Determination of structural elements of the L2/HNK-1 carbohydrate epitope required for its function

The L2/HNK-1 carbohydrate epitope has been shown to carry an unusual 3'-sulfoglucuronic acid linked O-glycosidically through a neolactosyl-type backbone to a ceramide residue. Using monoclonal antibodies, the same or a closely related epitope has also been detected N-glycosidically linked to glycoproteins, amongst them several neural cell adhesion molecules. We used synthetic glycolipids carrying sulfated or non-sulfated glucuronic acid attached to ceramide through glycans of different length to show that not only the sulfated glucuronic acid but also the neolactosyl-type backbone is essential for the recognition of the L2/HNK-1 carbohydrate by a monoclonal antibody, its binding to laminin and its role in neural cell migration and outgrowth of processes from neurons and astrocytes.

[Preoperative and postoperative variations of human hepatocyte growth factor (hHGF) in hepatectomized patients]

We clinically analyzed significance of serum human hepatocyte growth factor (hHGF) concentrations (ng/ml) before and after hepatectomies. We examined 39 hepatectomized patients (Group H) and 8 non-hepatectomized patients as control (Group C). In group H, hHGF levels elevated significantly on postoperative 1st, 3rd, 5th, and 7th days (0.59 +/- 0.24, 0.47 +/- 0.23, 0.38 +/- 0.16, 0.38-0.14, respectively) compared with the preoperative value (0.27 +/- 0.11). On the 3rd day hHGF levels in Group H (0.45 +/- 0.22) were significantly higher than those in Group C (0.30 +/- 0.06). Nineteen cases of 2-segmentectomy and 8 cases of partial resection showed significantly higher hHGF levels on the 3rd day than those in Group C. In 12 patients with liver cirrhosis, hHGF levels were significantly higher on the 5th and 21st days than those in 27 patients without cirrhosis. Three patients with hepatic failure showed significantly higher hHGF levels correlated conversely with preoperative serum albumin and hHGF levels on the 1st day after operation significantly correlated with operative time, blood loss during the operation. It was suggested that serum hHGF level correlated with hepatic functional reserve. We concluded that serial measurement of hHGF was useful for evaluation of postoperative damage of hepatic functions, and prolonged high hHGF levels might suggest hepatic failure.

Androgen receptors, 5 alpha-reductase activity and androgen-dependent proliferation of vascular smooth muscle cells

To assess the direct effect of androgen on the development of atherosclerosis, we investigated the effect of androgen and its receptor expression in rat vascular smooth muscle cells (VSMC) isolated from rat aorta. We detected the androgen receptor mRNA in VSMC by reverse transcription of the total RNA coupled with amplification of the resulting cDNA by polymerase chain reaction. Binding studies revealed the presence of a single class of binding sites for testosterone (Kd 7.37 nM, Bmax 10.59 fmol/mg protein) and dihydrotestosterone (DHT; Kd 4.89 nM, Bmax 11.37 fmol/mg protein) in VSMC. Measurement of 5 alpha-reductase activity suggested that testosterone is converted to DHT in VSMC (Km 0.36 microM, Vmax 623 fmol/mg protein/h). Moreover, in the present study, DHT significantly stimulated DNA synthesis of VSMC (120-160% of control). The mitogenic activity of testosterone is much less potent than that of DHT. Considering these results, we concluded that androgen may directly accelerate atherosclerosis by stimulating the proliferation of VSMC.

