RT Journal Article
SR Electronic
T1 Frequency-Dependent Modes of Synaptic Vesicle Endocytosis and Exocytosis at Adult Mouse Neuromuscular Junctions
JF The Journal of Neuroscience
JO J. Neurosci.
FD Society for Neuroscience
SP 1093
OP 1105
DO 10.1523/JNEUROSCI.2800-10.2011
VO 31
IS 3
A1 Yuka Maeno-Hikichi
A1 Luis Polo-Parada
A1 Ksenia V. Kastanenka
A1 Lynn T. Landmesser
YR 2011
UL http://www.jneurosci.org/content/31/3/1093.abstract
AB During locomotion, adult rodent lumbar motoneurons fire in high-frequency (80–100 Hz) 1–2 s bursts every several seconds, releasing between 10,000 and 20,000 vesicles per burst. The estimated total vesicle pool size indicates that all vesicles would be used within 30 s; thus, a mechanism for rapid endocytosis and vesicle recycling is necessary to maintain effective transmission and motor behavior. However, whether such rapid recycling exists at mouse neuromuscular junctions (NMJs) or how it is regulated has been unclear. Here, we show that much less FM1-43 dye is lost per stimulus with 100 Hz stimulation than with 10 Hz stimulation even when the same number of vesicles undergo exocytosis. Electrophysiological data using folimycin show this lesser amount of dye loss is caused in part by the rapid reuse of vesicles. We showed previously that a myosin light chain kinase (MLCK)–myosin II pathway was required for effective transmission at 100 Hz. Here, we confirm the activation of MLCK, based on increased nerve terminal phospho-MLC immunostaining, with 100 Hz but not with 10 Hz stimulation. We further demonstrate that activation of MLCK, by increased extracellular Ca2+, by PKC (protein kinase C) activation, or by a MLCK agonist peptide, reduces the amount of dye lost even with 10 Hz stimulation. MLCK activation at 10 Hz also resulted in more vesicles being rapidly reused. Thus, MLCK activation by 100 Hz stimulation switches the mechanism of vesicle cycling to a rapid-reuse mode and is required to sustain effective transmission in adult mouse NMJs.