cyclic-gmp and 8-bromoadenosine-3--5--cyclic-monophosphorothioate

Although it is well established that cyclic adenosine monophosphate (cAMP) signalling via cAMP-dependent protein kinase (PKA)within neurons plays an important role in depression and antidepressant treatment, the importance of several newly discovered targets that function independently from PKA, such as exchange protein activated by cAMP (Epac), remains unexplored in this regard. In this study we used a cAMP analogue that inhibits PKA but not Epac (Rp-8-Br-cAMP), to explore the modifying actions of these two targets on immobility in the forced swim test (FST) and cerebellar cAMP response element binding protein (CREB) phosphorylation in rats. In addition, we assessed central cAMP and cGMP levels and investigated the involvement of cGMP-dependent protein kinase (PKG) on any observed effects by using a selective PKG inhibitor (Rp-8-Br-PET-cGMPS).Interestingly, Rp-8-Br-cAMPS strongly reduced immobility in the FST and induced an increase in the phosphorylation of CREB in the cerebellum, effects that were unaltered by the co-administration of Rp-8-Br-PET-cGMPS. Furthermore, Rp-8-Br-cAMPS increased the accumulation of cAMP and cGMP in the hippocampus, frontal cortex and cerebellum of these rats. Together, these results suggest that in addition to activating PKA, elevated cAMP may also stimulate other targets that mediate antidepressant activity. According to the pharmacodynamic profile of Rp-8-Br-cAMPS and taking into consideration what has recently been discovered regarding the cAMP signalling system, a likely candidate is the guanine nucleotide exchange factor, Epac.

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Animals; Antidepressive Agents; Behavior, Animal; Cerebellum; Cyclic AMP; Cyclic AMP Response Element-Binding Protein; Cyclic AMP-Dependent Protein Kinases; Cyclic GMP; Cyclic GMP-Dependent Protein Kinases; Depression; Guanine Nucleotide Exchange Factors; Male; Phosphorylation; Protein Kinase Inhibitors; Rats; Rats, Sprague-Dawley; Second Messenger Systems; Swimming; Thionucleotides

The Epac family of cAMP-regulated guanine nucleotide exchange factors (cAMPGEFs, also known as Epac1 and Epac2) mediate stimulatory actions of the second messenger cAMP on insulin secretion from pancreatic beta cells. Because Epac2 is reported to interact in vitro with the isolated nucleotide-binding fold-1 (NBF-1) of the beta-cell sulphonylurea receptor-1 (SUR1), we hypothesized that cAMP might act via Epac1 and/or Epac2 to inhibit beta-cell ATP-sensitive K+ channels (K(ATP) channels; a hetero-octomer of SUR1 and Kir6.2). If so, Epac-mediated inhibition of K(ATP) channels might explain prior reports that cAMP-elevating agents promote beta-cell depolarization, Ca2+ influx and insulin secretion. Here we report that Epac-selective cAMP analogues (2'-O-Me-cAMP; 8-pCPT-2'-O-Me-cAMP; 8-pMeOPT-2'-O-Me-cAMP), but not a cGMP analogue (2'-O-Me-cGMP), inhibit the function of K(ATP) channels in human beta cells and rat INS-1 insulin-secreting cells. Inhibition of K(ATP) channels is also observed when cAMP, itself, is administered intracellularly, whereas no such effect is observed upon administration N6-Bnz-cAMP, a cAMP analogue that activates protein kinase A (PKA) but not Epac. The inhibitory actions of Epac-selective cAMP analogues at K(ATP) channels are mimicked by a cAMP agonist (8-Bromoadenosine-3', 5'-cyclic monophosphorothioate, Sp-isomer, Sp-8-Br-cAMPS), but not a cAMP antagonist (8-Bromoadenosine-3', 5'-cyclic monophosphorothioate, Rp-isomer, Rp-8-Br-cAMPS), and are abrogated following transfection of INS-1 cells with a dominant-negative Epac1 that fails to bind cAMP. Because both Epac1 and Epac2 coimmunoprecipitate with full-length SUR1 in HEK cell lysates, such findings delineate a novel mechanism of second messenger signal transduction in which cAMP acts via Epac to modulate ion channel function, an effect measurable as the inhibition of K(ATP) channel activity in pancreatic beta cells.

