Damage to the inner ear as a result of environmental noise is a major cause of deafness in the developed world. In new research, scientists now report evidence that the delicate sensory hair cells of the inner ear might react to being damaged by triggering calcium signals in surrounding tissues. The findings help further our understanding of how the ear reacts to damage, not only by loud, prolonged noise, but also by loud sound for just short periods – the kind of sound we are subjected to every day in noisy streets and trains, in workplaces, and in the use of personal audio players.
The researchers, Dr. Jonathan Gale of University College London, and Valeria Piazza, Catalin Ciubotaru and Dr. Fabio Mammano of the Venetian Institute of Molecular Medicine in Padova, have found that adenosine triphosphate, otherwise known as ATP, can activate a cascade of signals in tissues of the inner ear. Gale and colleagues found that when deliberately damaged, the sensory receptor cells of the hearing organ, the cochlea, released ATP, which then produced a wave of a critical cellular messenger, calcium ions, that spread from the cells surrounding the damaged cell to other cells in the inner ear. It turns out that the inner ear cells were extremely sensitive to ATP, and may well express an as yet unknown novel receptor for ATP. Rather than trying to study this subtle process in live animals, the work was done using tissue preparations, but published experiments from another ear research group have shown that the levels of ATP inside the ears of animals exposed to loud (110 dB SPL) noise for only 15 minutes increased to just the right amount to activate the mechanism described in the new work.
The authors note that much work is required to understand the effects of elevating ATP concentration in the inner ear. Nonetheless, the noise levels required to activate this mechanism are just those that would be heard in nightclubs and in particular when using personal headphones, and it is clear that this kind of noise exposure is damaging to the inner ear.
Source: Eurekalert & othersLast reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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