Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.11.11 (AMPK)
12,425 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A persistent question concerning mechanisms underlying long-term, activity-dependent synaptic plasticity is whether the sites of alterations are presynaptic, postsynaptic, or both. Recently, we discovered a chemical method of inducing long-term depression (LTD) of synaptic strength at Schaffer collateral-CA1 synapses by simultaneously elevating [cGMP] and inhibiting cAMP-dependent protein kinase (PKA). Chemical LTD (CLTD) is activity-independent, occluded by stimulus-evoked LTD, and requires access of pharmacologic agents to presynaptic terminals. In the present study, we used fluorescence and two-photon imaging of presynaptic terminals with the fluorescent dye N-(3-triethylammoniumpropyl)-4-(4-(dibutylamino)styryl) pyridinium dibromide (FM1-43) to determine directly if inducing CLTD is associated with a long-term reduction in transmitter release. In presynaptic Schaffer collateral-CA1 terminals of control hippocampal slices loaded with FM1-43, electrical stimulation (10 Hz/2 min) elicited a frequency-dependent destaining that peaked at 20% reduction in fluorescence. In contrast, when we first induced CLTD by a 30 min treatment of slices with the type V phosphodiesterase inhibitor zaprinast (20 microm) plus the PKA inhibitor N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H-89; 10 microm), then washed for 60 min, the destaining of FM1-43 fluorescence evoked by the same stimulation was reduced to 4%. Treatment and washout of slices with either drug singly had a significantly smaller effect on stimulus-evoked FM1-43 destaining. Only CLTD was associated with virtually complete suppression of stimulus-evoked FM1-43 release, the first direct evidence for at least one form of LTD being mediated by persistent reduction of presynaptic transmitter release.
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PMID:FM1-43 imaging reveals cGMP-dependent long-term depression of presynaptic transmitter release. 1156 78

Long-lasting forms of synaptic plasticity like the late phase of LTP (L-LTP) typically require an elevation of cAMP, the recruitment of the cAMP-dependent protein kinase (PKA), and ultimately the activation of transcription and translation; some forms also require brain-derived neurotrophic factor (BDNF). Both cAMP and BDNF can activate mitogen-activated protein kinase (MAPK/ERK), which also plays a role in LTP. However, little is known about the mechanisms whereby cAMP, BDNF, and MAPK interact. We find that increases in cAMP can rapidly activate the BDNF receptor TrkB and induce BDNF-dependent long-lasting potentiation at the Schaffer collateral-CA1 synapse in hippocampus. Surprisingly, in these BDNF-dependent forms of potentiation, which are also MAPK dependent, TrkB activation is not critical for the activation of MAPK but instead appears to modulate the subcellular distribution and nuclear translocation of the activated MAPK.
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PMID:Some forms of cAMP-mediated long-lasting potentiation are associated with release of BDNF and nuclear translocation of phospho-MAP kinase. 1160 44

Reversal of long term potentiation (LTP) may function to increase the flexibility and storage capacity of neuronal circuits; however, the underlying mechanisms remain incompletely understood. We show that depotentiation induced by low frequency stimulation (LFS) (2 Hz, 10 min, 1200 pulses) was input-specific and dependent on N-methyl-d-aspartate (NMDA) receptor activation. The ability of LFS to reverse LTP was mimicked by a brief application of NMDA. This NMDA-induced depotentiation was blocked by adenosine A(1) receptor antagonist. However, the reversal of LTP by LFS was unaffected by metabotropic glutamate receptor antagonism. This LFS-induced depotentiation was specifically prevented by protein phosphatase (PP)1 inhibitors, okadaic acid, and calyculin A but not by the PP2A or PP2B inhibitors. Furthermore, by using phosphorylation site-specific antibodies, we found that LFS-induced depotentiation is associated with a persistent dephosphorylation of the GluR1 subunit of amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor at serine 831, a protein kinase C and calcium/calmodulin-dependent protein kinase II (CaMKII) substrate, but not at serine 845, a substrate of cAMP-dependent protein kinase. This effect was mimicked by bath-applied adenosine or NMDA and was specifically prevented by okadaic acid. Also, the increased phosphorylation of CaMKII at threonine 286 and the decreased PP activity seen with LTP were overcome by LFS, adenosine, or NMDA application. These results suggest that LFS erases LTP through an NMDA receptor-mediated activation of PP1 to dephosphorylate amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors and CaMKII in the CA1 region of the hippocampus.
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PMID:Characterization of the mechanism underlying the reversal of long term potentiation by low frequency stimulation at hippocampal CA1 synapses. 1167 81

