Nitric oxide stimulates Ca(2+)-independent synaptic vesicle release

Area of Science:

• Neuroscience
• Cell Biology
• Biochemistry

Background:

• Exocytosis is a fundamental process for neurotransmitter release.
• Calcium (Ca2+) influx is traditionally considered essential for triggering exocytosis.
• The role of other signaling molecules in exocytosis remains an area of active research.

Purpose of the Study:

• To investigate the effect of nitric oxide (NO) on exocytotic release from hippocampal synaptosomes.
• To determine the underlying mechanisms of NO-stimulated exocytosis, particularly its dependence on intracellular Ca2+.

Main Methods:

• Utilized a novel fluorescence method with the dye FM1-43 to monitor exocytotic vesicle release.
• Employed various NO donors (sodium nitroprusside, S-nitroso-N-acetylpenicillamine, 3-morpholino-sydnonimine, acidified sodium nitrite).
• Measured neurotransmitter release using [3H]L-glutamate and intracellular Ca2+ levels with Indo-1/AM.

Main Results:

• Nitric oxide significantly stimulated transient vesicle release from synaptosomes.
• NO-stimulated release was comparable to KCl-induced release in time course and neurotransmitter release.
• NO-stimulated release was independent of intracellular Ca2+ rise; in fact, NO decreased intracellular Ca2+.
• The Ca2+ channel blocker Cd2+ did not inhibit NO-stimulated release.
• NO appears to act on the Ca2+-sensitive pool of vesicles.

Conclusions:

• Nitric oxide is a physiological mediator that can induce vesicle exocytosis without increasing intracellular Ca2+.
• This Ca2+-independent pathway provides a new perspective on the regulation of synaptic transmission.
• NO-mediated exocytosis may serve as a valuable tool for studying the molecular mechanisms of vesicle release.