Presynaptic Release Probability and Readily Releasable Pool Size Are Regulated by Two Independent Mechanisms during Posttetanic Potentiation at the Calyx of Held Synapse

At the immature calyx of Held, the fast decay phase of a Ca2+ transient induced by tetanic stimulation (TS) was followed by a period of elevated [Ca2+]i for tens of seconds, referred to as posttetanic residual calcium (Cares). We investigated the source of Cares and its contribution to posttetanic potentiation (PTP). After TS (100 Hz for 4 s), posttetanic Cares at the calyx of Held was largely abolished by tetraphenylphosphonium (TPP+) or Ru360, which inhibit mitochondrial Na+-dependent Ca2+ efflux and Ca2+ uniporter, respectively. Whereas the control PTP lasted longer than Cares, inhibition of Cares by TPP+ resulted in preferential suppression of the early phase of PTP, the decay time course of which well matched with that of Cares. TS induced significant increases in release probability (Pr) and the size of the readily releasable pool (RRP), which were estimated from plots of cumulative EPSC amplitudes. TPP+ or Ru360 suppressed the posttetanic increase in Pr, whereas it had little effect on the increase in RRP size. Moreover, the posttetanic increase in Pr, but not in RRP size, showed a linear correlation with the amount of Cares. In contrast, myosin light chain kinase (MLCK) inhibitors and blebbistatin reduced the posttetanic increase in RRP size with no effect on the increase in Pr. Application of TPP+ in the presence of MLCK inhibitor peptide caused further suppression of PTP. These findings suggest that Cares released from mitochondria and activation of MLCK are primarily responsible for the increase in Pr and that in the RRP size, respectively.

[1]  W. Ho,et al.  Interplay between Na+/Ca2+ Exchangers and Mitochondria in Ca2+ Clearance at the Calyx of Held , 2005, The Journal of Neuroscience.

[2]  R. Zucker,et al.  Mitochondrial Involvement in Post-Tetanic Potentiation of Synaptic Transmission , 1997, Neuron.

[3]  S. Mirzoeva,et al.  Identification of novel classes of protein kinase inhibitors using combinatorial peptide chemistry based on functional genomics knowledge. , 1999, Journal of medicinal chemistry.

[4]  E. Neher,et al.  Quantitative Analysis of Calcium-Dependent Vesicle Recruitment and Its Functional Role at the Calyx of Held Synapse , 2007, The Journal of Neuroscience.

[5]  R S Zucker,et al.  Calcium in motor nerve terminals associated with posttetanic potentiation , 1989, The Journal of neuroscience : the official journal of the Society for Neuroscience.

[6]  I. Forsythe,et al.  Presynaptic Mitochondrial Calcium Sequestration Influences Transmission at Mammalian Central Synapses , 2002, The Journal of Neuroscience.

[7]  L. Landmesser,et al.  NCAM 180 Acting via a Conserved C-Terminal Domain and MLCK Is Essential for Effective Transmission with Repetitive Stimulation , 2005, Neuron.

[8]  Felix Felmy,et al.  Probing the Intracellular Calcium Sensitivity of Transmitter Release during Synaptic Facilitation , 2003, Neuron.

[9]  R. Gopalakrishna,et al.  Modifications of cysteine-rich regions in protein kinase C induced by oxidant tumor promoters and enzyme-specific inhibitors. , 1995, Methods in enzymology.

[10]  Gautam B. Awatramani,et al.  Modulation of Transmitter Release by Presynaptic Resting Potential and Background Calcium Levels , 2005, Neuron.

[11]  R. Schneggenburger,et al.  Posttetanic potentiation critically depends on an enhanced Ca2+ sensitivity of vesicle fusion mediated by presynaptic PKC , 2007, Proceedings of the National Academy of Sciences.

[12]  David E. Clapham,et al.  The mitochondrial calcium uniporter is a highly selective ion channel , 2004, Nature.

[13]  J. Borst,et al.  An increase in calcium influx contributes to post-tetanic potentiation at the rat calyx of Held synapse. , 2006, Journal of neurophysiology.

[14]  E. Barrett,et al.  Extrusion of Ca2+ from mouse motor terminal mitochondria via a Na+–Ca2+ exchanger increases post‐tetanic evoked release , 2006, The Journal of physiology.

[15]  R. Zucker,et al.  Residual Ca2 + and short-term synaptic plasticity , 1994, Nature.

[16]  J. Stull,et al.  Dedicated Myosin Light Chain Kinases with Diverse Cellular Functions* , 2001, The Journal of Biological Chemistry.

[17]  T. Gunter,et al.  Kinetics of mitochondrial calcium transport. II. A kinetic description of the sodium-dependent calcium efflux mechanism of liver mitochondria and inhibition by ruthenium red and by tetraphenylphosphonium. , 1986, The Journal of biological chemistry.

[18]  D W Tank,et al.  The role of presynaptic calcium in short-term enhancement at the hippocampal mossy fiber synapse , 1994, The Journal of neuroscience : the official journal of the Society for Neuroscience.