We previously found that the nitric oxide (NO)-cGMP-cGMP-dependent protein kinase (PKG) signaling pathway acts in parallel with the cAMP-cAMP-dependent protein kinase (PKA) pathway to produce protein and RNA synthesis-dependent late-phase long-term potentiation (L-LTP) and cAMP response element-binding protein (CREB) phosphorylation in the CA1 region of mouse hippocampus. We have now investigated the possible involvement of a downstream target of PKG, ryanodine receptors. L-LTP can be induced by either multiple-train tetanization, NO or 8-Br-cGMP paired with one-train tetanization, or the cAMP activator forskolin, and all three types of potentiation are accompanied by an increase in phospho-CREB immunofluorescence in the CA1 cell body area. Both the potentiation and the increase in phospho-CREB immunofluorescence induced by multiple-train tetanization or 8-Br-cGMP paired with one-train tetanization are reduced by prolonged perfusion with ryanodine, which blocks Ca(2+) release from ryanodine-sensitive Ca(2+) stores. By contrast, neither the potentiation nor the increase in immunofluorescence induced by forskolin are reduced by depletion of ryanodine and inositol-1,4,5-triphosphate (IP3)-sensitive Ca(2+) stores. These results suggest that NO, cGMP, and PKG cause release of Ca(2+) from ryanodine-sensitive stores, which in turn causes phosphorylation of CREB in parallel with PKA during the induction of L-LTP.
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PMID:Ryanodine receptors contribute to cGMP-induced late-phase LTP and CREB phosphorylation in the hippocampus. 1220 48

This study assessed the effects of drugs which manipulate the cAMP system on afterdischarges (ADs) induced in the CA1 region of rat hippocampal slices. The adenylate cyclase activator forskolin (50 microM) and the phosphodiesterase inhibitor rolipram (0.1 and 1 microM) enhanced AD generation. These effects were reversed by the cAMP-dependent protein kinase inhibitors H-89 (5 microM) and Rp-cAMPS (100 microM). These findings suggest that AD generation can be modulated through cAMP generation and the subsequent activation of the cAMP-dependent protein kinase.
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PMID:Cyclic AMP-mediated modulation of epileptiform afterdischarge generation in rat hippocampal slices. 1221 11

Protein kinases and phosphatases play antagonistic roles in regulating hippocampal long-term potentiation (LTP), with kinase inhibition and phosphatase activation both impairing LTP. The late phase of LTP (L-LTP) requires activation of cAMP-dependent protein kinase (PKA) for its full expression. One way in which PKA may critically modulate L-LTP is by relieving an inhibitory constraint imposed by protein phosphatases. Using mutant PKA mice [R(AB) transgenic mice] that have genetically reduced hippocampal PKA activity, we show that deficient L-LTP in area CA1 of mutant hippocampal slices is rescued by acute application of two inhibitors of protein phosphatase-1 and protein phosphatase-2A (PP1/2A) (okadaic acid and calyculin A). Furthermore, synaptic facilitation induced by forskolin, an adenylyl cyclase activator, was impaired in R(AB) transgenics and was also rescued by a PP1/2A inhibitor in mutant slices. Inhibition of PP1/2A did not affect early LTP (E-LTP) or basal synaptic transmission in mutant and wildtype slices. Our data show that genetic inhibition of PKA impairs L-LTP by reducing PKA-mediated suppression of PP1/2A.
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PMID:Genetic and pharmacological demonstration of a role for cyclic AMP-dependent protein kinase-mediated suppression of protein phosphatases in gating the expression of late LTP. 1245 50

