MEM Alpha Medium with Nucleosides, No Phenol Red

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• MEM Alpha (α-MEM) and Minimum Essential MediumMEM alpha (α-MEM) is Eagle's Minimum Essential Medium enriched with all the non-essential amino acids, sodium pyruvate, lipoic acid, ascorbic acid, biotin and vitamin B12, and is supplied either with or without ribonucleosides and deoxyribonucleosides. It uses the same salt base as MEM — 2,200 mg/L sodium bicarbonate matched to a 5% CO2 atmosphere, 1,000 mg/L glucose and 1.8 mM calcium — and is the standard medium for mesenchymal stromal cells, bone marrow cultures, osteoblasts, CHO-DXB11 and CHO-DG44 selection, and many primary cell types. The nucleoside-free version is required for HAT and methotrexate-based selection systems.
• Phenol Red in Cell Culture MediaPhenol red (phenolsulfonphthalein) is a pH indicator added to cell culture media at roughly 5-15 mg/L, where it turns yellow below about pH 6.8 and pink to fuchsia above about pH 8.2, with the normal red-orange of healthy medium sitting near pH 7.4. Medium turning yellow means acidification - almost always lactate from cell metabolism, from an overgrown culture or from bacterial contamination - while medium turning pink or purple means the medium has gone alkaline, nearly always because CO2 has escaped from the bicarbonate buffer. Phenol red does no buffering itself and is purely diagnostic; use phenol-red-free medium for fluorescence and absorbance assays, and for oestrogen-responsive cell work, where the dye interferes with the readout.