Pharmacological properties of nociceptin/orphanin FQ-induced stimulation and inhibition of cyclic AMP formation in distinct layers of rat olfactory bulb

1. We recently reported that nociceptin/orphanin FQ (N/OFQ) inhibited forskolin-stimulated adenylyl cyclase activity and increased basal enzyme activity in membranes of the external plexiform layer (EPL) and granule cell layer (GRL), respectively, of the rat main olfactory bulb. In the present study we have characterized the pharmacological profile of the inhibitory and stimulatory responses by examining the effects of various N/OFQ receptor agonists and antagonists. 2. N/OFQ(1 - 13)NH(2) fully mimicked the inhibitory and stimulatory effects of N/OFQ with EC(50) values of 0.9 and 6.5 nM, respectively. N/OFQ(1 - 7) was inactive at concentrations up to 1 microM, whereas Ac-RYYRIK-NH(2) and [Phe(1)Psi(CH(2)NH)Gly(2)]N/OFQ(1 - 13)-NH(2) behaved as partial agonists in eliciting both responses. 3. The nonpeptidyl N/OFQ receptor antagonist J-113397 competitively counteracted the inhibitory and stimulatory effects of N/OFQ with pA(2) values of 8.63 and 8.70, respectively. Similarly, the peptidyl antagonist [Nphe(1)]N/OFQ(1 - 13)NH(2) potently antagonized the two effects with pA(2) values of 8.03 and 8.45, respectively. None of the antagonists per se affected adenylyl cyclase activity. 4. These data show that in distinct layers of rat olfactory bulb both the inhibitory and stimulatory effects of N/OFQ on cyclic AMP formation display pharmacological properties consistent with the involvement of N/OFQ receptors.

Cyclic GMP-dependent vasodilatory properties of LASSBio 294 in rat aorta

. The effects of LASSBio 294, a new 3,4-methylenedioxybenzoyl-2-thienylhydrazone, on vascular tonus were investigated in isolated rat aortic rings. 2. LASSBio 294 induced a concentration-dependent relaxation of intact rat aortic rings with an inhibitory concentration (IC(50)) of 74 microM (95% confidence limits: 59 - 92). The mechanical removal of the endothelium abolished this effect. 3. In aortic rings with intact endothelium the effect of 100 microM LASSBio 294 was not altered by the pharmacological inhibition of NOS and cyclo-oxygenase pathways with 500 microM L-NAME and 10 microM indomethacin, respectively. 4. LASSBio 294 (100 microM) was able to relax aortic rings pre-contracted with high extracellular K(+) (KCl 100 mM). 5. The relaxant effect of LASSBio 294 was fully reversed (and prevented) by the addition of 1 microM ODQ (1H-(1,2,4)oxadiazolo[4,3-a]quinoxaline-1-one), a selective inhibitor of soluble guanylate cyclase. 6. LASSBio 294 (100 microM) had no direct effect on PDE3 and PDE4 activities, however, it increased by 150% cyclic GMP content in aortic rings pre-treated with 100 microM L-NAME and 10 microM indomethacin, as did 1 microM zaprinast, a selective PDE5 inhibitor. 7. In conclusion, LASSBio 294 induced relaxation of isolated rat aorta probably by directly increasing cyclic GMP content, possibly as a consequence of PDE5 inhibition.

Pharmacological and biochemical characterization of adenosine receptors in the human malignant melanoma A375 cell line

1. The present work characterizes, from a pharmacological and biochemical point of view, adenosine receptors in the human malignant melanoma A375 cell line. 2. Adenosine receptors were detected by RT - PCR experiments. A1 receptors were characterized using [3H]-DPCPX binding with a KD of 1.9+/-0.2 nM and Bmax of 23+/-7 fmol x mg(-1) of protein. A2A receptors were studied with [3H]-SCH 58261 binding and revealed a KD of 5.1+/-0.2 nM and a Bmax of 220+/-7 fmol x mg(-1) of protein. A3 receptors were studied with the new A3 adenosine receptor antagonist [3H]-MRE 3008F20, the only A3 selective radioligand currently available. Saturation experiments revealed a single high affinity binding site with KD of 3.3+/-0.7 nM and Bmax of 291+/-50 fmol x mg(-1) of protein. 3. The pharmacological profile of radioligand binding on A375 cells was established using typical adenosine ligands which displayed a rank order of potency typical of the different adenosine receptor subtype. 4. Thermodynamic data indicated that radioligand binding to adenosine receptor subtypes in A375 cells was entropy- and enthalpy-driven. 5. In functional assays the high affinity A2A agonists HE-NECA, CGS 21680 and A2A - A2B agonist NECA were able to increase cyclic AMP accumulation in A375 cells whereas A3 agonists Cl-IB-MECA, IB-MECA and NECA were able to stimulate Ca2+ mobilization. In conclusion, all these data indicate, for the first time, that adenosine receptors with a pharmacological and biochemical profile typical of the A1, A2A, A2B and A3 receptor subtype are present on A375 melanoma cell line.

Phenanthrolines--a new class of CFTR chloride channel openers

1. A number of phenanthrolines and benzoquinolines were examined for their ability to activate epithelial chloride secretion by measuring short circuit current (SCC) using the mouse colon epithelium. 1,10 phenanthroline stimulated electrogenic chloride secretion with an EC(50) of 612+/-10 microM and a Hill slope of 4.9+/-0.3. A similar pharmacology was demonstrated by both 1,7 and 4,7 phenanthrolines, 7,8 benzoquinoline and phenanthridine. 2. Evidence that the increase in SCC caused by 1,10 phenanthroline was due to chloride secretion is based upon (a) inhibition of the current by furosemide, (b) failure of cystic fibrosis (CF) colons to respond and (c) an associated net flux of (36)Cl(-). 3. 1,10 Phenanthroline affected neither the generation of cyclic AMP or the concentration of intracellular Ca(2+) in colonic epithelial cells. 4. 1,10 phenanthroline affected the chloride conductance of the apical membrane, as shown by an increase in chloride current in 'apical membrane only' preparations in the presence of an apical to basolateral chloride gradient. The increase in chloride current was inhibited by 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) and was not present in CF colons. 5. Additionally, 1,10 phenanthroline activated basolateral K(+) channels, both Ca(2+)- and cyclic AMP-sensitive channels, as shown by inhibitor studies with charybdotoxin (ChTX) and XE991, and after the apical membrane was permeabilized with nystatin. 6. The phenanthrolines and benzoquinolines described here, with dual actions affecting CFTR and basolateral K(+) channels, may constitute useful lead compounds for adjunct therapy in CF.