The contributions of HCO(3)(-)-dependent, DIDS-sensitive mechanisms to the maintenance of steady-state pH(i), and the regulation of their activities by cAMP-dependent protein kinase (PKA), were investigated in CA1 neurons with the H(+)-sensitive fluorophore, BCECF. The addition of HCO(3)(-)/CO(2) to neurons with "low" (pH(i) < or = 7.20) and "high" (pH(i) > 7.20) initial pH(i) values under Hepes-buffered conditions, increased and decreased steady-state pH(i), respectively. Conversely, under HCO(3)(-)/CO(2)-buffered conditions, DIDS caused pH(i) to decrease and increase in neurons with low and high initial pH(i) values, respectively. In the presence, but not the absence, of HCO(3)(-), the PKA inhibitor Rp-adenosine-3',5'-cyclic monophosphorothioate (Rp-cAMPS; 50 microM) evoked DIDS-sensitive increases and decreases in pH(i) in neurons with low and high initial pH(i) values, respectively. In contrast, in neurons with low initial pH(i) values, activation of PKA with the Sp isomer of cAMPS (Sp-cAMPS; 25 microM) elicited increases in pH(i) that were smaller in the presence than in the absence of HCO(3)(-), whereas in neurons with high initial pH(i) values, Sp-cAMPS-evoked rises in pH(i) were larger in the presence than in the absence of HCO(3)(-); the differences between the effects of Sp-cAMPS on pH(i) under the different buffering conditions were attenuated by DIDS. Consistent with the possibility that changes in the activities of HCO(3)(-)-dependent, DIDS-sensitive mechanisms contribute to the steady-state pH(i) changes evoked by the PKA modulators, in neurons with initial pH(i) values < or = 7.20, Rp-cAMPS concurrently inhibited Na(+)-independent Cl(-)-HCO(3)(-) exchange and stimulated Na(+)-dependent Cl(-)-HCO(3)(-) exchange; in contrast, Sp-cAMPS concurrently stimulated Na(+)-independent Cl(-)-HCO(3)(-) exchange and inhibited Na(+)-dependent Cl(-)-HCO(3)(-) exchange. Data from a limited number of neurons with initial pH(i) values > 7.20 suggested that the directions of the reciprocal changes in anion exchange activities (inhibition or stimulation) evoked by Rp- and Sp-cAMPS may be opposite in cells with low vs. high resting pH(i) values. Taken together, the results indicate that the effects of modulating PKA activity on steady-state pH(i) in rat CA1 neurons under HCO(3)(-)/CO(2)-buffered conditions reflect not only changes in Na(+)-H(+) exchange activity but also changes in Na(+)-dependent and Na(+)-independent Cl(-)-HCO(3)(-) exchange activity that, in turn, may be dependent upon the initial pH(i).
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PMID:Regulation of Cl--HCO3- exchangers by cAMP-dependent protein kinase in adult rat hippocampal CA1 neurons. 1248 90

Aging is associated with an impaired ability to maintain long-term potentiation (LTP), but the underlying cause of the impairment remains unclear. To gain a better understanding of the cellular and molecular mechanisms responsible for this impairment, the synaptic transmission and plasticity were studied in the CA1 region of hippocampal slices from adult (6-8 months) and poor-memory (PM)-aged (23-24 months) rats. The one-way inhibitory avoidance learning task was used as the behavioral paradigm to screen PM-aged rats. With intracellular recordings, CA1 neurons of PM-aged rats exhibited a more hyperpolarized resting membrane potential, reduced input resistance, and increased amplitude of afterhyperpolarization and spike threshold, compared with those in adult rats. Although a reduction in the size of excitatory synaptic response was observed in PM-aged rats, no obvious differences were found between adult and PM-aged rats in the pharmacological properties of excitatory synaptic response, paired-pulse facilitation, or frequency-dependent facilitation, which was tested with trains of 10 pulses at 1, 5, and 10 Hz. Slices from the PM-aged rats displayed significantly reduced early-phase long-term potentiation (E-LTP) and late-phase LTP (L-LTP), and the entire frequency-response curve of LTP and LTD is modified to favor LTD induction. The susceptibility of time-dependent reversal of LTP by low-frequency afferent stimulation was also facilitated in PM-aged rats. Bath application of the protein phosphatase inhibitor, calyculin A, enhanced synaptic response in slices from PM-aged, but not adult, rats. In contrast, application of the cAMP-dependent protein kinase inhibitors, Rp-8-CPT-cAMPS and KT5720, induced a decrease in synaptic transmission only in slices from the adult rats. Furthermore, the selective beta-adrenergic receptor agonist, isoproterenol, and pertussis toxin-sensitive G-protein inhibitor, N-ethylmaleimide, effectively restored the deficit in E-LTP and L-LTP of PM-aged rats. These results demonstrate that age-related impairments of synaptic transmission and LTP may result from alterations in the balance of protein kinase/phosphatase activities.
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PMID:Alterations in the balance of protein kinase and phosphatase activities and age-related impairments of synaptic transmission and long-term potentiation. 1254 30

