Phosphorylation regulates spontaneous and evoked transmitter release at a giant terminal in the rat auditory brainstem

• Published in: The Journal of physiology Vol. 526; no. 2; pp. 349 - 357
• Main Authors: Oleskevich, Sharon, Walmsley, Bruce
• Format: Journal Article
• Language: English
• Published: Oxford, UK The Physiological Society 15-07-2000; Blackwell Science Ltd; Blackwell Science Inc
• Subjects: 1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine - pharmacology; 2-Amino-5-phosphonovalerate - pharmacology; Animals; Cochlear Nucleus - physiology; Enzyme Inhibitors - pharmacology; Evoked Potentials - drug effects; Evoked Potentials - physiology; Excitatory Postsynaptic Potentials - drug effects; Excitatory Postsynaptic Potentials - physiology; In Vitro Techniques; Indoles - pharmacology; Maleimides - pharmacology; Original; Phorbol 12,13-Dibutyrate - pharmacology; Phosphorylation; Presynaptic Terminals - physiology; Protein Kinase C - metabolism; Rats; Rats, Wistar; Synaptic Transmission - drug effects; Synaptic Transmission - physiology; Tetradecanoylphorbol Acetate - pharmacology
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1111/j.1469-7793.2000.t01-1-00349.x

The role of phosphorylation in synaptic transmission was investigated at a large glutamatergic terminal, the endbulb of Held,
on bushy cells in the rat anteroventral cochlear nucleus (AVCN).
Whole-cell recordings of excitatory postsynaptic currents (EPSCs) were used to examine the effects of kinase inhibitors and
activators on low-frequency (baseline) evoked release, spontaneous release, paired-pulse facilitation (PPF) or depression
(PPD), repetitive stimuli and recovery from depression.
Application of the kinase inhibitor H7 (100 μ m ) reduced low-frequency evoked EPSC amplitude (by 15 %) and simultaneously increased PPF (or reduced PPD), with no significant
change in other aspects of transmission. H7 did not affect the amplitude or frequency of spontaneous miniature EPSCs.
Phorbol esters increased EPSC amplitude (by 50 %) with a concomitant decrease in PPF (or increase in PPD), and reduced the
final EPSC amplitude during repetitive stimuli. The effect of phorbol esters was due exclusively to protein kinase C (PKC)
activation, as the specific PKC inhibitor bis-indolylmaleimide (Bis) completely blocked the potentiating effect of phorbol
esters on EPSC amplitude.
Significantly, phorbol esters did not increase the evoked EPSC amplitude at connections in which release was maximized using
high extracellular calcium concentrations (4–6 m m ).
Phorbol esters increased the frequency of spontaneous miniature EPSCs in physiological calcium (by 275 %), and in high extracellular
calcium (by 210 %) when phorbol esters did not increase the evoked EPSC amplitude.
Our results are most consistent with the actions of H7 to decrease low-frequency release probability and phorbol esters to
increase low-frequency release probability at the endbulb-bushy cell synaptic connection in the AVCN. The effects of H7 and
phorbol esters on paired-pulse responses and tetanic depression appear to be largely consequential to these changes in low-frequency
release probability.