The roles of the C-terminal domain and type III domains of chitinase A1 from Bacillus circulans WL-12 in chitin degradation

The mature form of chitinase A1 from Bacillus circulans WL-12 comprises a C-terminal domain, two type III modules (domains), and a large N-terminal domain which contains the catalytic site of the enzyme. In order to better define the roles of these chitinase domains in chitin degradation, modified chiA genes encoding various deletions of chitinase A1 were constructed. The modified chiA genes were expressed in Escherichia coli, and the gene products were analyzed after purification by high-performance liquid chromatography. Intact chitinase A1 specifically bound to chitin, while it did not show significant binding activity towards partially acetylated chitosan and other insoluble polysaccharides. Chitinases lacking the C-terminal domain lost much of this binding activity to chitin as well as colloidal chitin-hydrolyzing activity. Deletion of the type III domains, on the other hand, did not affect chitin-binding activity but did result in significantly decreased colloidal chitin-hydrolyzing activity. Hydrolysis of low-molecular-weight substrates, soluble high-molecular-weight substrates, and insoluble high-molecular-weight substrates to which chitinase A1 does not bind were not significantly affected by these deletions. Thus, it was concluded that the C-terminal domain is a chitin-binding domain required for the specific binding to chitin and that this chitin-binding activity is important for efficient hydrolysis of the sufficiently acetylated chitin. Type III modules are not directly involved in the chitin binding but play an important functional role in the hydrolysis of chitin by the enzyme bound to chitin.

Effects of halothane and diltiazem on L-type calcium currents in single smooth muscle cells from rabbit portal veins

We have studied the effects of halothane and diltiazem on L-type voltage-dependent calcium currents (ICa) in single smooth muscle cells from rabbit portal veins using a whole cell voltage clamp technique. The threshold of ICa was -30mV and the peak current was reached at 0mV. Halothane (0.25, 0.5, 1.0, 1.5 and 2.0%) decreased ICa in a concentration-dependent manner and shifted the ICa activation threshold to the depolarizing side. Halothane 2.0% abolished ICa. Diltiazem 10(-8)-10(-6) mol litre-1, a calcium channel antagonist, also depressed ICa in a concentration-dependent manner. Administration of both 0.5% halothane and diltiazem 10(-7) mol litre-1 (concentrations lower than the clinical therapeutic range) abolished ICa; however, halothane did not exhibit use-dependent inhibition of ICa whereas diltiazem showed partial use-dependency. We conclude that the decrease in ICa produced by halothane is associated with a direct vasodilator effect of this anaesthetic, but is not explained by block of Ca2+ channels similar to the action of diltiazem. Furthermore, administration of low concentrations of both halothane and diltiazem decreased ICa and may reduce the contractility of the vascular smooth muscle cells.

Role of cyclic AMP-induced Cl conductance in aqueous humour formation by the dog ciliary epithelium

1. The effects of isoprenaline, a forskolin derivative NKH-477, and dibutyryl cyclic AMP (db cyclic AMP) on the membrane potential, conductance and cell volume of the dog non-pigmented ciliary epithelium (NPE) were investigated by intracellular potential recording, nystatin-perforated patch clamp technique and videomicroscopic cytometry. 2. The resting membrane potential of NPE was about -70 mV in physiological saline and was depolarized by isoprenaline in a dose-dependent manner with an ED50 of about 3 nM. This depolarization was competitively antagonized by the beta-adrenoceptor antagonist, timolol (pA2 = ca. 9) and almost completely blocked by the Cl transport blocker, DIDS. 3. In single dissociated NPE cells, 10 microM isoprenaline induced an inward current and caused a concomitant decrease in cell volume. The reversal potential measurement indicated that this inward current was carried mainly by Cl ion. DIDS (10 microM) abolished both the current and cell volume decrease. 4. NKH-477 (10 microM) or db cyclic AMP (1 mM) also induced an inward current together with a cell volume decrease, the properties of which were similar to those caused by isoprenaline. 5. These results suggest that beta-adrenoceptor stimulation in NPE leads to an increased rate of aqueous humour production by increasing Cl- efflux via an elevation of cyclic AMP and this effect is efficiently blocked by timolol.

