Microtubule subunits of guinea pig vestibular epithelial cells

Guinea pig cochlear supporting cells have microtubules which are composed of 15, instead of the ordinary 13, protofilaments. The microtubules form a large and stiff bundle involving abundant actin filaments to provide effective rigidity to the cell specialized for transduction of extremely high-frequent mechanical stimuli. We examined microtubules in guinea pig vestibular end organs with the transmission electron microscopy after treatment with tannic acid. Solitary microtubules occurred abundantly in the supranuclear region of type I hair cells, but sparsely in type II hair cells. Individual microtubules consisted of an ordinary set of 13 protofilaments in these hair cells as well as in the supporting cells. Supporting cells were characterized by cytoskeletal bundles of 2 to 30 microtubules which were found to be connected with actin filaments via cross-linking units. Results from the present investigation indicate that such less-organized microtubules of 13 protofilaments are sufficient for vestibular supporting cells which are specialized for detection of lower-frequency vibration together with fellow sensory cells.