Jan. 31, 2005 New Haven, Conn. -- A toxic chemical painted on the bottom of large vessels to protect against barnacles may cause hearing difficulties in whales and other mammals, according to a study by Yale researchers published in the Biophysical Journal.
The chemical tributyltin oxide (TBT) affects the mechanical activity of the outer hair cells, which modulate and boost incoming sound energy to the inner hair cells, according to senior author Joseph Santos-Sacchi, professor of surgery and neurobiology at Yale School of Medicine.
TBT is known to damage the immune system and the hormonal system of marine mammals, "but this is the first time it has been demonstrated that TBT could be working directly on the auditory system," said Santos-Sacchi. Mammals are the only group of animals that have outer hair cells.
Sensitive hearing in mammals relies on cochlear amplification resulting from the motor activity of outer hair cells. The protein prestin along with its interaction with intracellular chloride ions are key to this motor activity.
Santos-Sacchi and his colleagues used guinea pigs in their study and found rapid and profound effects of TBT on the outer hair cells as they studied the effects of TBT on chloride ion exchange across the outer hair cell membrane.
He said TBT bypasses the normal chloride ion pathway, thereby altering the ion's modulating effects of prestin; this may have a negative affect on cochlear amplification.
"This observation identifies a new environmental threat for marine mammals by TBT, which is known to accumulate in the food chain," Santos-Sacchi said. "It also is now important to assess the impact of TBT exposure on marine mammal communication."
Co-authors include Lei Song and Achim Seeger, both of Yale. The research was supported by the National Institutes of Health.
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