A primitive fish lures scientists to Maine
BAR HARBOR, Maine - The Mount Desert Island Biological Lab has been perched on the Maine coast for nearly a century, in a sort of eddy beside the main tourist route to Bar Harbor.
Scientists still do their lab work in shingled cottages at water's edge, but it is not the scenery that has drawn 70 principal investigators from 29 states and 10 countries here this year.
The big attraction is the primitive minishark that graces the lab's logo - the spiny dogfish, bane of commercial fishermen everywhere.
On a recent morning in Dr. Patricio Silva's lab, six internal medicine residents from Beth Israel Deaconess Medical Center in Boston were preparing for study little bits of dogfish tissue, pale pink and about the size of a pinky finger.
These inconsequential-looking organs are shark rectal glands, which pump excess salt from sharks' blood.
With one artery, one vein, and a single duct to excrete the salt, they are elegant models for studying salt-transport mechanisms. And as such, they help researchers understand, on a cellular level, the salt imbalances at the root of human conditions such as hypertension, kidney disease, and congestive heart failure. In the late 1950s, this gland was where the abnormality present in cystic fibrosis was first understood.
"It's a perfect model," said Silva, a Temple University professor of medicine who has been working with these glands here every summer since 1973.
Dogfish, among the most ancient animals with pressurized circulatory systems, are believed to have evolved 400 million years ago. They - along with their equally primitive cousin, the little skate - are well-suited to the lab's work: They are big enough to study easily and their cells tend to be large, and they are cold-water species with slow metabolisms, making them relatively stable in labs. As a bonus, freshly harvested glands function on the lab bench for eight hours or more.
Dr. Franklin Epstein, a nephrologist at Beth Israel who was assisting the residents one recent morning, has been working with dogfish rectal glands at the lab since 1968. He said the cells of the glands have chloride channels - pathways salt travels into and out of the cells - that function like those in human cells. He cites polycystic kidney disease as an example. The disease involves many cysts getting bloated with fluid, impairing kidney function. The secretion of chloride solution into the cysts is similar to the shark rectal gland mechanism, Epstein said, and slowing cyst growth could help people with kidney disease.
Understanding how chloride channels work can also help cystic fibrosis patients. Shark rectal glands have high concentrations of a protein that is named for the disease, the cystic fibrosis transmembrane conductance regulator, or CFTR. In cystic fibrosis patients, the protein does not function properly, and salt transport is impaired.
Dartmouth physiology professor Bruce Stanton has spent summers at the lab studying CFTR function in killifish. His research shows that arsenic significantly impairs the protein's function, and suggests that chronic exposure to low levels of arsenic - which he says is found in some New England well water - could increase the severity of cystic fibrosis symptoms. (Stanton is studying killifish instead of dogfish because they survive in fresh water, better suited to studying the arsenic effect.)
In the early years, dogfish were abundant in Frenchman Bay, next to the lab. Too abundant, some say. Spiny dogfish, named for the protective spines in front of each of their dorsal fins, have long been unpopular with fishermen because they take baits intended for cod and other valuable groundfish.
Dogfish are edible and in the 1990s they were rebranded as "Cape shark" to make them sound more toothsome, and landings increased. They were declared overfished by the National Marine Fisheries Service in 1998, and protective regulations followed. They've recovered a bit, and many fishermen now say they can't get baited hooks intended for other fish past schools of dogfish.
The dogfish used for lab research, about 3,000 annually, are gillnetted by a local fisherman. Visiting scientists also study other cold-water sea life readily available nearby, such as sea urchins, hagfish, sculpins, and skates.
This lab was first established at Harpswell, Maine, in 1898, and moved here in 1921. "The whole idea was motivated by the Darwinian revolution, and the understanding that higher species evolved from lower species and that life began in the sea," Epstein said. "A primary motivating factor is a faith, almost a religious faith, that what is true of primitive forms of life is also true of more advanced forms of life."
The dogfish may be primitive, but the lab is not. In July, it dedicated a new $7 million, 15,000-square-foot building with traditional cottage styling and modern green-building technology. The lab's Center for Comparative Toxicology focuses on the biological effects of toxins on cell membrane transport, and human health. Its Center for Marine Functional Genomics Study is studying marine organisms to understand the relationship between gene sequences and biological function. Some scientists are now working here year-round, and the facilities are increasingly used by visiting groups like the Beth Israel residents
Back in Silva's lab, the residents conduct a simple experiment designed to help them understand the cellular mechanisms of salt transport. They drip into the gland's artery a solution that should increase output from the salt duct. They wait 10 minutes, discussing a recent bike ride at Acadia National Park. The procedure soon has its intended effect, and the flow of salt solution increases.
"Wow," says Silva, "that's some gland."
Murray Carpenter can be reached at murrcarpenter@gmail.com. 