>On Thu, 7 Oct 1999, Stephen Black went:
>
>> I've long assumed that the passive channels that allow Na+ to move
>> into the cell in the resting state are different from the
>> voltage-gated sodium channels that open during the action potential.
>> But I'm beginning to wonder if I'm wrong.
>
>and David Epstein went:
>My impression has always been that there's no special class of
>"passive" sodium channels, and that a few voltage-gated sodium
>channels just happen to be open during conditions when they "should"
>be closed.
>
>I don't think I've ever seen the question addressed explicitly.
>
I have always assumed, as has Steven, that there were passive channels (for
sodium and potassium) which permitted flow of Na & K ions in accordance
with their diffusion gradients. The Na/K pumps maintain the concentrations,
and counter the diffusion of these ions through their passive channels.
Active channels for these ions would be voltage-gated and operate during
the action potential. Carlson, in his Physiology of Behavior text (6th ed)
notes that "By the way, cell biologists have discovered approximately 75
different types of ion channels, and more will undoubtedly be discovered."
(p.37) but does not provide a reference for this statement.
George
George Goedel
Professor & Chairperson
Department of Psychology
Northern Kentucky University
Highland Hts., KY 41099-2000
(606) 572-5574
[EMAIL PROTECTED]
