Heinz J.M. Hansen

Cu uptake, metabolism and elimination in fed and starved European eels (Anguilla anguilla) during adaptation to water-borne Cu exposure

64Cu accumulation and total Cu concentrations were measured in gill filaments, plasma, liver and bile of fed and starved European eels (Anguilla anguilla) during 28 days of exposure to 12 and 94 micrograms Cu l-1. Branchial Cu uptake was found to be 0.03 and 0.13 microgram Cu g gill filament-1 h-1 at 12 and 94 micrograms Cu l-1, respectively, throughout 28 days of Cu exposure. At least during exposure to 94 micrograms Cu l-1, the basolateral membrane seemed to be the rate limiting step for branchial Cu uptake. The plasma accounted for at least 70% of the 64Cu labelled Cu present in the blood at both Cu concentrations. The plasma Cu concentration was gradually increased from 0.64 to 1.92 and 2.68 micrograms ml-1 during the first 6 days of Cu exposure; it was partly normalized to 1.07 and 1.45 micrograms ml-1 after 28 days of exposure to 12 and 94 micrograms Cu l-1, respectively, despite a constant branchial Cu uptake, indicating an increased turnover of plasma Cu. The hepatic accumulation of 64Cu was similar in fed and starved eels (0.55 microgram Cu g liver-1 h-1) at both Cu concentrations during the 28 days of exposure. The hepatic total Cu concentrations were lower in the fed fish compared to the starved fish and increased only marginally from 3 to 28 days of exposure indicating a high turnover of hepatic Cu during acclimation. Hepatic Cu elimination, measured as 64Cu in the bile, was highest in the fed fish at the highest Cu concentration and was stimulated during acclimation at least in the starved fish.

Influence of preexposure to sublethal levels of copper on 64Cu uptake and distribution among tissues of the European eel (Anguilla anguilla)

The effect of preexposure to copper was examined in European eels with respect to uptake and distribution of 64Cu among tissues. Eels were exposed in freshwater to 8 and 64 μg Cu · L−1 for 0, 6 and 28 days before 64Cu incubation. The accumulation of copper in gill, liver and muscle tissue was studied by the uptake of 64Cu during 67 hr of exposure to 8 and 64 μg · L−1. The Cu accumulation rate in muscle tissue was inversely related to bodyweight. Although the accumulation rates in liver and muscle tissues were significantly reduced after 6 and 28 days of preexposure to 64 μg · L−1 (but not to 8 μg · L−1), the accumulation rates in the gills were not affected by preexposure. We suggest that the excretion rate of copper was stimulated by the applied preexposure to 64 μg Cu · L−1.

The influence of environmental salinity, temperature, ionizing irradiation and yellow or silver stage on lipid metabolism in the gills of the European ELL (Anguilla anguilla)

1. The influence of temperature on the incorporation of [32P]phosphate and [14C]acetate into gill lipids in vivo depends also on environmental salinity. 2. Ionizing irradiation (1000 r) results in a relatively enhanced incorporation of [32P]phosphate into phosphatidyl choline and of [14C]acetate into triglycerides and wax esters in vivo. 3. When gill tissue is removed from the animal and incubated in vitro, a pronounced dependence of lipid metabolism on previous environmental salinity is not observed.

The effect of prolonged fasting on total lipid synthesis and enzyme activities in the liver of the European eel (Anguilla anguilla)

The extent of fatty acid synthesis from [1-14C]acetate in liver slices was reduced 6-fold when eels were fasted for 1-7 weeks and 20-fold when fasted for 39 weeks; thereafter hepatic lipogenesis seemed to remain constant for up to 95 weeks of fasting. After a 1-3 week fast some hepatic enzyme activities were reduced (acetyl-CoA carboxylase decreased 2-fold and fatty acid synthetase declined 5-fold), while others remained unchanged (glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, alpha-glycerol phosphate dehydrogenase as well as malic enzyme and ATP-citrate lyase). The optimum temperature for measuring both total lipid synthesis and lipogenic enzyme activity in eel liver was found to be 30 degrees C.