Evidence that the anti-spasmogenic effect of the beta-adrenoceptor agonist, isoprenaline, on guinea-pig trachealis is not mediated by cyclic AMP-dependent protein kinase

1. The spasmolytic and anti-spasmogenic activity of beta-adrenoceptor agonists on airways smooth muscle is thought to involve activation of the cyclic AMP/cyclic AMP-dependent protein kinase (PKA) cascade. Here we have tested the hypothesis that PKA mediates the anti-spasmogenic activity of isoprenaline and other cyclic AMP-elevating agents in guinea-pig isolated trachea by utilizing a number of cell permeant cyclic AMP analogues that act as competitive 'antagonists' of PKA. 2. Anion-exchange chromatography of guinea-pig tracheae resolved two peaks of PKA activity that corresponded to the type I ( approximately 5%) and type II ( approximately 93%) isoenzymes. 3. Pre-treatment of tracheae with zardaverine (30 microM), vasoactive intestinal peptide (VIP) (1 microM) and the non-selective activator of PKA, Sp-8-CPT-cAMPS (10 microM), produced a non-parallel rightwards shift in the concentration-response curves that described acetylcholine (ACh)-induced tension generation. The type II-selective PKA inhibitor, Rp-8-CPT-cAMPS (300 microM), abolished this effect. 4. Pre-treatment of tracheae with Sp-8-Br-PET-cGMPS (30 microM) produced a non-parallel rightwards shift of the concentration-response curves that described ACh-induced tension generation. The selective cyclic GMP-dependent protein kinase (PKG) inhibitor, Rp-8-pCPT-cGMPS (300 microM), abolished this effect. 5. Pre-treatment of tracheae with isoprenaline (1 microM) produced a 10 fold shift to the right of the ACh concentration-response curve by a mechanism that was unaffected by Rp-8-Br-cAMPS (300 microM, selective inhibitor of type I PKA), Rp-8-CPT-cAMPS (300 microM) and Rp-8-pCPT-cGMPS (300 microM). 6. We conclude that the anti-spasmogenic activity of Sp-8-CPT-cAMPS, zardaverine and VIP in guinea-pig trachea is attributable to activation of the cyclic AMP/PKA cascade whereas isoprenaline suppresses ACh-induced contractions by a mechanism(s) that is independent of PKA and PKG.

Identification and quantification of phosphodiesterase 4 subtypes in CD4 and CD8 lymphocytes from healthy and asthmatic subjects

In the present study, for the first time, PDE4 subtypes were identified and semi-quantified in both CD4 and CD8 lymphocytes from healthy and asthmatic individuals. CD4 and CD8 lymphocytes from healthy and mild asymptomatic asthmatic subjects (receiving beta-agonist therapy only) were isolated from peripheral venous blood using appropriate antibody coated paramagnetic beads. PDE4 subtypes and beta-actin were identified by digoxigenin (DIG)-labelling reverse transcriptase-polymerase chain reaction and semi-quantified by DIG-detection enzyme-linked immunosorbance assay. In CD4 and CD8 lymphocytes PDE4A, PDE4B and PDE4D were detected, with no significant differences observed between healthy and asthmatic groups. In CD8 lymphocytes, enzyme subtype expression was lower and showed more intersubject variability. In functional studies investigating the effects of various PDE inhibitors on PHA-induced proliferation of mononuclear cells from healthy and asthmatic subjects, CDP840 (0.03 - 10 microM), rolipram (0.1 - 10 microM) and theophylline (10 microM - 1 mM) inhibited PHA-induced proliferation of mononuclear cells from healthy and asthmatic subjects in a concentration-dependent manner, although no significant difference was observed between the groups investigated. In additional studies, total monocyte cyclic AMP PDE activity was investigated in cells isolated from asthmatic subjects both prior to and 24 h after allergen challenge. Total monocyte cyclic AMP PDE activity remained unaffected following challenge of asthmatic subjects with either house dust mite or cat dander and was inhibited in a concentration-dependent manner by rolipram (0.01 - 100 microM) both before and after allergen challenge.

Cyclic AMP elevating agents and nitric oxide modulate angiotensin II-induced leukocyte-endothelial cell interactions in vivo