IL-1 induces intracisternal type A virus and retrovirus type C in pancreatic beta-cells of NOD mice

Recent observations have suggested a role for interleukin 1 (IL-1), a macrophage-derived cytokine, in the autoimmune beta-cell destruction, that is associated with type 1 diabetes. In this study, we investigated the effects of human recombinant IL-1 beta on pancreatic beta-cells from NOD and NON mice (diabetes-resistant NOD-related strain), focussing upon the appearance of intracisternal type A virus (IAP) and retrovirus type C. NOD mice pancreatic islets were incubated with or without IL-1 (0.1, 1, 10, 100 U/ml) for 10 days. Thereafter, the islets were examined using an electron microscope. When the islets of NOD mice were incubated with the IL-1 (10, 100 U/ml) under condition of high glucose, IAP and endogenous retrovirus type C frequently appeared in the beta-cells. Retrovirus type C was present as a cluster. In contrast, IAP and retrovirus type C were rarely found in beta-cells from the control group. When the islets of NON mice were incubated with or without IL-1 (10 U/ml) in the presence of high glucose, IAP was rarely found in beta-cells and retrovirus type C was undetectable in beta-cells. This study indicated that IL-1 is an important effector that leads to insulitis or aggravates insulitis in NOD mice.

Cyclic bcl-2 gene expression in human uterine endometrium during menstrual cycle

To investigate an apoptotic role for bcl-2 in menses, we studied bcl-2 protein production throughout the cycle. Bcl-2 protein was observed in endometrial glandular, stromal and myometrial smooth-muscle cells. Glandular cells expressed bcl-2 at proliferative through early secretory phases but not at late secretory through menstrual phases. This cyclic expression of bcl-2 gene was similar to that of oestrogen and progesterone receptors. Thus bcl-2 expression in glandular cells may be regulated by ovarian hormones. The disappearance of bcl-2 expression in glandular cells at late secretory phase was consistent with the appearance of apoptotic cells in the same phase.

Carrier-mediated transport of H1-antagonist at the blood-brain barrier: mepyramine uptake into bovine brain capillary endothelial cells in primary monolayer cultures

The transport mechanism of the H1-antagonist mepyramine at the blood-brain barrier (BBB) was studied by using primary cultured monolayers of bovine brain capillary endothelial cells (BCEC). The initial uptake of [3H]mepyramine into the BCEC showed strong temperature and concentration dependency, indicating that it involves both saturable and nonsaturable processes. Transport at the luminal membrane may be the rate-limiting process in the transcellular transport, since the values of the uptake coefficient of [3H]mepyramine at the luminal membrane (609 microliters/mg protein/min) and the transcellular permeability coefficient (488 microliters/mg protein/min) are very similar. The initial uptake of [3H]mepyramine was not affected by metabolic inhibitors, but was stimulated by preloading with the drug. Mepyramine appears to be transported into the BCEC by a carrier-mediated transport system which does not require metabolic energy, probably via a facilitated diffusion mechanism.

Prostaglandin F2 alpha activates phospholipase D independently from activation of protein kinase C in osteoblast-like cells

We previously reported that prostaglandin F2 alpha (PGF2 alpha) receptor is coupled to pertussis toxin (PTX)-sensitive GTP-binding protein (G protein) in osteoblast-like MC3T3-E1 cells [Miwa et al. (1990): Biochem Biophys Res Commun 171:1229-1235]. In the present study, we examined the effect of PGF2 alpha on the activation of phosphatidylcholine-hydrolyzing phospholipase D in MC3T3-E1 cells. PGF2 alpha stimulated the formation of choline in a dose-dependent manner in the range between 10 nM and 10 microM. The formation of choline was stimulated by 12-O-tetradecanoylphorbol-13-acetate (TPA), a protein kinase C (PKC)-activating phorbol ester. 4 alpha-Phorbol 12, 13-didecanoate, a PKC-nonactivating phorbol ester, had little effect on choline formation. The formation of choline stimulated by a combination of PGF2 alpha and TPA was additive. Staurosporine, an inhibitor for protein kinases, which inhibited the effect of TPA on choline formation, dose-dependently enhanced the formation of choline induced by PGF2 alpha. NaF, an activator of G protein, stimulated the formation of choline. The formation of choline stimulated by a combination of PGF2 alpha and NaF was not additive. NaF-induced formation of choline was dose-dependently enhanced by staurosporine. PTX dose-dependently inhibited the PGF2 alpha-induced formation of choline. These results strongly suggest that PGF 2 alpha activates phospholipase D independently from the activation of PKC in osteoblast-like cells and PTX-sensitive G protein is involved in the PGF2 alpha-induced phospholipase D activation.