[19]  T. Aiuchi,et al.  Effects of probes of membrane potential on metabolism in synaptosomes. , 1985, Biochimica et biophysica acta.

[20]  P. Verstreken,et al.  Synaptic Mitochondria Are Critical for Mobilization of Reserve Pool Vesicles at Drosophila Neuromuscular Junctions , 2005, Neuron.

[21]  H. von Gersdorff,et al.  The pool of fast releasing vesicles is augmented by myosin light chain kinase inhibition at the calyx of Held synapse. , 2008, Journal of neurophysiology.

[22]  R. Rübsamen,et al.  The Medial Nucleus of the Trapezoid Body in the Gerbil Is More Than a Relay: Comparison of Pre- and Postsynaptic Activity , 2003, Journal of the Association for Research in Otolaryngology.

[23]  Doyun Lee,et al.  Target Cell-Specific Involvement of Presynaptic Mitochondria in Post-Tetanic Potentiation at Hippocampal Mossy Fiber Synapses , 2007, The Journal of Neuroscience.

[24]  T. Ishikawa,et al.  Mechanisms underlying presynaptic facilitatory effect of cyclothiazide at the calyx of Held of juvenile rats , 2001, The Journal of physiology.

[25]  W. Regehr,et al.  Short-term synaptic plasticity. , 2002, Annual review of physiology.

[26]  Y. Takagishi,et al.  Localization of myosin II and V isoforms in cultured rat sympathetic neurones and their potential involvement in presynaptic function , 2005, The Journal of physiology.

[27]  A. C. Meyer,et al.  Released Fraction and Total Size of a Pool of Immediately Available Transmitter Quanta at a Calyx Synapse , 1999, Neuron.

[28]  T. A. Ryan.  Inhibitors of Myosin Light Chain Kinase Block Synaptic Vesicle Pool Mobilization during Action Potential Firing , 1999, The Journal of Neuroscience.

[29]  Takeshi Sakaba,et al.  Roles of the Fast-Releasing and the Slowly Releasing Vesicles in Synaptic Transmission at the Calyx of Held , 2006, The Journal of Neuroscience.

[30]  Adrian Y. C. Wong,et al.  Distinguishing between Presynaptic and Postsynaptic Mechanisms of Short-Term Depression during Action Potential Trains , 2003, The Journal of Neuroscience.

[31]  K. Moulder,et al.  Reluctant Vesicles Contribute to the Total Readily Releasable Pool in Glutamatergic Hippocampal Neurons , 2005, The Journal of Neuroscience.

[32]  L. Trussell,et al.  Desensitization of AMPA receptors upon multiquantal neurotransmitter release , 1993, Neuron.

[33]  John F. Wesseling,et al.  Augmentation Is a Potentiation of the Exocytotic Process , 1999, Neuron.

[34]  Y. Goda,et al.  Myosin Light Chain Kinase Is Not a Regulator of Synaptic Vesicle Trafficking during Repetitive Exocytosis in Cultured Hippocampal Neurons , 2006, The Journal of Neuroscience.

[35]  Lu-Yang Wang,et al.  Coincident Activation of Metabotropic Glutamate Receptors and NMDA Receptors (NMDARs) Downregulates Perisynaptic/Extrasynaptic NMDARs and Enhances High-Fidelity Neurotransmission at the Developing Calyx of Held Synapse , 2007, The Journal of Neuroscience.

[36]  B. Sakmann,et al.  Transmitter release modulation by intracellular Ca2+ buffers in facilitating and depressing nerve terminals of pyramidal cells in layer 2/3 of the rat neocortex indicates a target cell‐specific difference in presynaptic calcium dynamics , 2001, The Journal of physiology.

[37]  T. Otis,et al.  Direct Measurement of AMPA Receptor Desensitization Induced by Glutamatergic Synaptic Transmission , 1996, The Journal of Neuroscience.

[38]  E. Neher,et al.  Vesicle pools and short-term synaptic depression: lessons from a large synapse , 2002, Trends in Neurosciences.

[39]  J. Borst,et al.  Dynamics of the readily releasable pool during post‐tetanic potentiation in the rat calyx of Held synapse , 2007, The Journal of physiology.

[40]  H. Coste,et al.  The bisindolylmaleimide GF 109203X is a potent and selective inhibitor of protein kinase C. , 1991, The Journal of biological chemistry.

[41]  J. Borst,et al.  Post‐tetanic potentiation in the rat calyx of Held synapse , 2005, The Journal of physiology.

[42]  R. Schneggenburger,et al.  Presynaptic Ca2+ Requirements and Developmental Regulation of Posttetanic Potentiation at the Calyx of Held , 2005, The Journal of Neuroscience.

[43]  K. Muramoto,et al.  Myosin II is involved in transmitter release at synapses formed between rat sympathetic neurons in culture , 1994, Neuron.

[44]  D W Tank,et al.  A quantitative measurement of the dependence of short-term synaptic enhancement on presynaptic residual calcium , 1994, The Journal of neuroscience : the official journal of the Society for Neuroscience.