Properties of Ca2+-ATPase from the gill of rainbow trout (Salmo gairdneri)

Isolation of viable cell types from the gill epithelium of Japanese eel Anguilla japonica

High-purity viable cells with low mitochondria (pavement cells) and mitochondria-rich content (chloride cells) were successfully isolated from the gill epithelium of Japanese eels, using three-step Percoll gradient low-speed centrifugation. Cytochemistry (silver staining for chloride, rhodamine-123, and Mitotracker for mitochondria and actin/spectrin immunofluorescence) and scanning electron microscope images were used to identify the cell types in the gill epithelium of the eel. Pavement cells were isolated at 97 and 98% purity for freshwater- and seawater-adapted eels, respectively, and chloride cells were obtained at 89 and 92% purity. The enzymatic activities of the isolated cells were determined. Na+-K+-ATPase, Mg2+-ATPase, and succinate dehydrogenase were found mainly in the chloride cell. Alkaline Ca2+-ATPase and low- and high-affinity Ca2+-ATPase were about twice as high in the chloride cell compared with the pavement cell. Transfer of eels to seawater resulted in enlargement of chloride cell sizes and significant increases in Na+-K+-ATPase, Mg2+-ATPase, and succinate dehydrogenase activities, while all Ca2+-ATPases declined by approximately 60-80%. This is the first report demonstrating the successful isolation of freshwater chloride cells and also an exclusive method of getting high-purity seawater chloride cells. The isolated cells are viable and suitable for further cytological and molecular studies to elucidate the mechanisms of ionic transport.

Lipid composition and microsomal ATPase activities in gills and kidneys of warm- and cold-acclimated sea bass (Dicentrarchus labrax L.)

The response to cold of gill and kidney membrane lipid composition and microsomal (Na(+)+K(+))-ATPase, Na(+)-ATPase and Mg(2+)-ATPase activities in reared sea bass (Dicentrarchus labrax L.) was investigated. Fish acclimation was carried out according to the seasonal cycle from August to March. No cold-promoted increase in fatty acid unsaturation was shown in gill and kidney polar lipids and in total lipids of mitochondria and microsomes. In both tissues the (Na(+)+K(+))-ATPase exhibited positive compensation for cold acclimation whereas the Na(+)-ATPase displayed negative compensation. The Mg(2+)-ATPase showed no compensation in the gills and positive compensation in the kidneys. During cold acclimation the break in the Arrhenius plot of the (Na(+)+K(+))-ATPase decreased, whereas breaks of both the Na(+)-ATPase and the Mg(2+)-ATPase activities remained unchanged. The results indicate that the sea bass does not adopt membrane unsaturation as a cold-facing strategy. The cold-promoted enhancement of (Na(+)+K(+))-ATPase activity in osmoregulatory tissues may be advantageous to maintain efficient osmoregulation under thermodynamically unfavourable conditions.

Effects of ambient ion concentrations on gill ATPases in fresh water eel,Anguilla anguilla

Branchial activities of Na(+),K(+)-ATPase (ouabain sensitive), Mg(2+) ATPase (ouabain insensitive) and kinetic analysis of high and low affinity Ca(2+) ATPase were measured inAnguilla anguilla that had been acclimated to demineralized water (DW, Ca < 10 μM), freshwater (FW, Ca = 2 mM), and Low calcium freshwater (L-Ca, Ca = 0.9 mM). Na(+),K(+)-ATPase activity decreased while ouabain insensitive activity increased when ambient Ca(2+) decreased. Two kinetic forms of Ca(2+) ATPase could be resolved in each environmental condition. The stimulation coefficients of both sites or enzymes were not affected by ambient Ca(2+) concentrations. The maximal velocity of both the high and the low affinity Ca(2+) ATPase was increased when external Ca(2+) was decreased during acclimation. The low affinity Ca(2+) ATPase and the Mg(2+) stimulated enzyme could be a non specific enzyme accepting either Ca(2+) or Mg(2+). Results are compared with previous results in the literature and in relation to the branchial morphology and ionic exchanges in fish.

Characterization of two Ca-ATPases in gill epithelium from the killifish (Fundulus heteroclitus)

1. Two Ca-ATPases in the gill microsomal fraction from the killifish (Fundulus heteroclitus) have been characterized. 2. A (Ca2+ + Mg2+)-ATPase which has a high affinity for Ca2+, requires Mg2+ for activity and may be stimulated by calmodulin. 3. A (Ca2+ + Na+)-ATPase which has a low affinity for Ca2+ requires Na+ for activity, does not require Mg2+ and is probably not stimulated by calmodulin. 4. These enzymes may play a physiological role in killifish calcium regulation.

