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cAMP Content (camp + content)
Selected AbstractsPresence of a functional receptor for GLP-1 in osteoblastic cells, independent of the cAMP-linked GLP-1 receptorJOURNAL OF CELLULAR PHYSIOLOGY, Issue 2 2010Bernardo Nuche-Berenguer Glucagon-like peptide 1 (GLP-1) controls glucose metabolism in extrapancreatic tissues through receptors other than the pancreatic cAMP-linked GLP-1 receptor; also, GLP-1 induces an insulin- and PTH-independent bone anabolic action in insulin-resistant and type-2 diabetic rats. Here we searched for the presence and characteristics of GLP-1 receptors in osteoblastic MC3T3-E1 cells. [125I]-GLP-1 specific binding to MC3T3-E1 cells was time- and temperature-dependent, reaching maximal value at 30,min at 25°C; in these conditions, [125I]-GLP-1 binding was dissociable, and displaced by GLP-1, partially by GLP-2, but not by exendin-4 (Ex-4), exendin-9 (Ex-9), glucagon or insulin; Scatchard analysis of the unlabeled GLP-1 data showed high and low affinity binding sites; cross-linking of GLP-1 binding revealed an estimated 70,kDa band, almost undetectable in the presence of 10,6,M GLP-1. GLP-1, Ex-9, insulin or glucagon failed to modify cellular cAMP content, while GLP-2 and Ex-4 increased it. However, GLP-1 induced an immediate hydrolysis of glycosylphosphatidylinositols (GPIs) generating short-lived inositolphosphoglycans (IPGs), and an increase in phosphatidylinositol-3 kinase (PI3K) and mitogen activated protein kinase (MAPK) activities; Ex-4 also affected GPIs, but its action was delayed with respect to that of GLP-1. This incretin was found to decrease Runx2 but increased osteocalcin gene expression, without affecting that of osteoprotegerin or the canonical Wnt pathway activity in MC3T3-E1 cells which do not express the pancreatic GLP-1 receptor. Our data demonstrate for the first time that GLP-1 can directly and functionally interact with osteoblastic cells, possibly through a GPI/IPG-coupled receptor. J. Cell. Physiol. 225: 585,592, 2010. © 2010 Wiley-Liss, Inc. [source] High glucose inhibits fructose uptake in renal proximal tubule cells: Involvement of cAMP, PLC/PKC, p44/42 MAPK, and cPLA2JOURNAL OF CELLULAR PHYSIOLOGY, Issue 3 2004Su Hyung Park The precise signal that regulates fructose transport in renal proximal tubule cells (PTCs) under high glucose conditions is not yet known although fructose has been recommended as a substitute for glucose in the diets of diabetic people. Thus, we investigated that effect of high glucose on fructose uptake and its signaling pathways in primary cultured rabbit renal PTCs. Glucose inhibited the fructose uptake in a time- and dose-dependent manner. A maximal inhibitory effect of glucose on fructose uptake was observed at 25 mM glucose after 48 h, while 25 mM mannitol and l -glucose did not affect fructose uptake. Indeed, 25 mM glucose for 48 h decreased GLUT5 protein level. Thus, the treatment of 25 mM glucose for 48 h was used for this study. Glucose-induced (25 mM) inhibition of fructose uptake was blocked by pertussis toxin (PTX), SQ-22536 (an adenylate cyclase inhibitor), and myristoylated amide 14,22 (a protein kinase A inhibitor). Indeed, 25 mM glucose increased the intracellular cAMP content. Furthermore, 25 mM glucose-induced inhibition of fructose uptake was prevented by neomycin or U-73122 (phospholipase C inhibitors) and staurosporine or bisindolylmaleimide I (protein kinase C inhibitors). In fact, 25 mM glucose increased the total PKC activity and translocation of PKC from the cytosolic to membrane fraction. In addition, PD 98059 (a p44/42 mitogen-activated protein kinase (MAPK) inhibitor) but not SB 203580 (a p38 MAPK inhibitor) and mepacrine or AACOCF3 (phospholipase A2 inhibitors) blocked 25 mM glucose-induced inhibition of fructose uptake. Results of Western blotting using the p44/42 MAPK and GLUT5 antibodies were consistent with the results of uptake experiments. In conclusion, high glucose inhibits the fructose uptake through cAMP, PLC/PKC, p44/42 MAPK, and cytosolic phospholipase A2 (cPLA2) pathways in the PTCs. © 2004 Wiley-Liss, Inc. [source] Effect of Repeated Doses of Ethanol