Quick Question on Endocytosis

[Nooro]

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Quick Question (Free Response):

Rate of endocytosis vary from cell type to cell type. What cel would be predicted to have the highest rate of endocytosis?

macrophage
erythrocyte
osteoblast
neuron

Answer is Macrophage, and I understand that a macrophage engulfs bacteria and what not and endocytizes foreign bodies. BUT, don't neuron's endocytize neortransmitters more frequently???


Also is it just me and my computer or is the search button no longer there?

 

[yunan]

I thought neurons have neurotransmitter receptors, so neurotransmitters aren't endocytized.

Quick Question (Free Response):

Rate of endocytosis vary from cell type to cell type. What cel would be predicted to have the highest rate of endocytosis?

macrophage
erythrocyte
osteoblast
neuron

Answer is Macrophage, and I understand that a macrophage engulfs bacteria and what not and endocytizes foreign bodies. BUT, don't neuron's endocytize neortransmitters more frequently???


Also is it just me and my computer or is the search button no longer there?

 

[Nooro]

Ahh good point my bad, i guess i was thinking that they are exocytized from the first neuron and there are receptors on the 2nd, thanks...... also any word on that search button??

 

[perfectmoment]

it's been disabled as SDN undergoes hardware upgrades.

 

[scooter31]

Theres a google search toolbar at the bottom of the pages, if you need a search fxn.

Happy studying...

 

[Nooro]

ahhh those crazy sdn peoples, thanks guys.

 

[sanche60]

I thought the same thing when I answered that question. The presynaptic terminal does use endocytosis to reuptake the neurotransmitter in some cases. Since neuronal function is usually related to quick signals and maintaining a controlled environment in the synapse I selected neurons as well. Tricky question.

 

[topdogg82]

well first remember that neurotransmitters arent always uptaken after use- they can diffuse out of the synapse, be degraded by enzymes like acetylcholinesterase, or be taken back into the presynaptic terminal by an uptake carrier. also, neurotransmitters are released through exocytosis from the presynaptic membrance, and bind to exterior receptors on the postsynaptic membrance, so endocytosis isnt really a factor in its actual functioning i think. however, before releasing the neurotransmitters, the presynaptic neuron does take in calcium through endocytosis, so maybe that was what you were thinking of?

 

[jmnykrkts]

well first remember that neurotransmitters arent always uptaken after use- they can diffuse out of the synapse, be degraded by enzymes like acetylcholinesterase, or be taken back into the presynaptic terminal by an uptake carrier. also, neurotransmitters are released through exocytosis from the presynaptic membrance, and bind to exterior receptors on the postsynaptic membrance, so endocytosis isnt really a factor in its actual functioning i think. however, before releasing the neurotransmitters, the presynaptic neuron does take in calcium through endocytosis, so maybe that was what you were thinking of?

Actually calcium entry at the presynaptic terminal is mediated by voltage-gated calcium channels that open up when the cell is depolarized (ie. when an action potential reaches the terminal). As far as I know there is no endocytosis involved in this process.

 

[topdogg82]

oh my bad. i guess i just assumed it would be endocytosis but the voltage gated channel thing makes more sense b/c thats how action potentials spread anyways. thanks.

 

[sanche60]

endocytosis does occur. It is necessary to replenish the synaptic vesicle pool. It involves the coating of the endocytotic vesicle with clathrin and then shuttling it to be filled with more neurotransmitter. I guess this is somewhat arguable since the proposal of the "kiss and run" concept for neurotransmitter release. Either way this is probably way more info then is required for the MCAT, but since i took neurology and biology of the brain it just popped into my mind when i saw the question.

 

[jmnykrkts]

endocytosis does occur. It is necessary to replenish the synaptic vesicle pool. It involves the coating of the endocytotic vesicle with clathrin and then shuttling it to be filled with more neurotransmitter. I guess this is somewhat arguable since the proposal of the "kiss and run" concept for neurotransmitter release. Either way this is probably way more info then is required for the MCAT, but since i took neurology and biology of the brain it just popped into my mind when i saw the question.

You're definitely right about endocytosis occurring at axon terminals. This is well established (and I don't think the 'kiss and run' hypothesis necessarily argues against that). However, it is NOT required for Ca entry.

 

[sanche60]

first off the kiss and run method does argue against endocytosis because it states that the synaptic vessicles do not undergo complete exocytosis i.e. complete fusion with the membrane thereby making endocytosis unnecessary. Second off the question asked for endocytotic rates and did not mention entry of calcium. All i was saying is that endocytosis occurs in neurons. Oh, and i never even mentioned calcium in any of my previous posts?
Canada ehhh?

 

[jmnykrkts]

first off the kiss and run method does argue against endocytosis because it states that the synaptic vessicles do not undergo complete exocytosis i.e. complete fusion with the membrane thereby making endocytosis unnecessary. Second off the question asked for endocytotic rates and did not mention entry of calcium. All i was saying is that endocytosis occurs in neurons. Oh, and i never even mentioned calcium in any of my previous posts?
Canada ehhh?

