ATPgammaS approximately BzATP > dATP > ATP > ADPbetaS > 2MeSATP. 2 ADPbetaS, AMPalphaS and A3P5PS behaved as partial agonists of the human P2Y11 receptor. At high concentrations, these three nucleotides were able to partially inhibit the ATP response. 3 Suramin was a more potent antagonist than reactive blue 2, whereas pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid was completely inactive. The P2Y11 receptor proved to be sensitive to suramin in a competitive way with an apparent Ki value of 0.82+/-0. 07 microM. 4 The ATP derivative AR-C67085 (2-propylthio-beta, gamma-dichloromethylene-D-ATP), a potent inhibitor of ADP-induced platelet aggregation, was the most potent agonist of the P2Y11 receptor, among the various nucleotides tested. 5 The pharmacological profile of the recombinant human P2Y11 receptor is closely similar to that of the cyclic AMP-coupled P2 receptor recently described in HL-60 cells, suggesting that it is the same receptor.

Integrin-associated protein stimulates alpha2beta1-dependent chemotaxis via Gi-mediated inhibition of adenylate cyclase and extracellular-regulated kinases

Integrin-associated protein (IAP/CD47) augments the function of alpha2beta1 integrin in smooth muscle cells (SMC), resulting in enhanced chemotaxis toward soluble collagen (Wang, X-Q., and W.A. Frazier. 1998. Mol. Biol. Cell. 9:865). IAP-deficient SMC derived from IAP(-/-) animals did not migrate in response to 4N1K (KRFYVVMWKK), a peptide agonist of IAP derived from the COOH-terminal domain of thrombospondin-1 (TSP1). When normal SMC were preincubated with 4N1K or an anti-alpha2beta1 function-stimulating antibody, cell migration to soluble collagen was significantly enhanced. 4N1K-induced chemotaxis was blocked by treatment of SMC with pertussis toxin indicating that IAP acts through Gi. In agreement with this, 4N1K evoked a rapid decrease in cAMP levels which was intensified in the presence of collagen, and forskolin and 8-Br-cAMP both inhibited SMC migration stimulated via IAP. 4N1K strongly inhibited extracellular regulated kinase (ERK) activation in SMC attaching to collagen and reduced basal ERK activity in suspended SMC. Pertussis toxin treatment of SMC significantly activated ERK, suggesting that an inhibitory input was alleviated. Inhibition of ERK activity by (a) the MAP kinase kinase (MEK) inhibitor, PD98059, (b) antisense oligonucleotide depletion of ERK, and (c) expression of mitogen-activated protein (MAP) kinase phosphatase-1 in SMC all led to increased migration to collagen, 4N1K, or 4N1K plus collagen. Thus, IAP stimulates alpha2beta1 integrin-mediated SMC migration via Gi-mediated inhibition of ERK activity and suppression of cyclic AMP levels. Both of these signaling pathways could directly modulate the state of the integrin as well as impact downstream components of the cell motility apparatus.

Cannabinoid CB1 receptors fail to cause relaxation, but couple via Gi/Go to the inhibition of adenylyl cyclase in carotid artery smooth muscle

1. The aim of the current study was to characterize which cannabinoid receptors, if any, are present on rat carotid artery smooth muscle. Additionally, the effects of cannabinoids on carotid artery tone, on cyclic AMP accumulation and on forskolin-induced relaxation were examined in the same tissue. 2. Stimulation of carotid arteries with forskolin (10 microM) significantly increased cyclic AMP accumulation, an effect that was inhibited in a concentration-dependent manner by the cannabinoid receptor agonist, methanandamide. 3. Similar inhibition was seen with the CB1 agonist HU-210 but this inhibition was not mimicked by the CB2 agonist, WIN 55,2212-2. 4. The inhibitory effect of methanandamide on cyclic AMP accumulation was prevented by incubation of the arteries with pertussis toxin and was significantly reduced by LY320135, a selective CB1 antagonist, but not by SR 144528, a CB2-selective antagonist. 5. Methanandamide failed to relax carotid arteries pre-contracted with phenylephrine, but inhibited forskolin-induced relaxation of these arteries. This functional inhibition of relaxation by methanandamide was inhibited by CB1-selective (LY320135 and SR 141716A), but not a CB2-selective antagonist (SR 144528). 6. These data demonstrate the presence of functional G protein-linked cannabinoid receptors of the CB1 subtype in the rat carotid artery, but show that these receptors inhibit cyclic AMP accumulation rather than cause relaxation.

Domains determining agonist selectivity in chimaeric VIP2 (VPAC2)/PACAP (PAC1) receptors

1 The VPAC2 and PAC1 receptors are closely related members of the Group II G protein-coupled receptor family. At the VPAC2 receptor, VIP is equipotent to PACAP-38 in stimulating cyclic AMP production, whereas at the PAC1 receptor PACAP-38 is many fold more potent than VIP. In this study, domains which confer this selectivity were investigated by constructing four chimaeric receptors in which segments of the VPAC2 receptor were exchanged with the corresponding segment from the PAC1 receptor. 2 When expressed in COS 7 cells all the chimaeric receptors bound the common ligand [125I]PACAP-27 and produced cyclic AMP in response to agonists. 3 Relative selectivity for agonists was determined primarily by the amino terminal extracellular domain of the PAC1 receptor and the VPAC2 receptor. The interchange of other domains had little effect on the potency of PACAP-38 or PACAP-27. 4 For chimaeric constructs with a PAC1 receptor amino terminal domain, the substitution of increasing portions of the VPAC2 receptor decreased the potency of VIP yet increased that of helodermin. 5 This suggests that the interaction of VIP/helodermin but not PACAP with the PAC1 receptor may be influenced (and differentially so) by additional receptor domains.

