| | Re: Cell culture condition and cancer biology
Thank you (for the :good work" comment) and Response to room air question.
Standard incubators are hooked to CO2 tank, fitted with CO2 sensor that is set to maintain 5% CO2, mainly for maintaining the pH of the media. (Please Note: Even this 5% CO2 is abnormal (not physiological)). The tank has inlet which constantly equilibrate with room air, and whenever CO2 levels drops, CO2 is pumped in until it reaches 5%. Room air consists of 78% Nitrogen, 21% Oxygen and 1% of other gases, so in standard tissue culture incubator, except for 5% CO2, cells are exposed to same level of oxygen that is present in atmospheric room air (ambient). This amount of oxygen is present only in the upper airway, and it gradually drops from the alveoli, through circulation finally reaching to about 5-2.7% in the interstitial space where many of the cells are often present. For most cells this is Normoxia, hypoxia is 1% and below. Hypoxia can occur due to two reasons, 1) large tissue mass where the penetration by diffusion is reduced and 2) increased consumption. However you must remember hypoxia or normoxia are relative terms, for example if you use lung cells or blood cells even 3% O2 is hypoxia, because lung cells are exposed to about 19% O2 and blood cells are exposed to about 15% O2. Oxygen sensing is crucial to diverse cellular mechanisms. Also dependence for O2 varies with different cell types, such as skeletal muscle cells could survive a day or 2 without oxygen, while brain cells could die within 3 minutes due to lack of oxygen.