The role of modulated gap junctional intercellular communication in epigenetic toxicology

The normal development and health of all multicellular organisms, including the human being, depend on the adaptive maintenance of the integrity of the genetic information (e.g., DNA protective and repair mechanisms), as well as of the homeostatic and cybernetic regulatory systems within and between tissues. The primary focus of the past and current toxicological studies and risk assessment practices has been to ascertain and predict the "genotoxicity" of various physical and chemical agents. The paradigm of "carcinogen as mutagen," while valuable for stimulating studies of the detection of mutagens and of their potential role in "causing" somatic and germ line diseases, has tended to blunt research on the role of nongenotoxic mechanisms in disease causation. This brief analysis will emphasize the need to consider the role of modulated gap junctional intercellular communication (GJIC) in any biological risk assessment model. It is based on the following assumptions and facts. Because gap junctions exist in all metazoans, they have been associated with the regulation of cell proliferation, development, differentiation, and the adaptive function of both excitable and nonexcitable coupled cells. A highly evolutionarily conserved family of genes codes for proteins (connexins), which, as hexameric units (connexons), form membrane-associated channels of gap junctions. Cells coupled by gap junctions will have their ions and small regulatory molecules equilibrated. Regulation of GJIC can be at the transcriptional, translational, or posttranslational levels. Transient down or up regulation of GJIC can be induced by endogenous or exogenous chemicals via many mechanisms at any of these three levels. Stable abnormal regulation has been associated with activated oncogenes, and normal regulation has been associated with several tumor suppressor genes. The dysfunction of these gap junctions might play a role in the actions of various toxic chemicals that have cell type/tissue/organ specificity. This could bring about distinct clinical consequences, such as embryo lethality or teratogenesis, reproductive dysfunction in the gonads, neurotoxicity of the central nervous system, hyperplasia of the skin, and tumor promotion of initiated tissue. Modulation of GJIC should be viewed as a scientific basis of "epigenetic toxicology" because the alteration of intercellular communication would alter the internal physiological state of the cell. The inhibition of GJIC is a necessary component of mitogenesis (a necessary component of the multistage carcinogenic process). The modulation of GJIC can have both toxicological, as well as therapeutic potential.

Effect of intravenous calcitriol on secondary hyperparathyroidism in chronic hemodialysis patients

BACKGROUND

It has become evident that calcitriol can suppress parathyroid hormone (PTH) secretion by direct genomic actions. Intravenous calcitriol that bypasses gastrointestinal degradation might cause less degree of hypercalcemia and greater suppressive effect on PTH secretion. We investigated this PTH-suppressive effect of intravenous calcitriol in hemodialysis patients with secondary hyperparathyroidism.

METHODS

Calcitriol was administered at the end of each dialysis session three times a week in 20 uremic patients, for 12 weeks.

RESULTS

The mean dosage of calcitriol was 2.72 +/- 0.21 microgram per dialysis session. Serum intact PTH and C-PTH decreased (P < 0.05) after 6 weeks of treatment, while serum alkaline phosphatase (Alk-P) decreased 3 weeks later than PTH did. The individual maximal reduction of intact PTH, C-PTH and Alk-P were 77.80%, 67.36% and 45.98%. This PTH-suppression was dose-dependent. Despite the significant reduction of intact PTH by 58.17% after 6 weeks of treatment, no significant increase of serum calcium was found. An increase in serum calcium is not essential for this PTH-suppressive effect of calcitriol. Our observations thus provide another evidence to support the direct inhibitory effect of calcitriol on PTH secretion. Serum calcium, phosphorus, magnesium, albumin and osteocalcin levels did not change significantly. No side effect was found during treatment.

CONCLUSIONS

Intravenous calcitriol is effective and safe in treating hemodialysis patients with secondary hyperparathyroidism. This treatment is more important in patients who are intolerant to oral vitamin D supply and who are candidates for surgical parathyroidectomy.

Two-step cell disruption for the extraction of membrane-associated recombinant protein from Saccharomyces cerevisiae

The use of rDNA technology to express heterologous proteins has been very successful during the last several years. Choice of an expression host is very important in order to retain the biological activity of recombinant proteins. Baker's yeast, Saccharomyces cerevisiae, is a eucaryotic GRAS organism suitable for the expression of biologically active proteins. Specifically, hepatitis B surface antigen (HBsAg) is expressed in baker's yeast. Because the yeast cells need to be disrupted for the recovery of bioactive intracellular proteins and because the protein HBsAg is hydrophobic and has a tendency to become associated with cell membranes, the use of detergent increases the recovery yield. In order to remove most of the contaminants from yeast, a two-step disruption/extraction scheme has been developed that facilitates downstream processing. Furthermore, it also has the advantage of minimizing proteolytic actions on the recombinant protein by removing most of the contaminants and proteases into the supernatant during the first disruption step, while keeping the desired protein in the pellet fraction. Final recovery is then achieved by the extraction process. Parameters affecting the disruption/extraction processes have been discussed.

