permeability, conductance

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reza_rzm
Posts: 34
Joined: Tue Aug 23, 2005 10:07 am

permeability, conductance

Post by reza_rzm »

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?
Last edited by reza_rzm on Mon Jul 16, 2007 5:11 pm, edited 2 times in total.
ted
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Post by ted »

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.
channels

Re: permeability, conductance

Post by channels »

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
ted
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Re: permeability, conductance

Post by ted »

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.
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