Subcellular Localization and Properties of 5'-Nucleotidase in the Rat Liver

Simultaneous determination of adenosine and its metabolites by capillary electrophoresis as a rapid monitoring tool for 5′-nucleotidase activity

A simple and rapid capillary electrophoretic method was developed for the simultaneous determination of micro-molar adenosine, hypoxanthine and inosine in enzyme assays without using radioactive labeled substrates. Prior to electrophoretic separation, addition of acetonitrile and sodium chloride to the assay solution and brief centrifugation are recommended for the purpose of sample cleanup and sample stacking. Under the optimal condition, the good separation with high efficiency was achieved in 6 min. Using deoxyadenylate as an internal standard, the linear range of the method was 5-200 microM, and the concentration limits of detection of adenosine, hypoxanthine and inosine were 2.2, 3.6 and 1.4 microM, respectively. Application of the proposed method was demonstrated by the activity assay of 5'-nucleotidase from Hep G2 cells.

Modulation of glucose transporters in rat diaphragm by sodium tungstate

Oral administration of sodium tungstate is an effective treatment for diabetes in animal models. We examined the effects of 6 weeks of oral administration of tungstate on glucose transporters (GLUT) in streptozotocin-induced diabetic rat diaphragm. Diabetes decreased GLUT4 expression while tungstate treatment normalized not only GLUT4 protein but also GLUT4 mRNA in the diabetic rats. Furthermore, treatment increased GLUT4 protein in plasma and internal membranes, suggesting a stimulation of its translocation to the plasma membrane. Tungstate had no effect on healthy animals. There were no differences in the total amount of GLUT1 transporter in any group. We conclude that the normoglycemic effect of tungstate may be partly due to a normalization of the levels and subcellular localization of GLUT4, which should result in an increase in muscle glucose uptake.

Ecto 5'-nucleotidase and nonspecific alkaline phosphatase. Two AMP-hydrolyzing ectoenzymes with distinct roles in human airways

In human airways, extracellular adenosine regulates epithelial functions supporting mucociliary clearance, an important airway defense mechanism against bacterial infection. Thus, defining the mechanisms of adenosine generation is critical for elucidating the role of this nucleoside in airway homeostasis. In this study, we identified the source of adenosine on the mucosal surface of human airway epithelia. Polarized primary cultures of human nasal or bronchial epithelial cells were assayed for transepithelial transport, cytosolic and cell surface adenosine production. Ussing chamber experiments indicated that serosal 1 microM [(3)H]adenosine was not transported to the mucosal compartment. Messenger RNA for the cytosolic AMP-specific 5'-nucleotidase (CN-I) was not detected in human bronchial epithelial cells, suggesting that mucosal adenosine did not originate from intracellular pools. In contrast, extracellular 0.1 mm ATP was rapidly dephosphorylated into adenosine on the mucosal epithelial surface. We identified two ectonucleotidases that mediated the conversion of AMP to adenosine: ecto 5'-nucleotidase (ecto 5'-NT, CD73) and alkaline phosphatase (AP). Both mucosal and serosal epithelial surfaces displayed ecto 5'-NT activity (K(m) = 14 microM, V(max) = 0.5 nmol x min(-1) x cm(-2)), whereas AP activity was restricted to the mucosal surface (K(m,)(high) = 36 microM, V(max) = 1.2 nmol x min(-1) x cm(-2); K(m,)(low) = 717 microM, V(max) = 2.8 nmol x min(-1) x cm(-2)). In bronchial cultures and tissues, ecto 5'-NT accounted for >80% of total activity toward 0.01 mm AMP, compared with <15% for 5 mm AMP. The proximal airway AP isoform was identified as nonspecific AP (NS AP) by levamisole sensitivity and mRNA expression. The two ectoenzymes presented opposite airway distributions, ecto 5'-NT and NS AP mRNA dominating in higher and lower airways, respectively. Collectively, these experiments support a major role for extracellular nucleotide catalysis and for ecto 5'-NT and NS AP in the regulation of adenosine concentrations on airway surfaces.

Downregulation of protein kinase C inhibits activation of mitochondrial K(ATP) channels by diazoxide

BACKGROUND

The mitochondrial K(ATP) (mitoK(ATP)) channel has been shown to confer short- and long-term cardioprotection against prolonged ischemia via protein kinase C (PKC) signaling pathways. However, the exact association between PKC or its isoforms and mitoK(ATP) channels has not yet been clarified. The present study tested the hypothesis that the activity and translocation of PKC to the mitochondria are important for cardiac protection elicited by mitoK(ATP) channels. Methods and Results-PKC was downregulated by prolonged (24-hour) treatment with phorbol 12-myristate 13-acetate (4 microgram/kg body weight) before subsequent experiments in rats. Langendorff-perfused rat hearts were subjected to 40 minutes of ischemia followed by 30 minutes of reperfusion. Effects of PKC downregulation on the activation of mitoK(ATP) channels and other interventions on hemodynamic, biochemical, and pathological changes were assessed. Subcellular localization of PKC isoforms by Western blot analysis and immunocytochemistry demonstrated that PKC-alpha and PKC-delta were translocated to the sarcolemma and that PKC-delta was translocated to the mitochondria after diazoxide treatment. In hearts treated with diazoxide (80 micromol/L), a significant improvement in cardiac function and an attenuation of cell injury were observed. In PKC-downregulated hearts, protection was abolished because mitoK(ATP) channels could not be activated by diazoxide.

CONCLUSIONS

These data suggest that PKC activation is required for the opening of mitoK(ATP) channels during protection against ischemia and that this effect is linked to isoform-specific translocation of PKC-delta to the mitochondria.

Simultaneous assessment of ecto- and cytosolic-5'-nucleotidase activities in brain micropunches

We propose a new methodology for simultaneous assessment of ecto- and cytosolic-5'-nucleotidase that can be utilized in brain to measure the activity of these enzymes in micropunches of tissues. It is based on the differential sensitivity of both enzymes to alpha,beta-methyleneadenosine 5'-diphosphate (AMP-CP) and the requirements for magnesium as a co-factor. The design of assay protocol contains an internal validation by allowing comparisons between total level of 5'-nucleotidase activity with that calculated from the sum of individual activities of the ecto- and cytosolic-5'-nucleotidases. We have applied this new approach to assess the activity of ecto- and cytosolic-5'-nucleotidase in the brain regions relevant to sleep regulation. The level of both enzymes was significantly lower in the cerebral cortex than other brain regions tested.

