p38 Mitogen- Activated Protein Kinase Contributes to Adenosine A1 Receptor- Mediated Synaptic Depression in Area CA1 of the Rat Hippocampus.
Adenosine is arguably the most potent and widespread presynaptic modulator in the CNS, yet adenosine receptor signal transduction pathways remain unresolved. Here, we demonstrate a novel mechanism in which adenosine A(1) receptor stimulation leads to p38 mitogen- activated protein kinase ( MAPK) activation and contributes to the inhibition of synaptic transmission. Western blot analysis indicated that selective A(1) receptor activation [with N(6)-cyclopentyladenosine (CPA)] resulted in rapid increases in phosphorylated p38 (phospho-p38) MAPK immunoreactivity in membrane fractions, and decreases in phospho-p38 MAPK in cytosolic fractions. Immunoprecipitation with a phospho-p38 MAPK antibody revealed constitutive association of this phosphoprotein with adenosine A(1) receptors. Phospho-p38 MAPK activation by A(1) receptor stimulation induced translocation of PP2a (protein phosphatase 2a) to the membrane. We then examined the actions of p38 MAPK activation in A(1) receptor-mediated synaptic inhibition. Excitatory postsynaptic field potentials evoked in area CA1 of the rat hippocampus markedly decreased in response to adenosine (10 mum), the A(1) receptor agonist CPA (40 nm), or a 5 min exposure to hypoxia. These inhibitory responses were mediated by A(1) receptor activation because the selective antagonist DPCPX (8-cyclopentyl-1,3-dipropylxanthine) (100 nm) prevented them. In agreement with the biochemical analysis, the selective p38 MAPK inhibitor SB203580 [4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)-1H-imidazole] (25 mum) blocked the inhibitory actions of A(1) receptor activation, whereas both the inactive analog SB202474 [4-ethyl-2-(p-methoxyphenyl)-5-(4'-pyridyl)-1H-imidazole] (25 mum) and the ERK 1/2 (extracellular signal-regulated kinase 1/2) MAPK inhibitor PD98059 [2'-amino-3'-methoxyflavone] (50 mum) were ineffective. In contrast, the p38 MAPK inhibitors did not inhibit GABA(B)-mediated synaptic depression. These data suggest A(1) receptor-mediated p38 MAPK activation is a crucial step underlying the presynaptic inhibitory effect of adenosine on CA3-CA1 synaptic transmission.[1]References
- p38 Mitogen-Activated Protein Kinase Contributes to Adenosine A1 Receptor-Mediated Synaptic Depression in Area CA1 of the Rat Hippocampus. Brust, T.B., Cayabyab, F.S., Zhou, N., Macvicar, B.A. J. Neurosci. (2006) [Pubmed]
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