Somatic cell genetic and biochemical characterization of cell lines resulting from human genomic DNA transfections of Chinese hamster ovary cell mutants defective in sterol-dependent activation of sterol synthesis and LDL receptor expression

We have isolated several non-leaky mutant Chinese hamster ovary (CHO) cell clones (M4, M19, and M21) requiring cholesterol and unsaturated fatty acid for growth. These mutants belong to the same complementation group as the mutant M1 cells previously reported from this laboratory. M19 cells reverted to lipid prototrophy at very low frequency and were chosen as recipients to perform DNA-mediated gene-transfer experiments using total human genomic DNAs. Biochemical characterization of these transfectant clones indicated that, unlike their parental M19 cells, they were able to exhibit activation of cholesterol biosynthesis and LDL receptor expression in response to sterol removal from the growth medium. RNA blotting analysis indicated that these transfectants were able to increase HMG-CoA synthase gene transcripts in response to sterol removal. From the genomic DNAs of a representative secondary transfectant cells, we cloned a unique human DNA fragment (designated as h lambda 2) and showed that h lambda 2 closely linked with the presumptive human M1 gene.

Pharmacological relevance of peripheral type benzodiazepine receptors on motor nerve and skeletal muscle

1. Effects of agonists and antagonists of peripheral and central benzodiazepine receptors (pBZR and cBZR) on neuromuscular transmission were studied in mouse isolated phrenic nerve-diaphragm preparations. 2. Ro5-4864, a pBZR agonist, had no effect on the neuromuscular transmission but increased muscle contractility and antagonized the tetanic fade induced by neostigmine. 3. Ro5-4864 inhibited the regenerative tonic endplate depolarization caused by repetitive stimulation in the presence of neostigmine without affecting the amplitude and decay time of miniature and evoked single endplate potentials. 4. All the effects of Ro5-4864 were shared by PK11195, a pBZR antagonist, but not by clonazepam and flumazenil, a cBZR agonist and antagonist, respectively. 5. It is suggested that peripheral type benzodiazepine receptors modulate presynaptic function and muscle contraction.

Effects of estrogen and estrogen receptor in normal human melanocytes

Normal human melanocytes were cultured selectively with F12 culture medium supplemented with growth hormones, phorbol ester and 1% of fetal calf serum. The estrogen receptors were analyzed using hydroxylapatite-column assay with tritiated 17-beta-estradiol as the binding ligand. Phenol red- free medium was used when the changes in cell numbers, melanin content and tyrosinase were assessed after incubating with physiological concentration of 17-beta estradiol (10(-12) and 10(-9) M). It was found that the melanocytes contained both cytosol (5.42 +/- 1.11 fmol/mg protein) and nuclear (59.13 +/- 17.12 fmol/mg protein) estrogen receptor. In response to estradiol, the cell number increased but both the melanin content and the tyrosinase activity decreased in a dose related pattern. These data suggested the presence of estrogen receptor with biological function in normal human melanocytes.

Mechanism of expression and role in transcriptional control of the proto-oncogene NFKB-2/LYT-10

The NFKB-2 gene (previously LYT-10, NF-kappa Bp100 or NF-kappa Bp97) codes for a NF-kappa B/rel related protein which is highly homologous to NFKB-1 (previously NF-kappa Bp105) within its rel, poly-glycine and ankyrin domains. The NFKB-2 gene is a candidate proto-oncogene since it is involved in lymphoma-associated chromosomal aberrations. In order to gain insight into the physiological function and role in tumorigenesis of NFKB-2, we have analysed its mechanism of expression and role in transcriptional regulation. We report that, contrary to previous studies, a single 3.2 kb mRNA species and its 100 kD (p100) primary translation product is detectable in all cell types tested. A second NFKB-2 protein, p52, corresponding to the amino-terminal half (rel domain) of NFKB-2 p100, is detectable in the same cell types and derives from the post-translational processing of p100. While p100 is constitutively localized in the cytoplasm, NF-kappa B induction by TPA treatment of Hela cells is associated with cytoplasmic/nuclear translocation of NFKB-2 p52 and its appearance within DNA-binding NF-kappa B complexes. NFKB-2 p52 differs from NFKB-1p50 in its differential affinity for kappa B sequences: by itself it binds H2/HLA-kappa B sites more efficiently than HIV/IgK-kappa B sites, while it can bind both sites efficiently when complexed with Rel-A(p65). Transient co-transfection of expression and reporter plasmids in cells devoid of endogenous NF-kappa B activity showed that p52 has no intrinsic transcriptional activation capabilities: it can stimulate Rel-A(p65)-driven transcription by formation of p65/p52 heterodimers, whereas, overexpressed, it down-regulates p65-dependent transcription by formation of inactive p52/p52 homodimers. These results indicate that the NFKB-2 gene codes for an inducible NF-kappa B transcription factor with the capability of differentially regulating NF-kappa B transcription depending on its abundance in the nucleus.

