Hi all,

I make my aCSF using the following: 126 mM NaCl, 2 mM CaCl2, 10 mM glucose, 2 mM MgSO4.7H2O, 3 mM KCl, 1.25 mM NaH2PO4.2H2O and 26.4 mM NaHCO3 bubbled with carbogen gas (95% O2, 5% CO2). The pH is usually 7.2-7.4.

However, recently I checked the pH of my aCSF (at 30 degrees with bubbling) and it was 7.85.

To get the pH to read 7.4 I had to reduce the concentration of NaHCO3 to 10.6mM. This reduced the osmolarity and so I added 17mM NaCl to balance it back to 300mOsm.

I have since recorded hippocampal brain slices using this new adapted aCSF and the cells look fine and I can record LTP.

Does anyone have an idea as to why the pH has increased? Or has anyone seen a lower concentration of NaHCO3 used in aCSF before?