use Cs to replace K inside. Ba inside is toxic

Thank you Jeffry Lansman. That is true, but most of the recent studies use Ba in in vivo injections in to various brain sites and I have also got the same salt (BaCl2) but the doses reported in papers varied from 200 micro molar in in slice patch clamps to 2-3 millimolar injected In vivo.

Dear Rehaan,

I have worked with whole-mount retina and brain slices, and often using as low as 0.1 mM BaCl2 (bath solution) is sufficient to block most Kir channels, and prolonged application of doses higher than 1 mM can be toxic to the neurons. I suggest you do a dose response in vivo, as it is hard to compare with previous studies done in vitro. In in vivo studies one usually needs higher doses as the limitation in the injectable amount and subsequent dilution by the bodily fluids. Furthermore the dilution of Ba2+ will decrease as you get further from the infusion loci, and this may cause non-uniform effects. Therefore it may be a good idea to do your own dose-response in your own set-up. For example, keeping everything else constant, you can do infusions of 10, 100 1000 micromolar and 4000 micromolar (make sure that the BaCl2 is dissolved well). I think this will be an important step. If you really have to pick one dose, I would pick 1000 micromolar.

Best wishes,

Refik

Dear Refik, thank you very much for your invaluable inputs. Yes I will go by dose-response observations and will start from 400 micronolar then 800 then 1500 micromolar and will see the effect.

I dissolved the BaCl2 salt in 0.9% normal saline and used it as vehicle injections in control groups. What do you suggest regarding the medium as a solvent in to which we must dissolve the barium salt.