Regulation of the Readily Releasable Vesicle Pool by Protein Kinase C

Abstract

Modulation of the size of the readily releasable vesicle pool has recently come under scrutiny as a candidate for the regulation of synaptic strength. Using electrophysiological and optical measurement techniques, we show that phorbol esters increase the size of the readily releasable pool at glutamatergic hippocampal synapses in culture through a protein kinase C (PKC)-dependent mechanism. Phorbol ester activation of PKC also increases the rate at which the pool refills. These results identify two powerful ways that activation of the PKC pathway may regulate synaptic strength by modulating the readily releasable pool of vesicles.

A Specific Role for Ca2+-Dependent Adenylyl Cyclases in Recovery from Adaptive Presynaptic Silencing

“…5D). This result suggests that neither stimulation of PKC pathways (Stevens and Sullivan, 1998;Wierda et al, 2007) nor a direct effect of the phorbol on vesicle priming (Betz et al, 1998;Wierda et al, 2007) interferes with presynaptic silencing in the same way that cAMP stimulation does.…”

Myristoylated alanine rich C kinase substrate (MARCKS) heterozygous mutant mice exhibit deficits in hippocampal mossy fiber-CA3 long-term potentiation

“…Consistent with the proposed role of PKC in the regulation of synaptic efficacy, exogenous activation of PKC with phorbol esters induces the movement of neurotransmitter vesicles from reserve pools to the readily releasable pool at active release sites (Stevens and Sullivan, 1998;Brager et al, 2002;Shoji-Kasai et al, 2002;Kumakura et al, 2004), which is positively correlated with synaptic release probability (Schikorski and Stevens, 1997). The maintenance of synaptic vesicles in reserve pools, and their movement to the readily releasable pool, is also regulated by the filamentous (F) actin cytoskeleton (Gotow et al, 1991;Doussau and Augustine, 2000;Morales et al, 2000;Trifaro et al, 2002), and accumulating evidence suggests that the maintenance phase of LTP requires synaptic F-actin cytoskeletal assembly-disassembly dynamics (Kim and Lisman, 1999;Krucker et al, 2000;Fukazawa et al, 2003;Lang et al, 2004;Matsuzaki et al, 2004).…”

“…F-actin cytoskeletal plasticity is required for vesicular trafficking (Doussau and Augustine, 2000;Morales et al, 2000;Trifaro et al, 2002), dendritic motility (Matus, 2000), and the maintenance phase of LTP (Kim and Lisman, 1999;Krucker et al, 2000;Fukazawa et al, 2003). MARCKS binds and crosslinks F-actin in a PKC phosphorylation-dependent manner (Hartwig et al, 1992;Bubb et al, 1999;Yarmola et al, 2001), and PKC-mediated phosphorylation of MARCKS results in the movement of synaptic vesicles from reserve pools to active release sites in cultured cells and synaptosomes (Vitale et al, 1995;Stevens and Sullivan, 1998;Walaas and Sefland, 2000;Rose et al, 2001;Yang et al, 2002). Furthermore, anti-MARCKS antibodies, or F-actin destabilizing agents, increase spontaneous neurotransmitter release in PC12 cells (Shoji-Kasai et al, 2002), whereas MARCKS overexpression (two-fold) impaired PKCinduced enhancement of neurotransmitter release in human neuroblastoma SH-SY5Y cells (Hartness et al, 2001).…”

“…Therefore, a 50% reduction in MARCKS in mossy fiber axon terminals may compromise the regulation of F-actin cytoskeletal rigidity, resulting in less restriction in the movement of synaptic vesicles from reserve pools to active release sites. Since PTP is associated with the initial depletion of the readily-release vesicle pool (Brager et al, 2002) and is followed by a redistribution of synaptic vesicles from reserve pools to the readily-release pool (Applegate et al, 1987;Brager et al, 2002), a failure to maintain vesicles in reserve/surplus pools would be predicted to impair long-term, but not short-term, elevations in neurotransmitter release probability (Markram and Tsodyks, 1996;Stevens and Sullivan, 1998;Yawo, 1999;Brager et al, 2002). If this model is correct, future ultrastuctural analysis of mossy fiber terminals should reveal a paucity of vesicles in reserve pools in heterozygous Marcks mutant mice.…”

Arginine vasopressin-induced glucagon release: interaction with glucose and cyclic AMP-dependent protein kinase

“…The filling of the RRP, measured as recovery from depletion, is enhanced by elevated [Ca 2+ ]j (Von Ruden and Neher, 1993). Protein Kinase C (PKC) (Gillis et al, 1996, Stevens andSullivan, 1998;;Smith et al, 1998;Sudhof, 2000) and PKA are also involved in the regulation of the size of RPP, which means the transfer of vesicles from the resting and reverse pools to reverse and RRP pool, respectively.…”