Can anybody tell how to measure the extracellular concentration of sodium and potassium ion of nerve cells ?
Hi, question is how fast and how accurately you want to do this and what equipment you have to hand ? There are now K+ dyes available for extracellular recording but they are not very accurate if your extracellular space is less than the Abbe limit and can't be resolved (less than 250 nm). There are of course a few 'traditional methods to do this. Depending on what you have availably in terms of equipment:
1. Extracellular ion sensitive micro electrodes. Pros good point accuracy measurement. cons poor time resolution (response time slow) and they tend to 'make' a several micron space so don't really reflect the real K concentration. Also there are iononophores availably for Na as well.
2. If your cell has well characterised K currents and you have good whole cell voltage clamp, you can use the change in reversal potential of the K current to measure the resting and dynamic changes in extracellular K concentration. this is very accurate and has good time resolution but requires a bit of nifty calculation. If they have prominent Na currents you could use them as well to determine the extracellular Na concentration.
Hope that helps (I can send you refs for the 2nd option if you are interested.
good luck!
Euan
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