Purification, characterization, and bioassay of teleocalcin, a glycoprotein from salmon corpuscles of Stannius

This report describes the isolation of teleocalcin, a glycoprotein hormone from the corpuscles of Stannius (CS) of sockeye salmon (Oncorhynchus nerka), using affinity, gel exclusion, and ion exchange chromatography. In discontinuous, gradient (10-20%) SDS gels under nonreducing conditions, teleocalcin had an estimated molecular weight of of 39,300 and migrated as a single band. Two bands with estimated molecular weights of 28,000 and 32,000 were obtained upon reduction and carboxymethylation of the molecule. In acid-urea gels, teleocalcin migrated as one band with an Rf of 0.17. Amino acid sequence analysis revealed single residues for the first 19 amino acids, with phenylalanine as the N-terminal residue. Teleocalcin did not resemble parathyroid hormone (PTH) with respect to amino acid composition and exhibited no cross-reactivity in two PTH radioimmunoassays. Gas-liquid chromatographic analysis of teleocalcin demonstrated that mannose was the principal sugar present (1.86%) and glucosamine was the only hexosamine identified (2.49%). Smaller quantities of galactose (0.49%), fucose (0.44%), and sialic acid (1.6%) were also found. In bioassays using juvenile rainbow trout (Salmo gairdneri), teleocalcin significantly reduced the rate of net branchial 45Ca uptake at dosages as low as 0.02 microgram/g body wt. This inhibitory effect was dependent upon the branchial calcium uptake cycle that has been identified in this species. Pronounced inhibition was observed during periods of high uptake whereas little or no effect was obtained during the low uptake phase. The results are discussed in relation to a possible role of teleocalcin in regulating this cycle.

The effect of pH and/or calcium-enriched freshwater on gill Ca2+-ATPase activity and osmotic water inflow in rainbow trout (Salmo gairdneri)

Rainbow trout (Salmo gairdneri) were exposed to pH 5.0-5.1, 6.6 and/or calcium-enriched freshwater for 14 days. Hematocrit, gill Ca2+-ATPase enzyme activities, gill osmotic water inflow, plasma calcium and osmolarity were measured. No significant changes in plasma calcium ion levels were found. The typical increase in hematocrit usually associated with exposure of fish to acidified water was not found in the present study and is discussed. Plasma osmolarity decreased in fish exposed to calcium-enriched freshwater (60 mg Ca2+ X 1(-1) ) in comparison to fish exposed to control freshwater conditions (2 mg Ca2+ X 1(1) ), irrespective of the pH level. Gill Ca2+-ATPase enzyme activities were measured for both low affinity (3 mM Ca2+) and high affinity (100 microM) activity. Exposure of rainbow trout to low pH (pH 5.0-5.1) did not affect the specific activity of Ca2+-ATPase enzyme. However, low affinity Ca2+-ATPase activity in fish exposed to calcium-enriched freshwater did show a significant reduction. The increase in gill osmotic water permeability in fish exposed to calcium-enriched freshwater is interpreted as a result of the increase in osmolarity of the ambient media.

Ca2+-dependent phosphatase and Ca2+-dependent ATPase activities in plasma membranes of eel gill epithelium--III. Stimulation of branchial high-affinity Ca2+-ATPase activity during prolactin-induced hypercalcemia in American eels

Infusions of ovine prolactin for 10 days induced hypercalcemia in unfed American eels, Anguilla rostrata LeSueur, that tentatively was related to stimulation of branchial Ca2+-uptake mechanisms. Analysis of ATPase activities in the plasma membranes of the branchial epithelium in prolactin treated eels showed a specific stimulation of high-affinity Ca2+-ATPase. The results of this study form further evidence that the high-affinity Ca2+-ATPase activity represents the Ca2+-pump of the branchial epithelium.

Ca2+ ATPase inhibition in trout gill microsomes following in vitro and in vivo treatments with 2,4,5.T

Bioassay experiments were performed after exposure for 96 hr to various concentrations of trichlorophenoxyacetic acid (2,4,5.T). The sensitivity of juvenile trout was considerably higher than that of mature animals. The activity of the microsomal Ca2+ ATPase in trout gill under the effect of 2,4,5.T was investigated. In vitro studies showed an inhibitory effect on the Ca2+ ATPase, occurring at sublethal concentrations of the herbicide. In vivo exposure to various sublethal concentrations of 2,4,5.T during 96 hr involved a significant inhibition of the microsomal Ca2+ ATPase. The sensitivity of the microsomal Ca2+ ATPase from gills to 2,4,5.T is related to the toxicity of this herbicide.

