Susumu Kikuchi

Mitochondria-rich (chloride) cells in the gill epithelia from four species of stenohaline fresh water teleosts

SummaryThe mitochondria-rich (chloride) cells have been found to be present in the gill epithelia of four species of stenohaline fresh water teleosts. The cytoplasm of these chloride cells contains an extensive network of cytoplasmic tubules which communicate with intercellular spaces bordering the lateral and basal cell surfaces. Numerous vesicles with fairly electron-dense interiors are also present in the apical cytoplasm of chloride cells. The apical surface of a chloride cell forms an apical pit, but the lumen of the pit does not appear to be in continuity with the interior of the apical vesicles and tubules inside the cell.When Carassius auratus were kept in 100, 200, 300, and 400 mOsm-diluted sea water for a month, no appreciable changes occurred in the number and fine structure of the chloride cells, except for a dilation of the apical vesicles and a slight decrease in diameter of the cytoplasmic tubules in these cells in the fishes kept in 300 and 400 mOsm.These results suggest that chloride cells may be a rather common occurrence in the gill epithelia of stenohaline fresh water teleosts, and may function in ion-transport in these fishes in fresh water environments.

The fine structure of the gill epithelium of a fresh-water flea, Daphnia magna (Crustacea: Phyllopoda) and changes associated with acclimation to various salinities

SummaryTwo kinds of epithelial cells, dark and light types, are alternately arranged in the gill of Daphnia magna. The dark cell has numerous mitochondria and an elaborate tubular system containing two kinds of cytoplasmic tubules, small about 70 nm in diameter, and large about 130 nm in diameter. The former occur in bundles and seem to be smooth surfaced endoplasmic reticulum. The latter, lined with a ridged surface coat and frequently open at the lateral and basal cell membrane, are regarded as extensions of the cell membrane. The apical cell membrane of the dark cell is modified by repeated subunits of a cytoplasmic coat on the inner leaflet of the unit membrane. The light cell exhibits a high degree of basal infoldings of the cell membrane, which represent a magnification of the surface area of the cell. Large mitochondria between the infoldings often come into intimate association with the infolded cell membrane to form a regular array of parallel mitochondria interposed with the double cell membranes.The results suggest that at least the dark epithelial cells play an important role in the osmoregulation of this animal.

The ultrastructure of the sternal gills forming a striking contrast with the coxal gills in a fresh-water amphipod (crustacea)

Sternomoera yezoensis has specialized sterna with 21 sternal gills in addition to six pairs of coxal gills. Despite a common high permeability to chloride ions, the epithelia of these two kinds of gills are diametrically opposed in the polarity of the cell membrane-mitochondria complex. The coxal gill epithelium (4-6 microm thick) is characterized by a well-developed AIS (apical infolding system) associated with a huge number of large mitochondria. The AIS exceeds two-thirds of the epithelial thickness and forms a highly sophisticated, subcuticular labyrinth. On the contrary, the sternal gill epithelium, an extension of the sternal epithelium proper, is extremely thick (10-15 microm) and is characterized by a very deep BIS (basolateral infolding system) associated with numerous slender mitochondria. The BIS reaches nine-tenths of the epithelial thickness and forms a giant, baso-lateral labyrinth. Shallower, less elaborate AIS and BIS without mitochondrial association originate from the opposite sides of these epithelia. Although AIS and BIS interpenetrate in the sternal gill epithelium, they never communicate. The results indicate that in addition to the coxal gills, the sterna with the sternal gills function as transporting as well as respiratory organs, though the functional difference between these two kinds of gills remains to be elucidated.

The osmoregulatory tissue around the afferent blood vessels of the coxal gills in the estuarine amphipods, Grandidierella japonica and Melita setiflagella.

