Toshio Arima

Quick-freeze, deep-etch visualization of the 'cytoskeletal spring' of cochlear outer hair cells.

SummaryThe lateral membrane system of the cochlear outer hair cell, consisting of the lateral plasma membrane, pillars, filamentous lattice and subsurface cisternae, is considered to be involved in the contractile movement of the isolated cochlear outer hair cell. The filamentous lattice, called the cytoskeletal spring, has been identified in the demembranated cochlear outer hair cell treated with the detergent Triton X-100. In this study, the quick-freeze, deep-etch method was applied to demonstrate the three-dimensional organization of both the filamentous and membranous structures of the lateral membrane system of cochlear outer hair cells. Treatment with saponin revealed that the inner leaflet of the lateral plasma membrane of the cochlear outer hair cell possesses more membrane particles than the outer leaflets, and that the pillars are closely associated with membrane particles in the inner leaflet of the lateral membrane. The presence of filamentous bridges between the filamentous lattice and the subsurface cisternae was also detected. We propose that the lateral membrane system in the cochlear outer hair cell may play an important role in the tuning mechanisms within the cochlea in normal hearing.

Double‐axis rotary replication for deep‐etching

We have developed a simple new method of rotary shadowing, double‐axis rotary replication, for observing three‐dimensional structures in deep‐etched, rapid‐frozen tissues. The technical details of this method are described and compared with the conventional fixed‐angle rotary shadowing procedure.

Cytoskeletal organization in the supporting cell of the guinea pig organ of Corti

The rapid-freeze, deep-etch method was used to visualize the three-dimensional organization of cytoskeletons in the supporting cells of the guinea pig organ of Corti. Deep-etched replicas showed that both the head and basal portions of the pillar cell were composed of a filamentous network consisting of several kinds of fibrous elements, into which numerous microtubules and actin filaments were tightly inserted. Myosin S1-decoration showed that the main constituent element in such filamentous networks in the basal portion of the pillar cell was the actin and tiny cross-bridges interconnected the randomly oriented adjacent actin filaments.

Regular structures on the microvillar surface membrane of ileal epithelial cells in suckling rat intestine

Freeze-fracture deep-etch studies were done to examine regular patterns of surface membrane particles in the suckling rat ileal epithelium by using quick-freezing method. In addition to the presence on the luminal surfaces of well-developed endocytic complexes, latticed particles were consistently observed on almost the entire apical membrane between microvilli and frequently on the microvilli. These particles seemed to be partly integrated in the outer half layer of membranes. After rinsing with phosphate-buffered saline, patterns on the microvilli appeared to be parallel circle lines rather than latticed particles found in fresh preparations. Filipin treatment showed the presence of filipin-sterol complexes on most of the particle-covered membrane areas except small tubules and vesicles. Possibilities were suggested that these latticed particles were transferred to the apical surface along the outer half layer of membranes, and released or secreted into the intestinal lumen.

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.

A deep-etching study of the guinea pig tracheal cilium with special reference to the ciliary transitional region

The fine structure of the cilium was examined by freeze-fracture-etch studies. In the interior of the transitional region, three types of plate structures were clearly observed. While the terminal plate contained fine fibrillar linkers suspending the central core plates from its peripheral doublet microtubules, two other types of plates had no suspending linkers. At the upper level of transitional region, one of the central microtubules elongated deeper than the other in the space surrounded by ring structure. Axosome-like structure was not observed in our replicas. Central vesicle of the basal body was also suspended by fine fibrillar linkers from peripheral triplets. Though membrane particles of ciliary necklace were recognized on protoplasmic and external fracture faces, and the external surface, particle arrays were not observed on protoplasmic surface. Instead, Y-shaped, cross bridges, one end of which attached to the doublet microtubules, merged in the circular ridge structure at opposite ends. This circular ridge structure at the necklace region may play a role as an anchoring site of both membrane particles of the necklace and cross bridges from peripheral doublet microtubules.

Three-dimensional visualization of basal body structures and some cytoskeletal components in the apical zone of tracheal ciliated cells

The ciliated cells of tracheal epithelium were mechanically fragmented to remove the cytoplasmic soluble contents, and the apical zone was examined to clarify the three-dimensional structures of basal body and cytoskeletal filaments using freeze-fracture-etch approaches. The basal body was connected to the apical plasma membrane by definite laminae, formerly called alar sheets. The distal one-half of the basal foot was composed of several smooth-surfaced 12-nm fibrils. Intermediate filament networks extended to the lower half plane of the basal body, and enmeshed the basal body tightly by tiny 5- to 8-nm fibrils. Actin core bundles of microvilli also had tiny crosslinking fibrils. Some actin filaments were seen to run horizontally at the upper half plane of the basal body. Tracheal cilated cells also had circular actin filament bundles just inside the zonula adherens as many other epithelial cells. These cytoskeletal networks which enmeshed both basal bodies and core filaments of microvilli may function as a coordinator of ciliary beating.

Fine structure of the human cochlear aqueduct: a light and transmission electron microscopic study of decalcified temporal bones

The morphologic features of the human cochlear aqueduct were examined using both light and electron microscopy. The lumen of the cochlear aqueduct was observed to be filled with dense, irregular connective tissue corresponding to dura mater. At the entrance to the cerebrospinal fluid space, the dense connective tissue in the ductal lumen was covered with a thin layer of a few flattened cells, which was contiguous with the arachnoid membrane of the brain. A simple low cuboidal epithelium also separated the perilymphatic space from the lumen of the duct. Our observations confirm the presence of a barrier membrane at the opening to the perilymphatic space, and suggest that no transport occurs in the human cochlear aqueduct.

Ultrastructure of the guinea pig cochlear aqueduct. An electron microscopic study of decalcified temporal bones.

The ultrastructure of the guinea pig cochlear aqueduct was examined using semi-thin and thin sections. The lumen of the cochlear aqueduct was occupied by a sparse meshwork of fibroblasts and delicate connective tissue trabeculae. The periotic tissue lining the bony wall of the aqueduct was composed of multiple layers of both elongated cells and densely arranged laminae of collagen fibrils. These structures were identical to those of the dura mater and the arachnoid. The opening to the perilymphatic space of the scala tympani also contained connective tissue trabeculae, but the arrangement of fibroblasts was more compact here than in the main part of the duct. These structural features suggest that fluid can move freely through cochlear aqueduct, and that the effects of sudden pressure changes in the CSF may be protected against by the densely and perpendicularly arranged fibroblast at the opening to the perilymphatic space.

Dynamics of swallowing in tetanus

An 82-year-old man developed an uncommon type of swallowing disturbance with tetanus. Initially, he could masticate his food but could not pass it into the esophagus. The mechanism of swallowing in this patient was studied radiologically and endoscopically. The disturbance in the second stage of deglutition was associated predominantly with his advanced age and the slow clinical progress of the tetanus. The patient was cured by treating the disease.