Angiotensin (Ang-II) is a key molecule in the development of cardiac ischaemic disorders and displays proinflammatory activity in vivo. Since intracellular cyclic nucleotides elevating agents have proved to be effective modulators of leukocyte recruitment, we have evaluated their effect on Ang-II-induced leukocyte-endothelial cell interactions in vivo using intravital microscopy within the rat mesenteric microcirculation. Pretreatment with iloprost significantly inhibited (1 nM) Ang-II-induced increase in leukocyte rolling flux, adhesion and emigration at 60 min by 96, 92 and 90% respectively, and returned leukocyte rolling velocity to basal levels. Pretreatment with salbutamol or co-superfusion with forskolin exerted similar effects. When theophylline was administered, leukocyte rolling flux, adhesion and emigration elicited by Ang-II were significantly attenuated by 81, 89 and 71% respectively. Rolipram administration caused similar reduction of Ang-II-induced leukocyte responses. Co-superfusion of Ang-II with the NO-donor, spermine-NO, or 8-Br-cyclic GMP, or pretreatment with a transdermal nytroglycerin patch, resulted in a significant reduction of the leukocyte-endothelial cell interactions elicited by Ang-II. Salbutamol preadministration did not modify leukocyte-endothelial cell interactions elicited by either L-NAME or L-NAME+Ang-II, indicating that the inhibitory leukocyte effects caused by cyclic AMP-elevating agents are mediated through NO release. In conclusion, we have provided evidence that cyclic AMP elevating agents and NO donors, are potent inhibitors of Ang-II-induced leukocyte-endothelial cell interactions. Thus, they could constitute a powerful therapeutical tool in the control of the leukocyte recruitment characteristic of the vascular lesions that occur in cardiovascular disease states where Ang-II plays a critical role.

Effect of a tumour-produced lipid-mobilizing factor on protein synthesis and degradation

Treatment of murine myoblasts, myotubes and tumour cells with a tumour-produced lipid mobilizing factor (LMF), caused a concentration-dependent stimulation of protein synthesis, within a 24 h period. There was no effect on cell number or [(3)H] thymidine incorporation, but a similar concentration-dependent stimulation of 2-deoxyglucose uptake. LMF produced an increase in intracellular cyclic AMP levels, which was linearly (r(2)= 0.973) related to the increase in protein synthesis. The effect of LMF was attenuated by the adenylate cyclase inhibitor MDL(12330A), and was additive with the stimulation produced by forskolin. Both propranolol (10 microM) and the specific beta(3)-adrenergic receptor antagonist SR 59230A (10(-5)M), significantly reduced the stimulation of protein synthesis induced by LMF. Protein synthesis was also increased by 69% (P = 0.006) in soleus muscles of mice administered LMF, while there was a 26% decrease in protein degradation (P = 0.03). While LMF had no effect on the lysosomal enzymes, cathepsins B and L, there was a decrease in proteasome activity, as determined both by the 'chymotrypsin-like' enzyme activity, as well as expression of proteasome alpha-type subunits, determined by Western blotting. These results show that in addition to its lipid-mobilizing activity LMF also increases protein accumulation in skeletal muscle both by an increase in protein synthesis and a decrease in protein catabolism.

Agonist trafficking of G(i/o)-mediated alpha(2A)-adrenoceptor responses in HEL 92.1.7 cells

1. The ability of 19 agonists to elevate Ca(2+) and inhibit forskolin-induced cyclic AMP elevation through alpha(2A)-adrenoceptors in HEL 92.1.7 cells was investigated. Ligands of catecholamine-like- (five), imidazoline- (nine) and non-catecholamine-non-imidazoline-type (five) were included. 2. The relative maximum responses were similar in both assays. Five ligands were full or nearly full agonists, six produced 20 - 70% of the response to a full agonist and the remaining eight gave lower responses (< 20%) so that their potencies were difficult to evaluate. 3. Marked differences in the potencies of the agonists with respect to the two measured responses were seen. The catecholamines were several times less potent in decreasing cyclic AMP than in increasing Ca(2+), whereas the other, both imidazoline and ox-/thiazoloazepine ligands, were several times more potent with respect to the former than the latter response. For instance, UK14,304 was more potent than adrenaline with respect to the cyclic AMP response but less potent than adrenaline with respect to the Ca(2+) response. 4. All the responses were sensitive to pertussis toxin-pretreatment. Also the possible role of PLA(2), beta-adrenoceptors or ligand transport or metabolism as a source of error could be excluded. The results suggest that the active receptor states produced by catecholamines and the other agonists are markedly different and therefore have different abilities to activate different signalling pathways.

Dual effects of muscarinic M(2) acetylcholine receptors on the synthesis of cyclic AMP in CHO cells: dependence on time, receptor density and receptor agonists

1. Muscarinic M(2) receptors normally inhibit the production of cyclic AMP via G(i) proteins, but a stimulatory component occurs in their effect at high agonist concentrations, believed to be based on the activation of G(s) proteins. We investigated the conditions which determine the occurrence and extent of the stimulatory component in CHO cells stably expressing muscarinic M(2) receptors. 2. Biphasic concentration-response curves (decline followed by return towards control values) were obtained after 10 min incubation with carbachol, oxotremorine-M, acetylcholine, arecoline and arecaidine propargyl ester, but the upward phase was missing with oxotremorine, methylfurmethide, furmethide and pentylthio-TZTP. Shortening the incubation favoured the occurrence of the stimulatory component. Carbachol (1 mM) and oxotremorine-M (1 mM) brought about net stimulation (above 100% of control) of cyclic AMP synthesis during 2 min incubations. The stimulatory components disappeared after the density of receptors had been lowered with oxyphenonium mustard. 3. All agonists stimulated the synthesis of cyclic AMP in cells pretreated with pertussis toxin. 4. Most differences between agonists regarding the stimulatory component of their effect on cyclic AMP synthesis could be explained by differences in their efficacy and the induced receptor internalization. 5. We propose that the G(s)-mediated stimulatory component of the effect of muscarinic M(2) receptors on cyclic AMP synthesis only occurs if the density of activated receptors is high enough to saturate the G(i) proteins and proportionate to the receptors' low affinity for the G(s) proteins. It tends to be abolished by receptor internalization.

