On 2 Dec 2001 20:23:06 GMT, dag.stenberg at nospam.helsinki.fi wrote:
>2) increasing the permeability for Cl- will always cause inhibition, but
>this can occur without any change in membrane potential (because of
>"short-circuiting")
Um..no, not always. It depends on the concentration of Cl- in and
outside the cell. For example in the rat superior suprachiasmatic
nucleus (and probably also that of most mammals), GABA is excitatory
during the day and inhibitory at night. The difference is that during
the day the extracellular fluid has a low Cl- concentration so opening
the GABA receptor causes Cl- to flow out of the cell, not into it.
See:
Wagner S, et al (1997)
"GABA in the mammalian suprachiasmatic nucleus and it's role in diurnal
rhythmicity"
Nature vol 386; p173-7
Katz's "Beyond neurotransmission - Neuromodulation and it's importance
for information processing" Oxford Univ Press, 1999 also goes into some
detail about this on, from memory, pages 57-62.
About the best that can be said is that increasing membrane Cl-
permeability will most often cause inhibition, but not always.
Ian
