• Molecules and Cells
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• v.40 no.10
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• pp.752-760
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• 2017

A2B adenosine receptor (A2BAR) is known to be the regulator of bone homeostasis, but its regulatory mechanisms in osteoclast formation are less well-defined. Here, we demonstrate the effect of A2BAR stimulation on osteoclast differentiation and activity by RANKL. A2BAR was expressed in bone marrow-derived monocyte/macrophage (BMM) and RANKL increased A2BAR expression during osteoclastogenesis. A2BAR stimulation with its specific agonist BAY 60-6583 was sufficient to inhibit the activation of ERK1/2, p38 MAP kinases and $NF-{\kappa}B$ by RANKL as well as it abrogated cell-cell fusion in the late stage of osteoclast differentiation. Stimulation of A2BAR suppressed the expression of osteoclast marker genes, such as c-Fos, TRAP, Cathepsin-K and NFATc1, induced by RANKL, and transcriptional activity of NFATc1 was also inhibited by stimulation of A2BAR. A2BAR stimulation caused a notable reduction in the expression of Atp6v0d2 and DC-STAMP related to cell-cell fusion of osteoclasts. Especially, a decrease in bone resorption activity through suppression of actin ring formation by A2BAR stimulation was observed. Taken together, these results suggest that A2BAR stimulation inhibits the activation of ERK1/2, p38 and $NF-{\kappa}B$ by RANKL, which suppresses the induction of osteoclast marker genes, thus contributing to the decrease in osteoclast cell-cell fusion and bone resorption activity.

• The Korean Journal of Pharmacology
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• v.29 no.2
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• pp.175-182
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• 1993

As it has been reported that the depolarization-induced ACh release is modulated by activation of presynaptic $A_1-adenosine$ heteroreceptor in hippocampus and various lines of evidence indicate the adenosine effect is magnesium dependent, the present study was undertaken to delineate the role of endogenus adenosine as a modulator of hippocampal acetylcholine release in this study. Slices from the rat hippocampus were equilibrated with $[^3H]-choline$ and the release of the labelled product, $[^3H]-ACh$, was evoked by electrical stimulation(3Hz, $5\;V\;cm^{-1},$ 2ms, rectangular pulses), and the influence of various agents on the evoked tritium outflow was investigated. Adenosine, in concentrations ranging from $0.3\;to\;100\;{\mu}M$, decreased the $[^3H]-ACh$ release in a dose-dependent manner without changing the basal rate of release. $DPCPX(1{\sim}10{\mu}M)$, a selective $A_1-receptor$ antagonist, increased the $[^3H]-ACh$ release in a dose-related fashion with slight increase of basal tritium release. And the effects of adenosine were significantly inhibited by $DPCPX(2{\mu}M)$ treatment. CPCA, a specific $A_2-agonist$, in concentration ranging from $0.3\;to\;30\;{\mu}M$ decreased evoked tritium outflow with increase of basal rate of tritium release, and these effects were also abolished by $DPCPX(2{\mu}M)$ pretreatment. But, $CGS(0.1{\sim}10{\mu}M)$, a recently introduced potent $A_2-agonist$, did not alter the evoked tritium outflow. When the magnesium concentration of the medium was reduced to 0 mM, there was no change in evoked ACh release by adenosine. In contrast, increasing the magnesium concentration to 4 mM, the inhibitory effects of adenosine were significantly potentiated. These results indicate that $A_1-adenosine$ heteroreceptor is involved in ACh-release in the rat hippocampus and the inhibitory effects of adenosine mediated by $A_1-receptor$ is magnesium-dependent.

