Dear Aditi: The air bubble due to oxygenation with bicarbonate might cause the damage to electrode tip to some extent. 

Dear Aditi

When using bicarbonate buffer, you need to oxygenate, because O2 is creating the buffer.

With HEPES buffer, bubbling carbogen will depend on the deepness of your bath. But I will recommand a constant bubbling of the incoming bath solution to avoid any bubble in the bath. From my experience bubbling with carbogen (oxygenating) increase dramatically the survival of the cells, especially in multilayered cell cultures.

Hi Aditi

I have recorded from dissociated neurons in various conditions, but never done a systematic comparison between oxygen and non-oxygen bubbling conditions. I don't think it is necessary to bubble with oxygen, as the diffusional access to the dissociated neurons is very high, and I think it is unlikely they will be oxygen limited with atmospheric levels in the ACSF. Many studies have been successfully performed with HEPES buffered ACSF without oxygen bubbling, both in slices and dissociated neurons, though probably in thicker brain slices it makes more of a difference.

To my understanding, the CO2 component of carbogen is the more important part for maintaining the sodium bicarbonate pH buffering, and the oxygen component is not important for this effect.

If you can, keep it simple.

Jan

Thanks all for the answers. I think a little clarification is required. In our center we routinely patch from neurons derived from iPSCs with a HEPES buferred recording solution, which has given good results. In contrast, recently our cortical cultures have not been giving as wonderful recordings and we tried a bubbled oxygenation recording solution and got better results. Hence the confusion of what is kosher and more widely acceptable.