In article <yNIS3.2604$u3.171920 at typhoon1.rdc-detw.rr.com> Richard
Norman, rsnorman at mediaone.net writes:
>Incidentally, if you hold the membrane hyperpolarized, wouldn't the
>voltage-gated potassium channels close whereas the "leak" will persist?
>>And what about the numerous cell types (most of the body) that are not
>electrically excitable. Do they still have voltage-gated channels? They do
>have resting permeabilities and a resting potential primarily produced by
>>Wouldn't these argue against the window effect as the source?
Right. "Leak", as operationally defined, will persist at any potential
because it's ohmic, by definition. However, many of the "leak channels"
that have been cloned and studied at the single channel level (the ones
that come immediately to mind are the ClC-family of chloride channels
studied by Jentsch (sp?) and colleagues) have exactly this property that
Po (Open probability) doesn't change with voltages between -120 and +120
or so, even though you can clearly see channels opening and closing, so
you know that they're not just holes in the membrane. They are gated (by
something, or maybe just spontaneously by thermal fluctuations), they
have well defined conductance levels, ion selectivity etc. But in
macroscopic currents you'd be hard pressed to tell these from holes in
the membrane unless you looked at their ionic selectivity. But anyway,
you're right that these are probably not participating in any "excitable"
behaviour like spike firing, etc. They appear to be important in
regulating resting membrane conductance and also osmoregulation.
Most neurons that I'm familiar with do have some sort of tonically
active, ohmic, -channel-based- resting conductance that is separate from
any window current effect (or, if you're really hardcore, you might think
of them as just having humongously wide window voltage ranges ;-)