on Hepatic Mg2+ Homeostasis and MobilizationALCOHOLISM, Issue 7 2007Andrew Young The acute administration of a first dose of ethanol (EtOH) to rat liver cells reduces the amount of Mg2+ extruded by a second dose of EtOH or the subsequent addition of adrenergic agonists. In contrast, the Mg2+ extrusion normally elicited by the ,1 -adrenergic or , -adrenergic agonist does not impair the Mg2+ mobilization induced by the subsequent addition of EtOH. Inhibition of EtOH metabolism by 4-methylpyrazole abolishes almost completely the Mg2+ extrusion induced by the first dose of EtOH, and partially enlarges that elicited by the second dose of alcohol or the subsequent adrenergic stimulation. Ethanol-treated liver cells stimulated by the adrenergic agonist show a reduced level of membrane-bound G,s as well as a reduced cellular cAMP content. Analysis of cellular Mg2+ distribution indicates that EtOH administration decreases the Mg2+ content of the cytoplasm, mitochondria, and endoplasmic reticulum to a comparable extent. These data indicate that acute EtOH administration directly impairs cellular Mg2+ homeostasis and also prevents a further Mg2+ mobilization by additional doses of alcohol or ,1 -adrenoceptor and , -adrenoceptor agonist by decreasing cytosolic and intraorganelle Mg2+ content and by affecting G-protein membrane distribution/signaling. [source] Metabolic pathway of magnetized fluid-induced relaxation effects on heart muscleBIOELECTROMAGNETICS, Issue 8 2005Gayane Ayrapetyan Abstract The effect of magnetized physiological solution (MPS) on isolated, perfused snail heart muscle contractility, 45Ca uptake and intracellular level of cAMP, and cGMP was studied. The existence of the relaxing effect of MPS on heart muscle at room temperature (22 °C) and its absence in cold medium (4 °C) was shown. The MPS had a depressing effect on 45Ca uptake by muscles and intracellular cAMP content and an elevating effect on intracellular cGMP level. It is suggested that the relaxing effect of MPS on heart muscle is due to the decrease of intracellular Ca ions as the result of activation of cGMP-dependent Ca efflux. The MPS induced decrease of intracellular cAMP content can be considered as a consequence of intracellular Ca loss, leading to the Na,+,K-ATPase reactivation, and causing the decrease of the intracellular level of ATP, serving as a substrate and positive modulator of cyclase activity. Bioelectromagnetics © 2005 Wiley-Liss, Inc. [source] Regulation of MC1R signalling by G-protein-coupled receptor kinasesEXPERIMENTAL DERMATOLOGY, Issue 9 2004J. C. García-Borrón The melanocortin 1 receptor (MC1R) is a key regulator of melanocyte proliferation and differentiation and a major determinant of human skin phototype and skin cancer risk. Although the regulation of MC1R gene expression is fairly well understood, little is known about regulatory mechanisms acting at the protein level. In particular, no information is available on homologous desensitization of MC1R signalling. We studied MC1R and Mc1r desensitization and found that: 1) MC1R and Mc1r in melanoma cells undergo homologous desensitization, demonstrated by decreases in cAMP contents upon continuous exposure to agonists, 2) desensitization is not dependent on PKA, PKC, calcium mobilization or MAPKs but is agonist dose dependent, suggesting a role of receptor occupancy, 3) melanoma cells express two members of the GRK family of serine/threonine kinases, GRK2 and GRK6, 4. These kinases are expressed in normal melanocytes, 5) in cotransfection experiments performed with HEK 293T cells, GRK2 strongly impairs agonist-dependent signalling by MC1R or Mc1r, 6) expression of a dominant negative GRK2 mutant in melanoma cells increases their cAMP response to MC1R agonists, 7) cotransfection of HEK 293T cells with GRK6 and MC1R inhibits both basal and agonist-dependent signalling, and 8) cAMP production in agonist-stimulated melanoma cells is strongly impaired by enrichment with GRK6 following stable transfection. Therefore, GRK2 and GRK6 are key regulators of MC1R signalling and may be important determinants of normal and pathological skin pigmentation. [source] | |||||||||||||