Subcellular localization of cyclic ADP-ribosyl cyclase and cyclic ADP-ribose hydrolase activities in porcine airway smooth muscle

Recent studies have provided evidence for a role of cyclic ADP-ribose (cADPR) in the regulation of intracellular calcium in smooth muscles of the intestine, blood vessels and airways. We investigated the presence and subcellular localization of ADP-ribosyl cyclase, the enzyme that catalyzes the conversion of beta-NAD(+) to cADPR, and cADPR hydrolase, the enzyme that degrades cADPR to ADPR, in tracheal smooth muscle (TSM). Sucrose density fractionation of TSM crude membranes provided evidence that ADP-ribosyl cyclase and cADPR hydrolase activities were associated with a fraction enriched in 5'-nucleotidase activity, a plasma membrane marker enzyme, but not in a fraction enriched in either sarcoplasmic endoplasmic reticulum calcium ATPase or ryanodine receptor channels, both sarcoplasmic reticulum markers. The ADP-ribosyl cyclase and cADPR hydrolase activities comigrated at a molecular weight of approximately 40 kDa on SDS-PAGE. This comigration was confirmed by gel filtration chromatography. Investigation of kinetics yielded K(m) values of 30.4+/-1.5 and 695. 3+/-171.2 microM and V(max) values of 330.4+/-90 and 102.8+/-17.1 nmol/mg/h for ADP-ribosyl cyclase and cADPR hydrolase, respectively. These results suggest a possible role for cADPR as an endogenous modulator of [Ca(2+)](i) in porcine TSM cells.

Respective value of alkaline phosphatase, gamma-glutamyl transpeptidase and 5' nucleotidase serum activity in the diagnosis of cholestasis: a prospective study of 80 patients

We studied the value of alkaline phosphatase (AP), gamma-glutamyl transpeptidase (GGT), and 5'-nucleotidase (5'-NU) activities in the diagnosis of intrahepatic (IHC) versus extra-hepatic cholestasis (EHC). Eighty patients were included prospectively. All presented with cholestasis as defined by a concomitant increase in at least two of three cholestatic enzymes (AP, GGT, 5'-NU), a low cytolytic ratio (alanine aminotransferase/AP [xN/xN] < or = 5), and no evidence for associated liver tumor. We compared 43 patients with IHC due to chronic liver disease to 37 patients with EHC due to main bile duct obstruction. Fasting blood samples for activity determination (AP, GGT, 5'-NU) were taken before performing liver biopsy in cases of IHC and before endoscopic or surgical management in cases of EHC. Enzyme activities were compared using univariate and multivariate analysis. AP (276 IU/L [35-3,140] vs. 123 IU/L [37-699]: p < 0.0001), GGT (595 IU/L [98-5,200] vs. 211 IU/L [38-925]; p < 0.0001), and 5'-NU (32 IU/L [10-142] vs. 16 IU/L [4-107]: p < 0.0003) were significantly higher in EHC when compared to IHC. Only in GGT and 5'-NU activities were independent variables significantly linked to the mechanism of cholestasis. In IHC, the ratio GGT/5'-NU (xN/xN) was significantly lower than in EHC (2.8 [0.7-7.2] vs. 3.7 [1.8-10.5]: p < 0.006). A threshold of GGT/5'-NU < 1.9 had a sensitivity of 40% and a specificity of 100% for the diagnosis of IHC. Although such hepatobiliary enzymes cannot be regarded as diagnostic, they can provide useful information to orientate the clinician in the diagnosis of cholestasis.

Marked depletion of GLUT4 glucose transporters in transverse tubules of skeletal muscle from streptozotocin-induced diabetic rats

The principal goal of the present study was to determine the subcellular content of GLUT4 in diabetic rat muscle, and to test the hypothesis that a reduced abundance of the transporter protein in transverse tubules is responsible for impaired glucose utilization in that tissue. GLUT4 protein levels were measured in hindlimb muscle homogenates as well as in subcellular membrane fractions enriched with either plasma membranes, transverse tubules, or GLUT4-containing intracellular membranes from control and diabetic (streptozotocin-induced) rats. GLUT4 protein contents in diabetic muscle homogenates was reduced by 30% as compared to control rats. Subcellular fractionation experiments revealed that GLUT4 contents in transverse tubules-enriched fractions was markedly decreased (by 55-60%) in skeletal muscle of diabetic animals whereas no significant reductions in GLUT4 abundance was observed in the plasma membrane fraction. Moreover, GLUT4 was markedly depleted (by 45%) in the GLUT4-enriched intracellular membrane fraction. These results indicate that GLUT4 is markedly depleted in both the intracellular pool and in the cell surface membranes in muscle of STZ-diabetic rats. Most strikingly, this study demonstrates that transverse tubules and not the plasma membrane are the main sites of cell surface GLUT4 depletion in diabetic muscle.

Increased abundance of specific skeletal muscle protein-tyrosine phosphatases in a genetic model of insulin-resistant obesity and diabetes mellitus

Resistance to the biological action of insulin in its target tissues is a cardinal feature of non-insulin-dependent diabetes mellitus. Protein-tyrosine phosphatases (PTPases) have been postulated to play a key role in the regulation of the insulin action pathway, especially in skeletal muscle, the major site of insulin-mediated glucose disposal in vivo. To evaluate whether changes in the activity and/or abundance of candidate skeletal muscle PTPases is associated with severe resistance to insulin in an animal model, we measured PTPase enzyme activity and PTPase protein level by immunoblotting in subcellular fractions of skeletal muscle in lean (+/?), insulin-resistant obese (fa/fa), and diabetic (ZDF/Drt-fa/fa) Zucker rats. Using a phosphotyrosylmyelin basic protein substrate, the solubilized-particulate fraction PTPase activity was increased by 65% and 74% (P < .05) and in vitro dephosphorylation of a recombinant rat insulin receptor kinase domain was increased by 104% and 114% in obese and diabetic animals, respectively (P < .01). These changes in PTPase activity were associated with an increase in specific immunoreactivity of leukocyte common antigen-related PTPase ([LAR] by 42% and 50%), PTPase 1B (by 61% and 69%), and the SHZ domain containing PTPase (SH-PTP2) (by 44% and 48%) in the solubilized-particulate fraction of obese and diabetic animals, respectively (P < .05). In diabetic muscle, increased SH-PTP2 abundance was also associated with a shift of SH-PTP2 to a plasma membrane component, which may have important consequences for the activation of this enzyme in the insulin-resistant state. These results provide evidence that specific PTPases play a role in the insulin resistance of this genetic model of obesity and non-insulin-dependent diabetes.

