>potential, whereas for chloride the measured reversal potential tends
>to be dragged toward about -75 mV regardless of what's in the pipette
>solution. The predicted chlordide reversal in my intracellular
Could you please give me some sources in literature for this, since I cannot
mention this posting in my work, I think :-)
>if you measure the reversal potential. If you are studying a
Too late, no means and no time any more. Do you know a most likely Na reversal
potential I could simply assume for that kind of cells?
>Although it's possible that the pipette got some sodium from the bath,
>I think this would be a very small contribution. If you are using
>positive pressure while in the bath, that should blow the external
>solution away from the tip.
That's right. Actually I couldn't believe this myself. But what do I know? Maybe
the force of brownian motion can overcome the flux in some way. I have never
seen a diffusion equation taking into account the presence of material flow
under pressure. So maybe with solution under pressure one can forget about any
diffusion equation. Correct me please if I'm wrong.
>I think it's more likely that the cell simply has it's own mechanisms
>for allowing sodium entry at rest, through non-specific cation leak
>channels, pumps, etc. .... The predicted Nernst potential in this case is
>infinitely positive, which obviously doesn't happen. So there must be
>some sodium in there. It's either coming through leak channels,
>through the leak in the pipette-to-membrane seal (for whole-cell, this
>leak is often equivalent in conductance to many open channels)
That's what I thought, too. I supposed that the flow of Na out of the cell into
the pipette by diffusion would be compensated by an equally inflow from leak
channels and the seal into the cell. I could even imagine that most of the
external Na "tries" to get in at the seal where it is in direct vicinity of the
Na-hungry pipette tip which takes it away like a sort of vacuum cleaner. In that
case the original [Na] wouldn't perhaps even be touched very much. But maybe
these thoughts are too adventureous.