The bell-shaped, purple flowers of foxgloves are immediately recognizable, but this beautiful European wildflower is steeped in supernatural mystery. Also known as witches' gloves and dead man's bells, they've been used as both a folk medicine and a poison for centuries, owing to their potent effects on the human heart.
In fact, there's an old English saying that "foxgloves can raise the dead and kill the living." But how true is this? Can foxgloves really give you a heart attack?
To get to the bottom of this, we first need to understand how a healthy heart works. The heart itself contains thousands of cardiac cells that contract in time to pump blood around the body. Tiny electric signals regulate this pumping action, and every cell is involved in maintaining this electric activity.
"The membranes of the cardiac cells have lots of different ion channels and transporters which permit charged particles like sodium, potassium and chloride to cross the membrane in a controlled manner," Hugues Abriel, an ion channel researcher at the University of Bern in Switzerland, told Live Science. "This movement of ions generates an electrical current and potential difference across the membrane, and that's where the electricity comes from."
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Particularly important for regulating this electrical balance is the sodium-potassium pump. This membrane transporter uses energy to push sodium ions out of the cell while pumping potassium ions into the cell. Overall, this means the inside of every cardiac cell is negatively charged compared with the outside, and maintaining this gradient is vital to the proper functioning of the heart.
So what do foxgloves have to do with any of this?
"Foxgloves contain extremely potent compounds called cardiac glycosides — 'cardiac' for their function on the heart muscle and 'glycosides' to indicate that these compounds have sugar molecules attached to their chemical structure to help the body absorb them," Zhen Wang, a synthetic biologist who specializes in plant natural products at the State University of New York at Buffalo, told Live Science. "All foxglove species produce some amount of these cardiac glycosides, such as digoxin, and they bind very, very tightly to the sodium-potassium pump, inhibiting it so the transporter cannot pump those ions anymore."
Deactivating this pump causes a cascade of chemical problems within the cardiac cells that combine to make the heart suddenly beat much harder and much faster.
"There's an interplay between the different types of membrane transporters, so inhibiting one means another won't work as well," Abriel said. "Hitting the sodium-potassium pump has a knock-on effect which increases the calcium concentration inside the cardiac cells. This rise in calcium concentration acts as a trigger, causing electrical disturbances and making the heart cells contract harder and faster."
This disruption in the heart's natural rhythm, a dangerous type of arrhythmia known as ventricular fibrillation, can lead to sudden cardiac arrest and even death. "When the chambers of the heart are not contracting regularly, it can't pump blood, and the overall effect is as though the heart isn't beating anymore," Abriel said.
Despite its potentially dangerous and toxic effects, digoxin is also a valuable heart medication. "Digoxin is clinically prescribed for heart failure when other drugs have failed," Wang said. "Heart failure is when the patient's heart is so weak that it doesn't pump sufficiently so you want to increase the heart's pumping force. Although digoxin has serious side effects if overdosed, this is a special case where the benefit of the toxin outweighs the risk and could save the person's life."
So what does all of this mean for foxgloves? While digoxin is undoubtedly a powerful and dangerous compound, accidental poisonings with wild foxgloves are extremely rare, and the common purple foxglove (Digitalis purpurea) produces relatively small amounts of the toxin.
Nonetheless, if someone accidentally ingests any part of the plant, they should go to the emergency room (or the vet, in the case of a pet) as a precaution, Wang advised. "The cardiac glycosides are very potent and act very fast," she said. "At the hospital, they'll be able to treat you and help your body clear out that toxin."
This article is for informational purposes only, and is not meant to offer medical advice.
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Victoria Atkinson is a freelance science journalist, specializing in chemistry and its interface with the natural and human-made worlds. Currently based in York (UK), she formerly worked as a science content developer at the University of Oxford, and later as a member of the Chemistry World editorial team. Since becoming a freelancer, Victoria has expanded her focus to explore topics from across the sciences and has also worked with Chemistry Review, Neon Squid Publishing and the Open University, amongst others. She has a DPhil in organic chemistry from the University of Oxford.