Involvement of cyclic AMP systems in morphine physical dependence in mice: prevention of development of morphine dependence by rolipram, a phosphodiesterase 4 inhibitor

In this study, we examined whether morphine dependence was inhibited by rolipram, a cyclic AMP selective phosphodiesterase inhibitor in mice, since a role for the cyclic AMP systems in the development of morphine dependence has been reported. Mice, which received morphine (10 mg kg(-1) s.c.) twice a day for 5 days showed withdrawal syndromes such as jumping, rearing and forepaw tremor following naloxone challenge (5 mg kg(-1) i.p.) on the 6th day. Such mice exhibited a significant elevation of cyclic AMP levels in the thalamus compared to control mice. However, co-administration of rolipram (1 mg kg(-1) i.p.) with morphine for 5 days significantly attenuated the severity of the withdrawal syndrome and the increase in the cyclic AMP levels after the administration of naloxone. In naïve mice, acute morphine treatment (10 mg kg(-1) s.c.) decreased cyclic AMP levels in the thalamus and cerebral cortex 10 min later. The decrease of cyclic AMP levels induced by acute morphine treatment was blocked by co-administration of rolipram (1 mg kg(-1) i.p.). However, acute rolipram did not affect the naloxone-precipitated morphine withdrawal syndrome. These results suggest that the elevation of the cyclic AMP levels is involved in the development of morphine withdrawal syndrome and that blockade of the morphine-induced reduction of cyclic AMP levels by chronic rolipram inhibits the development of dependence and the behavioural and biochemical changes induced by naloxone. Furthermore, rolipram may be a useful drug for attenuating the development of morphine dependence.

Prostaglandin E(2) increases cyclic AMP and inhibits endothelin-1 production/secretion by guinea-pig tracheal epithelial cells through EP(4) receptors

Prostaglandin E(2) (PGE(2)) increased adenosine 3' : 5'-cyclic monophosphate (cyclic AMP) formation in tracheal epithelial cells and concomitantly decreased the production/secretion of immunoreactive endothelin (irET). Naturally occurring prostanoids and selective and non-selective EP receptor agonists showed the following rank order of potency in stimulating cyclic AMP generation by epithelial cells: PGE(2) (EP-selective)>16,16-dimethyl PGE(2) (EP-selective)>11-deoxy PGE(2) (EP-selective)>>>iloprost (IP/EP(1)/EP(3)-selective), butaprost (EP(2)-selective), PGD(2) (DP-selective), PGF(2alpha) (FP-selective). The lack of responsiveness of the latter prostanoids indicated that the prostanoid receptor present in these cells is not of the DP, FP, IP, EP(1), EP(2) or EP(3) subtype. Pre-incubating the cells with the selective TP/EP(4)-receptor antagonists AH23848B and AH22921X antagonized the PGE(2)-evoked cyclic AMP generation. This suggested that EP(4) receptors mediate PGE(2) effects. However, in addition to any antagonistic effects at EP(4)-receptors, both compounds, to a different extent, modified cyclic AMP metabolism. The selective EP(1), DP and EP(2) receptor antagonist (AH6809) failed to inhibit PGE(2)-evoked cyclic AMP generation which confirmed that the EP(2) receptor subtype did not contribute to the change in cyclic AMP formation in these cells. The PGE(2)-induced inhibition of irET production by guinea-pig tracheal epithelial cells was due to cyclic AMP generation and activation of the cyclic AMP-dependent protein kinase since this effect was reverted by the cyclic AMP antagonist Rp-cAMPS. These results provide the first evidence supporting the existence of a functional prostaglandin E(2) receptor that shares the pharmacological features of the EP(4)-receptor subtype in guinea-pig tracheal epithelial cells. These receptors modulate cyclic AMP formation as well as ET-1 production/secretion in these cells.

Differential coupling of the human P2Y(11) receptor to phospholipase C and adenylyl cyclase

1. The human P2Y(11) (hP2Y(11)) receptor was stably expressed in two cell lines, 1321N1 human astrocytoma cells (1321N1-hP2Y(11)) and Chinese hamster ovary cells (CHO-hP2Y(11)), and its coupling to phospholipase C and adenylyl cyclase was assessed. 2. In 1321N1-hP2Y(11) cells, ATP promoted inositol phosphate (IP) accumulation with low microM potency (EC(50)=8.5+/-0.1 microM), whereas it was 15 fold less potent (130+/-10 microM) in evoking cyclic AMP production. 3. In CHO-hP2Y(11) cells, ATP promoted IP accumulation with slightly higher potency (EC(50)=3.6+/-1.3 microM) than in 1321N1-hP2Y(11) cells, but it was still 15 fold less potent in promoting cyclic AMP accumulation (EC(50)=62.4+/-15.6 microM) than for IP accumulation. Comparable differences in potencies for promoting the two second messenger responses were observed with other adenosine nucleotide analogues. 4. In 1321N1-hP2Y(11) and CHO-hP2Y(11) cells, down regulation of PKC by chronic treatment with phorbol ester decreased ATP-promoted cyclic AMP accumulation by 60--80% (P<0.001) with no change in its potency. Likewise, chelation of intracellular Ca(2+) decreased ATP-promoted cyclic AMP accumulation by approximately 45% in 1321N1-hP2Y(11) cells, whereas chelation had no effect on either the efficacy or potency of ATP in CHO-hP2Y(11) cells. 5. We conclude that coupling of hP2Y(11) receptors to adenylyl cyclase in these cell lines is much weaker than coupling to phospholipase C, and that activation of PKC and intracellular Ca(2+) mobilization as consequences of inositol lipid hydrolysis potentiates the capacity of ATP to increase cyclic AMP accumulation in both 1321N1-hP2Y(11) and CHO-hP2Y(11) cells.