Vitamin E prevents endothelial injury associated with cisplatin injection into the superior mesenteric artery of rats

To clarify the pathogenesis of the vascular injury caused by the administration of anti-neoplastic drugs, cisplatin with lipiodol was infused into the superior mesenteric artery of rats. Morphological and biochemical changes in the vascular wall and the prophylactic effects of vitamin E were examined 4 days after administration. In the cisplatin-treated group, but not in the other groups, severe endothelial injury, such as vacuolation, subendothelial edema, and destruction of the internal elastic membrane, was observed. Superoxide dismutase, a potent scavenger of the superoxide anion, was markedly lower in the cisplatin group, and Na/K-ATPase, a marker of the plasma membrane, was also low in this group. These morphological changes were minimal, and enzyme activity was higher in the vitamin E-treated group than in the cisplatin-treated group. These findings indicate that endothelial injury after cisplatin administration could be caused by free radical-induced lipid peroxidation of the membrane system, and that such injury may be prevented by the co-administration of vitamin E.

Effect of hexachlorocyclohexane (HCH) on testicular plasma membrane of rat

The study deals with the analysis of residue of hexachlorocyclohexane (HCH) and its possible damaging potential on testicular plasma membrane of rats. In vitro studies were conducted by exposing plasma membrane of testis with 1.46 x 10(-5) M, 2.92 x 10(-5) M, 4.38 x 10(-5) M, 7.30 x 10(-5) M, 1.46 x 10(-4) M and 2.92 x 10(-4) M HCH at 37 degrees C for 15 min. The results indicate inhibition in the activity of the Ca(2+)-ATPase, Na(+)+K(+)+Mg(2+)-ATPase and 5'Nucleotidase. In vivo studies were carried out following repeated dermal exposure to HCH at a dose level of 50 or 100 mg/kg/day for 60 days to male rats. The results show significant decrease in the activities of 5'-Nucleotidase, Ca(2+)-ATPase, Na(+) + K(+)-ATPase and Mg(2+)-ATPase in the plasma membrane of testis following exposure to HCH. The analysis of the residues of HCH reveals the presence of significant quantities of its different isomers viz., alpha, beta, gamma and delta in the testicular plasma membrane of rats given in vivo dermal exposure of this pesticide. These results suggest that the presence of HCH residue may be a factor in inhibiting the marker enzymes of the plasma membrane of testis.

Tissue- and subcellular-distribution of the binding site of [3H]9- methyl-7-bromoeudistomin D, a potent caffeine-like Ca2+ releaser, in rabbits

Tissue and subcellular distribution of the binding site of 3H-labelled 9-methyl-7-bromoeudistomin D ([3H]MBED), a powerful caffeine-like Ca2+ releaser, were investigated in rabbits. The order of specific activities of total homogenates was liver > brain > other tissues. All binding was completely suppressed by 10 mM caffeine, indicating that all [3H]MBED binding sites are modulated by caffeine. [3H]MBED binding sites distributed mainly in membrane fractions rather than soluble fractions in most tissues. In lung and liver, [3H]MBED binding was enriched in microsomes. [3H]MBED may be useful as a probe to investigate the actions of caffeine at the molecular level not only in muscles but also in a variety of tissues including liver, kidney and lung.

Protein and enzyme content of plasma membranes derived from Walker 256 carcinoma cells grown as ascitic or solid tumours

A preliminary investigation of enzymes functioning at the cell surface indicates that when Walker 256 carcinoma cells growing ascitically are induced to grow as a solid tumour there is a marked increase in the activities of Na+, K(+)-ATPase, Mg(2+)-ATPase, 5'-nucleotidase, alkaline phosphatase and phosphodiesterase I; 5'-nucleotidase and alkaline phosphatase being particularly affected. These enzyme changes occur in the absence of any major alteration in the protein composition of the plasma membrane.

Effect of HDL1 infusion on biliary secretion in perfused rat liver

The effects of HDL1 lipoprotein infusion on biliary lipid secretion were studied in the in vitro model of rat perfused liver. A strong increase in bile flow was observed during and after lipoprotein infusion. This caused a significant rise in cholesterol, phospholipid and bile salt secretions. However, only the percentage of cholesterol increased with respect to the other bile lipids. The changes observed in the cholesterol/phospholipid molar ratio values of liver membrane subfractions (i.e., liver plasma membrane, mitochondria plus lysosomes and microsomes) isolated from the perfused rat liver after HDL1 administration were not significant.

Lipid peroxidation and myocardial vulnerability in hypertrophied SHR myocardium

In a comparison using age-matched Wistar-Kyoto rats (WKY), 16-week-old male spontaneously hypertensive rat (SHR) hearts were examined histologically and biochemically on the first and fourth day after administration of 20 mg/kg doxorubicin in order to examine whether membrane abnormalities in hypertrophied SHR myocardium are caused by lipid peroxidation. Morphological examination of the SHR revealed focal myocytolysis on the first day and severe cardiomyopathy involving diffuse myocytolysis and vacuolar degeneration in the left ventricle on the fourth day. The activity of a membrane-related enzyme, Na+/K(+)-ATPase, was already lower in control SHR than that of control WKY and was lower in both SHR and WKY than in the respective saline groups on the first day after administration, whereas the enzyme activity in the doxorubicin-treated SHR was not significantly different from that of the treated WKY. A thiobarbituric acid-reactant substance, a lipid peroxidation marker, was significantly higher in treated SHR than it was in the treated WKY on the first day. Furthermore, in comparison with WKY, alpha-tocopherol in the left ventricle in SHR was significantly lower on the fourth day after administration. These results show that a proneness to lipid peroxidation in the membrane system is closely associated with severity of doxorubicin-induced cardiomyopathy in SHR and suggests that membrane lipid peroxidation may cause a higher degree of vulnerability in hypertrophied SHR myocardium.

