Hiroshi Washioka

Demonstration of rod and cone photoreceptors in the lamprey retina by freeze-replication and immunofluorescence

SummaryIn common with other cyclostomata, the Japanese river lamprey (Lampetra japonica) has a retina consisting of distinct types of photoreceptor cells called long and short photoreceptor cells. After freeze-fracture, disc membranes of these photoreceptor cells were characterized in common by a homogeneous distribution of intramembrane particles on the protoplasmic fracture faces, in contrast to those of the myeloid bodies bearing scattering particles.Immunofluorescent examination was applied to the retina with monoclonal antibodies raised against bovine and chicken rhodopsins. Positive immunoreactivity was found to be limited to outer segments of the short cell, leaving the entire body of the long cell and all other components of the retina negative. The results suggest that the short cell is more closely related to a rod-type photoreceptor cell characterized by rhodopsin as its visual pigment.

Monomolecular surface film and tubular myelin figures of the pulmonary surfactant in hamster lung.

SummaryPerfusion fixation via pulmonary trunk was applied to the alveolar lining layer in situ at different lung volumes using a fixative containing tannic acid-ferrocyanide osmium. The monomolecular surface film and hypophasic tubular myelin figures were enhanced. In the range of transpulmonary pressure (1–10 cmH2O), the surface film appeared in the form of a single, electron-dense leaflet, 2.7±0.6 nm (M±SD) in thickness while trilaminar membrane structure was retained in all parts of the tubular myelin figures of the hypophase. The surface film was attached underneath at right angles with trilaminar membranes which formed the outermost parts of the tubular myelin. Such structural continuity was taken to support a view that the phospholipid unit membrane of the tubular myelin figure would be transformed at the hydrophobic phase into a pair of monomolecular leaflets, eventually forming the surface film.

Innervation and gap junctions of intestinal striated and smooth muscle cells in the loach

SummaryThe tunica muscularis of the proximal intestine of the loach consisted of intermingling striated and smooth muscle cells without forming any distinct sublayers. Close contacts devoid of intervention by a basal lamina sometimes occurred between these different types of muscle cells. Gap junctions were occasionally found between heterologous as well as homologous muscle cells. In freeze-fracture replicas, striated muscle cells were distinguished from smooth muscle cells by numerous, evenly distributed subsurface caveolae. These were relatively rare and linearly arranged in smooth muscle cells. Variously-sized and -formed aggregations of connexon particles were found in the protoplasmic fracture-face of both muscle cells. Striated muscle cells had aggregates of connexon particles taking the form of either a small solid polygon or an annulus with a particle-free central region. In smooth muscle cells, the particles were arranged either in variously-sized patches or in straight lines. Topologically, heterologous gap junctions observed in ultrathin section were thought to correspond to the small patchy aggregations. Striated muscle cells in the gut had neuromuscular junctions, which differed morphologically from “cholinergic” nerve terminals at neuromuscular junctions of typical skeletal muscle cells. The smooth muscle cells had close apposition with axonal terminals containing many granular vesicles and a variable number of small, clear vesicles. Occasionally, a “cholinergic”-type axonal terminal with a presynaptic active site was found close to a smooth muscle cell.

Intramembrane Particles in the Postsynaptic Membranes of the S-, F-, and C-Type Synapses by Freeze-Fracturing, and Deep-Etching Studies on the Xenopus Spinal Cord

In the CNS, the S-, F-and C~type of synapses used to be classified with TEM based on the appearance of synaptic vesicles and the specialization of synaptic membranes (Charlton and Gray, 1966; Uchizono, 1975; Watanabe/ 1981): The S-type, or Gray’s type I, synapse has spherical synaptic vesicles and more or less electron-dense substances in the subsynaptic cytoplasm. The F-type, or Gray’s type II, has flattened vesicles and symmetrically thickened pre-and postsynaptic membranes. The C-type is remarkable because of the subsurface cistern in the subsynaptic cytoplasm.