Effects of a range of beta2 adrenoceptor agonists on changes in intracellular cyclic AMP and on cyclic AMP driven gene expression in cultured human airway smooth muscle cells

1. The effects of the selective beta2 adrenoceptor agonists salbutamol, terbutaline and salmeterol and the non-selective beta adrenoceptor agonist isoprenaline on [3H]-cyclic AMP formation and cyclic AMP response element (CRE) driven luciferase expression, assessed using the construct p6CRE/luc, were studied in primary cultures of human airway smooth muscle (HASM) cells. 2. Optimal transfection conditions for transient expression of pGL3 Control were 4 microg DNA/well71 in a 6 well plate and 1.8 microl Transfectam/microg DNA. Expression was maximal at 48 - 72 h. 3. Salbutamol (maximum response 19%, EC50 0.6 microM), terbutaline (maximum response 38%, EC50 2.3 microM) and salmeterol (maximum response 18%, EC50 0.0012 microM) were all partial agonists for cyclic AMP formation compared with isoprenaline (EC50 0.08 microM). However, all of the beta2 adrenoceptor agonists produced increases in CRE-driven luciferase activity, in cultured HASM transfected with the vector p6CRE/luc, which were equivalent or greater (salmeterol) than those seen with isoprenaline. 4. Both salbutamol and salmeterol were more potent at increasing luciferase expression than in elevating cyclic AMP levels in these cells. The potency ratios (EC50 (cyclic AMP)/EC50 (LUC)) for the agents studied were isoprenaline: 0. 2 fold, terbutaline: 3 fold, salbutamol: 24 fold, salmeterol: 38 fold. 5. These data suggest that important quantitative differences exist in the ability of beta2 adrenoceptor agonists to increase whole cell cyclic AMP levels in airway smooth muscle and to drive gene expression via a CRE-driven mechanism.

The effects of endomorphin-1 and endomorphin-2 in CHO cells expressing recombinant mu-opioid receptors and SH-SY5Y cells

1 Endomorphin-1 and -2 (E-1/E-2) have been proposed as endogenous ligands for the mu-opioid receptor. The aims of this study are to characterize the binding of E-1/E-2 and the subsequent effects on cyclic AMP formation and [Ca2+]i levels in SH-SY5Y and Chinese hamster ovary (CHO) cells expressing endogenous and recombinant mu-opioid receptors. 2 E-1 displaced [3H]-diprenorphine ([3H]-DPN) binding in CHO micro and SH-SY5Y membranes with pKi values of 8.02+/-0.09 and 8.54+/-0.13 respectively. E-2 displaced [3H]-DPN binding in CHOmu and SH-SY5Y cells with pKi values of 7.82+/-0.11 and 8.43+/-0.13 respectively. E-1/E-2 bound weakly to CHOdelta and CHOkappa membranes, with IC50 values of greater than 10 microM. 3 In CHOmu cells, E-1/E-2 inhibited forskolin (1 microM) stimulated cyclic AMP formation with pIC50 values of 8.03+/-0.16 (Imax = 53.0+/-9. 3%) and 8.15+/-0.24 (Imax = 56.3+/-3.8%) respectively. In SH-SY5Y cells E1/E2 inhibited forskolin stimulated cyclic AMP formation with pIC50 values of 7.72+/-0.13 (Imax=46.9+/-5.6%) and 8.11+/-0.31 (Imax = 40.2+/-2.8%) respectively. 4 E-1/E-2 (1 microM) increased [Ca2+]i in fura-2 loaded CHOmu cell suspensions in a thapsigargin sensitive and naloxone reversible manner. Mean increases observed were 106+/-28 and 69+/-6.7 nM respectively. In single adherent cells E-1/E-2 (1 microM) increased [Ca2+]i with a mean 340/380 ratio change of 0.81+/-0.09 and 0.40+/-0.08 ratio units respectively. E-1/E-2 failed to increase intracellular calcium in CHOdelta, CHOkappa and SH-SY5Y cells. 5 These data show that E-1/E-2 bind with high affinity and selectivity to mu-opioid receptors and modulate signal transduction pathways typical of opioids. This provides further evidence that these two peptides may be endogenous ligands at the mu-opioid receptor.

Regulation of cyclic AMP by extracellular ATP in cultured brain capillary endothelial cells

1 In primary unpassaged rat brain capillary endothelial cell cultures (RBECs), using reverse-transcriptase PCR with primers specific for P2Y receptor subtypes, we detected mRNA for P2Y2, P2Y4 and P2Y6, but not P2Y1 receptors. 2 None of the various nucleotides tested reduced forskolin elevated cyclic AMP levels in RBECs. ATP and ATPgammaS, as well as adenosine, enhanced cyclic AMP accumulation in the presence of forskolin. 3 Comparison of the concentration response curves to ATPgammaS with those for ATP and adenosine, at different incubation times, indicated that the response to purine nucleotides was not wholly dependent on conversion to adenosine. Adenosine deaminase abolished the response to adenosine but only reduced the response to ATP by about 50%. These results suggest the participation of a receptor responsive to nucleotides. 4 Isobutylmethylxanthine and 8-sulphophenyltheophylline prevented the cyclic AMP response, while neither 8-cyclopentyl-1, 3-dipropylxanthine nor SCH58261 were effective antagonists. 2-chloradenosine gave a robust response, but neither 2-chloro-N6-cyclopentyladenosine nor CGS 21680 were agonists. 5 These results show that adenosine and ATP can elevate the cyclic AMP levels of brain endothelial cells by acting on receptors which have a pharmacology apparently distinct from known P2Y and adenosine receptors.