The Beat of a Heart> UM research on fruit flies may reveal ways to treat human heart disease

Researchers at the University of Maine are studying the electrochemical signals that control a maggot’s heartbeat in the hope of finding ways to treat human heart disease.

Unique equipment developed by Harold “Dusty” Dowse, an associate professor of zoology and mathematics at UM, allows the research team to precisely measure heartbeat in the late-stage larvae of fruit flies.

The tiny insect has been studied for decades, and much is known about its genetics. By observing changes in heart rate and rhythm in different strains of flies, the Maine researchers hope to identify genes that tell the heart when to beat.

“Hopefully, what we learn from this very much simpler [circulatory] system can be extrapolated to mammalian and thus human conditions,” said Dowse.

Abnormalities in heart rhythm kill at least 250,000 Americans each year. Since 1990, the UM research has received more than $100,000 in financial support from the American Heart Association and other sources.

“The heart association has been very generous to us in the past,” said Dowse.

There are profound differences between the circulatory systems of humans and fruit fly larvae. In the maggot, a tubular heart extends from its posterior to its brain. The insect has no veins or arteries; contractions in the heart simply wash its cells in blood.

Even so, the genetic and electrochemical basis of heartbeat appears to be very similar in people and flies. A human gene that causes “Long QT syndrome” was first identified in the insect.

In the United States, Long QT kills as many as 200 young and apparently healthy people each year. An estimated 20,000 Americans have the defect, which killed Boston Celtics star Reggie Lewis.

“Pacemaker” cells in fruit fly hearts also respond in much the same way as human heart cells to chemicals that cause, or interfere, with the rhythmic pulsation of the heart.

“At the cellular level, we think there are shared properties between human and fruit-fly hearts,” said John Ringo, a professor of zoology and member of the research team.

Given the similarities, fruit flies are an ideal way to study heartbeat, according to Dowse. They can be raised by the thousands at little cost in glass jars.

“You can raise a new generation in two weeks,” he said. “You can do in one year what might take 10 years to do in mice.”

The UM researchers have studied almost 200 mutant strains of fruit flies, but found only a handful of genes that strongly affect the heart. Much of the work is being done by two graduate students in zoology: Erik Johnson and Nancy Bray.

The system Dowse developed to record heartbeat is deceptively simple. He used a common binocular microscope, but put a light-sensitive transistor in one of the eyepieces.

When one of the ricelike maggots is ready to transform itself into a mature fly, it becomes quite still and begins to develop a tough outer covering. Before the translucent covering turns brown, one of the team members places the insect on a glass slide and puts it under the microscope.

A bright light shining through the maggot allows the researcher to focus on the heart. As it beats, the amount of light passing through the heart changes.

The photo-transistor senses the rythmic flickering. It sends the information, through a series of amplifiers, to a personal computer that records the information.

In addition to studying genetically induced differences in heartbeat, the team is also investigating the effects of temperature and chemicals. They have injected the larvae with everything from common heart medicines to puffer fish poison and heavy water.

Eventually, it might be possible to screen new heart medication on fruit flies before testing it on mammals.

“Fruit flies are ironclad in the sense that you can subject them to much chemical and temperature stress and not kill them,” said Ringo.

Despite the physical differences between people and maggots, Dowse wasn’t surprised to find similarities in the regulation of heartbeat.

“Evolution can be very conservative,” he said. “When it gets something that works, it sticks with it.”