24S-Hydroxycholesterol enhances synaptic vesicle cycling in the mouse neuromuscular junction: Implication of glutamate NMDA receptors and nitric oxide.
24S-hydroxycholesterol (24S-HC) is a brain-derived product of lipid metabolism present in the systemic circulation, where its level can change significantly in response to physiological and pathophysiological conditions. Here, using electrophysiological and optical approaches, we have found a high sensitivity to 24S-HC of the synaptic vesicle cycle at the mouse neuromuscular junctions. Treatment with 24S-HC increased the end plate potential amplitude (EPP) in response to a single stimulus and attenuated the EPP amplitude rundown during high frequency (HF) activity but had no influence on miniature EPP amplitude or frequency. The effects on evoked responses were associated with enhanced FM1-43 dye loading and unloading by endo- and exocytosis. Comparison of electrophysiological and optical data revealed an increase in the rate of vesicular cycling. The impact of 24S-HC was abolished or potentiated by stimulation or inhibition of NMDA-receptors respectively. Moreover, 24S-HC, acting in the same manner as the endothelial NO synthase (eNOS) inhibitor cavtratin, suppressed an increase in NO-sensitive dye fluorescence during HF stimulation, while l-glutamate had the opposite effect. Inhibitors of NOS (l-NAME and cavtratin, but not the neuronal NOS inhibitor TRIM), a scavenger of extracellular NO and a protein kinase G blocker all had stimulatory effects, similar to those of 24S-HC, on exocytosis induced by HF activity and completely masked the effect of 24S-HC. The data suggest that 24S-HC enhances synaptic vesicle cycling due to an attenuation of retrograde NO signaling that depends on eNOS. In this regard, 24S-HC counteracts the effects of NMDA-receptor stimulation at mouse neuromuscular junctions.
Department of Normal Physiology, Kazan State Medical University, Butlerova st. 49, Kazan, 420012, Russia.
M R
MR
Kasimov
Department of Normal Physiology, Kazan State Medical University, Butlerova st. 49, Kazan, 420012, Russia.
M R
MR
Fatkhrakhmanova
Department of Normal Physiology, Kazan State Medical University, Butlerova st. 49, Kazan, 420012, Russia.
K A
KA
Mukhutdinova
Department of Normal Physiology, Kazan State Medical University, Butlerova st. 49, Kazan, 420012, Russia. Electronic address: fysio@rambler.ru.
A M
AM
Petrov
D000818:Animals; D051242:Caveolin 1 / Q000494:pharmacology; D004705:Endocytosis / Q000187:drug effects*; D019706:Excitatory Postsynaptic Potentials; D005089:Exocytosis / Q000187:drug effects*; D018698:Glutamic Acid / Q000494:pharmacology; D006888:Hydroxycholesterols / Q000494:pharmacology*; D051379:Mice; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009469:Neuromuscular Junction / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism / Q000502:physiology*; D010446:Peptide Fragments / Q000494:pharmacology; D011109:Polymethacrylic Acids / Q000494:pharmacology; D016194:Receptors, N-Methyl-D-Aspartate / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology*; D013572:Synaptic Vesicles / Q000187:drug effects / Q000502:physiology*
D051242:Caveolin 1; D006888:Hydroxycholesterols; D010446:Peptide Fragments; D011109:Polymethacrylic Acids; D016194:Receptors, N-Methyl-D-Aspartate; C571371:caveolin-1 (82-101); D009569:Nitric Oxide; C091347:vinyl ethyl methacrylate; D018698:Glutamic Acid; C044563:24-hydroxycholesterol; D019331:NG-Nitroarginine Methyl Ester
24S-hydroxycholesterol; 24S-hydroxycholesterol (PubChem CID: 121948); NMDA receptor; Neuromuscular junction; Neurotransmitter release; Nitric oxide; Nitric oxide (PubChem CID: 145068); Synaptic vesicle recycling