Ultrastructure Of Chloride Cells Research Articles

Reaction of osmoregulatory system of sterlet Acipenser ruthenus Linnaeus, 1758 (Acipenseridae) on influence of hyperosmotic medium

Some features of response to hyperosmotic environment (artificial sea water with a salinity of 12.5–12.7 ‰ (403–409 mosm/l) were studied in the osmoregulatory system of freshwater sturgeon species from the Volga river, starlet Acipenser ruthenus Linnaeus, 1758. Morphofunctional changes were traced in certain elements of the organ complex responsible for the osmoregulatory process. 72 hours after the immature sterlet individuals (age 2+) were transferred from fresh water to the hyperosmotic medium, blood serum osmolarity becomes iso-osmotic respective to the external environment. The interrenal gland responds to saline exposure by increasing cortisol concentration in the blood serum. A high cortisol level (75.13 ± 12.96 vs. 19.29 ± 6.36 ng/ml in the control group) persists throughout the entire experimental period (7 days), which indicates that fishes are under stress. The cortisol excretion into the bloodstream is not followed by an increased activity of the transport enzyme, Na+/K+ ATPase, in homogenate of the gills and an increased Na+ concentration in chloride cells, was identified by A-gold technique. The ultrastructure of chloride cells, being the main site for the removal and sorption of monovalent ions (Na+, K+, Cl-) in fishes, does not display the characteristic of an active excretion in sterlet. Thus, cortisol does not provide a stimulating effect on increasing Na+/K+ ATPase activity, an enzyme needed to transport excess ions from the body. The thyroid gland responds by increasing the thyroxin (T4) concentration during 3–6 hours of saline exposure. In the next 114 hours, the concentration of this hormone decreases to its initial level (in the control group). The thyroxin dynamics in serum does not correlate with the dynamics of serum osmolarity. So it seems possible to conclude that no functional relationship exists between the effector “organ” (the set of numerous chloride cells of the gills epithelium) and the endocrine glands (interrenal and thyroid) controlled by the hormones of tropic pituitary cells. In sterlet dwelling in hyperosmotic medium the kidney keeps a higher Na+/K+ ATPase activity, as compared with the gills. High Na+ concentration in the urine (163.2 ± 5.3 meq/l), close to its concentration in the hyperosmotic environment, high Na+ proportion (87.1 ± 0.1%) in the total concentration of major urinary cations, low level of water sorption (50.8 ± 4.0%) in the renal tubules, high diuresis (0.58 ± 0.09, ml/hr/100 g body weight) determine high level of Na+ excretion in the urine (100.95 ± 13.21 meq/ml/hr /100 g body weight). The important role of the kidney in removing Na+ excess under hyperosmotic environment underlies the osmoconformity strategy in sterlet.

Ultrastructure of chloride cells in branchial epithelium of juvenile masu salmon Oncorhynchus masou (Salmonidae) at different salinities

Ultrastructure of chloride cells in branchial epithelium of juvenile masu salmon Oncorhynchus masou (Salmonidae) at different salinities

Morphofunctional changes of the interrenal gland and of ultrastructure of chloride cells in intact and hypophysectomized juveniles of starred sturgeon Acipenser stellatus (Acipenseridae) in the course of adaptation to sea water

The impact of hypophysectomy on the state of the interrenal gland and ultrastructure of chloride cells of gills is investigated in 18-month old juveniles of starred sturgeon Acipenser stellatus in the process of its adaptation to artificial sea water (14.6‰). Hypophysectomized juveniles, similarly to intact juveniles, are able to support a relative stability of osmolarity of blood serum in the course of adaptation to sea water by transition from hyperosmotic to hypoosmotic type of osmoregulation. Changes in the investigated parameters of cells of the interrenal gland (volume of nuclei, areas of cells and of lipophilic vacuoles) occurring in the hypophysectomized and in intact specimens in the process of adaptation to sea water are generally similar, but have different dynamics. In contrast to many teleostean species, in acipenserids the hypophyectomy does not cause atrophy of the interrenal gland. The latter is incorporated in the process of regulation in the course of adaptation of fish to sea water. Hypophyecotmy results in partial destruction of organoids in some chloride cells of gills. However, when the fish are transferred to sea water, the structural changes occur in chloride cells characteristic of their transition to the excretory state. This may happen only at activation of the transport enzyme Na+/K+-ATPase of these cells by cortisol produced by the interrenal gland. In the absence of hypophysis, the functional connection of organs of the axis hypothalamus (ACTH-immunopositive cells of tuberal nucleus) → the interrenal gland → chloride cells is realized in the fish.

Structural and functional features of gill epithelium and the brood pouch of pipefish Sygnathus acusimilis (Syngnathidae, Gasterosteiformes) during adaptation to dilute sea water

Study of the dilate sea-water tolerance of the pipefish Syngnathus acusimilis indicated that it successfully acclimatized to an abrupt change in water salinity from 5 to 32‰. Larvae in the brood pouch also successfully acclimatized to salinity change, and, after several days, juveniles left the brood pouch and continued to live. In freshwater, adult and fry perished during several minutes. In the gill epithelium of S. acusimilis, chloride cells of only a marine type were found. A comparison of the ultrastructure of chloride cells of gill epithelium and mitochondrion-rich cells of the brood pouch of S. acusimilis demonstrated their high similarity. The ultrastructure of cells of the brood pouch indisputably attests to their involvement in maintaining an osmotic and ionic homeostasis in the cavity of the brood pouch.

