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### permeability, conductance

Posted: Thu Sep 21, 2006 4:55 pm
Dear Friends,

as you know for some ionic current (e.g T-current), insted of conductance,

I=Gbar_ion *m^q*h*p *(v-E_rev)

we use permebility (GHK equation.)

I=P_ion *m^q*h*p *GHK()

the unite of conductance is [ S/cm2] (simens/area) and unite of permeability is [cm/sec ] (length/time)

let me define for a special ion

G_ion [s/cm2] -------> conductance density in section A
area(cm2) -----> area of section A
P_ion [cm/sec] -------> ion permeability in section A

g [s] ---------------> conductance of one channel

then, we can calculate number of channel in section A, as follow

n= G_ion*area/g ----> number of channel

N=G_ion/g -----> channel density

right?

if yes,then what should we do if we have permeability?

Do we have the same relation?
Do we can define permeability for one channel?

Posted: Thu Sep 21, 2006 8:36 pm
You forgot to mention that GHK(v, ci, co) must return a value whose units
are (millicoul/cm3).

If there are n channels in a 1 cm2 patch of membrane, and membrane
permeability is P cm/sec, then the permeability of a single channel is P/n
and also has units of cm/sec.

Why? Because the units of permeability are really cm3 / (sec cm2). To
see why this is so, consider the equation for transmembrane flux:
permeability * concentration_difference * area = flux
where
flux is in units of millimoles/sec
area is in units of cm2
and concentration difference is in moles/liter = millimoles/milliliter = millimoles/cm3
That's why membrane permeability, in cm/sec, is equal to the permeability of
a single channel, in cm/sec, times the number of channels in a 1 cm2
patch of membrane.

### Re: permeability, conductance

Posted: Wed Aug 26, 2009 10:38 pm
Hi all,
I recently found this forum and I am very happy to be a part of this forum.
I had a query regarding the channel permeability and conductance which is as follows:

I came across a problem where I found that the channel density is expressed in permeability. Now by using this information I would like to calculate the channel density per unit area. However I haven't been able to figure out the direct relationship between permeability and conductance. Can some kind soul help me in this regards, please!
The permeability value for a type of channel is P = 5.5× 10−5 cm/s. I would like to understand how many channels are expressed in per unit area? Is this possible?
Thank you so much
Channels

### Re: permeability, conductance

Posted: Sat Aug 29, 2009 1:48 pm
channels wrote:I came across a problem where I found that the channel density is expressed in permeability.
Presumably this is the "permeability of a unit area of membrane."
Now by using this information I would like to calculate the channel density per unit area.
You need the permeability of a single channel. Without that, you're asking a question analogous to "if a bag of apples costs \$5, how many apples are in a bag?"
However I haven't been able to figure out the direct relationship between permeability and conductance.
Has nothing to do with it, unless you know the conductance of a single channel.