• Biomolecules & Therapeutics
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• v.20 no.1
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• pp.27-35
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• 2012

Oroxylin A is a flavone isolated from a medicinal herb reported to be effective in reducing the inflammatory and oxidative stresses. It also modulates the production of brain derived neurotrophic factor (BDNF) in cortical neurons by the transactivation of cAMP response element-binding protein (CREB). As a neurotrophin, BDNF plays roles in neuronal development, differentiation, synaptogenesis, and neural protection from the harmful stimuli. Adenosine $A2_A$ receptor colocalized with BDNF in brain and the functional interaction between $A2_A$ receptor stimulation and BDNF action has been suggested. In this study, we investigated the possibility that oroxylin A modulates BDNF production in cortical neuron through the regulation of $A2_A$ receptor system. As expected, CGS21680 ($A2_A$ receptor agonist) induced BDNF expression and release, however, an antagonist, ZM241385, prevented oroxylin A-induced increase in BDNF production. Oroxylin A activated the PI3K-Akt-GSK-$3{\beta}$ signaling pathway, which is inhibited by ZM241385 and the blockade of the signaling pathway abolished the increase in BDNF production. The physiological roles of oroxylin A-induced BDNF production were demonstrated by the increased neurite extension as well as synapse formation from neurons. Overall, oroxylin A might regulate BDNF production in cortical neuron through $A2_A$ receptor stimulation, which promotes cellular survival, synapse formation and neurite extension.

• The Korean Journal of Physiology and Pharmacology
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• v.22 no.3
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• pp.225-234
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• 2018

Adenosine is a naturally occurring breakdown product of adenosine triphosphate and plays an important role in different physiological and pathological conditions. Adenosine also serves as an important trigger in ischemic and remote preconditioning and its release may impart cardioprotection. Exogenous administration of adenosine in the form of adenosine preconditioning may also protect heart from ischemia-reperfusion injury. Endogenous release of adenosine during ischemic/remote preconditioning or exogenous adenosine during pharmacological preconditioning activates adenosine receptors to activate plethora of mechanisms, which either independently or in association with one another may confer cardioprotection during ischemia-reperfusion injury. These mechanisms include activation of $K_{ATP}$ channels, an increase in the levels of antioxidant enzymes, functional interaction with opioid receptors; increase in nitric oxide production; decrease in inflammation; activation of transient receptor potential vanilloid (TRPV) channels; activation of kinases such as protein kinase B (Akt), protein kinase C, tyrosine kinase, mitogen activated protein (MAP) kinases such as ERK 1/2, p38 MAP kinases and MAP kinase kinase (MEK 1) MMP. The present review discusses the role and mechanisms involved in adenosine preconditioning-induced cardioprotection.

• Proceedings of the Korean Biophysical Society Conference
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• 1997.07a
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• pp.32-32
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• 1997

The regulatory role of A$\sub$2A/ adenosine receptors in P$_2$ purinoceptor-mediated calcium signaling was investigated in rat pheochromocytoma (PC12) cells. When PC12 cells were treated with 2-p-(2-carboxyethyl)phenethylamino-5'-N-ethylcarboxamidoadenosine (CGS21680), a specific agonist of the A$\sub$2A/ adenosine receptor, extracellular ATP-evoked [(CA$\^$2+/)]$\sub$i/ rise was inhibited by 20%.(omitted)

• The Korean Journal of Physiology and Pharmacology
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• v.1 no.2
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• pp.135-142
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• 1997

