primary afferent depolarization

John Anderson anderson at CSHL.ORG
Mon Jan 25 16:36:23 EST 1993

>   From: knowled at ccsmtp.ccf.org (Doug Knowles)
>   Date: 25 Jan 93 16:52:34 GMT
>   The amount of transmitter released is dependent on the amount of
>   calcium which enters the presynaptic terminal, which is dependent 
>   on the amplitude of the action potential in the presynaptic
>   terminal.  Prior depolarization of the terminal (e.g. by inceased
>   extracellular K+) reduces the difference between the (depolarized)
>   resting potential and the peak of the action potential, thus 
>   reducing the action potential amplitude.  This causes less calcium
>   entry, less transmitter release, and a smaller postsynaptic 
>   potential.
>   I'm not sure why the calcium entry is dependent on the amplitude
>   of the action potential, rather than absolute membrane potential
>   difference.  

This is exactly what bothers me.

>Probably because of the time and voltage dependence
>   of the calcium channels.  I'll have to defer to my more informed
>   biophysics colleagues  (Bill?).

Does anybody know?


John E. Anderson
W. M. Keck Structural Biology Laboratory
Cold Spring Harbor Laboratory

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