Experimental Biology 2011 - Comparative Physiology of Anoxia, Hypoxia and Hypercapnia

Image source: http://water.me.vccs.edu/concepts/oxycycle.html

Humans need to inhale oxygen to support life. We also need to get rid of carbon dioxide, a byproduct of metabolism. Living in environments with very little oxygen (hypoxia) or very high carbon dioxide (hypercapnia) levels can be life-threatening for humans. This is because a build-up of carbon dioxide in our bodies results in acidosis, which can be fatal if the excess carbon dioxide cannot be disposed of. Life in an oxygen barren anoxic environment is lethal to humans as we rely on oxygen to sustain our metabolism and keep our cells alive.

There are surprisingly many animals that thrive in these seemingly dangerous environments. These were the focus of some of the wonderful abstracts presented at this year's Experimental Biology conference in Washington, DC. I will highlight some of my favorites:

-Imagine living in a paper bag, where the carbon dioxide that you breath accumulates over time. That is similar to what semi-fossorial rodents experience as they spend their days living underground in burrows. Living underground provides shelter and protection from predators. With offspring present, the levels of carbon dioxide can be higher than that of the atmosphere outside the burrow, where the animals spend time foraging at night. Researchers Inbal Brickner-Braun and Dr. Berry Pinshow (Ben-Gurion University of the Negev, Midreshet Ben Gurion, Israel) studied the metabolism of female Sundevall's jirds (Meriones crassus, pictured above) under atmospheric and hypercapnic conditions. They found that the energetic costs of life underground were no different than life above ground for these animals. I doubt we could say the same for humans living under hypercapnic conditions. ("Semi-fossorial rodents may not pay an energetic cost for their ability to tolerate high burrow PCO2")

-Another study presented by Inbal Brickner-Braun and Dr. Berry Pinshow showed that the Sundevall's jirds were also resistant to large changes in blood pH even under conditions of hypercapnia. This means that, unlike humans, these animals are resistant to the development of acidosis. ("The oxy-hemoglobin dissociation curve of a semi-fossorial rodent in the content of its burrow's hypercapnic environment")

-Drs. Isa Maria Lindgren (Johns Hopkins University) and Jordi Altimiras (Linkoping University, Sweden) found that exposing chicken eggs to hypoxic conditions may lead to heart failure in the adult birds as they saw increases in early markers of the disorder after only 5 weeks post-hatching. ("Postnatal Beta-adrenergic desensitization caused by chronic prenatal hypoxia is linked to an increase in Gs and decreased B1AR/B2AR ratio")

-The western painted turtle (Chrysemys picta bellii), pictured above, is remarkably tolerant of life in anoxic environments. Under anoxic conditions brain activity is depressed but the cells remain alive. Researchers David William Hogg and Dr. Leslie Buck from the University of Toronto discovered that levels of the neurotransmitter GABA are elevated in the brains of turtles in anoxic environments, which they believe serves to protect the brain from hyper-excitability. ("Anoxia-mediated elevation in phasic GABAA receptor currents is essential for anoxia-tolerance in turtle cortex")