Evidence for cocaine and methylecgonidine stimulation of M(2) muscarinic receptors in cultured human embryonic lung cells

1. Muscarinic cholinoceptor stimulation leads to an increase in guanylyl cyclase activity and to a decrease in adenylyl cyclase activity. This study examined the effects of cocaine and methylecgonidine (MEG) on muscarinic receptors by measurement of cyclic GMP and cyclic AMP content in cultured human embryonic lung (HEL299) cells which specifically express M(2) muscarinic receptors. 2. A concentration-dependent increase in cyclic GMP production was observed in HEL299 cells incubated with carbachol, cocaine, or MEG for 24 h. The increase in cyclic GMP content was 3.6 fold for 1 microM carbachol (P < 0.01), 3.1 fold for 1 microM cocaine (P < 0.01), and 7.8 fold for 1 microM MEG (P < 0.001), respectively. This increase in cyclic GMP content was significantly attenuated or abolished by the muscarinic receptor antagonist atropine or the M(2) blocker methoctramine. 3. In contrast, cocaine, MEG, and carbachol produced a significant inhibition of cyclic AMP production in HEL299 cells. Compared to the control, HEL299 cells treated with 1 microM cocaine decreased cyclic AMP production by 30%. MEG and carbachol at 1 microM decreased cyclic AMP production by 37 and 38%, respectively. Atropine or methoctramine at 1 or 10 microM significantly attenuated or abolished the cocaine-induced decrease in cyclic AMP production. However, the antagonists alone had neither an effect on cyclic GMP nor cyclic AMP production. Pretreatment of HEL299 cells with pertussis toxin prevented the cocaine-induced reduction of cyclic AMP production. 4. Western blot analysis showed that HEL299 cells specifically express M(2) muscarinic receptors without detectable M(1) and M(3). Incubation of HEL299 cells with cocaine, carbachol, and atropine did not alter the expression of M(2) protein levels. However, the inducible isoform of nitric oxide synthase (iNOS) was induced in the presence of cocaine or carbachol and this induction was significantly attenuated after addition of atropine or methoctramine. 5. The present data show that cocaine and MEG significantly affect cyclic GMP and cyclic AMP production in cultured HEL299 cells. Our results also show that these effects result from the drug-induced stimulation of M(2) muscarinic receptors accompanied with no alterations of receptor expression. However, the induction of iNOS by cocaine may result in the increase in cyclic GMP production.

Activation of peroxisome proliferator-activated receptors (PPARs) by their ligands and protein kinase A activators

The nuclear peroxisome proliferator-activated receptors (PPARs) alpha, beta, and gamma activate the transcription of multiple genes involved in lipid metabolism. Several natural and synthetic ligands have been identified for each PPAR isotype but little is known about the phosphorylation state of these receptors. We show here that activators of protein kinase A (PKA) can enhance mouse PPAR activity in the absence and the presence of exogenous ligands in transient transfection experiments. Activation function 1 (AF-1) of PPARs was dispensable for transcriptional enhancement, whereas activation function 2 (AF-2) was required for this effect. We also show that several domains of PPAR can be phosphorylated by PKA in vitro. Moreover, gel retardation experiments suggest that PKA stabilizes binding of the liganded PPAR to DNA. PKA inhibitors decreased not only the kinase-dependent induction of PPARs but also their ligand-dependent induction, suggesting an interaction between both pathways that leads to maximal transcriptional induction by PPARs. Moreover, comparing PPAR alpha knockout (KO) with PPAR alpha WT mice, we show that the expression of the acyl CoA oxidase (ACO) gene can be regulated by PKA-activated PPAR alpha in liver. These data demonstrate that the PKA pathway is an important modulator of PPAR activity, and we propose a model associating this pathway in the control of fatty acid beta-oxidation under conditions of fasting, stress, and exercise.

Essential role of L-arginine uptake and protein tyrosine kinase activity for NO-dependent vasorelaxation induced by stretch, isometric tension and cyclic AMP in rat pulmonary arteries

1. The NO-dependent component of cyclic AMP-induced vasorelaxation in rat pulmonary arteries is critically dependent on extracellular L-arginine but independent of endothelial cell intracellular [Ca(2+)]. We examined whether L-arginine uptake was also essential for NO production induced by passive stretch or isometric tension, processes also reported to be Ca(2+)-independent. 2. The passive length-tension curve was depressed by physiological concentrations of L-arginine (400 microM; P<0.05). Inhibition of the y(+) transporter with 10 mM L-lysine, NO synthase with L-NAME (100 microM), or protein tyrosine kinase with erbstatin A (30 microM) caused identical upward shifts (P<0.001), alone or in combination. Tyrphostin 23 was similar to erbstatin A, whilst the inactive analogue tyrphostin A1 and genistein were without effect. 3. L-arginine (400 microM) shifted the PGF(2 alpha) concentration-response curve under isometric conditions to the right (P<0.05), whereas L-NAME or L-lysine caused a leftward shift (P<0.001). Tyrphostin 23 (30 microM) more than reversed the L-arginine-induced suppression of PGF(2 alpha)-induced tension; subsequent addition of L-NAME had no effect. The L-lysine-sensitive component of CPT cyclic AMP-induced vasorelaxation was abolished by erbstatin A. 4. ACh-induced vasorelaxation was approximately 80% inhibited by L-NAME, but was not affected by L-lysine or 400 microM L-arginine. Erbstatin A reduced the vasorelaxation by only approximately 25%. 5. We conclude that activation of NO production by stretch, isometric tension, or cyclic AMP in rat pulmonary arteries is critically dependent on the presence and uptake of physiological concentrations of extracellular L-arginine, and protein tyrosine kinase activity. This directly contrasts with ACh-induced vasorelaxation, which was independent of extracellular L-arginine, and relatively unaffected by tyrosine kinase inhibition.

