Secrets of Seals

Hypoxia (oxygen deprivation of the heart muscle) affects approximately 300,000 people in Canada, five million in the United States, and 10 million in Europe. However, there are air-breathing mammals that hold their breath for hours while deep-sea diving, with no ill effect. What can we learn from them?

The search for an answer has taken Shane B. Kanatous, PhD, to Antarctica. Kanatous is a scientist in skeletal muscle physiology and marine biology, and a postdoctoral research fellow in internal medicine at The University of Texas Southwestern Medical Center at Dallas. During his 10-week research trip, which ended in December 2002, Kanatous's research focused on the Weddell seal, whose aerobic capacity, lipid metabolism, and ability to store oxygen in skeletal muscles are awe-inspiring.

Seals are superbly adapted for what they do. They travel under ice, in the dark, in water at a temperature of -2C (28F), diving deep to find food. Breathing holes can be as far as a mile apart. Even though they are under water for up to two hours at a time, their physiology allows them to regulate the myoglobin in their muscles and to withstand the harmful effects of oxygen deprivation. Since the control and regulation of myoglobin plays a key role in protecting the heart from disease, this has implications for humans.

In the Field

In Antarctica, a six-month season of 24-hour daylight lasts until February, gale force winds are typical, and even the handful of idyllic wind-free days can be dangerous to the unwary. Such days of startling sunshine and stark beauty – when the temperature is a mild -9C (15F) and just a sweatshirt provides enough warmth for the acclimatized – can turn into raging whiteout conditions within minutes.

Calm days are particularly welcome during fieldwork, which involves drilling breathing holes to attract the adult seals (average weight: 992 pounds/450 kilograms) and locating the rookeries to find pups and juveniles. Unlike Arctic seals, which are difficult to approach due to their fear of predators (human hunters, polar bears, etc.), Antarctica's Weddell seals have no natural land enemies, so are docile and approachable.

Kanatous is studying the development of the seals' muscle aerobic capacity, lipid metabolism, and oxygen storage, which, as they mature, allow them to travel underwater for long periods without breathing (pups do not dive, and juveniles cannot dive as deeply, or for as long, as adults).

Biopsies are taken from the major swimming muscle (m. longissimus dorsi). Kanatous conducts biopsies out on the ice, in the case of pups and juveniles, and in the laboratory, in the case of adults. The researchers herd an adult seal into a seal sled (essentially a large, rectangular box on sled runners), which is towed behind a snow vehicle (a Piston Bully), and transport it to the lab. Kanatous sedates the animal with an intra-muscular injection of ketamine and valium. He applies a local anesthetic (lidocaine) to the biopsy site. Then, he makes a puncture through the skin using a #10 scalpel blade, and collects a 50 to 75 mg sample using a standard biopsy needle. Finally, he gives his phocine patient an injection of antibiotics.

At Home in Antarctica

Although the environment is quite different, the lab tests (such as Western Blot) are the same as if the research were conducted in Dallas. The acoustics are the most striking difference, with the effect being "pretty much like you're standing inside of a drum when the wind is blowing." And, since the wild weather can trap scientists indoors for 36 hours or more, the overall research experience is at once as dull, boring, and depressing as it is dangerous, fun, and exciting.

The 34-year-old Kanatous is accustomed to the varied challenges of working in Antarctica: this visit is his third to the continent since 1997. In the past, his research has taken him to New Zealand, the Bahamas, the Dominican Republic, Belize, Hawaii, Alaska (up to the Aleutian Islands and Point Barrow), Prince William Sound, and all along the eastern coast of the United States. The son of Puerto Rican and Lebanese parents, Kanatous grew up in New York. His taste for adventure and his love for marine biology were fueled by watching Jacques Cousteau's televised explorations of the undersea world.

This latest expedition was funded by a grant from the National Science Foundation Office of Polar Programs. The grant paid for everything: travel, cold-weather gear, lab equipment, and logistical support from McMurdo Station (the onsite community that exists to aid all Antarctic continental science and support activities. See Great White Space). Planning for a trip takes months, as even the omission of one lab chemical could shut down an experiment.

Trying to Solve the Myoglobin Mystery

Marine mammals are the only mammalian species that routinely exercise while holding their breath. And while doing so, they experience levels of hypoxia even more extreme than being on top of Mt. Everest. They dive 100 times a day, but never experience coronary heart disease.

"How does an animal succeed in an environment where humans would fail?" Kanatous asks. One factor, he says, is that Weddell seals have 14 times more myoglobin in their skeletal muscles than the most elite terrestrial athlete. Myoglobin helps prevent some of the massive problems associated with coronary heart disease.

"So what are the cues in environmental and molecular signals that turn on a protein such as myoglobin to such high levels in these animals?" Kanatous asks. "If we can discover that, we can apply that to human coronary functions." He believes that by identifying the factors controlling the myoglobin protein, medication or gene therapy could be developed to treat the effects of heart disease or any malady related to oxygen deprivation.

The answer for treating such diseases is in solving the physiological mystery that enables seals to thrive in low-oxygen environments, he says. However, the solution is just the beginning. "Even if I found the answer tomorrow, it would take a number of years of proving what I found. People have been looking at these animals for the same adaptations since the early 1930s, but as techniques and technologies grow, so does our ability to find the answer … to apply it to human medicine. That's what I'm hoping for in this research. That is my biggest hope."

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