Date: Mon, 8 Jan 2001 14:33:46 -0600 (CST)

Wednesday January 3 6:04 PM ET

By Merritt McKinney 

NEW YORK (Reuters Health) - Seeing a tarantula may make your heart skip a beat, but the venom holds promise as a treatment for a common heart-rhythm disorder, researchers report. In experiments in rabbit hearts, a substance found in tarantula venom inhibited atrial fibrillation without affecting other normal functions of the heart. 

Atrial fibrillation, which can increase the risk of stroke, is the most common type of arrhythmia, or heart-rhythm disorder. The condition causes the upper heart chambers--called atria--to contract so quickly that they do not pump enough blood into the heart's lower chambers, or ventricles. Drugs may be prescribed to keep the potentially life-threatening condition under control. 

Previous research has suggested that certain ion channels--openings in cells that play a key role in a coordinated heartbeat--are involved in atrial fibrillation. So Dr. Frederick Sachs, of the State University of New York at Buffalo, and colleagues set out to find a substance that blocks the channels that trigger abnormal heart rhythms. 

In an interview with Reuters Health, Sachs said that he and his colleagues tested the venom of many types of insects and spiders, but only the venom from one type of tarantula blocked the ion channels. When the investigators analyzed the venom, they identified a short protein called GsMtx-4 that was responsible for the effect. When the researchers tested the protein on rabbit hearts that were induced to beat irregularly, the substance blocked atrial fibrillation, according to a report in the January 4th issue of the journal Nature. ``It worked better than I ever imagined,´´ Sachs said in the interview. ``It worked in every one of these rabbit hearts.''  

The protein is promising, according to Sachs, since it blocks atrial fibrillation without causing any harmful effects to the heart. It makes sense that the substance would not be toxic, since it comes from a type of tarantula whose bite is not harmful to people, he noted. The next step is to test the protein in live rabbits to make sure that it does not affect other parts of the body besides the heart, Sachs said. ``We believe that GsMtx-4 could be the first of a new class of antiarrhythmic agents to be directed against the causes rather than the symptoms of fibrillation,´´ Sachs and his colleagues conclude in the report. 

SOURCE: Nature 2001;409:35-36.