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Adenosine Triphosphate; Animals; ATP-Binding Cassette Transporters; Cell Line; Cyclic AMP; Cyclic GMP; Guanine Nucleotide Exchange Factors; Humans; Insulin-Secreting Cells; Kinetics; Membrane Potentials; Potassium Channels; Potassium Channels, Inwardly Rectifying; Rats; Receptors, Drug; Sulfonylurea Receptors; Thionucleotides

Puerarin, an isoflavonoid derived from the Chinese medicinal herb Radix puerariae, has been suggested to be useful in the management of various cardiovascular disorders. The present study examined the effect of acute exposure (30 min) to puerarin on vascular relaxation. Rings from porcine coronary artery of either sex were used. The highest concentration of puerarin (100 microM) produced a small but statistically significant relaxation of U46619-contracted rings. Vascular relaxations were also studied in the presence of lower concentrations of puerarin (0.1, 1 and 10 microM) which had no direct relaxation effect. Puerarin enhanced vasorelaxation to endothelium-independent relaxing agents, sodium nitroprusside and cromakalim. However, puerarin had no effect on vasorelaxation induced by endothelium-dependent relaxing agents, bradykinin and calcium ionophore A23187. The potentiating action of puerarin (10 microM) on sodium nitroprusside-mediated relaxation was not affected by the nitric oxide synthase inhibitor, N(omega)-nitro-L-arginine methyl ester (L-NAME; 300 microM), or by the disruption of the endothelium with Triton X-100. The effect of puerarin was reversible following a washout period. The potentiating effects were comparable with the 3'-5'-cyclic adenosine monophosphate (cyclic AMP) analogues, 8-bromoadenosine-3'-5'-cyclic monophosphate (8-Br-cyclic AMP; 10 muM) and Sp-isomer [S nomenclature refers to phosphorus] of adenosine-3', 5'-cyclic monophosphorothioate (Sp-cyclic AMPS; 3 microM), but not the 3'-5'-cyclic guanosine monophosphate (cyclic GMP) analogue, 8-bromoguanosine-3'-5'-cyclic monophosphate (8-Br-cyclic GMP; 3 microM). The cyclic AMP antagonist, Rp-isomer [R nomenclature refers to phosphorus] of 8-bromoadenosine-3', 5'-cyclic monophosphorothioate (Rp-8-Br-cyclic AMPS; 10 microM), but not cyclic GMP antagonist, Rp-isomer of 8-bromoguanosine-3', 5'-cyclic monophosphorothioate (Rp-8-Br-cyclic GMPS; 10 microM), reversed the effects of puerarin (10 microM) on the enhancement of vasorelaxation to sodium nitroprusside. Our results demonstrated that puerarin enhanced sodium nitroprusside-induced relaxation, possibly via the cyclic AMP-dependent pathway.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; 8-Bromo Cyclic Adenosine Monophosphate; Animals; Coronary Vessels; Cyclic AMP; Cyclic GMP; Dose-Response Relationship, Drug; Drug Synergism; Endothelium, Vascular; Enzyme Inhibitors; Female; In Vitro Techniques; Isoflavones; Male; NG-Nitroarginine Methyl Ester; Nitric Oxide Synthase; Nitroprusside; Plant Roots; Pueraria; Signal Transduction; Swine; Thionucleotides; Vasoconstriction; Vasoconstrictor Agents; Vasodilation; Vasodilator Agents

