Researchers have found that triclosan, an antimicrobial agent widely used in oral care products such as toothpaste and mouthwash, impairs muscle contraction at a cellular level. In tests on animals, they evaluated the effects of the chemical on muscle activity, using doses similar to those that people and animals may be exposed to in everyday life and discovered that it significantly slowed swimming in fish and reduced muscular strength in mice.

Initial in vitro experiments revealed that triclosan impaired the ability of isolated heart and muscle cells and skeletal muscle fibers to contact. In particular, the researchers investigated the effects on molecular channels in muscle cells that control the flow of calcium ions, which are responsible for muscle contraction. Normally, electrical stimulation of isolated muscle fibers under experimental conditions evokes a muscle contraction, the fundamental basis of any muscle movement, including heartbeats. In the presence of triclosan, however, the normal communication between the two proteins that function as the calcium channel was disrupted, causing skeletal and cardiac muscle failure.

In addition, triclosan significantly impaired cardiovascular and hemodynamic functions in living animals. The researchers observed a 25 percent decrease in cardiac output in anesthetized mice within 20 minutes of exposure to the chemical. They also found that triclosan-treated mice had a mean decrease of 18 percent in grip strength, a widely used measure of mouse limb strength, for up to 60 minutes compared with controls.

In further experiments with the fathead minnow, a small fish commonly used as a model organism for studying the potential impacts of aquatic pollutants, the researchers observed that triclosan adversely affected the fish’s swimming performance during both normal swimming and swim tests designed to imitate fish being threatened by a predator.

Although translating these results to humans would require further research, the scientists think that the study provides strong evidence that triclosan could affect animals and humans at current levels of exposure. As the findings suggest that triclosan could act as a potent cardiac depressant, especially in patients with underlying heart failure, the researchers recommend that regulatory agencies reconsider whether the chemical should be permitted in consumer products.

The Environmental Protection Agency estimates that more than 1 million pounds of triclosan are produced each year in the U.S. The chemical has been detected in urine and blood samples, as well as in human breast milk. According to the organization, consumer products containing triclosan are the primary source of human exposure.

The research was conducted in a collaborative study between the University of California, Davis, and the University of Colorado Denver.

The findings were published online on Aug. 13 in the Proceedings of the National Academy of Science of the United States of America ahead of print.

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