Effect of vitamin D3 on prostaglandin E2 synthesis in osteoblast-like cells

We previously showed that prostaglandin (PG) F2 alpha stimulates PGE2 synthesis in osteoblast-like MC3T3-E1 cells, and that the activation of protein kinase C (PKC) amplifies the effect of PGF2 alpha through the potentiation of phospholipase A2 activity (H. Tokuda, Y. Oiso and O. Kozawa, J Cell Biochem. 48: 262-268, 1992). In the present study, we investigated the effects of vitamin D3 on PGF2 alpha-induced PGE2 synthesis in MC3T3-E1 cells. The pretreatment with 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3], an active form of vitamin D3, significantly inhibited the PGF2 alpha-induced PGE2 synthesis in a dose-dependent manner in the range between 1 pM and 1 nM. This inhibitory effect of 1,25-(OH)2D3 was dependent on the time of pretreatment up to 8 h. On the contrary, the pretreatment with 24,25-dihydroxyvitamin D3, an inactive form of vitamin D3, had little effect on the PGF2 alpha-induced PGE2 synthesis in these cells. However, the pretreatment with 1,25-(OH)2D3 no longer affected the amplification of PGF2 alpha-induced PGE2 synthesis by 12-O-tetradecanoylphorbol-13-acetate, a PKC activator. These results strongly suggest that 1,25-(OH)2D3 inhibits PGF2 alpha-induced PGE2 synthesis in osteoblast-like cells, however, the activation of PKC reverses this inhibitory effect of 1,25-(OH)2D3.

[Left atrial function during left ventricular diastole evaluated by left atrial angiography and left ventriculography]

The left atrium (LA) stores part of the right ventricular stroke volume during ventricular systole for passive release into the left ventricle (LV) during ventricular early diastole and active release during ventricular late diastole (passive and active contraction). The rest of the right ventricular stroke volume flows through the LA from the pulmonary vascular bed to the LV (LA conduit function). The factors affecting these LA functions were evaluated during ventricular diastole by left atrial angiography and left ventriculography in 21 patients with normal LV ejection fraction (0.53-0.76), but without coronary artery disease and valvular heart disease, aged 40-70 years. LV stroke volume was calculated from left ventriculograms. The maximal LA volume, minimal LA volume, and LA volume at the beginning of the left atrial active contraction were calculated from the left atrial angiograms, and further corrected by a regression equation (true volume = 0.91 x calculated volume -1.1). The LA reservoir volume, LA passive contraction volume, LA active contraction volume, and LA conduit volume were obtained. LA conduit volume correlated significantly with LV stroke volume (r = 0.97), but not with maximal LA volume and LA reservoir volume. LA active contraction volume correlated significantly with LA reservoir volume, LA volume at the beginning of LA active contraction, and maximal LA volume (r = 0.85, 0.60, 0.54, respectively). LA passive contraction volume did not correlate with any factor, and was grossly independent of LV stroke volume. LA conduit volume may be associated with LV diastolic function, and LA active contraction volume appears to increase with increased LA volume.

