Physiology and pathophysiology of inner ear melanin

The presence of melanin in the inner ear was established more than a century ago, but the exact biological function of the pigment in the labyrinth has yet to be determined. In this brief review, the correlation of pigmentation and inner ear function, as well as the presumed role of melanocytes in hereditary diseases are discussed. Special attention was drawn to the composition of melanin and its presumed function as a biological reservoir for divalent ions and as an ion exchanger, as well as an intracellular buffering system for calcium. It is pointed out that melanin is capable of binding ototoxic drugs. Finally, morphological responses of melanocytes to local disturbance of Ca++ homeostasis in the inner ear are described as 1) intracellular movement and intraepithelial deposition of melanosomes; 2) cell motility; 3) neomelanogenesis; and 4) enhanced exocytotoxic/endocytotic activity. The possible consequences of this malfunction of the melanocytes on the inner ear function are discussed.