Formation of phosphatidylethanolamine as a putative regulator of salt transport in the gills and esophagus of the rainbow trout (Oncorhynchus mykiss)

Abstract Rainbow trout ( Oncorhynchus mykiss ) adapted to brackish water (BW) showed 32 P-phospholipid patterns in gill and esophagus tissues dominated by phosphatidylcholine (PC) when the fish were incubated in vivo either in fresh water (FW) at 5, 16°C or in BW at 5°C, and corresponding patterns dominated by phosphatidylethanolamine (PE) when the fish were incubated in vivo either in seawater (SW) at 5, 16°C or in BW at 16°C, in both cases with ( 32 P) phosphate as the precursor labeling the polar headgroups. Equivalent incorporations in the same fish with (1 14 C) acetate as precursor, labeling the lipophilic moiety, showed 14 C-phospholipid patterns in gill and esophagus tissues dominated by PC, practically independent of ambient salinity and temperature. Eels ( Anguilla anguilla ) similarly incubated in vivo in FW at 18°C showed 32 P-phospholipid patterns in gill tissue dominated by PE after preadaptation to either FW or SW; corresponding patterns after preadaptation to BW showed PE = PC. We suggest that PE participates in a stabilization of the integral membrane proteins that regulate the function of apical ion channels. The absence of PE dominated 32 P-phospholipid patterns in FW after preadaptation to isosmotic BW would indicate that the fish do not experience an osmotic challenge under these circumstances.

Comparative studies on lipid metabolism in various salt transporting organs of the European eel (Anguilla anguilla). Mono-unsaturated phosphatidylethanolamine as a key substance.

1. Incorporation in vivo into tissue lipids of (1-14C)acetate added to the water in the incubation tank showed the same relative distribution pattern of 14C-activity among various phospholipids in the gills, the esophagus and the intestine, when the eel was incubated in sea-water; in fresh water this pattern was found only in the intestine, while both the gills and the esophagus showed a relative excess of 14C-label in phosphatidylethanolamine (PE). 2. Similar studies with (32P)phosphate also showed a relative excess of (32P)PE in both the gills and esophagus in fresh water compared to sea-water, and no such difference in the intestine. 3. As long as the labelled precursors were added to the water in the incubation tank both (14C)PE and (32P)PE were not identical to unlabelled PE on thin-layer chromatograms, and the 14C-labelled lipids contained predominantly C16:1 and C18:1 fatty acids. 4. However, when the two precursors were injected directly into the eel there was no longer any marked difference between the distribution patterns of radioactivity among gill phospholipids in fresh water and sea-water; there was no longer any difference between labelled and unlabelled PE on thin-layer chromatograms, and the 14C-labelled gill lipids contained predominantly C16:0 and C18:0 fatty acids. 5. The corresponding liver lipids were affected neither by a change in environmental salinity nor in precursor application.

Comparative studies on lipid metabolism in salt-transporting organs of the rainbow trout (Oncorhynchus mykiss W.). Further evidence of monounsaturated phosphatidylethanolamine as a key substance

Abstract 1. 1. A drop in ambient temperature from 18 to 6°C results in a drop by a factor of 4 in the incorporation in vivo of (32P) phosphate and (1-14C) acetate into lipids in trout intestine, kidney and liver, independent of environmental salinity, when the two precursors are added to the water in the incubation tank. 2. 2. In sea-water a similar mean temperature factor of 5 applies to the incorporation into gill tissue lipids in trout as well as in eels (Anguilla anguilla). 3. 3. However, in fresh water a factor of 5 applies only to the incorporation into eel and trout gill lipids of (1-14C) acetate but not of (32P) phosphate; the latter precursor is subject to a drop in incorporation by as much a factor as 60 as the ambient temperature goes down from 19 to 6°C. 4. 4. The relative incorporation (% of total phospholipid) into phosphatidylethanolamine of (32P) phosphate and (1-14C) acetate shows a positive linear correlation with the ratio 32 P 14 C of the corresponding total incorporations into eel and trout gill lipids. 5. 5. The 14C-labelled trout fatty acids tend to be less unsaturated at 6 than at 18°C in all tissues, apart from gill tissue in sea-water, where they seem unchanged.

