Three-dimensional visualizations of the inner ear hair cell of the guinea pig. A rapid-freeze, deep-etch study of filamentous and membranous organelles.

The fine structure of the filamentous and membranous organelles in the stereocilia and in the cuticular plate of sensory hair cells from the guinea pig was examined using a rapid-freeze, deep-etch method. In fixed and unfixed tissue the outer surface of the plasma membrane of the stereocilia had numerous surface protrusions of various sizes and shapes, while the protoplasmic fractured face of the membrane had rather sparse intramembrane particles. Many tiny cross links were present between the adjacent actin filaments and between actin filaments and the plasma membrane of the stereocilia. Numerous fibrils radiating from the hair rootlet were attached to the peripheral actin filaments in the cuticular plate. The radiating fibrils differed from the tiny cross links which interconnected the adjacent, randomly-oriented actin filaments in the cuticular plate. These complex structures consisting of actin filaments in the hair rootlets, radiating fibrils, and peripheral actin filaments may play an important role in regulating stereociliary bending.