Why so many K+ channels?

Lyle Borg-Graham lyle at ai.mit.edu
Tue Feb 28 12:55:10 EST 1995

In article <Michael_Lebow-270295195047 at cis-ts5-slip6.cis.brown.edu> Michael_Lebow at brown.edu (Michael Lebow) writes:

     ... why (are) there are so many different types of voltage-gated
     potassium channels expressed in the nervous system? I understand the
     advantage of having a few different types (i.e. delayed rectifier,
     a-current...) but what is the functional importance of dozens of
     different channels?

Possibly the following - on one hand, the sometimes rather subtle
differences in the kinetics/voltage-dependencies between the different
K+ (and other) channels will always have *some* differential impact on
a cell's transfer function, and since we only have a vague idea of
what target cells care about (wrt to input dynamics), it remains to be
disproven that some difference in effect between two channels is
functionally relevant in all cases. On the other hand, even if two
channels had the same functional effect on the transfer function, if
those channels have different sensitivities to modulators ([Ca++]i,
pancrinic factors, etc.), then their complete contributions to the
cell state will be distinct and potentially interesting. Thus it may
be that some channels are included in order to make a cell aware of,
or distinguish between, variations within a given spectrum of
neuromodulatory states, and adjust its response accordingly.

One thing for sure, if all the nervous system needed was an "action
potential" for communication, all that would be needed is a *single*
transient channel (i.e. one that has an activating and an inactivating
characteristic, for example, the original squid Na+ channel), with
some fairly weak constraints on the relation between the kinetics of
activation and inactivation. The major contribution of a second,
repolarizing channel (e.g. squid K+ channel) is to remove the
limitation on the signal bandwidth imposed by the resting membrane
time constant. All the rest of the channels build on that theme.

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