Gill lipid metabolism and unidirectional Na+ flux in the european eel (Anguilla anguilla) after transfer to dilute media : the formation of wax alcohols as a primary response

Abstract The present study investigated the mechanism involved when fish tighten their gill membrane after transfer to dilute media. Ten individually assayed eels adapted to fresh water (FW) and labelled with radioactive 22 Na in the plasma showed mean exchange rates in equilibrium with ambient radioactive 24 Na in FW at 70 μmol kg −1 h −1 . Just after transfer to demineralized water (DW), the mean Na + release rate went up to 120 μmol kg −1 h −1 ; after 24 h in DW it came down again and levelled off at 40 μmol kg −1 h −1 during a period of up to 2 weeks. During the same period the mean Na + uptake rate was 12 μmol kg −1 h −1 , i.e., the general picture in DW was a net Na + loss. In another similar experiment, groups of three FW-adapted eels were incubated in vivo for up to 24 h with ( 14 C ) acetate added as lipid precursor to the ambient water. Incubation in FW showed about 20% of the total 14 C -activity incorporated into gill lipids as ( 14 C ) wax alcohols (WA; octadecanol and eicosanol). This percentage went up to 50% shortly after transfer to DW and came down again to about 20% after 2 weeks in DW. Single eels labelled with 22 Na in the plasma showed a statistically significant positive linear correlation of percentage ( 14 C ) wax alcohols with log [ 22 Na efflux]. Based on the observed parallel between Na + flux and gill lipid metabolism, it is suggested that the eel reacts at first to a loss of Na + by synthesizing wax alcohols that can tighten the gill membrane.

The effect of Cu on gill and esophagus lipid metabolism in the rainbow trout Oncorhynchus mykiss

Abstract Rainbow trout Oncorhynchus mykiss were exposed to 0, 100, 300 and 800 μgl −1 ambient Cu in brackish water (BW) for 4 days at 13 °C and subsequently transferred to either clean BW, clean fresh water (FW) or clean seawater (SW) at 16 °C. After incubation with 32 P-phosphate and 14 C-acetate added as precursors to the water the fish showed a degradation, depending on previous [CU], of 32 P- and 14 C-labelled gill membrane phospholipids if they had been transferred to SW or remained in BW. Corresponding experiments where the fish were exposed to Cu in BW for 12 days showed a similar subsequent degradation in SW and BW of both gill and esophagus membrane phospholipids, however to a much lesser degree in gill tissue than after 4 days. Plasma Na + was similarly reduced by up to 8%, depending on previous ambient Cu, but in this case only after transfer to FW and only after 4 days of exposure. Both the effect on membrane lipid metabolism and plasma Na + thus showed acclimation to ambient Cu but there was apparently no direct correlation between the two different types of observed changes in membrane function.

Compartmentation of gluconeogenesis in the fasted eel (Anguilla anguilla)

Abstract 1. 1. In the fed state, the same relative incorporation of injected 14 C-labelled alanine, serine, aspartate and glutamate into glyceride-glycerol in eel liver in vivo points to the enzyme phosphoenolpyruvate carboxykinase as rate limiting in gluconeognesis. 2. 2. Equivalent experiments in the fasted state show an enhancement of the incorporation of 14 C-activity into glyceride-glycerol, twice as high from either alanine, lactate or pyruvate, and seven times as high from serine, as that from either aspartate, glutamate, acetate or propionate. 3. 3. This difference between the incorporation of specific precursors depending on nutrition state is interpreted as a hormone-induced compartmentation of gluconeogenesis in favour of an effective protein utilization in the fasted eel.