> 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
>> I'm not sure why the calcium entry is dependent on the amplitude
> of the action potential, rather than absolute membrane potential
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