Biochemical regulation of the activity of gamma-glutamylcysteine synthetase from rat liver and kidney by glutathione

Rat liver and kidney gamma-glutamylcysteine synthetase (gamma GCS) had similar catalytic properties and consisted of heavy and light subunits, but the molecular structure of the two enzymes was not the same as evidenced by the results of SDS-PAGE and disc gel electrophoresis. Unlike kidney enzyme, most of liver gamma GCS was in a reduced enzyme form which did not have disulfide linkage between heavy and light subunits. Although the oxidized form of the two enzymes which subunits were linked with disulfide bond(s) could be dissociated to a similar extent by GSH, liver gamma GCS was inhibited by GSH to a much greater extent. These results suggest that the relative sensitivity of the gamma GCS enzymes to inhibition by GSH might be related to the inherent dissociability of heavy and light subunit of gamma GCS.

Isolation and characterization of a toxic phospholipase A2 from the venom of the Taiwan habu (Trimeresurus mucrosquamatus)

A toxic phospholipase A2 (PLA2) was isolated from Taiwan-habu-snake (Trimeresurus mucrosquamatus) venom by sequential chromatographies on CM-52, Sephadex G-75 and S-Sepharose columns. This basic PLA2 has a single polypeptide with an estimated M(r) of 15,000. The PLA2 activity was Ca(2+)-dependent and inactivated by p-bromophenacyl bromide and its specific antibody. The toxic PLA2-induced myotoxic and direct haemolytic effects as well as respiratory distress in mice with an intraperitoneal LD50 of 1.17 micrograms/g body weight. The histological examination showed it caused haemorrhage and congestion in the viscera of mice. It was also cytotoxic to myeloma cells (NS-1), baby-hamster-kidney (BHK) cells and human umbilical endothelial cells. By neutralization experiments with a specific antibody against toxic PLA2, it was found that the enzymic activity of toxic PLA2 is essential for its myotoxicity, but it is not the only factor responsible for the lethal toxicity.

The essentiality of B chain in stabilizing the structure of the A chain in beta 1-bungarotoxin from Bungarus multicinctus venom

The dynamic of Trp residue in beta 1-bungarotoxin (beta 1-Bgt), the A chain of beta 1-Bgt and phospholipase A2 (PLA2) was assessed by fluorescence measurement. Acrylamide quenching studies showed that the exposure degree of the Trp in PLA2 is higher than the Trp in beta 1-Bgt. The Trp of beta 1-Bgt had a higher accessibility for iodide, reflecting that the basic nature of the B chain might exert an attractive electrostatic force for iodide and increase the susceptibility of Trp in the A chain to iodide. Removal of the B chain of beta 1-Bgt did not significantly affect the exposure degree of Trp in the A chain. Alternatively, the polarity of the environment around the Trp and the hydrophobic character of ANS and substrate binding sites in the separated A chain changed. Measurement of Trp fluorescence with increasing temperature showed that the stability of structure of beta 1-Bgt was higher than those of the separated A chain and PLA2. These results suggest that the B chain might interact with the A chain and stabilize the conformation of the A chain in beta 1-Bgt.

Localization of acyl coenzyme A:cholesterol acyltransferase gene to human chromosome 1q25

Acyl coenzyme A:cholesterol acyltransferase (ACAT) is an intracellular enzyme that catalyzes the formation of cholesterol esters from cholesterol and long-chain fatty acyl-coenzyme A. It is believed that ACAT plays a key role in lipoprotein metabolism and atherogenesis. Recently our laboratory succeeded in molecular cloning and functional expression of human macrophage ACAT cDNA. We have now mapped the ACAT gene to chromosome 1, band q25 by using fluorescence in situ hybridization to metaphase chromosomes, and by Southern blotting analysis of human--hamster somatic cell hybrid panels.