The application of taurine (2-aminoethanesulfonic acid) induces a long-lasting increase of synaptic efficacy and axon excitability (LLP-TAU) in rat hippocampal CA1 area. After taurine withdrawal, LLP-TAU lasted at least 3 h. This fact prompted us to assess whether the mechanisms involved in the maintenance of this particular potentiation were similar to those implicated in the late phase of long-term potentiation (L-LTP). In the presence of KN-62, an inhibitor of calcium/calmodulin-dependent protein kinase, taurine perfusion (10 mM, 30 min) did not affect the induction of LLP-TAU. However, LLP-TAU maintenance was completely suppressed by KT5720, an inhibitor of the cAMP-dependent protein kinase (PKA). Moreover, the late phase of LLP-TAU was blocked by inhibiting protein synthesis with anisomycin. In addition, taurine perfusion increased the phosphorylation of cAMP response element-binding protein (CREB), although did not affect cAMP levels. These features of LLP-TAU do not appear to be caused by the activation of D1/D5 dopamine receptors, as taurine also induced synaptic potentiation in the presence of SCH23390, an antagonist of this type of receptors. Finally, the late phase of both L-LTP and LLP-TAU occluded mutually. These results suggest that taurine triggers the sequence of some of the molecular events involved in the induction of L-LTP.
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PMID:Taurine-induced synaptic potentiation and the late phase of long-term potentiation are related mechanistically. 1255 19

Multiple trains of high-frequency synaptic stimulation evoke long-term potentiation (LTP) of synaptic transmission in hippocampal area CA1, which has been correlated with hippocampal long-term memory and requires the activation of cAMP-dependent protein kinase (PKA). To assess whether postsynaptic PKA is necessary for the expression of LTP, we made prolonged whole-cell voltage-clamp recordings from CA1 pyramidal neurons in mouse hippocampal slices during postsynaptic infusion of cell-impermeant modulators of PKA. Repeated stimulation (four 100 Hz trains at 5 min intervals) of the Schaffer collateral pathway increased synaptically evoked EPSCs for up to 2 hr. The postsynaptic infusion of either a cell-permeant PKA inhibitor (Rp-cAMPS) or a cell-impermeant PKA inhibitor (PKI(6-22)) did not alter post-tetanic peak potentiation, but it caused significant decay of EPSCs to pretetanization amplitudes within 1.5 hr. In contrast, postsynaptic infusion of PKI(6-22) did not alter a more modest, decaying form of LTP evoked by a single 100 Hz train. Paired-pulse facilitation was unchanged during most of the duration of LTP, suggesting that postsynaptic mechanisms, including PKA activation, are involved in the expression of LTP induced by multitrain stimulation. The postsynaptic infusion of a constitutively active isoform of the PKA catalytic subunit (Calpha) into CA1 pyramidal neurons increased EPSC sizes to elicit long-lasting synaptic facilitation. Thus, mimicking the activation of PKA in postsynaptic CA1 pyramidal neurons is sufficient for inducing persistent synaptic facilitation. Activation of apostsynaptic PKA is necessary for the expression of LTP in CA1 pyramidal neurons and is sufficient for initiating persistent synaptic facilitation.
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PMID:Postsynaptic application of a peptide inhibitor of cAMP-dependent protein kinase blocks expression of long-lasting synaptic potentiation in hippocampal neurons. 1259 2


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