Okadaic acid reverses the inhibitory effect of protein kinase C on alkaline phosphatase activity in osteoblast-like cells

We previously reported that fetal calf serum-induced alkaline phosphatase activity is suppressed due to the activation of protein kinase C in osteoblast-like MC3T3-E1 cells (Miwa et al. (1991) Bone Miner. 14, 15-25; Kotoyori et al. (1994) Horm. Metab. Res. 26, 116-118). In the present study, we examined the effect of okadaic acid, a potent and specific inhibitor of protein phosphatase type 1 and 2A, on fetal calf serum-induced alkaline phosphatase activity in MC3T3-E1 cells. The pretreatment with okadaic acid enhanced the fetal calf serum-induced alkaline phosphatase activity in a dose-dependent manner in the range between 0.1 and 5 nM. 1-Norokadaone, a less potent analogue of okadaic acid, had little effect on the fetal calf serum-induced alkaline phosphatase activity. Okadaic acid partially reversed the suppression of fetal calf serum-induced alkaline phosphatase activity by 12-O-tetradecanoylphorbol-13-acetate, a protein kinase C activator. The effect of okadaic acid was dose-dependent in the range between 0.1 and 5 nM. The patterns of the dose-dependency of both okadaic acid effects on fetal calf serum-induced alkaline phosphatase activity and on the suppression by 12-O-tetradecanoylphorbol-13-acetate were similar. These results strongly suggest that protein phosphatase type 1 and/or 2A act as a regulator of alkaline phosphatase activity at a point downstream from protein kinase C in osteoblast-like cells.

pH-zone-refining counter-current chromatography: a displacement mode applied to separation of dinitrophenyl amino acids

A new mode of pH-zone-refining counter-current chromatography operates in a manner analogous to displacement chromatography. The method uses a retainer base (acid) in the stationary phase to retain analytes in the column and a displacer acid (base) to elute the analytes in the decreasing order of pKa and hydrophobicity. The elution produces a train of highly concentrated rectangular solute peaks with minimum overlap. Utility of the method is demonstrated in the separation of dinitrophenyl amino acids in a two-phase solvent system composed of methyl tert.-butyl ether and water. Compared with the original mode of pH-zone-refining counter-current chromatography, the present mode is more amenable to ligand-affinity separation which may cover a broader range of analytes including non-ionizable compounds.

A syndrome of female pseudohermaphrodism, hypergonadotropic hypogonadism, and multicystic ovaries associated with missense mutations in the gene encoding aromatase (P450arom)

We report the features of a new syndrome of aromatase deficiency due to molecular defects in the CYP19 (P450arom) gene in a 46,XX female. At birth, the patient presented with a nonadrenal form of female pseudohermaphrodism. At 17 months of age, laparotomy revealed normal female internal genital structures; the histological appearance of the ovaries was normal. FSH concentrations were markedly elevated at 9.4 ng/mL LER 869, and estrone and estradiol levels were undetectable (< 37 pmol/L). By 14 yr of age, she had failed to exhibit breast development. The clitoris had enlarged to 4 x 2 cm, and pubic hair was Tanner stage IV. The plasma concentration of testosterone was elevated at 3294 pmol/L, as was androstenedione at 9951 pmol/L. Plasma estradiol levels were below 37 pmol/L. ACTH and dexamethasone tests indicated a nonadrenal source of testosterone and androstenedione. Plasma gonadotropin levels were in the castrate range. Pelvic sonography and magnetic resonance imaging showed multiple 4- to 6-cm ovarian cysts bilaterally. Despite increased circulating androgens and clitoral growth, the bone age was 10 yr at chronologic age 14 2/12 yr. Estrogen replacement therapy resulted in a growth spurt, breast development, menarche, suppression of gonadotropin levels, and resolution of the cysts. The clinical findings suggested the diagnosis of P450arom deficiency. Analyses of genomic DNA from ovarian fibroblasts demonstrated two single base changes in the coding region of the P450arom gene, one at 1303 basepairs (C-T), R435C, and the other at 1310 basepairs (G-A), C437Y, in exon 10. The molecular genetic studies indicate that the patient is a compound heterozygote for these mutations. Expression of these mutations showed that the R435C mutation had 1.1% the activity of the wild-type P450arom enzyme, whereas the C437Y mutation demonstrated no activity. The cardinal features of this syndrome are a consequence of P450arom deficiency: 1) the fetal masculinization in this syndrome can be ascribed to defective placental conversion of C19 steroids to estrogens, leading to exposure of the female fetus to excessive amounts of testosterone; 2) the pubertal failure, mild virilization, multicystic ovaries, and hyperstimulation of the ovaries by FSH and LH are the result of the inability of the ovary to aromatize testosterone and androstenedione to estrogens; and 3) the striking delay in bone age at 14 2/12 yr supports the notion that estrogens, in contrast to androgens, are the major sex steroid driving skeletal maturation during puberty. Familial P450arom deficiency, although rare, may be more common than previously suspected.(ABSTRACT TRUNCATED AT 400 WORDS)