Subcellular fractionation of rainbow trout gonads with emphasis on microsomal enzymes involved in steroid metabolism

Rainbow trout gonads were subfractionated by differential centrifugation with emphasis on obtaining preparations suitable for the study of steroid-metabolizing enzymes. A fractionation scheme was evaluated for the mature testis and for 3 ovarian developmental stages. The distribution of cell organelles among the fractions was determined using enzyme-markers and electron microscopy. The fractionation scheme was found to be suitable for separating mitochondria and microsomes which were recovered at similar yields to those that had been reported for other extraheptic fish tissues. Fractionation of the mature ovary was fraught with problems probably because a large yolk protein cytosole fraction interfered with the recovery of microsomes. However, no difference in the specific activity of microsomal NADPH-cytochrome c-reductase between the various organ preparations was evident. The testis microsomes contained detectable amounts of cytochrome P450, whereas its content in the various ovary microsomes was too low to be detected. Progesterone 17 alpha-hydroxylase was detected in microsomes from testes and early developing ovaries, and microsomal aromatase activity was present in microsomes from early developing, mature and postovulatory ovaries. Furthermore, the testis microsomes contained a highly active UDP glucuronosyltransferase with testosterone used as a substrate.

Effects of tryptophane on SHRSP offspring growth

The effects of tryptophane on growth and hypertension of offspring obtained from mothers given L-tryptophane prior to mating: In the tryptophane group, body weights were heavier and blood pressures were higher than in the control group. Stroke lesion incidence rates were also much higher in the tryptophane group. At 20 weeks of age, brain enzyme activities were lower and serotonin content was higher in the tryptophane group in comparison with the control. These results suggest that dietary tryptophane may affect precocious maturation and as well as affect elevation in blood pressures due to brain serotonin turnover.

Cerium-induced light-microscopic demonstration of 5'-nucleotidase activity in the lymphatic capillaries of the proximal oesophagus of the rat

Lymphatic capillaries with narrow lumina cannot be identified with certainty by means of conventional light microscopy. This, however, can be achieved with great precision by means of labelling the 5'-nucleotidase activity which is high in lymphatic capillaries. In blood capillaries, on the other hand, it is either lacking or much less pronounced depending on the organ. The reactions performed thus far occurred primarily in the presence of lead ions which had a toxic effect on the enzymes. In cerium, however, this inhibiting influence can be neglected. 2 light-microscopic procedures of labelling the 5'-nucleotidase activity, which make use of cerium, are presented and compared here for the first time. The cerium perhydroxide technique is especially suited for demonstrating the lymphatic capillaries. In comparison to the previous enzyme histochemical methods, a definitely more precise demonstration of the endothelia of small lymphatics now is possible. The reason for this is that this method only reacts to regions of high enzyme activity. As opposed to previous tests on cryostat sections, the lumen of the lymphatic capillary is nearly always identifiable as such if employing this type of reaction. These properties of the cerium-perhydroxide reaction allow definite statements regarding the distribution of the lymphatic capillaries in the tissue. Its simple and rapid course of reaction favour the use of this method in clinical problems. In the other technique presented, the manganese dioxide technique, the demonstration of lymphatic capillaries is by far less exact due to its greater sensitivity even to low enzyme activities.

5'-Nucleotidase and adenosine deaminase in developing fetal guinea pig brain and the effect of maternal hypoxia

The activity of key enzymes of adenosine metabolism was studied in the developing fetal guinea pig brain. The activities of 5'-nucleotidase and adenosine deaminase were determined in the brains of fetal guinea pigs at 30, 35, 40, 45, 50, 55, and 60 days of gestation. The level of 5'-nucleotidase activity was extremely low at 30 and 35 days of gestation but increased rapidly during the 40 to 60 day period. The enzyme activity increased in the presence of Mg2+ with the Mg2+ - dependent activation increasing with the age of gestation. This Mg2+ - dependent activity was primarily associated with the membrane fraction. Prenatal hypoxia significantly increased the fetal brain M2+ - independent 5'-nucleotidase activity at 45 days of gestational age and beyond. Prior to this age, no effect was evident. Furthermore, following hypoxia, the Mg2+ - dependent activation of 5'-nucleotidase activity was lost. The activity of adenosine deaminase was present at 30 days of gestation and, unlike 5'-nucleotidase, it remained at the same level until 60 days. The results indicate that the term fetal guinea pig brain has the enzymatic mechanisms of adenosine metabolism and thus the potential for adenosine-mediated regulation of cerebrovasculature during hypoxia.

Insulin-induced decrease in 5'-nucleotidase activity in skeletal muscle membranes

Insulin releases inositol phosphoglycans from myocytes in culture [(1986) Science 233, 967-972], which display insulinomimetic activity. Because 5'-nucleotidase is anchored to the membrane through inositol-containing phospholipid glycans, we investigated whether insulin could release the enzyme from the membrane. Membranes prepared from hindquarter muscles of rats perfused with insulin showed a 23% decrease in 5'-nucleotidase activity. Isolated membranes from muscle exposed to insulin in vitro also showed a small but reproducible decrease (9%) in 5'-nucleotidase activity relative to unexposed controls. Phospholipase C from Staphylococcus aureus released 60% of the membrane-bound 5'-nucleotidase. We propose that insulin may activate an endogenous phospholipase C that cleaves phospholipid-glycan-anchored proteins.

Glomerular and vascular atrial natriuretic factor receptors in saralasin-sensitive and -resistant two-kidney, one-clip hypertensive rats

We have investigated whether there is a relation between renin dependency of two-kidney, one-clip (2K1C) hypertensive rats and the density of renal glomerular and vascular atrial natriuretic factor (ANF) receptors. Conscious 2K1C rats with blood pressure of 150 mm Hg or higher were classified according to their sensitivity to the blood pressure-lowering effect of the angiotensin II antagonist saralasin. Both hypertension groups had lower body weights and greater relative heart weights than normotensive controls. Hematocrit was lower and plasma volume higher in saralasin-resistant animals than in either saralasin-sensitive or control rats. Plasma renin activity was higher in the saralasin-sensitive group than in the resistant rats. Plasma ANF concentration was greater in saralasin-resistant than in either normotensive or saralasin-sensitive animals. ANF was reduced in both atria of saralasin-resistant 2K1C animals but only in the left atrium of the sensitive group. Both hypertensive groups showed an increased ventricular ANF concentration. The number of glomerular ANF binding sites was significantly lower in the clipped kidney of both hypertensive groups. This lower density of binding sites was accompanied by an increased affinity. In saralasin-sensitive rats, the density of glomerular ANF receptors in the nonclipped kidney was significantly higher than in the controls. Saralasin-resistant rats exhibited a decreased number of vascular ANF binding sites in both mesenteric arteries and aorta. We conclude that through modulation of its glomerular and vascular receptors, ANF may contribute to the differential sodium handling of saralasin-sensitive and -resistant 2K1C hypertensive rats and to the reduced vascular responsiveness to ANF observed in the saralasin-resistant hypertensive rats.

