Why resistance under 300 Ω.cm2 is not reliable for epithelial cells in electrophysiology?
We identify ENaC surface activity level by measuring current in the Ussing chamber. The epithelial cells that we work with, makes a nice baseline current. After adding ENaC-blocker amiloride, the current falls immediately to its approx. 5%. The remaining ~5% current is thought to occur via other channels that are not blocked by amiloride. If it is thought that resistance under 300 Ω.cm2 shows the cells have not tight junctions much enough to block leakage, then firstly if current flatlines at 15 uA and ends at 1 uA after adding amiloride, then where is the leakage (the 1 uA can be or via other channels or leakage)? Secondly, if the purpose is to identify the “amiloride short circuit current” then even if there is some leakage, how can it affect the amiloride short circuit current where it is known that amiloride doesn’t block leakage current?
I need the reason, the mechanism that resistance under 300 Ω.cm2 can affect the amiloride short circuit current.
Kind regards,
Hi Sahib, transepithelial resistance is a complex function of transcellular and the paracellular ion transport. When you measure TEER with a voltohmmeter you detect the sum of the paracellular shunt resistance (dependent on the tight junctions) and the transcellular resistance (dependent on the channelome of the cell). I assume your low TEER values come from the high ENaC activity, for eg. we see similar values in CFTR-overexpressing cells. This you can monitor in the Ussing chamber when you apply intermittent current/voltage pulses in open/short circuited configuration and determine the resistance by Ohm´s law: Isc = Vte / Rte (Rte=ΔVte/ΔI). So in your case, there would be low basal Rte, which would greatly increase upon amiloride treatment.
Thank you, Anita Balazs, for your answer. Yes, I agree with you, when I add amiloride, the Rts increases and the software collecting data shows the Rts in real-time graph. I asked an expert about it, he said because it is many decades that resistance under 300 Ω.cm2 is accepted as non-reliable. But if this is the case, then I need to know why? :)
The idea that TEER values less than a certain cut-off are considered non-reliable is rather old-fashioned, as TEER is not straightforward indicator of culture quality in general. You have to consider the cellular system you´re using, which could be on a wide spectrum from tight to leaky, as well as if you over-express channels the transcellular ion-conductance will increase, thus resistance will be lower than in the mother cell-line. For eg. here DOI: 10.1385/1-59259-861-7:183 they use filters of primary human airway epithelia, when TEER >150 Ω.cm2. In your case I would argue this expert that you have low TEER due to high ENaC activity and when it is blocked you have high resistance - indicating good paracellular resistance - ergo healthy cultures. Best of luck!
- Badges
- Science topic
- Similar topics
- Entomology
- Resistance