A nonhuman primate model for human cerebral malaria: rhesus monkeys experimentally infected with Plasmodium fragile

We studied the brains of rhesus monkeys infected with the primate malaria parasite Plasmodium fragile. Electron microscopy showed that, in these animals, erythrocytes infected with P. fragile undergo sequestration and that parasitized red blood cells adhere to endothelial cells in the cerebral microvessels by means of knobs. Cerebral microvessels with sequestered parasitized red blood cells were shown by immunohistochemical analysis to possess the platelet glycoprotein CD36, thrombospondin, and intracellular adhesion molecule-1. The formation of rosettes also was observed in the cerebral microvessels. In a fashion similar to human cerebral malaria, P. fragile produced neurological symptoms in the animals. Thus, rhesus monkeys infected with P. fragile, like those monkeys infected with Plasmodium coatneyi, can be used as a primate model to study human cerebral malaria.

[Hearing loss following discharge from the NICU]

We experienced 10 pediatric cases born between November of 1988 and November of 1992, whose ABR were normal at the time of discharge from the NICU, who subsequently developed hearing impairment. These children underwent thorough evaluations and the causes of their hearing loss are discussed herein. All 10 were born at full term, birth weights ranged from 2500g to 3826g, and all had severe cardiovascular and/or pulmonary disorders. Eight of the 10 had persistent pulmonary hypertension of the newborn (PPHN). During the four year period in which these 10 infants were born, a total of 25 PPHN cases were diagnosed in our NICU, i.e. the rate of hearing loss in PPHN infants was 32% (8/25). All 10 infants were intubated and maintained on mechanical ventilation for an average of 30 days. Five cases also required high frequency oscillation and six received extracorporeal membrane oxygenation (ECMO). During the same time period there were only eight surviving ECMO cases such that the rate of hearing loss was 75% (6/8). All 10 were treated with an aminoglycoside, furosemide and a muscle relaxant. As These infants are at very high risk for hearing impairment, follow-up at 6 and 12 months of age is essential.

Doxazosin and 48-hour ambulatory blood pressure monitoring in normotensive subjects

The effect of long-term doxazosin treatment on normotensive subjects was evaluated by 48-hour ambulatory blood pressure (BP) monitoring (ABPM). Eight normotensive volunteers were given 1 mg of doxazosin per day, and the dose was titrated every week up to 8 mg/day. The 48-hour ABPM, using a noninvasive device, was performed before treatment and during the 4th week of treatment. Doxazosin did not decrease the average 48-hour systolic BP, but diastolic BP decreased slightly (3 mmHg). This slight decrease in 48-hour diastolic BP was observed during the daytime. The 48-hour pulse rate (PR) was clearly elevated by doxazosin, which was attributed to tachycardia at night. Thus, the present study using 48-hour ABPM indicated that long-term doxazosin treatment may result in only slight daytime hypotension with apparent nighttime tachycardia in normotensive subjects.

