Seiitiro Utida

Development and degeneration of the chloride cell during seawater and freshwater adaptation of the Japanese eel, Anguilla japonica

SummaryTwo types of chloride cells were recognized in the gill epithelium of the fresh-water eel. Following transfer of the eel to sea water the number of strongly acidophilic cells (type A cells) increased markedly during the first week of adaptation. Simultaneously the cell size increased and cell inclusions such as mitochondria and smooth endoplasmic reticulum were also developed. On the other hand, the number of weakly acidophilic cells (type B cells) increased only during the initial 3 days of adaptation and thereafter decreased. This decrease in number of type B cells showed a mirror image of the increase in number of type A cells. Considering the changes in number and fine structures of type B cells, it is likely that the type B cell is a transitional stage of the typical chloride cell (type A cell). When seawater adapted eels were transferred to fresh water, the chloride cell degenerated slowly during 10 weeks. The involvement of the chloride cell in salt secretion of the gill of the seawater eel is discussed.

Changes in activity of sodium-potassium-activated adenosinetriphosphatase in gills durign adaptation of the Japanese eel to sea water

Abstract 1. 1. When the eels were transferred from fresh water to sea water the Na + -K + ATPase activity of gills increased gradually for 5 days, and thereafter greatly increased within the following 2 days. This high activity was maintained for a long period. 2. 2. The properties of the ATPase of the eel gills were similar to those of mammaliam tissues. 3. 3. In view of the fact that ouabain inhibits the active excretion of sodium ions in the gills of sea-water-adapted eels, ouabain-sensitive Na + -K + ATPase seems to play an important role in the ionic regulation of eels.

Relationship between the activity of Na+-Ks+-activated adenosinetriphosphatase and the number of chloride cells in eel gills with special reference to sea-water adaptation

Abstract 1. 1. Na+-K+ ATPase activity and the number of chloride cells of gills increased five- to six-fold during the first week after transferring the eels from fresh water to sea water and decreased to the fresh-water level within 4 weeks after returning to fresh water. 2. 2. When the eels were adapted to media of various salinities, both the enzyme activity and the number of chloride cells increased in proportion to the increase of external salinity. 3. 3. The Na+-K+ ATPase of the gill seems to be localized mainly in the chloride cell and to be involved in the salt excretion of eels in sea water.

Hormonal control of the intestine and urinary bladder in teleost osmoregulation

Three varieties of osmoregulatory surface in teleosts are considered herein: the intestine, which is under bihormonal control (cortisol and prolactin); the urinary bladder, which is under unihormonal control (prolactin); and the gallbladder, which is not under hormonal control. Water movement in the isolated intestine of the eel increases during seawater adaptation, and cortisol is required to maintain the enhanced water absorption. This water movement is associated with the active transfer of ions, especially Cl ions. In freshwater eels, potential difference (PD) and short-circuit current (Isc) across the intestine were nearly zero or slightly serosa-negative, whereas in seawater eels and in freshwater eels injected with cortisol, the negativity of the PD and Isc increased. Development of a Cl− pump in seawater and cortisol-treated freshwater eels was further confirmed by ion-flux study. Prolactin injection into seawater eels decreased the rate of salt and water absorption in the gut. Prolactin seems to act on the gut surface as an antagonist to cortisol, by suppressing the Cl− pump and lowering permeability to water. In the isolated urinary bladder of flounders, water movement is reduced after transfer to fresh water or to dilute sea water. Prolactin injection into seawater flounders decreased osmotic permeability to water to the level of freshwater fish. This water movement is also associated with active transport of ions: ouabain inhibited both net influx of Na ions and water. In contrast to the eel intestine, there is no difference in net Na+ fluxes between freshwater and seawater flounder bladders; prolactin stimulates Na+ reabsorption. In sea water, the flounder bladder seems to absorb water from the urine by actively absorbing Na ions. In fresh water, the bladder seems to absorb mainly Na (and Cl) ions, and prolactin is involved in these changes by decreasing permeability to water and by stimulating the Na+ pump. On the other hand, the ion- and water-absorption capacity of the gallbladder isolated from the eel does not show any response to environmental salinity change nor to cortisol or prolactin treatment. It is suggested that cortisol may act primarily at the level of ion pumps, and prolactin primarily at the level of permeability barriers.

Effects of ACTH and cortisol on water movement in isolated intestine of the eel, Anguilla japonica.