A comparison of agonist-specific coupling of cloned human alpha(2)-adrenoceptor subtypes

The agonist-specific coupling properties of the three cloned human alpha(2)-adrenoceptor subtypes have been compared, when expressed at similar levels in Chinese hamster ovary (CHO) cell lines, using noradrenaline and (+/-)-meta-octopamine as agonists. Noradrenaline can couple the receptor to both the inhibition and stimulation of forskolin-stimulated cyclic AMP production in all three receptor subtypes, with the relative strength of the coupling to the pathways varying for each of the receptor subtypes. meta-Octopamine selectively couples the alpha(2A)-adrenoceptor only to the inhibition of forskolin-stimulated cyclic AMP production. However, meta-octopamine couples the alpha(2B)- and alpha(2C)-adrenoceptors to both the inhibition and stimulation of forskolin-stimulated cyclic AMP production. The relative potency of meta-octopamine to noradrenaline varies between the different alpha(2)-adrenoceptor subtypes. The effects of meta-octopamine are around two orders of magnitude less potent than those of noradrenaline on both the alpha(2A)- and alpha(2B)-adrenoceptor subtypes. In contrast, in the case of the alpha(2C)-adrenoceptor, meta-octopamine is only one order of magnitude less potent than noradrenaline in the stimulation of forskolin-stimulated cyclic AMP production and, in addition, is equipotent with noradrenaline in the inhibition of forskolin-stimulated cyclic AMP production and has an increased maximal response. This raises the possibility that meta-octopamine may have physiologically important actions via alpha(2C)-adrenoceptors in vivo. The results show that the modulation of cyclic AMP production occurs in both a subtype- and agonist-specific manner for alpha(2A)-adrenoceptors and in a subtype specific manner for alpha(2B)- and alpha(2C)-adrenoceptors.

Regulation of exocytosis by protein kinases and Ca(2+) in pancreatic duct epithelial cells

We asked if the mechanisms of exocytosis and its regulation in epithelial cells share features with those in excitable cells. Cultured dog pancreatic duct epithelial cells were loaded with an oxidizable neurotransmitter, dopamine or serotonin, and the subsequent release of these exogenous molecules during exocytosis was detected by carbon-fiber amperometry. Loaded cells displayed spontaneous exocytosis that may represent constitutive membrane transport. The quantal amperometric events induced by fusion of single vesicles had a rapid onset and decay, resembling those in adrenal chromaffin cells and serotonin-secreting leech neurons. Quantal events were frequently preceded by a "foot," assumed to be leak of transmitters through a transient fusion pore, suggesting that those cell types share a common fusion mechanism. As in neurons and endocrine cells, exocytosis in the epithelial cells could be evoked by elevating cytoplasmic Ca(2+) using ionomycin. Unlike in neurons, hyperosmotic solutions decreased exocytosis in the epithelial cells, and giant amperometric events composed of many concurrent quantal events were observed occasionally. Agents known to increase intracellular cAMP in the cells, such as forskolin, epinephrine, vasoactive intestinal peptide, or 8-Br-cAMP, increased the rate of exocytosis. The forskolin effect was inhibited by the Rp-isomer of cAMPS, a specific antagonist of protein kinase A, whereas the Sp-isomer, a specific agonist of PKA, evoked exocytosis. Thus, PKA is a downstream effector of cAMP. Finally, activation of protein kinase C by phorbol-12-myristate-13-acetate also increased exocytosis. The PMA effect was not mimicked by the inactive analogue, 4alpha-phorbol-12,13-didecanoate, and it was blocked by the PKC antagonist, bisindolylmaleimide I. Elevation of intracellular Ca(2+) was not needed for the actions of forskolin or PMA. In summary, exocytosis in epithelial cells can be stimulated directly by Ca(2+), PKA, or PKC, and is mediated by physical mechanisms similar to those in neurons and endocrine cells.

Functional, biochemical and molecular biological evidence for a possible beta(3)-adrenoceptor in human near-term myometrium

The possible existence of a beta(3)-adrenoceptor (beta(3)-AR) in human near-term myometrium was investigated by in vitro functional and biochemical studies and analysis of mRNA expression. SR 59119A and SR 59104A and CGP 12177 (two selective agonists and a partial agonist, respectively, of the beta(3)-AR), salbutamol and terbutaline (beta(2)-AR agonists) each produced a concentration-dependent relaxation of the myometrial spontaneous contractions. There were no differences in pD(2) values for the relaxing potencies of terbutaline, salbutamol, CGP 12177 and SR 59119A. The rank order for their relaxing efficacies was SR 59119A>SR 59104A>terbutaline approximately salbutamol approximately CGP 12177 (E(max)=52+/-7%, 42+/-12% and approximately 30% respectively). Propranolol, a beta(1)- and beta(2)-AR antagonist, and ICI 118551, a beta(2)-AR antagonist (both at 0.1 microM), did not affect the SR 59119A-induced relaxation whereas SR 59230A, a selective beta(3)-AR antagonist (1 microM), significantly reduced the maximal relaxing effect of SR 59119A. SR 59119A and salbutamol induced a significant increase in cyclic AMP levels that was antagonized by SR 59230A but not by propranolol for SR 59119A, and by propranolol but not by SR 59230A for salbutamol. The beta(3)-AR mRNA was positively expressed in myometrium preparations in a reverse transcription polymerase chain assay. The results presented provide the first evidence for the existence of the beta(3)-AR subtype in human near-term myometrium and suggest that the effects of SR 59119A might be mediated through an increase in cyclic AMP level.

