It’s Cold in the Ocean, But Sea Otters Are Warmer Inside

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Sea otters run hot. It’s not just a way of speaking: Scientists have discovered that hairy mammals’ metabolisms run three times faster than would normally be expected from a creature their size, and burn calories quickly.

They seem to use most of this energy to generate heat, keeping themselves at 98.6 degrees Fahrenheit in the cold ocean where staying warm is a matter of life and death. But the details of their conversion of food and oxygen into large heat reserves were unclear. Now researchers studying the muscles of sea otters report that this feat involves an unexpected use of mitochondria in muscle cells. their work Published Thursday in the journal Science.

Unlike whales and polar bears, sea otters don’t have a thick layer of insulating fat, and their famous fur – the world’s thickest, with 2.6 million hairs per square inch – alone isn’t enough to keep them alive. in an ocean that can stand on the brink of freezing. Muscles generate heat as they contract, but scientists have known for some time that there is another way muscles can help animals stay warm, a cellular process with the pleasant name of proton leakage.

Inside nearly all animal cells, tiny pill-shaped organelles called mitochondria break down sugar molecules to get energy. (Mitochondria are often called the powerhouses of the cell.) In the final stage of this process, protons pass through a membrane. In biology textbooks, protons usefully seep through tiny rotating pores and move them like water wheels to make adenosine triphosphate, a compound that serves as the molecular battery that powers cellular processes.

But reality is not always so orderly. If the protons are accumulating faster than the tiny water wheels can clear them, they will leak through the membrane by other means. And in skeletal muscle cells, this proton leak generates a significant amount of heat. This is thought to contribute to keeping arctic animals warm, said Traver Wright, a professor at Texas A&M University and author of the new paper.

Dr. To see how much proton leakage can occur in sea otters, Wright and colleagues put muscle cell samples from 21 animals in a special chamber that allowed the researchers to monitor the ins and outs of the cells’ mitochondria. They found that sea otters can leak enormous amounts of protons, suggesting they have the capacity to generate significant amounts of heat. And they were surprised to discover that this ability is present in both small otters and adult adults.

Dr. In general, an organism’s metabolic capacity is linked to its activity level, Wright said. But usually young otters at an age to rest on their mothers; adults of all sizes; and even a relatively inactive captive otter had similarly high metabolisms and a large capacity for proton leakage. In fact, they even had higher rates than the Iditarod sled dogs.

About dogs, Dr. “Their fugitive metabolic rates are not as high as in sea otters,” Wright said. For otters, “this heat production is really the driver of their metabolic development,” he added.

The results show that sea otters churn out calories even without doing much physical activity because that energy is directly converted into heat. Dr. Wright said that otters are among the only animals so far for which proton leakage can explain nearly all of their high metabolism.

The researchers hope to study the metabolisms of various animals. they have already published related business over elephant sealsGigantic creatures whose lives include both frantic diving and eating at sea, as well as laying on the beach for weeks.

Interestingly, the metabolic capacity of the seals does not decrease when they lie on the sand for a month. People who get a similar break from the act with a piƱa colada and beach reading wouldn’t be so lucky.

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