Kiyoshi Hama

Fine structure of the afferent synapse of the hair cells in the saccular macula of the goldfish, with special reference to the anastomosing tubules.

SummaryThe fine structure of the afferent synapse has been studied in the hair cells of the goldfish saccular macula.A spherical dense body which is surrounded by synaptic vesicles is observed in association with the presynaptic membrane. An alternating, parallel arrangement of dense bars and of rows of synaptic vesicles is observed on the presynaptic membrane beneath the dense body. Each row consists of five to six immediately available synaptic vesicles, and five to six such rows of vesicles are observed per synapse.Sometimes anastomosing tubules are found around the dense body. The tubules are formed by direct infolding of the plasma membrane. Many coated vesicles are found at the periphery of the anastomosing tubules.A possible role of the anastomosing tubules in the turnover of the synaptic vesicle membrane is discussed.

Transformation of intramembrane particles of HVJ (Sendai virus) envelopes from an invisible to visible form on aging of virions.

Abstract When HVJ virions harvested from embryonated eggs 3 days after infection are freeze-fractured, large intramembrane particles, with a mode of 150-A diameter, are exposed on the E fracture faces but not on the P fracture faces. The intramembrane particles seem to be hydrophobic parts of viral spikes of HANA and F glycoproteins. No intramembrane particles are observed in young virions harvested 1 day after infection, although many spikes project from their envelopes. When young virions are incubated at 37° for 2 days in vitro , large intramembrane particles develop and are exposed on the E fracture face: These particles resemble those observed in old virions harvested from eggs 3 days after infection. Besides this difference in intramembrane particles, morphological differences are seen between young virions and old virions aged in ovo or in vitro : in young virions the nucleocapsid strand is regularly folded under the envelope and the virion structure is rigid; but in old virions, aged in ovo or in vitro , the nucleocapsid strand is irregularly folded and detached from the envelope, and the virions are no longer rigid but are easily distorted by external forces. From these findings, the possible correlation between the transformation of intramembrane particles from an invisible to visible form and the disruption of the regular arrangement of the nucleocapsid under the viral envelope is discussed.

Fine structure of the ordinary lateral line organ

SummaryThe lateral line organ of the spotted shark is characterized by its semi-cylindrical shape. Each organ (neuromast) is so closely apposed to the next that the individual neuromasts are almost continuous. The neuromast is composed of receptor cells, supporting cells and mantle cells. The receptor cells bear one kinocilium and up to 40 stereocilia. Bi-directional arrangement of the receptor cells as occurs in teleosts was demonstrated. Afferent and efferent nerve endings were found at the base of the receptor cells. The supporting cells extend from the basal lamina to the free surface. Long microvilli and a cilium-like “ciliary rod” project from the top of each supporting cell. The cell contains relatively few elements of the Golgi apparatus and little rough endoplasmic reticulum, but mitochondria and filaments are abundant. The mantle cell limits the lateral margin of the neuromast. It is distinguished from the supporting cell because of its long crescent-shaped nucleus and scarce, short microvilli. Myelinated nerve fibres are found in the subepithelial connective tissue but not in the epithelium.The fine structure of the shark lateral line organ suggests that this organ is in an intermediated step of evolution between that of lamprey and teleost.

Gap junctions between the supporting cells in some acoustico-vestibular receptors

SummaryExtensive gap junctions are found between the supporting cells in acoustico-vestibular receptors (saccular macula of the goldfish; ampullar crista, utricular macula and organ of Corti of the guinea pig). The fine structural details of these gap junctions were examined using lanthanum hydroxide staining and freeze-fracture replicas, as well as conventional thin sections. It was found in the lanthanum treated saccular macula of the goldfish that the gap junction globules consist of five or six subunits surrounding a central 2 nm hole. Similar subunits of the gap junction globule are also found in freeze-fracture replicas of the saccular macula of the goldfish and the ampullar crista of the guinea pig. Possible functions of the extensive gap junctions between supporting cells of these receptors are discussed.