A quantitative histochemical study of 5'-nucleotidase activity in rat liver using the lead salt method and polyvinyl alcohol

5'-Nucleotidase (EC 3.1.3.5) activity was demonstrated in cryostat sections of rat liver using the Wachstein-Meisel medium and polyvinyl alcohol as tissue stabilizer. Optimum activity was obtained using an incubation medium containing 5 mM AMP, 10 mM magnesium chloride, 7.2 mM lead nitrate, 0.1 M Tris-maleate buffer, pH 7.2, and 17% (w/v) polyvinyl alcohol (Sigma, type III). The activity was localized at the bile canalicular and sinusoidal side of the plasma membranes of liver parenchymal cells as well as in the plasma membranes of endothelial cells of central veins and in fibroblasts surrounding portal tracts. The reaction was specific for 5'-nucleotidase because it was inhibited by ADP. Alkaline phosphatase did not interfere in the reaction. Cytophotometric analysis revealed a linear relationship between the formation of the final reaction product and incubation times up to 20 min and section thicknesses up to 8 micron. The activity in pericentral zones was 1.35 times the activity in periportal zones. The Michaelis constant for AMP was 1.4 mM in pericentral zones and 0.8 mM in periportal zones, suggesting that the bile canalicular and sinusoidal enzymes differ in their kinetic characteristics.

A quantitative histochemical study of 5'-nucleotidase activity in rat liver after ischaemia

The lead salt method of Wachstein and Meisel15 has been applied using incubation media containing polyvinyl alcohol for the localization and quantification of 5'-nucleotidase (E.C.3.1.3.5) activity in cryostat sections from rat liver after ischaemia in vitro and ischaemia in vivo followed by different periods of re-perfusion. 5'-Nucleotidase activity at the bile canaliculi, especially in the pericentral areas, had already decreased after 60 min of ischaemia in vitro, although the total activity as measured densitometrically was not changed. After 120-240 min of ischaemia, a significant decrease of the total 5'-nucleotidase activity was found. At that stage, signs of irreversible cell damage were recognized. Short periods of re-perfusion (1 h) after ischaemia in vivo induced a decreased bile canalicular 5'-nucleotidase activity throughout the entire liver, but a restoration after longer periods of re-perfusion was observed (5, 24, and 48 h). Necrotic areas recognized by a decreased lactate dehydrogenase activity after all periods of re-perfusion showed decreased total 5'-nucleotidase activities. A correlation was observed between the decrease in bile canalicular 5'-nucleotidase activity and the disappearance of microvilli of the bile canaliculi. It is concluded that a decrease in the bile canalicular 5'-nucleotidase activity can be used as a very sensitive marker for ischaemic liver cell damage. Assessment of the irreversibility of the cell injury has to be determined using additional parameters such as a decreased lactate dehydrogenase activity.

Insulin-induced translocation of glucose transporters in rat hindlimb muscles

Insulin causes a translocation of glucose transporters from intracellular microsomes to the plasma membrane in adipocytes. To determine whether insulin has a similar effect in rat hindlimb muscles, we used glucose-inhibitable cytochalasin B binding to estimate the number of glucose transporters in membrane fractions from insulinized and control muscles. Insulin treatment caused an approx. 2-fold increase in cytochalasin B-binding sites in a plasma membrane fraction and an approx. 70% decrease in cytochalasin B-binding sites in an intracellular membrane fraction. In order to detect this effect of insulin, it was necessary to develop a procedure for isolating a plasma membrane fraction and an intracellular membrane fraction that were not contaminated with sarcoplasmic reticulum. Our results show that, as in adipocytes, insulin stimulates translocation of glucose transporters from an intracellular membrane pool to the plasma membrane in hindlimb skeletal muscles.

Diurnal variation in 5'-nucleotidase activity in rat liver. A quantitative histochemical study

The diurnal variation of 5'-nucleotidase activity in periportal and pericentral areas of rat liver parenchyma has been determined with quantitative histochemical means. 5'-Nucleotidase activity was estimated using microdensitometry in cryostat sections after being incubated with a medium according to Wachstein and Meisel (1957). It appeared that 5'-nucleotidase activity was significantly higher in pericentral areas than in periportal areas throughout the daily cycle and showed a maximum at the end of the light period. It was concluded that 5'-nucleotidase activity may be related with the capacity to diminish messenger RNA resulting in protein breakdown.

Decreased density of vascular receptors for atrial natriuretic peptide in DOCA-salt hypertensive rats

We have previously found that vascular receptors for atrial natriuretic peptide (ANP) in the rat are down-regulated by volume expansion. For this reason vascular ANP receptor density and affinity were examined in a model of volume-expanded hypertension, the deoxycorticosterone acetate (DOCA)-salt hypertensive rat. The density of mesenteric vascular ANP binding sites was decreased in DOCA-salt hypertensive rats from a control value in uninephrectomized rats of 203 +/- 25 fmol/mg protein to 60 +/- 13 fmol/mg protein (p less than 0.01). The sensitivity of norepinephrine-precontracted aorta to ANP was significantly reduced in DOCA-salt hypertensive rats (p less than 0.001). DOCA-salt hypertensive rats infused intravenously for 4 days with ANP, 100 to 300 ng/hr, did not experience a lowering of blood pressure, in contrast to the significant reduction in blood pressure seen in two-kidney, one clip Goldblatt hypertensive rats similarly infused. In the latter there was no natriuretic response to ANP, while in the DOCA-salt hypertensive rats natriuresis occurred without lowering of blood pressure. In the DOCA-salt hypertensive rats plasma ANP concentration was increased to 68 +/- 8 fmol/ml from 10 +/- 1 fmol/ml in uninephrectomized rats. In conclusion, raised ANP concentration in plasma of volume-expanded hypertensive rats (DOCA-salt hypertension) may result in decreased density of ANP vascular receptors. These results suggest that a decrement in the number of ANP receptors may be a cause of decreased sensitivity of vascular responses to ANP in vitro and resistance to the blood pressure-lowering action of ANP in vivo.