Abstract In Japanese cultured eels, the rate of sodium and water movement across the isolated intestine increases after transferring the eel from freshwater to seawater, and this increase is abolished by hypophysectomy. A single intraperitoneal injection of ACTH into freshwater eels produced a significant augmentation of the intestinal water movement within 24 hours, and the response was dose-dependent. Other hypophyseal hormones, such as prolactin, TSH, growth hormone, oxytocin, lysine vasopressin, and arginine vasotocin were without effect. Among the corticosteroids, only cortisol or cortisol acetate had an augmentative effect on the water movement in the isolated intestine, whereas cortisone acetate, corticosterone, progesterone, aldosterone, and DCA had little effect. The response to cortisol was also dose-dependent. Sodium transport in the isolated intestine was also increased by treatment with cortisol to a greater extent as in the case of water movement. With a single injection of cortisol acetate, the rate of intestinal water movement changed in similar fashion to that occurring after transferring the eel to seawater. The significance of these results is discussed in relation to possible involvement of the pituitary-interrenal axis in seawater adaptation of the eel.

Sodium-potassium-activated adenosinetriphosphatase activity in gills of fresh-water, marine and euryhaline teleosts.

Abstract 1. 1. The activities of Na+K+ ATPase in the gills of stenohaline teleosts were much higher in marine species than in fresh-water species. 2. 2. In euryhaline species (eel, trout and goby) the enzyme activities of the gills were also higher in fish adapted to sea water than in fish adapted to fresh water.

Central nervous system control of osmoregulation in the eel (Anguilla japonica)

Abstract 1. 1. Participation of the central nervous system in teleost osmoregulation was studied using cultured Japanese eel, Anguilla japonica . 2. 2. Removal of the telencephalon had no effect on survival and plasma ion concentrations either in fresh water or in sea water. 3. 3. “Decerebrated” eels (with entire prosencephalon and mesencephalon removed) adapted to both fresh water and sea water, and ingested almost the same amount of water as the intact eel during the course of sea-water adaptation. 4. 4. Vagotomized eels died 4–5 days after transfer to sea water, whereas they survived well in fresh water. 5. 5. The drinking rate of the vagotomized eel was about half that of the sham-operated eel on the first day of sea water adaptation and was reduced to about 10 per cent by the third day.

Studies on water and ion movements in the isolated urinary bladder of selected fresh-water, marine and euryhaline teleosts

Abstract 1. 1. A reduction in osmotic permeability to water and an increase in sodium and chloride absorption were observed in the isolated urinary bladder of three species of flounders after their acclimation to hypotonic media and after prolactin treatment. 2. 2. Bladders of stenohaline fresh-water fishes were nearly impermeable to water; active absorption of sodium was indicated in some species. 3. 3. Osmotic permeability was variable in marine fishes, but was especially noticeable in aglomerular Porichthys and Lophius. 4. 4. Euryhaline fishes of sea-water origin modify their bladders from a permeable state in sea water to a relatively impermeable state in fresh water. Prolactin seems to be involved in this modification. Bladders from euryhaline fish of fresh-water origin appear impermeable, irrespective of environmental salinity.

Adaptive Changes in Ion and Water Transport Mechanism in the Eel Intestine

Living in aquatic environments with a wide range of salt concentration, teleost fishes are known to maintain their osmotic pressure and electrolyte concentrations at levels largely independent of the salinity of their environment. Freshwater teleosts, which are hyperosmotic to the environment, tend to gain water by osmosis. They drink little water and the kidneys have the task of removing excess water. In contrast, seawater teleosts constantly face a pressing problem in water conservation because of their hypertonic environment. In order to replace the osmotic loss of water, they drink surrounding sea water and absorb water with monovalent ions from the intestine. The excess sodium and chloride ions are extruded by the gill, leaving osmotically free water in the body1–4.

Plasma renin activity in Japanese eels (Anguilla japonica) adapted to seawater or in dehydration

The hypothesis that the renin-angiotensin system regulates glomerular filtration rate (GFR) by constricting the efferent glomerular arterioles, was tested in the Japanese eels (Anguilla japonica) by determining the plasma renin activity (PRA). The fish was dehydrated by transfer to 100% and 50% sea water, or by removal from water. In all conditions, urine volume and GFR were decreased within 1 hr. In 100% sea water an initial increase in PRA for 0.5–8 hr was observed. On transfer to 50% sea water or exposure to air, PRA was unchanged or slightly increased for 2–24 hr. It is necessary to consider the possibility that angiotensin may act in this species on intrarenal and extrarenal sites other than the efferent arterioles.