Test performances of three diagnostic procedures in evaluating thyroid nodules: physical examination, ultrasonography and fine needle aspiration cytology

A retrospective study was performed to determine the reliability of physical examination (PE), ultrasonography (US) and fine-needle aspiration cytology (FNA) in the evaluation of thyroid nodules. Preoperative diagnoses of 252 euthyroid patients comprised 126 with benign lesions, 114 with papillary carcinoma and 12 with follicular carcinoma made by PE, US and FNA were reviewed. The specificity of PE, US and FNA for malignancy was 98%, 90% and 98%, respectively. The sensitivity of PE, US and FNA for malignancy was 63%, 78% and 80%. The sensitivity for papillary carcinoma of the three procedures was 68%, 83%, 88%, whereas that for follicular carcinoma was 25%, 25%, 8%, respectively. When all the test results were negative, the likelihood ratio favoring papillary carcinoma was 0.008 whereas that favoring follicular carcinoma was 0.6. The histological category of carcinoma should be considered when evaluating diagnostic procedures for thyroid nodules. No negative test result is conclusive for ruling out the possibility of follicular carcinoma.

Effects of phenylephrine on membrane currents in single smooth muscle cells of taenia caeci

Procedures used for dissociation of taenia caeci smooth muscle cells usually damage alpha 1-adrenoceptors. This paper describes modes of isolation under which alpha 1-adrenoceptors of taenia caeci do not lose their function. It has been found that antioxidants (dithiothreitol or taurine) are able to protect receptors from injury caused by digestive enzymes. A high concentration of bovine serum albumin also protects receptors from enzyme injury if a relatively specific enzyme (collagenase Type XI, Sigma) is used. Phenylephrine (10 mcmol/l) studied both in muscle strips using the double sucrose gap method and in isolated smooth muscle cells using whole cell current clamp conditions substantially hyperpolarized the smooth muscle membrane. This hyperpolarization was blocked by pretreatment of the tissues or cells by prazosin (1 mcmol/l). Phenylephrine (1-50 mcmol/l), under whole cell patch clamp conditions, enhanced the frequency and amplitude of spontaneous transient outward currents (STOCs), which were voltage- and temperature-dependent, and elicited a low amplitude sustained outward current. Phenylephrine (10 mcmol/l) reduced the inward and enhanced the outward component of the total whole cell current evoked by voltage steps from the holding potential of -50 mV to -10 mV. Under experimental conditions when only calcium current was recorded, phenylephrine significantly enhanced its amplitude. These results are in favor of the assumption that phenylephrine induced hyperpolarization is at least partially the consequence of calcium influx, which activates potassium conductance.

Role of iron and glutathione redox cycle in acetaminophen-induced cytotoxicity to cultured rat hepatocytes

The aims of this study were to investigate the roles of iron as a catalyst in reactive oxygen metabolite-mediated cellular injury and of the endogenous antioxidant defenses against acetaminophen-induced cytotoxicity in cultured rat hepatocytes. Hepatocytes were isolated and cultured from either 3-methylcholanthrene-treated or untreated rats. Cytotoxicity was evaluated by measuring 51Cr and lactate dehydrogenase release. Acetaminophen caused dose-dependent cytotoxicity in 3-methylcholanthrene-treated, but not untreated, cells. There was a good correlation between 51Cr and lactate dehydrogenase release values. Pretreatment with both diethyl maleate, which covalently binds glutathione as catalyzed by glutathione-S-transferase, and bis(chloroethyl)-nitrosourea, an inhibitor of glutathione reductase, enhanced acetaminophen-induced cytotoxicity. Inhibition of endogenous catalase activity by pretreatment with aminotriazole did not affect acetaminophen-induced cellular damage. Addition of exogenous catalase failed to protect against acetaminophen-induced cytotoxicity. Preincubation with both deferoxamine, a ferric iron chelator, and phenanthroline, a ferrous iron chelator, diminished acetaminophen-induced cytotoxicity. These results indicate that iron is crucial in mediating acetaminophen-induced cytotoxicity and that the glutathione redox cycle, but not catalase, plays a critical role in the endogenous defenses against acetaminophen-induced cellular damage in cultured rat hepatocytes in vitro.