Preparation and characterization of subcellular fractions from the liver of C57B1/6 mice, with special emphasis on their suitability for use in studies of epoxide hydrolase activities

The present study was designed to prepare and characterize subcellular fractions from the liver of male C57B1/6 mice, with special emphasis on their suitability for use in studies of epoxide hydrolase isozymes. The effects of different washing and pelleting procedures on the mitochondrial, microsomal and cytosolic fractions were studied. It was found that 133,000 gav for 60 min (i.e. more extensive force than the usual 105,000 gav for 60 min) was necessary to obtain a membrane-free cytosolic fraction, while one wash for microsomes and two washes for mitochondria yielded reasonably pure fractions. The purity of the different fractions obtained by differential centrifugation was then determined using established enzyme markers and morphological examination with the electron microscope. Several enzymes involved in drug metabolism were also measured in these fractions. The subcellular distributions obtained here for marker enzymes closely resemble those reported for rat liver. Starvation had no significant effect on the epoxide hydrolase activities nor did the addition of mouse bile or rat liver cytosol, which might contain inhibitors. The change in epoxide hydrolase activities with time after preparation of the subcellular fractions was studied, as well as the effect of freeze-thawing. The subfractions prepared here are suitable for the further characterization of the different forms of epoxide hydrolase present in mouse liver, as well as for other studies requiring well-characterized subfractions.

Biochemical effects of gentamicin on rat kidney cortex. I. Analytical subfractionation of control tissue

As a first step in studies of the molecular mechanism(s) underlying gentamicin toxicity, rat kidney cortex has been subfractionated using differential centrifugation. An analytical, rather than preparative approach was used. DNA was used as a marker for the nuclei, cytochrome oxidase for mitochondria, acid phosphatase for lysosomes, catalase for peroxisomes, NADPH-cytochrome c reductase for the endoplasmic reticulum, p-nitrophenyl-alpha-mannosidase (at pH 5.5) for the Golgi apparatus, AMPase for the plasma membrane in general, and alkaline phosphatase for the brush border, and lactate dehydrogenase for the cytosol. In addition, electron microscopy was performed on the subfractions obtained. The distributions of subcellular markers obtained here for the rat kidney cortex closely resemble the corresponding distributions reported for rat liver. This procedure can now be used to look for biochemical and/or toxic changes which might be reflected in an altered distribution pattern for marker enzymes.

Subcellular localization and properties of cytochrome P-450 and UDP glucuronosyltransferase in the rainbow trout kidney

Rainbow trout kidney was subfractionated by differential centrifugation to obtain preparations suitable for the study of xenobiotic metabolizing enzymes and to ascertain the distribution of these activities in the cell. The cytochrome P-450-dependent monooxygenase, NADPH-cytochrome c reductase, and UDP glucuronosyltransferase, which are enzymes important in the biotransformation of xenobiotics, were enriched in the microsomal fraction. Another xenobiotic-metabolizing enzyme, epoxide hydrolase, was enriched in the mitochondrial and microsomal fractions almost to the same extent. Cytochrome P-450-dependent monooxygenase and UDP glucuronosyltransferase activities were characterized in the trout kidney microsomes. The cytochrome P-450 deethylation of 7-ethoxycoumarin and 7-ethoxyresorufin as well as the glucuronidation of p-nitrophenol in the kidney were found to proceed at rates comparable to those occurring in the liver. The difference spectrum of the complex between carbon monoxide and reduced trout kidney microsomes showed a peak at 448.5 nm. Addition of 7-ethoxycoumarin to kidney microsomes produced an absorbance change in difference spectrum similar to the substrate binding spectrum found in rainbow trout liver and rat liver microsomes.

Phosphatidylinositol-specific phospholipase C of murine lymphocytes

Phosphatidylinositol-specific phospholipase C (PI-phospholipase C) was found primarily in the cytosolic fraction of murine splenic lymphocytes. However, small but significant amounts of the activity of the enzyme were detected in the microsome and plasma membrane fractions. Both the cytosolic and membrane-bound phospholipases C specifically hydrolyzed inositol phospholipids, phosphatidylinositol, phosphatidylinositol 4-phosphate, and phosphatidylinositol 4,5-bisphosphate. PI-Phospholipase C activity was detected in the cytosolic and microsome fractions from both T-cell-enriched and B-cell-enriched spleen cells. The membrane-bound enzyme was distinguishable from the cytosolic enzyme in the following properties. The cytosolic PI-phospholipase C showed optimal activity at pH 6.0 while the membrane-bound enzyme had two pH optima between pH 5.0 and 7.0. The activity of the cytosolic enzyme was first detected at 1 microM Ca2+, and maximum activity was observed at 100 microM Ca2+, while the membrane-bound PI-phospholipase C required higher Ca2+ concentrations, of millimolar order. The membrane-bound enzyme could hardly be extracted with 1 M NaCl but was extracted with 0.4% cholate.A portion of the membrane-bound PI-phospholipase C activity in the cholate extract was absorbed by concanavalin A-Sepharose and specifically eluted with an alpha-methylmannoside solution. The cytosolic enzyme, which was water soluble, did not bind to concanavalin A-Sepharose. Trypsinization of lymphocytes before subcellular fractionation caused a significant decrease in the PI-phospholipase C activity in the microsome fraction but almost no loss at all of the cytosolic enzyme activity.

Properties of cytosol 5'-nucleotidase and its role in purine nucleotide metabolism

5'-Nucleotidase which was found first in chicken liver and found to be located in cytosol was purified and characterized. This enzyme is termed cytosol 5'-nucleotidase for convenience. Some properties of this enzyme are summarized in Table 7. (Table: see text) The specific activity of cytosol 5'-nucleotidase in chicken liver cytosol is higher than that in rat liver cytosol. In response to a high protein diet the activity of cytosol 5'-nucleotidase in chicken liver increased, concurrently with those of purine nucleoside phosphorylase and xanthine dehydrogenase. Of the three enzymes, the activity of cytosol 5'-nucleotidase reached a maximum most rapidly. In rat liver, the activities of these three enzymes did not increase on administration of a high protein diet. From these results the principal physiological function of the cytosol 5'-nucleotidase is assumed to be dephosphorylation of IMP as the first step in the pathway of uric acid formation from IMP, which is important in the elimination of nitrogen of amino acids and proteins in a uricotelic animal. An allosteric property of this enzyme is considered to be important for control of adenine and guanine nucleotide pools, especially in connection with the biosynthetic activity of the purine nucleotides in uricotelic animals.