Pulmonary hypertension is characterized by vascular remodeling involving smooth muscle cell proliferation and migration. Calcitonin gene-related peptide (CGRP) and nitric oxide (NO) are potent vasodilators, and the inhibition of aortic smooth muscle cell (ASMC) proliferation by NO has been documented, but less is known about the effects of CGRP. The mechanism by which overexpression of CGRP inhibits proliferation in pulmonary artery smooth muscle cells (PASMC) and ASMC following in vitro transfection by the gene coding for prepro-CGRP was investigated. Increased expression of p53 is known to stimulate p21, which inhibits G(1) cyclin/cdk complexes, thereby inhibiting cell proliferation. We hypothesize that p53 and p21 are involved in the growth inhibitory effect of CGRP. In this study, CGRP was shown to inhibit ASMC and PASMC proliferation. In PASMC transfected with CGRP and exposed to a PKA inhibitor (PKAi), cell proliferation was restored. p53 and p21 expression increased in CGRP-treated cells but decreased in cells treated with CGRP and PKAi. PASMC treated with CGRP and a PKG inhibitor (PKGi) recovered from inhibition of proliferation induced by CGRP. ASMC treated with CGRP and then PKAi or PKGi recovered only when exposed to the PKAi and not PKGi. Although CGRP is thought to act through a cAMP-dependent pathway, cGMP involvement in the response to CGRP has been reported. It is concluded that p53 plays a role in CGRP-induced inhibition of cell proliferation and cAMP/PKA appears to mediate this effect in ASMC and PASMC, whereas cGMP appears to be involved in PASMC proliferation.

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Animals; Aorta; Calcitonin Gene-Related Peptide; Cell Division; Cells, Cultured; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Cyclic GMP; Cyclic GMP-Dependent Protein Kinases; Enzyme Inhibitors; Male; Myocytes, Smooth Muscle; Pulmonary Artery; Rats; Rats, Sprague-Dawley; Thionucleotides; Transfection

The aim of the present study was to investigate the involvement of adenosine 3',5'-cyclic monophosphate (cAMP) cascade in the acute impairment of contraction by 17beta-estradiol in porcine coronary arteries, and to elucidate the signaling pathway leading to the activation of this cascade by the hormone. Isometric tension was recorded in isolated rings of porcine coronary arteries. The contraction to U46619 was reduced significantly following 30 min incubation with 1 nM 17beta-estradiol or 1 nM isoproterenol. There was no additive effect when 17beta-estradiol and isoproterenol were administered together. The effect of 17beta-estradiol was mimicked by both the cyclic AMP analogue 8-Br-cAMP and the guanosine 3',5'-cyclic monophosphate (cyclic GMP) analogue 8-Br-cGMP. In rings with and without endothelium, the modulatory effect of 17beta-estradiol was abolished by the adenylyl cyclase inhibitor, SQ 22536, but was unaffected by the guanylyl cyclase inhibitor, ODQ. Both the cAMP antagonist Rp-8-Br-cAMPS and the cGMP antagonist inhibitor Rp-8-Br-cGMPS inhibited the effect of 17beta-estradiol. The effect of 17beta-estradiol was unaffected by the protein kinase A inhibitor, KT5720, but was abolished by the protein kinase G (PKG) inhibitor, KT5823, which also abolished the effect of isoproterenol. These data support our earlier findings that 17beta-estradiol (1 nM) acutely impairs contractile responses of porcine coronary arteries in vitro. This acute effect of 17beta-estradiol involves cAMP in vascular smooth muscles and the activation of PKG.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; 8-Bromo Cyclic Adenosine Monophosphate; Adenine; Adenylyl Cyclase Inhibitors; Animals; Carbazoles; Coronary Vessels; Cyclic AMP; Cyclic AMP-Dependent Protein Kinases; Cyclic GMP; Cyclic GMP-Dependent Protein Kinases; Drug Interactions; Estradiol; Indoles; Isometric Contraction; Isoproterenol; Muscle, Smooth, Vascular; Swine; Thionucleotides; Time Factors

The second messenger cyclic GMP (cGMP) plays a role in the anxiolytic-like behavioral response of mice to nitrous oxide (N2O). This study was conducted to determine whether this behavioral effect of N2O is affected by inhibition of cGMP-dependent protein kinase (PKG). N2O-induced behavior in the light/dark exploration test was significantly attenuated by the PKG inhibitors H-8 and Rp-8-pCPT-cGMPS but not Rp-8-pCPT-cAMPS, an inhibitor of cAMP-dependent protein kinase. These findings implicate PKG in the mediation or modulation of the anxiolytic-like behavioral response to N2O.