Effects of arsenic on osmoregulation in the tilapia Oreochromis mossambicus reared in seawater

The effects of arsenic (As2O3) on plasma osmolarity, Na and K concentrations, the activity of gill Na−K-ATPase, and on the ultrastructure of gill chloride cells were compared between seawater tilapia (Oreochromis mossambicus) and freshwater tilapia in the Institute of Zoology, Academia Sinica, between 1989 and 1991. Arsenic was found to be more lethal in seawater tilapia [96 h LC50 (median lethal concentration): 26.5 ppm] than in freshwater ones (71.7 ppm). No significant effect was found on plasma ion concentrations and osmolarity, enzyme activity or the ultrastructure of chloride cells in freshwater tilapia after 96 h exposure to 70 ppm arsenic. In contrast, 96 h exposure to 15 ppm arsenic caused evident effects in seawater tilapia: an increase in plasma osmolarity and activity of gill Na−K-ATPase, as well as better development of the chloride cell tubular system. These data suggest that the lethal effect of arsenic may be partially attributed to a hydromineral disturbance in seawater tilapia, but in freshwater tilapia arsenic perhaps causes destruction in some physiological mechanisms other than osmoregulation. The activation of gill Na−K-ATPase and chloride cells in seawater tilapia appears to indicate an adaptation in the osmoregulatory mechanism to arsenic exposure, i.e., to enhance secreting ions or arsenic in the gills.

Ultrastructure of the pseudobranch in the euryhaline Cyprinodontid fish, Rivulus marmoratus.

AbstractThe ultrastructure of the pseudobranch of the euryhaline, self‐fertilizing fish, Rivulus marmoratus (Cyprinodontidae) was studied with thin sectio and freeze‐fracture transmission electron microscopy. In specimens raised from birth in 1% or 200% seawater, the pseudobranch contains two mitochondria‐rich cell types, pseudobranchial cells and chloride cells, each of which has an extensive tubular system. Chloride cells only occur on the lateral aspects of the pseudobranch, with their apical crypts open to the environment. Apical crypt invagination to a “pit” structure and multicellular complexes occur in both salinity extremes. The ultrastructure of chloride cells in 1% and 200% SW is consistent with that described previously in the opercular epithelium, opercular skin, and gill of this species; elaboration of mitochondria and basolateral membrane accompanies increased environmental salinity (King et al.: Cell and Tissue Research 257:367–377, 1989). Pseudobranchial cells constitute the majority of the cells; they do not extend to the surface but have a more organized tubular system that is continuous with the basal membrane. These cells do not exhibit ultrastructural changes in response to increased salinity. © 1993 Wiley‐Liss, Inc.

The ultrastructure of chloride cells in the gills of the teleostOreochromis mossambicus during exposure to acidified water

Branchial chloride cells, which actively take up ions in the gills of freshwater fish, were studied in tilapia (Oreochromis mossambicus) exposed to sublethally acidified freshwater. Structural damage of cells, resulting in cell death by necrosis, only occurred transiently, when the reduction of water pH was acute rather than gradual. The most prominent effects of water acidification were the rapid increase in the number of chloride cells and the changes in frequency of the different stages of the chloride cell cycle. In the opercular inner epithelium, a twofold increase in cells occurred 48 h after gradual acidification. Cell density stabilized after 4 weeks at a level 5 times that of control fish. Four transitory stages were distinguished in the chloride cell cycle: accessory or replacement cells, immature, mature, and degenerating (apoptotic) cells. In control fish, mature chloride cells dominated (over 50%) with immature and apoptotic cells totalling about 40%. After 4 weeks in acid water, only 13% of the cells were mature. Immature and apoptotic cells dominated, each representing about 40% of the total number of chloride cells. Mature cells apparently age rapidly under these conditions. Thus, chloride cells turn over quickly in acid water, with a minor increase in ion transport capacity of the gills. This conclusion is supported by the observation that opercular and branchial Na+/K+ ATPase activities in treated fish are only 40%–50% higher than in controls.

Ultrastructure of chloride cells in young adults of the anadromous sea lamprey, Petromyzon marinus L., in fresh water and during adaptation to sea water

The chloride cells in the interlamellar areas of the gills of young adult, anadromous sea lampreys, Petromyzon marinus L., captured in fresh water undergo structural modification during the adaptation of these animals to sea water. In fresh water the chloride cells are partially overlapped by mucus-secreting superficial cells and contain an extensive reticulum of cytoplasmic tubules, which are confluent with both lateral and basal plasma membranes, numerous mitochondria, a Golgi complex of moderate size, and numerous apical vesicles. Adaptation to sea water results in a retraction of the superficial cells, exposing the entire apical surface of the chloride cells, and a proliferation of both cytoplasmic tubules and mitochondria. Extensive enlargement of the Golgi complex in the chloride cells of these animals suggests the involvement of this organelle in the proliferation of cytoplasmic tubules. The extracellular tracer, ruthenium red, enters the tubules from the lateral or basal intercellular spaces in both freshwater- and seawater-adapted animals but never enters either tubules or vesicles from the apical surfaces, indicating that these are not confluent. The presence of dividing basal cells and newly-forming chloride cells, combined with evidence of degeneration of chloride cells, suggests that there is a turnover of this cell type. Both superficial and basal cells are phagocytic and involved in heterophagy of degenerating chloride cells. This phenomenon occurs in both fresh water and sea water indicating that the chloride cells may be functional in both environments.