Effect of chronic ethanol administration on enzyme and lipid properties of liver plasma membranes in long and short sleep mice

Mechanisms of alcoholic liver disease are still ill defined. We evaluated in two outbred lines of mice whether chronic ingestion of ethanol alters the lipid composition and/or enzyme activity of liver plasma membranes. Two mouse lines with different sensitivities towards the hypnotic effect of ethanol, designated long sleep and short sleep, were fed a liquid diet containing ethanol for 30 days. Ethanol intake reached 30 gm per kg per day in both lines, and serum ethanol levels were similar. In addition, hepatic triglyceride levels were similarly increased 2-fold with ethanol feeding. The following effects of ethanol treatment were observed in liver plasma membrane fractions: (i) Na+,K+-ATPase was significantly increased to 26% above control in long sleep only; (ii) alkaline phosphatase activity was 2-fold increased in both lines; (iii) 5'-nucleotidase, leucine aminopeptidase and Mg2+-ATPase activities remained unchanged in both lines; (iv) unesterified cholesterol and total phospholipid contents were unaltered in both lines, and (v) cholesteryl esters were increased in both lines, but to a greater extent in short sleep (1.5 vs. 4-fold). Thus, chronic ethanol ingestion induces specific alterations in liver plasma membrane structure and function, suggesting that adaptive responses to ethanol may be determined in part by inherited factors.

Calmodulin abolishes the changes in Ca2+ binding and transport by heart sarcolemmal membranes of spontaneously hypertensive rats

Both Ca2+ transport and binding properties of heart sarcolemmal membranes are altered in spontaneously hypertensive rats (SHR) when compared to their normotensive controls (WKY). The effects of calmodulin on these two processes were studied at free calcium concentrations presumed to be the physiological levels in the cytosol. At a calcium concentration of 2.10(-8)M, calmodulin did not significantly modify either binding or ATP-dependent accumulation of calcium by membranes of both origins. In contrast, at a free calcium concentration of 4.10(-7)M, calmodulin enhanced the calcium binding to SHR membranes and the ATP-dependent calcium transport by SHR and WKY membranes. Differences in calcium binding and ATP-dependent accumulation between the two substrains were suppressed in presence of calmodulin. These data demonstrate that modifications in calcium handling by SHR cardiac plasma membranes might be due to altered intracellular content or function of calmodulin in SHR.

Chronic ethanol increases liver plasma membrane fluidity

Purified plasma membrane fractions of cultured well-differentiated Reuber H35 hepatoma cells were studied after growth in the presence or absence of ethanol. Growth of cells in the presence of ethanol significantly increased plasma membrane 5'-nucleotidase activity but did not influence sodium-potassium adenosinetriphosphatase activity. Fluorescence polarization of lipophilic probes was used to study membrane lipid structure. Steady-state polarization of diphenylhexatriene (DPH), a probe of the hydrophobic core, was significantly lower in plasma membranes from cells grown in 80 mM ethanol for 3 weeks, compared to controls. Decreased polarization of DPH in plasma membranes was observed after 3-weeks growth of cells in as little as 1 mM ethanol. A 1-h exposure to 80 mM ethanol had no effect. Altered DPH polarization was due to a decrease in the order parameter of the probe. The rotational correlation time of the probe was virtually unchanged. Chronic ethanol treatment of cells did not alter the polarization of the membrane surface probe trimethylammoniodiphenylhexatriene. Plasma membranes from cells grown in 80 mM ethanol had decreased contents of both phospholipid and unesterified cholesterol, but the cholesterol to phospholipid ratio was unchanged. The percentages of sphingomyelin and phosphatidylserine in plasma membrane phospholipids were significantly decreased after ethanol treatment, while the phosphatidylcholine/sphingomyelin ratio was increased by 42%. Vesicles prepared from total plasma membrane lipids of ethanol-treated cells, as well as vesicles prepared from polar lipids alone, showed the same alterations in DPH polarization as did plasma membranes. The importance of ethanol metabolism in the observed plasma membrane changes was demonstrated in two ways.(ABSTRACT TRUNCATED AT 250 WORDS)

Partial purification and characterization of phospholipid N-methyltransferases from murine thymocyte microsomes

Significant amounts of phospholipid N-methyltransferase activity in murine thymocytes were found to be distributed on the plasma membrane. The enzyme activity had an optimum pH of 9. The presence of divalent cations, Mg2+ (10 mM) or Ca2+ (1 mM), and EGTA separately in the assay had only a small effect on the enzyme activity. However, addition of both 10 mM Mg2+ and 1 mM Ca2+ increased the enzyme activity. The presence of two enzymes for each conversion of phosphatidylethanolamine (PE) to phosphatidylmonomethylethanolamine (PME) and PME to phosphatidylcholine (PC) was suggested by the result of the determination of the incorporated radioactivity into PME, phosphatidyldimethylethanolamine (PDE) and PC; the apparent Km values for S-adenosyl-L-methionine were 20 and 400-500 microM for the conversion of PE to PME and for the conversion of PME to PC they were 5 microM and 40 microM. S-Adenosyl-L-homocysteine (AdoHcy), a known inhibitor of enzymatic methylation, competitively inhibited [14C]methyl incorporation into total lipid. The apparent Ki value for AdoHcy was 44.7 microM. Two phospholipid N-methyltransferases were partially purified by extraction with sodium deoxycholate, gel filtration on Sephadex G-75, and affinity column chromatography on AdoHcy-Sepharose. One enzyme, mainly catalyzing the formation of PME, was purified approximately 1548-fold and the other catalyzing the formation of PDE and PC, was purified approximately 629- to 703-fold. However, the former still contained a little activity for PDE and PC formation and the latter contained a little activity for PME formation. In these partially purified phospholipid N-methyltransferase preparations, little contaminating protein O-carboxylmethyltransferase activity was observed; however, significant PC-phospholipase A2 activity was detected. This result may suggest that phospholipid N-methyltransferases associate with phospholipase A2 in the thymocyte plasma membrane.