By electron microscopy of the coxal gills in two species of estuarine amphipod crustaceans, Grandidierella japonica and Melita satifragella, we found a patch-like, specialized tissue area which consisted of unique cells closely resembling the salt-excreting cells in the gill of the brine shrimp and so-called chloride cells in teleost gills. These cells were characterized by an abundance of mitochondria, two kinds of extensive networks of cytoplasmic tubules, well-developed lamellar infoldings of the basal cell membrane, sparse microvillous projections of the apical border, and numerous large vacuoles with several incomplete partitions. The large (60 nm in diameter) and the small (30 nm) cytoplasmic tubular networks were found in the basal and the apical portions of the cell, respectively. The large networks, which were both directly and indirectly (through the lamellar system) continuous with the basal cell membrane, were regarded as extensions of the cell membrane. Both the outer walls and the partition walls of the vacuoles were reinforced with a parallel array of microtubules. The results suggest that this unique tissue plays an important role in the active transport of electrolytes to maintain a constant osmotic pressure of the hemolymph under widely fluctuating salinities of the estuarine environments.

A tubular configuration of the granular endoplasmic reticulum forming a raft-like parallel array in the pinealocytes of two species of Japanese moles (mogera kobeae and M. wogura)

SummaryTen or more straight tubules, each of which consists of a double unit membrane of granular endoplasmic reticulum with a cylindrical profile, are joined side by side in a raft-like configuration in the cytoplasm of the pinealocytes of Japanese moles. They measure about 60 nm and 100 nm in their inner and outer diameters, respectively, and are often partially connected to unspecialized granular endoplasmic reticulum. Cisterns held between the inner and outer unit membranes with cylindrical profiles vary from 15 nm to 30 nm in width. Ensheathed portions of the cytoplasm are contiguous with cytoplasm outside the tubular units. The inner unit membranes of the tubules bear fewer ribosomal particles than the outer ones.

The structure and innervation of the sinu-atrial node of the mole heart

SummaryThe sinu-atrial node in the heart of the mole, Mogera wogera, contains myocytes which are devoid of atrial specific granules and which may be classified into two types: electron-lucent (majority) and dark (minority). Numerous unmyelinated axon terminals, containing synaptic vesicles, face the nodal myocyte surface with interspaces of less than 300 nm. There are about 6 terminals per myocyte profile and about 10 per profile at nuclear levels. Of a total of 2717 of these terminals 85.2% are 50–200 nm from the nodal myocytes, and 9.6% form closer neuromuscular junctions, with less than 50 nm interspace and some membrane specialization. Such specializations are almost exclusively found in relation to the dark, minority-type of nodal myocyte.Myelinated nerve fibers are also numerous within the mole SA node, and may terminate almost directly on a nodal myocyte. A few nerve fibers contain many mitochondria and may represent afferent endings.Nodal capillaries are smaller and fewer than capillaries in the juxtanodal myocardium, probably indicating a lesser blood supply to the SA node than to the ordinary myocardium.

ULTRASTRUCTURAL EVIDENCE FOR OSMOREGULATORY FUNCTION OF THE STERNAL EPITHELIA IN SOME GAMMARIDEAN AMPHIPODS

ABSTRACT The ion-permeabilities and the ultrastructure of the sternal epithelia were studied in 7 species of gammaridean amphipods. Evidence has been obtained that the sterna can be divided into 2 categories: ion-transporting and non-ion-transporting types. The sterna of Sternomoera japonica, Grandidierella japonica, Melita setiflagella, and Corophium uenoi, belonging to the former category, are covered by ion-permeable cuticular layers lined with a thick epithelium, which is characterized by both a shallow apical infolding system (AIS) and a well-developed basolateral infolding system (BIS). The AIS is composed of frequent lamellar infoldings without mitochondrial association originating from the apical sides of the epithelia and involves virtually every part of the apical cell membrane, forming elaborate intercellular channels in the subcuticular space. In contrast, the BIS consists of deep infoldings of the basolateral cell membranes and extensive interdigitations between epithelial cells, which are both associated with a large number of mitochondria. This BIS involves the greater part of the cell membrane and constitutes a complicated, giant labyrinth of the intercellular spaces above the basal lamina. The AIS and BIS never communicate in the sternal epithelia, though they sometimes interpenetrate. On the other hand, the sterna of Jesogammarus jesoensis, Jesogammarus hinumensis, and Haustorioides sp., belonging to the latter category, are composed of an ion-impermeable, thick cuticular layer and a thin epithelium characterized by a paucity of mitochondria and complete lack of the BIS and AIS, which are common to those of the ordinary epithelium of the body surface. The results suggest a rather widespread occurrence in amphipods of a variety of extrabranchial ion-permeable areas of the body surface. They also suggest that the sterna lined with thick, specialized epithelia, together with the gills, are involved in the active transport of electrolytes in osmoregulation as well as respiration.

