Interconnections between the stereovilli of the fish inner ear

Abstract

The sensory hair bundles from the macula sacculi of the European roach (Rutilus rutilus) were investigated by means of scanning and transmission electron microscopy. As recently described, the stereovilli (stereocilia) of a hair bundle are all interconnected. The horizontally oriented basal, shaft, and tip connectors and intermediate forms could be distinguished. In addition, vertical connectors were found linking the tip of a shorter stereovillus to its taller neighbor in a direction parallel to the physiological polarity of the cell. On the macula sacculi several fields of sensory cells are distinguished by the size of the stereovilli but not by the type of intervillus connections, except that the intermediate types are more frequent among the shorter stereovilli of a bundle and always associated with the presumably young cells at the edge of the sensory epithelium. Vertical connectors, which were not yet described in fish, also occur in all sensory cells. The structure of the vertical connector and pecularities of its attachment sites are described; its possible involvement in mechano-electric transduction is discussed.