At 6:47 PM +0000 1/19/99, Matt Jones wrote:
[snip]
> Also, 4-AP can increase spike amplitude and duration in
>myelinated axons, suggesting that there _are_ K+ channels in or near the
>nodes, and there is immunohistological evidence of this also, at least
>under some conditions.
What is the relevance of 4-AP (4-aminopyridine) to the presence or absence
of K channels? It of course opens this string to a delightful discussion
of potassium channel diversity, which is becoming more relevant to this
discussion by the millisecond. ;-)
>In intact central neuronal circuits, by the way, there an awful lot of
>things that generate afterhyperpolarizations, including recurrent
>inhibitory synaptic feedback. I believe that part of the "reason" for
>this is to more effectively remove inactivation of Na+ and Ca++ channels,
>so as to allow more rapid or more complex spike firing. A great example
>of this is in thalamic oscillations, in which GABA-mediated IPSPs
>_promote_ "rebound" spike firing by repriming T-type Ca++ channels.
And also rebound hyperpolarizations (back to potassium channels again.)
>rlh
Richard Hall
Comparative Animal Physiologist
Division of Sciences and Mathematics
University of the Virgin Islands
St. Thomas, USVI 00802
809-693-1386
rhall at uvi.edu
