Bioelectricity - GHK equation, how can I find permeability?

[aimee123]

Hi,

 

I have an excel spreadhsheet filled with data...external and internal concentrations, Vm for potassium, sodium and chloride, however I am struggling with two points..

 

a) how can I find the internal concentration for K, Na and Cl? I have an increasing exernal concentration, and the membrane voltage of the cell at that particular external voltage. e.g at K(external) = 25mM, and membrane voltage = -31.4mV, I can use inverse log laws and the GHK equation to calculate the internal concentration.

 

However, I have external concentrations between 25 and 300mM - how do I know which internal concentration to use?

 

b) my second question is, how do I calculate permeability of the three ions (PNa, PK and PCl) using my data? I have tried, but I end up just getting PK/PK (which could be anything!?)

 

Can anyone shed some light please?

 

Thanks

[zule]

a) Do you mean that the external concentrations of ions vary with the time? Does the membrane voltage remain constant?

 

b) Which are your data?

 

If you provide all the data you have been given, perhaps I can help you. But with the data you give, I don’t know exactly what the problem is about.

Edited January 8, 2010 by zule