Ionic channels classification

alex taylor ataylor at superior.carleton.ca
Fri Jul 21 09:28:05 EST 1995


In article <3um3m4$k6t at steele.ohsu.edu>, Matt Jones  <jonesmat at ohsu.edu> wrote:
>In article <3ukh36$rp8 at fiona.umsmed.edu> Jim Hutchins,
>hutchins at fiona.umsmed.edu writes:
>>I'm just doing this from memory, but I think it stands for anomalous
>
>This isn't quite right. The I-V relationship for most neurons shows
>strong outward rectification: there's a roughly exponential growth in
>*outward* current as the membrane potential is stepped in the positive
>direction, because voltage-dependent potassium channels (like the delayed
>rectifier) are activated at potentials positive to rest. The anomalous
>rectifiers are anomalous because they do just the opposite: they pass
>more current in the inward direction and at negative potentials. Currents
>like the H-current (for "hyperpolarised") and Q-current (for "queer", I
>think), and many of the ligand-activated G-protein coupled channels (like
>the 5-HT1A and GABA-B coupled channel) are inward or anomalous
>rectifiers. 
>
>The A-current is a normal outward rectifier. I have no idea why it's
>called the A-current. Maybe it's named after one of Chuck Stevens' kids
>(there's a rumor that the T, N and L-type calcium channels are named
>after Dick Tsien's kids).
>
>-Matt Jones

	Just to add to the confusion, the convention changes for
invertebrates. In Aplysia for instance the A-current delays the onset of
the action potential and thus can to an extent "shape" the response rate
of repetitively firing neurons. Hille has a pretty good classification of
channel types in "Ionic Channels of Exitable Membranes".

Alex Taylor
ataylor at ccs.carleton.ca



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