Preparation and characterization of subcellular fractions from the head kidney of the Northern pike (Esox lucius), with particular emphasis on xenobiotic-metabolizing enzymes

The present study was designed to prepare and characterize subcellular fractions from the head kidney of the Northern pike (Esox lucius), with special emphasis on the preparation of a microsomal fraction suitable for studying xenobiotic metabolism. The purity of the different fractions obtained by differential centrifugation as well as the recovery of different cell components was determined using both enzyme markers and morphological criteria. Finally, the subcellular distributions of several drug-metabolizing enzymes (NADPH-cytochrome c reductase, NADH-ferricyanide reductase, glutathione transferase, epoxide hydrolase) were determined. With the exception of NADPH-cytochrome c reductase, the subcellular distributions obtained here for drug-metabolizing and marker enzymes closely resembled those reported for rat liver. NADPH-cytochrome c reductase was apparently partially solubilized here from microsomal vesicles by an endogenous protease, which reduced its usefulness as a marker enzyme and raises questions concerning the measurement of activities catalyzed by the cytochrome P-450 system in these subfractions. In other respects the microsomal fraction prepared here from the pike head kidney seems well-suited for studies of drug metabolism.

Highly enriched, minimally disrupted plasma membrane vesicles from aortic myocytes grown in primary culture

A plasma membrane-enriched fraction (fraction 1B) has been obtained from rat aortic myocytes grown in primary culture. Plasma membrane markers, 5'-nucleotidase and ouabain-sensitive (Na+ + K+)-ATPase, are enriched 4.1- and 8.7-fold, respectively, in this fraction. Although endoplasmic reticulum marker NADPH-cytochrome c reductase is the most enriched in mitochondrial and heavy sucrose density gradient fractions, substantial enrichment of this marker is also observed in membrane fraction 1. This membrane preparation therefore contains a certain quantity of endoplasmic reticulum. Cytochrome c oxidase is de-enriched by a factor of 0.04 in fraction 1, indicating that it is essentially clear of mitochondrial contamination. Homogenization of aortic media-intima layers using a whole-tissue technique induces greater disruption of mitochondria and subsequent contamination of membrane fractions than does the procedure for cell disruption. Analysis of electrophoretic gels, vesicle density distribution and electron micrographs of enriched membrane fractions provide evidence that plasma membrane enriched from cultured myocytes is less traumatized than comparable fractions obtained from intact tissue. The potential value of such a highly enriched, minimally disrupted plasma membrane preparation is discussed.

Preparation and characterization of subcellular fractions suitable for studies of drug metabolism from the trunk kidney of the Northern pike (Esox lucius) and assay of certain enzymes of xenobiotic metabolism in these subfractions

The present study was designed to prepare and characterize subcellular fractions from the trunk kidney of the Northern pike (Esox lucius), with special emphasis on the preparation of a microsomal fraction suitable for studying xenobiotic metabolism. The purity of the different fractions obtained by differential centrifugation, as well as the recovery of different organelles, was determined using both enzyme markers and morphological examination with the electron microscope. Finally, the subcellular distributions of several drug-metabolizing enzymes (NADPH-cytochrome c reductase, NADH-ferricyanide reductase, glutathione transferase, epoxide hydrolase) were determined. With the exception of NADPH-cytochrome c reductase, the subcellular distributions obtained here for drug metabolizing and marker enzymes closely resembled those reported for rat liver. NADPH-cytochrome c reductase was apparently partially solubilized here from microsomal vesicles by an endogenous protease, which reduced its usefulness as a marker enzyme and raises questions concerning the measurement of activities catalyzed by the cytochrome P-450 system in these subfractions. In other respects the microsomes and supernatant fraction prepared here from the trunk kidney of the pike seem to be as well suited for investigations of drug metabolism as are the corresponding fractions from rat and pike liver.

Preparation of a human lung purified plasma membrane fraction: confirmation by enzyme markers, electron microscopy, and histamine H1 receptor binding

A simple and rapid method of isolating plasma membranes from human peripheral lung tissue is described. The method involves homogenization of tissue in 0.25 M sucrose-buffered medium followed by differential and sucrose density gradient centrifugation. Enzymatic and morphological characterization of the plasma membrane fraction revealed minimal contamination by nonplasma membrane fragments. The isolated plasma membranes showed an 18-fold purification of 5'-nucleotidase activity compared to the original homogenate. Electron-microscopic studies of the plasma membrane fraction revealed the presence of small membrane vesicles having a trilaminar membrane structure. To further examine the purity of the plasma membrane preparation, the binding of the H1 receptor antagonist, 3H pyrilamine, to the plasma membrane-enriched fraction was compared to the binding to crude membrane preparations. Both the plasma membrane-enriched fraction and the crude membrane preparation had similar Kd's for the histamine antagonist, but the plasma membrane-enriched fraction had a threefold greater binding capacity, reflecting the relative enrichment of plasma membranes of the preparation. Thus, a method has been developed for the isolation of plasma membranes from human peripheral lung which should provide material for a variety of biochemical and pharmacological studies.

Effects of papaverine on the relative distribution of 45Ca ions in subcellular fractions of hog biliary muscles

The mechanisms by which papaverine (Pap) relaxes smooth muscles of hog bile ducts were investigated with respect to the effects of Pap on the distribution of Ca ions in intracellular organelles. Muscles loaded with 45Ca ions in 139 mM KCl-Tyrode's solution were incubated with Pap, [3H]Pap or theophylline (ThP) in Tyrode's solution. The Pap and Ca contents of various subcellular fractions were measured. Pap (40 microM) had no effect on Ca influx into the muscle in normal and 139 mM KCl-Tyrode's solutions. Pap was distributed to a greater extent in the cytosol fraction (F4) than in microsome and mitochondria-enriched fractions (F3) and in the nuclei-enriched fraction (F2). Pap selectively accumulated in the plasma membrane-enriched fraction (PM-F) and was negligible in the sarcoplasmic reticulum-enriched fraction (SR-F) and the mitochondria-enriched fraction (Mit-F). The Ca release of PM-F was greater and more rapid than the release from SR-F or Mit-F. The increase in the content of Ca in PM-F induced by Pap was enhanced by oxalate, suggesting that the increase is based on the increase in Ca uptake, not on the reduced efflux. Pap increased dose-dependently the Ca content of PM-F and appeared to decrease the Ca contents of SR-F and Mit-F. ThP and cyclic AMP (4 microM) had no effect on the Ca uptake of PM-F and no influence on the effects of Pap. These results suggest that Pap relaxation of hog biliary smooth muscle results from the interaction of the drug with the plasma membrane causing cyclic AMP-independent sequestration of Ca.