Calcium-Dependent Isoforms of Protein Kinase C Mediate Posttetanic Potentiation at the Calyx of Held

Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA.
Neuron (Impact Factor: 15.05). 06/2011; 70(5):1005-19. DOI: 10.1016/j.neuron.2011.04.019
Source: PubMed


High-frequency stimulation leads to a transient increase in the amplitude of evoked synaptic transmission that is known as posttetanic potentiation (PTP). Here we examine the roles of the calcium-dependent protein kinase C isoforms PKCα and PKCβ in PTP at the calyx of Held synapse. In PKCα/β double knockouts, 80% of PTP is eliminated, whereas basal synaptic properties are unaffected. PKCα and PKCβ produce PTP by increasing the size of the readily releasable pool of vesicles evoked by high-frequency stimulation and by increasing the fraction of this pool released by the first stimulus. PKCα and PKCβ do not facilitate presynaptic calcium currents. The small PTP remaining in double knockouts is mediated partly by an increase in miniature excitatory postsynaptic current amplitude and partly by a mechanism involving myosin light chain kinase. These experiments establish that PKCα and PKCβ are crucial for PTP and suggest that long-lasting presynaptic calcium increases produced by tetanic stimulation may activate these isoforms to produce PTP.

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    • "Phorbol 12,13-dibutyrate (PDBu), a DAG analog, can enhance transmission by activating not only PKC Ca (Figure 1A) but also Ca 2+ -insensitive PKC isoforms and other presynaptic proteins (Brose and Rosenmund, 2002; Newton, 2010). At immature calyces, ∼35% of PDBu-mediated enhancement is independent of PKC Ca (Fioravante et al., 2011). We found that PDBu enhances release at functionally mature wild-type calyces (Figure 1C, black) but not at agematched αβ dko calyces (Figure 1C, purple). "
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    ABSTRACT: In presynaptic boutons, calcium (Ca2+) triggers both neurotransmitter release and short-term synaptic plasticity. Whereas synaptotagmins are known to mediate vesicle fusion through binding of high local Ca2+ to their C2 domains, the proteins that sense smaller global Ca2+ increases to produce short-term plasticity have remained elusive. Here, we identify a Ca2+ sensor for post-tetanic potentiation (PTP), a form of plasticity thought to underlie short-term memory. We find that at the functionally mature calyx of Held synapse the Ca2+-dependent protein kinase C isoforms α and β are necessary for PTP, and the expression of PKCβ in PKCαβ double knockout mice rescues PTP. Disruption of Ca2+ binding to the PKCβ C2 domain specifically prevents PTP without impairing other PKCβ-dependent forms of synaptic enhancement. We conclude that different C2-domain-containing presynaptic proteins are engaged by different Ca2+ signals, and that Ca2+ increases evoked by tetanic stimulation are sensed by PKCβ to produce PTP. DOI:
    eLife Sciences 08/2014; 3:e03011. DOI:10.7554/eLife.03011 · 9.32 Impact Factor
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    • "A previous study evaluated the effects of BIS-like PKC inhibitors on PTP as non-specific (Lee et al., 2008). However, the genetic evidence for an involvement of conventional PKCs (Fioravante et al., 2011) and for the PKC phosphorylation sites of Munc18-1 in PTP (present study), as well as our pharmacological evidence with specific peptide inhibitors, firmly establishes the role of PKC and Munc18-1 phosphorylation in PTP. An earlier study found that phorbol esters translocates PKCε at the calyx of Held (Saitoh et al., 2001). "
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    ABSTRACT: Transmitter release at synapses is regulated by preceding neuronal activity, which can give rise to short-term enhancement of release like post-tetanic potentiation (PTP). Diacylglycerol (DAG) and Protein-kinase C (PKC) signaling in the nerve terminal have been widely implicated in the short-term modulation of transmitter release, but the target protein of PKC phosphorylation during short-term enhancement has remained unknown. Here, we use a gene-replacement strategy at the calyx of Held, a large CNS model synapse that expresses robust PTP, to study the molecular mechanisms of PTP. We find that two PKC phosphorylation sites of Munc18-1 are critically important for PTP, which identifies the presynaptic target protein for the action of PKC during PTP. Pharmacological experiments show that a phosphatase normally limits the duration of PTP, and that PTP is initiated by the action of a ‘conventional’ PKC isoform. Thus, a dynamic PKC phosphorylation/de-phosphorylation cycle of Munc18-1 drives short-term enhancement of transmitter release during PTP. DOI:
    eLife Sciences 02/2014; 3(3):e01715. DOI:10.7554/eLife.01715 · 9.32 Impact Factor
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    • "In addition, PKCα and PKCß are differentially effective in these two phenomena. PKCß makes a much larger contribution to PTP than PKCα (Fioravante et al., 2011), whereas PKCα and PKCß make comparable contributions to glycine-induced enhancement. The different calcium signals that induce these forms of plasticity may underlie the differential contributions of these isoforms. "
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    ABSTRACT: Depolarization of presynaptic terminals that arises from activation of presynaptic ionotropic receptors, or somatic depolarization, can enhance neurotransmitter release; however, the molecular mechanisms mediating this plasticity are not known. Here we investigate the mechanism of this enhancement at the calyx of Held synapse, in which presynaptic glycine receptors depolarize presynaptic terminals, elevate resting calcium levels, and potentiate release. Using knock-out mice of the calcium-sensitive PKC isoforms (PKC(Ca)), we find that enhancement of evoked but not spontaneous synaptic transmission by glycine is mediated primarily by PKC(Ca). Measurements of calcium at the calyx of Held indicate that deficits in synaptic modulation in PKC(Ca) knock-out mice occur downstream of presynaptic calcium increases. Glycine enhances synaptic transmission primarily by increasing the effective size of the pool of readily releasable vesicles. Our results reveal that PKC(Ca) can enhance evoked neurotransmitter release in response to calcium increases caused by small presynaptic depolarizations.
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