I want to make a creature very similar to a human but with one major difference: they breathe like any human in their everyday life, but if they are suffocating, drowning, or there isn't O2 in the air they can survive for several hours (or maybe more) without air, obviously with reduced physical activity and metabolism (if it's necessary, the creature can be unconscious).
My question is: how they would be able to survive without oxygen. Basically I'm asking how to make a facultative anaerobic animal...
I know that humans are able to make lactic acid fermentation in their muscles when they are doing a lot of exercise and they can't breathe enough oxygen to feed all the cells. But that mechanism, called Cori cycle has a very limited use, the cells aren't able to get rid of all the lactic acid produced by the fermentation, and when the acid reaches a high concentration in the muscle it causes acute pain until you stop exercising. Also, it's very inefficient way of producing energy.
I need a mechanism that can be used by extended periods of time without collapsing due high levels of something (like acid in the above example).
The answer doesn't need to exactly provide a new mechanism to get energy without air, if you know how to improve the actual, you are free to post it here.
P.S: I found that Narwhal have some capabilities to reduce their air consumption while they are under water. In the english wikipedia there aren't described but they have:
- Reduce flow of blood to non-vital organs.
- Increased amount of myoglobin in their muscles (to store oxygen).
- Increased amount of slow twitch muscle fiber ("red" muscle) that contain high amount of myoglobin and mitochondria for large periods of constant use instead of fast twitch muscle fiber ("white" muscle) for small periods of strong use.