The progestin levonorgestrel induces endothelium-independent relaxation of rabbit jugular vein via inhibition of calcium entry and protein kinase C: role of cyclic AMP

The progestin and oestrogen component of oral contraceptives have been involved in the development of venous thromboembolic events in women. In the present study we determined the vasoactive effects of sex steroids used in oral contraceptives in isolated preconstricted rabbit jugular veins in the presence of diclofenac and examined the underlying mechanisms. The natural hormone progesterone, the synthetic progestins levonorgestrel, 3-keto-desogestrel, gestodene and chlormadinone acetate, and the synthetic estrogen 17 alpha-ethinyloestradiol induced concentration-dependent relaxations of endothelium-intact veins constricted with U46619. Levonorgestrel also inhibited constrictions evoked by either a high potassium (K(+)) solution or phorbol myristate acetate (PMA) in the absence and presence of extracellular calcium (Ca(2+)). In addition, levonorgestrel depressed contractions evoked by Ca(2+) and reduced (45)Ca(2+) influx in depolarized veins. Relaxations to levonorgestrel in U46619-constricted veins were neither affected by the presence of the endothelium nor by the inhibitor of soluble guanylyl cyclase, NS2028, but were significantly improved either by the selective cyclic AMP phosphodiesterase inhibitor rolipram or in the absence of diclofenac, and decreased by the protein kinase A inhibitor, Rp-8-CPT-cAMPS. Rolipram also potentiated relaxations to levonorgestrel in PMA-constricted veins in the presence, but not in the absence of extracellular Ca(2+). Levonorgestrel increased levels of cyclic AMP and inhibited PMA-induced activation of protein kinase C in veins. These findings indicate that levonorgestrel caused endothelium-independent relaxations of jugular veins via inhibition of Ca(2+) entry and of protein kinase C activation. In addition, the cyclic AMP effector pathway contributes to the levonorgestrel-induced relaxation possibly by depressing Ca(2+) entry.

Cyclic nucleotide-gated channels colocalize with adenylyl cyclase in regions of restricted cAMP diffusion

Cyclic AMP is a ubiquitous second messenger that coordinates diverse cellular functions. Current methods for measuring cAMP lack both temporal and spatial resolution, leading to the pervasive notion that, unlike Ca(2+), cAMP signals are simple and contain little information. Here we show the development of adenovirus-expressed cyclic nucleotide-gated channels as sensors for cAMP. Homomultimeric channels composed of the olfactory alpha subunit responded rapidly to jumps in cAMP concentration, and their cAMP sensitivity was measured to calibrate the sensor for intracellular measurements. We used these channels to detect cAMP, produced by either heterologously expressed or endogenous adenylyl cyclase, in both single cells and cell populations. After forskolin stimulation, the endogenous adenylyl cyclase in C6-2B glioma cells produced high concentrations of cAMP near the channels, yet the global cAMP concentration remained low. We found that rapid exchange of the bulk cytoplasm in whole-cell patch clamp experiments did not prevent the buildup of significant levels of cAMP near the channels in human embryonic kidney 293 (HEK-293) cells expressing an exogenous adenylyl cyclase. These results can be explained quantitatively by a cell compartment model in which cyclic nucleotide-gated channels colocalize with adenylyl cyclase in microdomains, and diffusion of cAMP between these domains and the bulk cytosol is significantly hindered. In agreement with the model, we measured a slow rate of cAMP diffusion from the whole-cell patch pipette to the channels (90% exchange in 194 s, compared with 22-56 s for substances that monitor exchange with the cytosol). Without a microdomain and restricted diffusional access to the cytosol, we are unable to account for all of the results. It is worth noting that in models of unrestricted diffusion, even in extreme proximity to adenylyl cyclase, cAMP does not reach high enough concentrations to substantially activate PKA or cyclic nucleotide-gated channels, unless the entire cell fills with cAMP. Thus, the microdomains should facilitate rapid and efficient activation of both PKA and cyclic nucleotide-gated channels, and allow for local feedback control of adenylyl cyclase. Localized cAMP signals should also facilitate the differential regulation of cellular targets.

Cholera toxin treatment of vascular smooth muscle cells decreases smooth muscle alpha-actin content and abolishes the platelet-derived growth factor-BB-stimulated DNA synthesis

The second messenger cyclic AMP regulates diverse biological processes such as cell morphology and cell growth. We examined the role of the second messenger cyclic AMP on rat aortic vascular smooth muscle cell (VSMC) morphology and the intracellular transduction pathway mediated by platelet-derived growth factor beta-receptor (PDGF-Rbeta). The effect of PDGF-BB on VSMCs growth was assessed by [(3)H]-thymidine incorporation. Tyrosine phosphorylation of PDGF-Rbeta, PLC-gamma1, ERK1 and ERK2, p125(FAK) and paxillin as well as Sm alpha-actin was examined by the chemiluminescence Western blotting method. Actin mRNA level was quantitated by Northern blotting. Visualization of Sm alpha-actin filaments, paxillin and PDGF-Rbeta was performed by immunfluorescence microscopy. Cholera toxin (CTX; 10 nM) treatment lead to a large and sustained increase in the cyclic AMP concentration after 2 h which correlated with change of VSMC morphology including complete disruption of the Sm alpha-actin filament array and loss of focal adhesions. Treatment of VSMCs with CTX did not influence tyrosine phosphorylation of p125(FAK) and paxillin but decreased the content of a Sm alpha-actin protein. Maximal decrease of 70% was observed after 24 h of treatment. CTX also caused a 90% decrease of the actin mRNA level. CTX treatment completely abolished PDGF-BB stimulated DNA-synthesis although PDGF-Rbeta level and subcellular distribution and translocation was not altered. Furthermore CTX attenuated the PDGF-BB-induced tyrosine phosphorylation of the PDGF-Rbeta, PI 3'-K, PLC-gamma1 and ERK1/2 indicating an action of cyclic AMP on PDGF-beta receptor. We conclude that although cyclic AMP attenuates the PDGF-Rbeta mediated intracellular transduction pathway, an intact actin filament may be required for the PDGF-BB-induced DNA synthesis in VSMCs.

