Cytoskeletal architecture of the chicken hair cells revealed with the quick-freeze, deep-etch technique.

Replicas of the apical surface of hair cells of the inner ear (vestibular organ) were examined after quick-freeze, deep-etch and rotary shadowing. With this technique we demonstrate how actin filaments are organized and associated with the plasma membrane in the stereocilia and cuticular plate as well as inside the junctional complex. In each stereocilium there are thread-like connectors running from the actin filament bundle to the limiting membrane. Many of the actin filaments in the cuticular plate are connected to the apical cell membrane by tiny branched connecting units like a 'crow's foot'. Where these 'feet' contact the membrane there is a small swelling. These branched 'feet' extend mainly from the ends of the actin filaments but some connect the lateral surfaces of the actin filaments as well. Actin filaments in the cuticular plate are also connected to each other by finer filaments, 3 nm in thickness and 74 +/- 14 nm in length. These 3 nm filaments (which measure 4 nm in replicas) connect actin filaments, not only of the same polarity, but of opposite polarities as documented by examining replicas of the cuticular plate which had been decorated with subfragment 1 (S1) of myosin. At the apicolateral margins of the cell we find two populations of actin filaments, one just beneath the tight junction as a network, the other at the level of the intermediate junction as a ring. The latter is composed of actin filaments that run parallel to each other; adjacent filaments often show opposite polarities, as evidenced by S1 decoration. Because of the polarity of the filaments this ring may be a 'contractile' ring.