Biochemical mechanisms affecting susceptibility to noise-induced hearing loss.

In magnesium (Mg)-deficient rats and guinea pigs, noise-induced hearing loss (NIHL) was found to be correlated to the decrease of Mg in serum and perilymph. Also, in noise-exposed humans, NIHL increased with decreasing serum Mg. During the process of mechanoelectrical transduction within the hair cells in the inner ear, membrane permeability of K+ and Ca2+ will transiently increase. Mg deficiency may additionally increase membrane permeability and, therefore, energy-dependent K+ and Ca2+ turnover. The increased release of catecholamines in Mg deficiency may affect the hair cells, either directly by increasing the intracellular concentration of free Ca2+ and/or indirectly by reducing the blood flow. Also, thromboxane A2, which is increased in Mg deficiency, may reduce the blood flow in the inner ear. By these mechanisms, Mg deficiency may cause energy depletion and irreversible damage to the hair cells.