Actually kiss and run is hypothesized as one way in which NTs may be released from the presynaptic terminal. It could be used as a mechanism for rapid replenishment of the vesicle pool (as opposed to the more laborious clathrin mediated endocytosis) in times of robust neuronal activity. eg. when you have a neuron undergoing a rapid firing sequence the cell doesn't have to waste time/energy on complete endo -and exo- cytosis of vesicles. Thisst does not necessarily preclude the occurrence of the exo/endocytosis cycling of vesicles during normal activity.
As per the Ca entry thing, if you just read a few posts prior to yours you would have understood why that was brought up.
Cheers.

 

[sanche60]

Actually kiss and run is hypothesized as one way in which NTs may be released from the presynaptic terminal. It could be used as a mechanism for rapid replenishment of the vesicle pool (as opposed to the more laborious clathrin mediated endocytosis) in times of robust neuronal activity. eg. when you have a neuron undergoing a rapid firing sequence the cell doesn't have to waste time/energy on complete endo -and exo- cytosis of vesicles. Thisst does not necessarily preclude the occurrence of the exo/endocytosis cycling of vesicles during normal activity.
As per the Ca entry thing, if you just read a few posts prior to yours you would have understood why that was brought up.
Cheers.

"Some people at first said that ‘kiss-and-run’ would happen during high rates of neuron (or nerve cell) activity," he said. However, his and others’ data now show that ‘kiss-and-run’ is actually the most prevalent form of neurotransmitter release and occurs during low levels of nerve stimulation. When nerve stimulation occurs at a high rate, endocytosis goes on as well, increasing the levels of vesicle reformation and allowing the neuron to maintain a high rate of neurotransmitter release

This was extracted from the baylor college of medicine web site. You are clearly wrong and confusing people. You quoted me and then start talking about calcium two posts ago when i said nothing about calcium so this also is confusing. Perhaps you should stop going off on tangents and address the original question of the original post. Better yet, go play hockey, hoser.

 

[jmnykrkts]

You are clearly wrong and confusing people. You quoted me and then start talking about calcium two posts ago when i said nothing about calcium so this also is confusing. Perhaps you should stop going off on tangents and address the original question of the original post. Better yet, go play hockey, hoser.

Your words:

"first off the kiss and run method does argue against endocytosis because it states that the synaptic vessicles do not undergo complete exocytosis i.e. complete fusion with the membrane thereby making endocytosis unnecessary."

It is incorrect that kiss and run argues against endocytosis. That is the point that I was addressing. You seem to have changed your position on the coexistence of the 2 mechanisms in your last post though. Good to see.

W/ regards to the role of kiss and run:
The website you're referring to is discussing the findings of one scientist or at most a small group of scientists. The precise role of kiss and run in transmitter release is still far from clear. There are in fact many who still believe that high levels of Ca -as you would get under conditions of robust activity- causes an increase in the frequency of kiss and run fusion. I personally haven't read enough studies in this area to have a strong opinion on the matter and as such I try to avoid speaking in such absolutes (unlike you who seems to be convinced by what you read on one website).

And as for the calcium thing, you responded to the thread immediately after a couple of posts that were discussing Ca and endocytosis. I shouldn't have quoted you when responding though - I admit that that may have been a bit confusing for people having trouble following 😉


Very original canadian insults by the way

 

[sanche60]

kiss and run does not require endocytosis, only exocytosis requires endocytosis. Therefore under normal conditions the rate of endocytosis is negligible. This is supported by the earlier post which states that kiss and run is the predominant form under normal stimulation. I also said that the situation with kiss and run is arguable in another earlier post. this is what i am saying, over and over again but just not getting through.

 

[jmnykrkts]

kiss and run does not require endocytosis, only exocytosis requires endocytosis. Therefore under normal conditions the rate of endocytosis is negligible. This is supported by the earlier post which states that kiss and run is the predominant form under normal stimulation. I also said that the situation with kiss and run is arguable in another earlier post. this is what i am saying, over and over again but just not getting through.

You did indeed say that the situation for kiss and run is arguable. Which is odd considering you now seem completely certain of the conditions for kiss and run despite the overwhelming uncertainty in the academic community. And you did also say that kiss and run "argues against" endocytosis. That's really what I was initially contending with.

 

[sanche60]

just because something is arguable does not mean i cannot have a stance or opinion on it. Understand?

 

[jmnykrkts]

just because something is arguable does not mean i cannot have a stance or opinion on it. Understand?

Fair enough. It just seems like your very definite opinion was a bit of a reactionary measure. A little suspect. It was only brought up try to and debase my point after I had suggested that kiss and run and endocytosis were not necessarily mutually exclusive.

 

[sanche60]

good game. nows lets both do something more productive with our lives.

 

[jmnykrkts]

good game. nows lets both do something more productive with our lives.

Agreed. Nice match.

 

[riceman04]

oh my bad. i guess i just assumed it would be endocytosis but the voltage gated channel thing makes more sense b/c thats how action potentials spread anyways. thanks.

What about receptor mediated endocytosis at the post synaptic junction?

 

[flippilf]

Without relevant scientific evidences, what would your body prefer to do? Of course, get rid of unwanted things out of the body, ie bacterias, etc. etc. haha... just a simple thought... anyone concur? or perhaps, disagree? if so, don't let the door hit ya... hehe...