Differential A(1)-adenosine receptor reserve for inhibition of cyclic AMP accumulation and G-protein activation in DDT(1) MF-2 cells

1. The A(1)-adenosine receptor (A(1)AdoR) reserve for N(6)-cyclopentyladenosine (CPA) mediated inhibition of (-)isoprenaline stimulated cyclic AMP accumulation and stimulation of [(35)S]-guanosine-5'-O-(thiotriphosphate) (GTPgammaS) binding, a measure of guanine nucleotide binding protein (G-protein) activation, was determined in DDT(1) MF-2 cells. 2. Inactivation of the A(1)AdoRs with the chemoreactive ligand 8-cyclopentyl-3-[3-[[4-(fluorosulphonyl)benzoyl]oxy]propyl]-1-p ropylx anthine (FSCPX) caused a progressive rightward shift of the concentration-response curves for CPA to inhibit cyclic AMP accumulation, with a maximum of 10 fold increase in the EC(50) value. In contrast, inactivation of A(1)AdoR's caused only a 1.7 fold rightward shift in the CPA concentration-response for stimulation of [(35)S]-GTPgammaS binding. 3. The A(1)AdoR occupancy-response relationship for CPA inhibition of cyclic AMP accumulation was hyperbolic with 43% receptor occupancy required to elicit the maximal response, i.e. a 57% A(1)AdoR reserve. In contrast, the A(1)AdoR occupancy-response relationship for CPA mediated stimulation of [(35)S]-GTPgammaS binding was linear indicating little or no receptor reserve for G-protein activation. The relationship between CPA stimulation of [(35)S]-GTPgammaS binding and cyclic AMP inhibition was also hyperbolic with 44% G-protein activation sufficient to cause maximal inhibition. 4. The data suggest that the A(1)AdoR reserve for CPA mediated inhibition of cyclic AMP accumulation occurs at the level of G-protein interaction with adenylyl cyclase. However, each A(1)AdoR appears to activate a constant fraction of the total G-protein population suggesting signal amplification at the receptor-G-protein level which may also contribute to the receptor reserve for CPA.

Inhibition of NFkappaB-mediated pro-inflammatory gene expression in rat mesangial cells by the enolized 1,3-dioxane-4, 6-dione-5-carboxamide, CGP-43182

1. CGP-43182 has been described as a potent inhibitor of group IIA secreted phospholipase A(2) (group IIA sPLA(2)) activity in vitro. In rat mesangial cells, inhibition of group IIA sPLA(2) activity by CGP-43182 results in a 70% reduction of cytokine-stimulated prostaglandin E(2) biosynthesis, suggesting that group IIA sPLA(2) participates in arachidonic acid release and eicosanoid formation. Under these conditions the cytosolic phospholipase A(2) is not affected. 2. In mesangial cells, in addition to inhibition of catalytic activity, the membrane-permeant CGP-43182 completely blocked interleukin 1beta (IL1beta)-stimulated group IIA sPLA(2) gene expression. 3. A further action of CGP-43182 was a complete inhibition of cyclo-oxygenase-2 gene expression, resulting in a drastic reduction of prostaglandin formation in mesangial cells. 4. Moreover, CGP-43182 completely blocked IL1beta-induced gene expression of the inducible nitric oxide synthase, leading to an inhibition of cytokine-stimulated nitric oxide formation. 5. In contrast, the stimulatory effect of the cell-permeant cyclic AMP-analogue, dibutyryl-cAMP, on the induction of these enzymes was not inhibited by CGP-43182. These data indicate that CGP-43182 interferes with IL1beta- but not cyclic AMP-activated transcriptional regulation. 6. By studying components of the upstream transcription machinery, we observed an inhibition of NFkappaB activation by CGP-43182 in IL1beta-treated cells. Moreover, we observed that CGP-43182 prevented the phosphorylation and proteolytic degradation of the endogenous NFkappaB inhibitor, IkappaB, a process necessary for NFkappaB activation. 7. From our data, we propose that CGP-43182 is a potent anti-inflammatory drug useful for preventing the consequences of a concerted action of cytokine-stimulated pro-inflammatory genes mediated by NFkappaB.

Characteristics of the Ca(2+)-dependent inhibition of cyclic AMP accumulation by histamine and thapsigargin in human U373 MG astrocytoma cells

1. Histamine, acting on H(1)-receptors, caused a Ca(2+)-dependent inhibition of forskolin- and isoprenaline-induced cyclic AMP accumulation in monolayers of human U373 MG cells (IC(50) 1.3+/-0.3 microM, maximum inhibition 66+/-3%). The inhibition was not reversed by the protein kinase inhibitor K-252A. 2. Thapsigargin also inhibited cyclic AMP accumulation (IC(50) 6.0+/-0.3 nM, maximum inhibition 72+/-1%). In the absence of extracellular Ca(2+) 5 microM thapsigargin caused only a 12+/-2% inhibition of cyclic AMP accumulation. 3. The inhibitory effect of 100 nM thapsigargin on forskolin-stimulated cyclic AMP accumulation was blocked by La(3+) (best-fit maximum inhibition 81+/-4%, IC(50) 125+/-8 nM). In contrast, the inhibitory action of 10 microM histamine was much less sensitive to reversal by 1 microM La(3+) (33+/-5% reversal, compared with 78+/-6% reversal of the inhibition by thapsigargin measured concurrently). However, in the presence of both thapsigargin and histamine the inhibition of cyclic AMP accumulation was reversed by 1 microM La(3+) to the same extent as the inhibition by thapsigargin alone. 4.++Thapsigargin (5 microM)+1 microM La(3+) caused only a 20+/-1% inhibition of histamine-stimulated phosphoinositide hydrolysis. 5. There was no indication from measurement of intracellular Ca(2+) of any persistent La(3+)-insensitive Ca(2+) entry component activated by histamine. 6. The results provide evidence that Ca(2+) entry is required for the inhibition by histamine and thapsigargin of drug-induced cyclic AMP accumulation in U373 MG astrocytoma cells. The differential sensitivity of the inhibitory action of the two agents to block by La(3+) suggests that more than one pathway of Ca(2+) entry is involved.