As it has been reported that the depolarization-induced norepinephrine (NE) release is modulated by activation of presynaptic $A_1$-adenosine heteroreceptor and various lines of evidence indicate that $A_2$-adenosine receptor also presents in hippocampus, and that the adenosine effect is magnesium dependent, the present study was undertaken to delineate the role of adenosine receptors in the modulation of hippocampal NE release. Slices from the rat hippocampus were equilibrated with $[^3H]-NE$ and the release of the labelled product, $[^3H]-NE$, was evoked by electrical stimulation (3 Hz, 5 V $cm^{-1}$, 2 ms, rectangular pulses), and the influence of various agents on the evoked tritium outflow was investigated. $N^6-cyclo-pentyladenosine$ (CPA), in concentrations ranging from 0.1 to 10 ${\mu}M$, decreased the $[^3H]-NE$ release in a dose-dependent manner without changing the basal rate of release, and these effects were significantly inhibited by 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 2 ${\mu}M$) treatment. When the magnesium concentration was reduced to 0.4 mM or completely removed, the evoked NE release increased along with decreased basal rate of release. In contrast, increasing the magnesium concentrations to 2.4 and 4 mM, decreased the evoked NE release. The CPA effects on evoked NE release were reducedby magnesium removal, but potentiated by 2.4 mM magnesium in the medium. 5-(N-cyclopropyl)-carboxamodiadenosine (CPCA, 1 & 10 ${\mu}M$), an $A_2$-agonist, decreased the evoked tritium outflow, and this effect was also abolished by DPCPX pretreatment. CGS, a powerful $A_2$-agonist, did not affect the evoked NE release. However, the effects of CPCA and CGS on evoked NE release were significantly increased by pretreatment of DPCPX in the magnesium-free medium. These results indicate that inhibitory effect of $A_1$-adenosine receptor on NE release is magnesium-dependent, and $A_2$-receptor may be present in the rat hippocampus.

• The Korean Journal of Physiology
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• v.22 no.2
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• pp.319-332
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• 1988

The regulations of renal function and renin release are influenced by neural, humoral and physical factors. During the last decade, considerable progress has been made in the identification and characterization of these extrinsic renal control systems. Mechanisms intrinsic to the kidney are also important for renal function. These include the autoregulation of blood flow, and the local control of renin secretion. Fundamental questions regarding the mechanism of these intrinsic controls remain unanswered. Recently, endogenous renal adenosine has been claimed to influence the tubuloglomerular feedback control and renin release. Two subclasses of adenosine receptors $A_1{\;}and{\;}A_2$ have been described. The present experiment was carried out to evaluate the effects of $N_6-cyclohexyladenosine$ $(CHA,{\;}A_1{\;}selective)$ and 5'-N-ethylcarbox-amide adenosine $(NECA,{\;}A_2{\;}selective)$ on the renal function and renin release in the unanesthetized rabbit. Intra-renal arterial infusion of NECA $(0.3{\sim}10.0n{\;}mole/min/rabbit)$ or CHA $(0.03{\sim}10.0n{\;}mole/min/rabbit)$ caused a prompt and dose-dependent decrease in urine volume, glomerular filtration rate (GFR), renal plasma flow (RPF), filtration fraction (FF), electrolyte excretion and free water clearance $(CH_2O)$, the effect being much more profound with CHA than with NECA. The NECA infusion resulted in a profound decrease of systemic blood pressure, but the CHA infusion did not. Both NECA and GHA infusions caused a prompt and dose-dependent decrease in renin secretion rate, again the effect being greater with CHA than with NEGA. These results suggest that both $A_1{\;}and{\;}A_2$ adenosine receptors may be involved in the intrinsic control of renal function and renin release, and that the $A_1$ receptors plays a more important role than the $A_2$ receptor in the regulation of renal fnction.

• The Korean Journal of Physiology and Pharmacology
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• v.14 no.3
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• pp.145-150
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• 2010

