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Calcium ions

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Calcium ions

Postby ferrari599 » Thu Nov 20, 2008 6:17 pm

How exactly do calcium ions cause the movement of vesicles - for instance how does the influx of calcium ions into a nerve ending bring about vesicles containing neurotransmitter moving towards the presynaptic membrane?

Thanks in advance
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Postby MohammedAmer » Fri Nov 28, 2008 7:22 am

In fact,they don't......the free-bound proportion of the vesicles at synapse are in a continous Brownian movement.So as the vesicles come close to membrane with excess calcium ion...that induce fusion of vesicle with membrane and exocytosis occurs.
I hope I have answered ur question.:)
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Postby MrMistery » Fri Nov 28, 2008 4:14 pm

That is very inaccurate.
The actual mechanism is something like this: a synaptic vesicle needs to fuse with the plasma membrane in order for the neurotransmitter to be released into the synaptic cleft. When the neuron is not firing, some vesicles are tethered to the plasma membrane(mainly through Rab proteins, but not only; some SNARE interactions are also involved, but they are not at their full capacity). There is a protein(synaptotagmin) that binds the SNAREs and does not allow them to fully interact, thereby precluding membrane fusion. Calcium binds to synaptotagmin and causes a conformational change in this protein, rendering it in a conformation in which it is unable to bind the SNARE complex. Now the SNARE complex can form, and the subsequent membrane fusion steps(not very well understood I am afraid) can take place, and the neutransmitter can be released.
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