Ultrastructure and ion permeability of the two types of epithelial cell arranged alternately in the gill of the fresh water branchiopod Caenestheriella gifuensis (Crustacea)

Abstract The adult freshwater branchiopod, Caenestheriella gifuensis, has, as respiratory organs, fifteen pairs of slender cone-shaped gills composed of a thick epithelium. The silver nitrate/nitric acid technique revealed that the gill epithelium consisted of two kinds of cell, types I and II, which were alternately arranged with irregular interdigitations to form a unique, daisy pattern. Only type I cells were darkly stained by this technique, indicating high permeability of these cells to chloride ions and appearing to be responsible for the ion transport and osmoregulation. Further, electron microscopy disclosed fine structural characteristics of the two distinct types of epithelial cell covered by an extremely thin and soft cuticle layer, suggesting high permeability to gases and ions. The type I epithelial cell was characterized by an abundance of mitochondria, well-developed infoldings of the basal cell membrane exceeding two-thirds of the epithelial thickness, (which produce a magnification of the basolateral surface area of the cell), sparse microvillous projections of the apical border, and complicated interdigitations with the other type of epithelial cell. In the type II epithelial cell, on the other hand, these characteristics were less developed. These results suggest that in addition to their respiratory function, type I epithelial cells are of the ion-transporting type and play an important role in the active absorption of electrolytes to maintain a constant osmotic pressure of the hemolymph in extremely salt-deficient, freshwater environments. The type II epithelial cells may function mostly as respiratory epithelial cells.

Distribution Pattern, Gill Area Relationships, and Fine Structural Characteristics of the Gill Epithelia in Supralittoral and Terrestrial Talitrid Amphipods

ABSTRACT The distribution patterns, gill size, gill distribution, and gill ultrastructure were compared among 6 talitrid amphipods that occur in a range of habitats near Mt. Hakodate, southern Hokkaido, Japan. Two are supralittoral beachfleas, one is a supralittoral and coastal terrestrial beachflea, one is a sandhopper, and the rest are landhoppers. In all species, the posterior gills are the largest. Reduced gill size of the supralittoral species compared with terrestrial species supports the previous suggestion that the supralittoral species inhabit extremely dry environments. The gill sizes of 2 terrestrial species, smaller than those of most of Bousfields (1984) group IVa landhoppers, confirm the belief that Japanese landhoppers invaded land via the dry supralittoral zone. In all species, the gills are covered by ion-permeable, thin cuticle layers and are composed of thick typical transporting-type epithelia characterized by both apical (AIS) and basal (BIS) infolding systems of the cell membranes. The AIS are better developed in terrestrial species than in supralittoral species. On the other hand, the BIS are associated with a large number of elongated mitochondria and are well developed in all species, resulting in the involvement of the greater part of the cell surface and the intercellular space. These facts strongly indicate that the gill epithelia should be regarded as ion-transporting, as well as respiratory, organs. Moreover, the gills may play important roles in the active transport of electrolytes to regulate osmotic pressures of body fluids in terrestrial or semiterrestrial environments in which the animals are frequently exposed to extremely hypotonic conditions.

Specialized Ion-Transporting Epithelium around the Blood Vessel of the Coxal Gills in a Deep-Sea Amphipod, Eurythenes gryllus

ABSTRACT Histological examination showed that the deep-sea amphipod Eurythenes gryllus possesses a unique tissue area around the afferent blood vessel of the gill, which exhibits well-developed infoldings of the basolateral cell membrane with many mitochondria. The location (i.e., around the afferent blood vessel) and the above ultrastructural characteristics indicate that this unique tissue is homologous with a type of osmoregulatory tissue which was described for the patchlike area of gills in two estuarine amphipods Grandidierella japonica and Melita setiflagella. We review the presence/absence of this specialized tissue for 12 species (including the above 3 species) belonging to 8 genera collected from deep-sea, coastal, brackish, supralittoral, and fresh-water areas. All but Sternomoerajaponica, the distribution of which is limited to fresh-water seepage flows in forests, possessed the tissue. The discovery of the specialized tissue in E. gryllus confirms the widespread occurrence of the tissue in amphipod species.