[Functional morphology of the outer hair cells of the human: new aspects]

Serial sections through the outer hair cells of the human organ of Corti were investigated using high-resolution electron microscopy. Delicate monostratified tubular structures of differing lengths are located on the cytoplasmic side of the hair-cell membrane. They are connected to the cell membrane via short fibers (pillars) arranged in pairs. The tubular structures, which are also termed subsurface cisterns (SSC), constitute an extensive network. This network lines the entire inner surface of the outer hair-cell membrane, and in contrast to the mammals investigated so far, also lines the base of the cell. The postsynaptic cisterns of the efferent synapses are integrated into this system. At the surface of the inner lamina of the cisterns, pores 8.5 nm in diameter are to be found. These are surrounded by protein complexes with a stellate arrangement. Similar protein complexes are located on the inner lamina of the postsynaptic cisterns. Pores 8.5 nm in diameter are also present in the outer lamina of the SSC. These constitute the base for the pillar filaments. At high magnification, the pillars are seen to have a lumen about 6 nm in diameter. Pores about 8 nm in diameter are again to be found where the pillars are anchored in the outer cell membrane. The pillars, consisting of actin, are probably ionic channels, and the pores of the inner lamina of the SSC surrounded by protein complexes are thought to be acetylcholine receptors. Since the postsynaptic cisterns of the efferent innervation of the outer hair cells are part of the overall system of the SSC, and acetylcholine is regarded as the neurotransmitter of efferent innervation, it would seem possible to regulate the subsurface cisterns, as a wall-stabilizing, contractile system, via the efferent innervation. On the basis of serial sections, a three-dimensional, true-to-scale model of the contractile wall system of the human outer hair cell was reconstructed.