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Animals; Anxiety; Cyclic AMP-Dependent Protein Kinases; Cyclic GMP; Cyclic GMP-Dependent Protein Kinases; Darkness; Enzyme Inhibitors; Exploratory Behavior; Isoquinolines; Male; Mice; Nitrous Oxide; Thionucleotides

To investigate the function cAMP-dependent protein kinase (PKA) exerts in the induction of long-term memory, changes in PKA activity induced by associative learning in vivo were measured in the antennal lobes (ALs) of honeybees. The temporal dynamics of PKA activation depend on both the sequence of conditioned and unconditioned stimuli and the number of conditioning trials. Only multiple-trial conditioning, which induces long-term memory (LTM), leads to a profound prolongation of PKA activation mediated by the NO/cGMP system. Imitation of this prolonged PKA activation in the ALs in combination with single-trial conditioning is sufficient to induce LTM. These findings not only demonstrate the close connection between conditioning procedure and temporal dynamics in PKA activation but also reveal that already during conditioning a distinct temporal pattern of PKA activation is critical for LTM induction in intact animals.

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Animals; Bees; Brain; Conditioning, Operant; Cyclic AMP-Dependent Protein Kinases; Cyclic GMP; Enzyme Activation; Enzyme Activators; Memory; Nitric Oxide; Photolysis; Sense Organs; Smell; Thionucleotides

The effect of the physiological vitamin D metabolite 24R, 25-dihydroxyvitamin D3 [24R,25(OH)2D3] on human osteoblastic cells was assessed. Physiological concentrations (10(-9)-10(-8) M) of 24R, 25(OH)2D3 significantly increased the cyclic guanosine 5'-monophosphate (cGMP) content in the human osteoblastic cells by approximately 200% in 5 to 15 min. In contrast, 24S, 25-dihydroxyvitamin D3 had only a weak effect on the cGMP content, and 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] did not affect the content. The production of osteocalcin was not induced by 10(-9)-10(-8) M of 24R,25(OH)2D3 in the absence of 1,25(OH)2D3. However, the same concentration of 24R,25(OH)2D3 showed stimulatory effects on osteocalcin synthesis in the presence of 10(-9) M 1, 25(OH)2D3. Rp-8Br-cyclic GMP, a specific inhibitor of cyclic GMP-dependent protein kinase, significantly inhibited the cooperative effect of 24R,25(OH)2D3 with 1,25(OH)2D3 on the osteocalcin synthesis, although Rp-8Br-cyclic AMP, a specific inhibitor of cyclic AMP-dependent protein kinase, did not affect the cooperative effect. In addition, okadaic acid enhanced the osteocalcin synthesis induced by 1,25(OH)2D3. These observations suggest that 24R,25(OH)2D3 has a unique activity of increasing cGMP contents in osteoblastic cells, and that the increase in cGMP contents may lead to the cooperative effect of 24R,25(OH)2D3 with 1, 25(OH)2D3 on osteocalcin synthesis. These data support the hypothesis that 24R,25(OH)2D3 has a physiological role in human bone and mineral metabolism.

Topics: 24,25-Dihydroxyvitamin D 3; 8-Bromo Cyclic Adenosine Monophosphate; Calcitriol; Cells, Cultured; Cyclic GMP; Drug Synergism; Humans; Okadaic Acid; Osteoblasts; Osteocalcin; Thionucleotides