It’s Cold in the Ocean but It’s Hotter Inside Every Sea Otter
To stay warm in frigid seas, the marine mammals rely on an unexpected use of the powerhouses of their cells. From a report: Sea otters run hot. It’s not just a manner of speaking: Scientists have found that the furry mammals’ metabolisms work at a rate three times what might normally be expected from a creature their size, burning swiftly through calories. They seem to be using much of that energy to generate heat, keeping themselves at a toasty 98.6 degrees Fahrenheit in the frigid ocean, where staying warm is a matter of life and death. But the details of their conversion of food and oxygen into vast reserves of heat have been obscure. Now researchers studying sea otters’ muscles report that the feat involves using the mitochondria in their muscle cells in an unexpected way. Their study was published Thursday in the journal Science.

Unlike whales and polar bears, sea otters don’t have a thick insulating layer of blubber, and their celebrated fur — the thickest in the world, with up to 2.6 million hairs per square inch — is not enough on its own to keep them alive in an ocean that can hover on the edge of freezing. Muscles generate heat as they contract, but scientists have known for some time there is another way that muscles can help animals keep warm, a cellular process with the delightful name of proton leak. Inside almost all animal cells, little pill-shaped organelles called mitochondria break down sugar molecules to extract energy. (Mitochondria are often called the powerhouses of the cell.) During the final stage of this process, protons pop through a membrane. In biology textbooks, the protons helpfully trickle through tiny spinning pores, driving them like water wheels to make adenosine triphosphate, a compound that serves as the molecular battery powering cellular processes.

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