Adenosine (Ado) is an important mediator of the endogenous defense against ischemia-induced injury in the heart. The action of Ado is mediated by activation of G protein-gated inwardly rectifying $K^+$ (GIRK) channels. In turn, GIRK channels are inhibited by reducing phosphatidylinositol 4,5-bisphosphate ($PIP_2$) through Gq protein-coupled receptors (GqPCRs). We previously found that GIRK channels activated by acetylcholine, a muscarinic M2 acetylcholine receptor agonist, are inhibited by GqPCRs in a receptor-specific manner. However, it is not known whether GIRK channels activated by Ado signaling are also regulated by GqPCRs. Presently, this was investigated in mouse atrial myocytes using the patch clamp technique. GIRK channels were activated by $100\;{\mu}M$ Ado. When Ado was repetitively applied at intervals of 5~6 min, the amplitude of second Ado-activated GIRK currents ($I_{K(Ado)}$) was $88.3{\pm}3.7%$ of the first $I_{K(Ado)}$ in the control. Pretreatment of atrial myocytes with phenylephrine, endothelin-1, or bradykinin prior to a second application of Ado reduced the amplitude of the second $I_{K(Ado)}$ to $25.5{\pm}11.6%$, $30.5{\pm}5.6%$, and $96.0{\pm}2.7%$, respectively. The potency of $I_{K(Ado)}$ inhibition by GqPCRs was different with that observed in acetylcholine-activated GIRK currents ($I_{K(ACh)}$) (endothelin-1>phenylephrine>bradykinin). $I_{K(Ado)}$ was almost completely inhibited by $500\;{\mu}M$ of the $PIP_2$ scavenger neomycin, suggesting low $PIP_2$ affinity of $I_{K(Ado)}$. Taken together, these results suggest that the crosstalk between GqPCRs and the Ado-induced signaling pathway is receptor-specific. The differential change in $PIP_2$ affinity of GIRK channels activated by Ado and ACh may underlie, at least in part, their differential responses to GqPCR agonists.

• Endocrinology and Metabolism
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• v.37 no.2
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• pp.221-232
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• 2022

Background Obesity, the prevalence of which is increasing due to the lack of exercise and increased consumption of Westernized diets, induces various complications, including ophthalmic diseases. For example, obesity is involved in the onset of cataracts. Methods To clarify the effects and mechanisms of midodrine, an α1-adrenergic receptor agonist, in cataracts induced by obesity, we conducted various analytic experiments in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a rat model of obesity. Results Midodrine prevented cataract occurrence and improved lens clearance in OLETF rats. In the lenses of OLETF rats treated with midodrine, we observed lower levels of aldose reductase, tumor necrosis factor-α, and sorbitol, but higher levels of hexokinase, 5'-adenosine monophosphate-activated protein kinase-alpha, adenosine 5'-triphosphate, peroxisome proliferator-activated receptor-delta, peroxisome proliferator-activated receptor gamma coactivator 1-alpha, superoxide dismutase, and catalase. Conclusion The ameliorating effects of midodrine on cataracts in the OLETF obesity rat model are exerted via the following three mechanisms: direct inhibition of the biosynthesis of sorbitol, which causes cataracts; reduction of reactive oxygen species and inflammation; and (3) stimulation of normal aerobic glycolysis.

• The Korean Journal of Pharmacology
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• v.29 no.2
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• pp.253-261
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• 1993

Possible changes in the role of insulin-sensitive cyclic nucleotide phosphodiesterase(PDE) in mediating the antilipolytic action of insulin were investigated in adipocytes from streptozotocin-induced diabetic rats. Isolated adipocytes prepared from epididymal adipose tissue were incubated, with or without insulin, at $37^{\circ}C$ for 15 min following pretreatment with various drugs or toxins, and three (plasma membranes, microsomal membranes, and cytosol) fractions prepared by differential centrifugation were then assayed for cAMP phosphodiesterase activity. The PDE activities only in the crude microsomal (P2) fractions were activated by insulin both in diabetic and control rats. The basal PDE activities in P2 fractions of adipocytes from diabetic rats were higher than those from control rats, although the maximal effects observed at 2 nM of insulin, $100\;{\mu}M$ of isoproterenol or the combination of both were not significantly different from each other. The insulin-stimulated PDE activities in P2 fractions of adipocytes from diabetic rats were not changed by PIA, a $A_{1}$ adenosine receptor agonist, whereas they were decreased to the basal PDE activities in those from control rats. In addition, the adipocytes from diabetic rats showed an increased sensitivity to pertussis toxin compared to those from controls. There were no differences between diabetic and control rats in the sensitivity of adipocytes to cholera toxin. These data indicate that the impaired signalling through inhibitory receptors such as adenosine receptors in adipocytes from streptozotocin-induced diabetes relates to the loss or the decreased function of $G_i$ proteins, and leads to the increased activity of the insulin-dependent PDE at the basal states.