Separation by velocity sedimentation of the gill epithelial cells and their ATPases activities in the seawater adapted eel Anguilla anguilla L

The separation of cell populations by sedimentation was carried out on heterogeneous suspensions of branchial cells of the seawater adapted eel Anguilla anguilla. The cell sedimentation rates vary mainly in relation to size and permit the separation of enriched fractions of chloride cells and respiratory cells. The method is described and discussed. The homogeneity of the separated populations was checked by microscopy and particle counting. An enrichment of 95% by volume concentration of the two main cell types was obtained. The separated cells had good viability (85-95% viable). This was controlled by Trypan blue exclusion tests. The adenosine triphosphatase activities of the different cell populations were measured and compared.

Ca2+-dependent phosphatase and ATPase activities in eel gill plasma membranes--I. Identification of Ca2+-activated ATPase activities with non-specific phosphatase activities

The characteristics of Ca2+-activated ATPase activities previously often postulated as components for the calcium transporting system in fish gills do not fulfil the requirements of a transport Ca2+-ATPase. The chelation of Ca2+- or Mg2+-ions is a prerequisite for the adenosinephosphate esters to serve as substrate for gill plasma membrane phosphatases. Ca2+-activated ATP hydrolysis results from the activity of a heterogeneous pool of phosphatases located in the plasma membranes of the branchial epithelium, as is concluded from substrate specificity tests and the effects of various inhibitors on these hydrolytic activities. In the present study only non-specific phosphatases could be shown.

Ca2+-activated adenosinetriphosphatase activity in the gills of freshwater-and seawater-adapted eels (Anguilla rostrata)

1. Ca2+ -activated ATPase activity was higher in the gills of freshwater acclimated eels than in the gills of seawater acclimated eels. 2. The properties of the enzyme and the amount of protein extracted were identical in freshwater and seawater acclimated eels.

A Cl-/HCO-3-ATPase in the gills of Carassius auratus. Its inhibition by thiocyanate

An ATPase is demonstrated in plasma membrane fractions of goldfish gills. This enzyme is stimulated by Cl- and HCO-3, inhibited by SCN-. Biochemical characterization shows that HCO-3 stimulation (Km = 2.5 mequiv./l) is specifically inhibited in a competitive fashion by SCN- (Ki = 0.25 mequiv./l). This residual Mg2+-dependent activity is weakly affected by SCN-. In the microsomal fraction chloride stimulation of the enzyme occurs in the presence of HCO-3 (Km for chloride = 1 mequiv/l); no stimulation is observed in the absence of HCO-3. Thiocyanate exhibits a mixed type of inhibition (Ki = 0.06 mequiv./l) towards the Cl- stimulation of the enzyme. Bicarbonate-dependent ATPase from the mitochondrial fraction is stimulated by Cl-, but this enzyme has a relatively weak affinity for this substrate (Km = 14 mequiv./l).

Relationship between net 45calcium influx across a perfused isolated eel gill and the development of post-stanniectomy hypercalcemia

The net 45calcium influx was measured in perfused isolated individual hemibranchs taken from Anguilla rostrata L. at various intervals following the surgical removal of the Corpuscles of Stannius. Total plasma calcium concentrations were recorded at the same time. A relationship between the development of post-stanniectomy hypercalcemia and the net rate of 45calcium uptake in the isolated gills is suggested. The net influx of 45calcium increased rapidly during the first week, peaked at two weeks and dropped back to control levels at three weeks. Plasma calcium levels followed the same trend over the first two weeks but continued to rise through the third week before dropping slightly during the fourth week. We conclude that the corpuscles of Stannius play some role in controlling the branchial uptake of calcium and that the gills are of primary importance in the appearance of post-stanniectomy hypercalcemia.

[Kinetics of Ca 2+ or Mg 2+ activated ATPase from lymphocyte plasma membranes]

The kinetic study of the C2+ ATPase activity of lymphocyte plasma memebranes allowed some properties of this enzyme to be evidenced. The Ca2+-activated hydrolysis of ATP is independent of a non-specific alkaline phosphatase. The substrate of the ATPase activity is the chelate Ca2+- ATP. Mg2+ may substitute for Ca2+ both as chelating ion and as activating ion. Several results suggest that we have only one ATPase, activated either by Ca2+-, or by Mg2+ with less efficiency; both chelates hve the same Km; pH values for maximum activity and transition temperatures are identical; the effects of free ions are also the same, activation at low concentration and inhibition at high concentration.