A study of the fine structure of the pit organ of the common Japanese sea eel Conger myriaster

SummaryThe fine structure of the pit organ of the sea eel has been studied by means of electron microscopy. The sensory epithelium of the pit organ consists of sensory cells and supporting cells. The apical surface of the sensory cell is studded with sensory hairs consisting of a kinocilium and stereocilia. The sensory cells are divided into two groups. In one, the kinocilium points dorsally and in the other the kinocilium points ventrally. The total number of sensory cells in one pit organ is about 100, and the ratio of cells with opposite polarity is about 1∶1.On the basis of these structural features, the pit organ is considered to be a mechano-receptor sensitive to the movement of liquid in a dorso-ventral direction. It may also serve as an ion receptor, sensitive to environmental ion concentration.Efferent nerve terminals make rare synaptic contacts on the afferent nerve fiber.

Fine structure of the afferent synapse and gap junctions on the sensory hair cell in the saccular macula of goldfish: A freeze-fracture study

SummaryMembrane specializations at the active zone of the afferent synapse in the saccular macula of goldfish are described.Those of the presynaptic membrane consist of three to six elongated aggregates of intramembrane particles separated by particle-free furrows on the concave part of the P face and its complementary figure, that is, an alternate arrangement of elongated aggregates of pits and smooth ridges on the convex part of the E face. The size of the specialized area is about 0.5 μm × 0.3 μm.Vesicle fusion sites are situated at the margin of the particle-free furrow and ridge of the presynaptic active zone. Round pores about 30–50 nm in diameter are seen on the P face around the active zone. They are probably openings of the anastomosing tubules or coated pits.A focal aggregate of intramembrane particles is observed on the E face of the postsynaptic membrane apposing the presynaptic active zone. The P face of the postsynaptic active zone shows pits and particles.Small gap junctions are found between hair cells and adjacent supporting cells. They are frequently associated with desmosomes. The possible functional significance of these gap junctions is discussed.

Measurement of partial specific thickness (net thickness) of critical-point-dried cultured fibroblast by energy analysis

The relative specimen thickness obtained with an energy analyser is one of the most important parameters in electron microscopy. It has been made clear that this parameter can be applied not only to inorganic specimens, but also to organic and biological specimens. Moreover, the partial specific thickness of a critical-point-dried cultured fibroblast, that is, a net thickness converted in terms of Epon, was calculated from the relative specimen thickness. The partial specific thickness of each domain of the critical-point-dried cultured fibroblast is: CC 0.05 microns, PE 0.14 microns, ED 0.32 microns and PN 0.54 microns. As a result, it is suggested that 27% of the volume of this specimen consists of biological materials.

A freeze-fracture study of afferent and efferent synapses of hair cells in the sensory epithelium of the organ of Corti in the guinea pig

SummaryAfferent and efferent synapses of hair cells in the organ of Corti of the guinea pig have been examined in freeze-fracture replicas.Afferent synapseIn the inner hair cells, intramembranous particles 10 nm in diameter are aggregated on the ridge on the P-face of the presynaptic membrane directly beneath the synaptic rod. In the outer hair cells, in which the synaptic rod is located in the presynaptic cytoplasm underneath the presynaptic membrane, small aggregations of intramembranous particles 10 nm in diameter can be found on the P-face of the presynaptic membrane corresponding to the site of the presynaptic dense projection. Intramembranous particles 10 nm in diameter are also densely aggregated on the P-face of the postsynaptic membrane of the outer hair cells.Efferent synapse of the outer hair cellsLarge intramembranous particles 13 nm in diameter are distributed in clusters composed of four to ten particles on the P-face of the presynaptic membrane. In the P-face of the postsynaptic membrane, disc-like aggregations of intramembranous particles 9 nm in diameter are found. The subsynaptic cistern covers the cytoplasmic surface of the postsynaptic membrane of the efferent synapse; it may cover more than one postsynaptic membrane when several efferent synapses are in close proximity to one another.