Building components contributors of the sick building syndrome

The sick building syndrome has been widely discussed from epidemiological perspectives. Although there is considerable difference in opinion regarding the concrete and objective evidence to support a distinct sick building syndrome and/or building-related illness, much data indicates that numerous variables within buildings can potentially influence human health. In this paper, we discuss in detail not only the potential and unique infectious diseases caused by Legionella, Pontiac fever, Q fever, and influenza, but also the data implicating noninfectious etiologies of sick building syndrome and building-related illnesses. In addition, the role of psychological factors, mass hysteria, and indoor pollution is discussed with respect to the nature of associations between exposure and symptoms. Finally, comparisons are made in different building construction types of old versus new buildings to highlight changes in modern construction that may have led to a putative increase in work-related symptomatology.

BCL-6 and the molecular pathogenesis of B-cell lymphoma

The results presented identify the first genetic lesion associated with DLCL, the most clinically relevant form of NHL. Although no proof yet exists of a role for these lesions in DLCL pathogenesis, the feature of the BCL-6 gene product, its specific pattern of expression in B cells, and the clustering of lesions disrupting its regulatory domain strongly suggest that deregulation of BCL-6 expression may contribute to DLCL development. A more precise definition of the role of BCL-6 in normal and neoplastic B-cell development is the goal of ongoing study of transgenic mice engineered either to express BCL-6 under heterologous promoters or lacking BCL-6 function due to targeted deletions. In addition to contributing to the understanding of DLCL pathogenesis, the identification of BCL-6 lesions may have relevant clinical implications. DLCL represent a heterogeneous group of neoplasms which are treated homogeneously despite the fact that only 50% of patients experience long-term disease-free survival (Schneider et al. 1990). The fact that BCL-6 rearrangements identify biologically and clinically distinct subsets of DLCL suggests that these lesions may be useful as markers in selection of differential therapeutic strategies based on different risk groups. Furthermore, the BCL-6 rearrangements can be used to identify and monitor the malignant clone with sensitive PCR-based techniques. Since clinical remission has been observed in a significant fraction of DLCL cases, these markers may serve as critical tools for sensitive monitoring of minimal residual disease and early diagnosis of relapse (Gribben et al. 1993).

Characterization of apoptosis induced by transforming growth factor beta 1 in human hepatoma cells

Apoptotic cell death plays a major role in the regulation of cell growth and this process may be activated by different agents through various pathways. The present study aimed to elucidated the mechanism of apoptosis caused by transforming growth factor beta 1 (TGF-beta 1) in human hepatoma cells. Several biological parameters which were reported to be crucial in the induction of programmed cell death in other experimental systems were measured. We found that TGF-beta 1-induced cell death is independent of cytosolic calcium and protein kinase C. Insulin and tumor promotor can rescue hepatoma cells from apoptosis, but the effect is time-dependent. Our results highlight that different apoptotic signal transduction pathways exist in different cell types. Apoptosis induced by TGF-beta 1 provides a good model for the understanding of cell death and the development of new anti-cancer drugs. Apoptotic cell death (apoptosis or programmed cell death) in normal tissue is a biological phenomenon that maintains hemostasis of systems of the body under physiological conditions. The features of apoptosis include condensation of chromatin, blebbing of the cell surface, transient increase in buoyant density and fragmentation of chromatin by a specific endonuclease.

Brequinar sodium, mycophenolic acid, and cyclosporin A inhibit different stages of IL-4- or IL-13-induced human IgG4 and IgE production in vitro

We investigated the effect of cyclosporin A (CsA), mycophenolic acid (MPA), and brequinar sodium (BQ) on human IgG4 and IgE synthesis induced by IL-4 or IL-13. BQ inhibited IL-4 and IL-13-induced IgG4 and IgE synthesis in cultures of peripheral blood mononuclear cells (PBMC) or highly purified B cells costimulated by anti-CD40 mAbs in a dose-dependent fashion. CsA and MPA had either suppressive or enhancing effects depending on the concentrations tested. Interestingly, BQ inhibited IgG4 and IgE synthesis at concentrations of 10(-6)-10(-8) M, which did not affect T or B cell proliferation, indicating that the inhibitory effects of BQ on Ig production were not directly related to inhibition of T or B cell proliferation. In contrast, the inhibitory effects of MPA on Ig production were directly associated with inhibitory effects on T and B cell proliferation. CsA blocked T and B cell proliferation at the same concentration (10(-7) M) which enhanced IgG4 and IgE synthesis, indicating that reduction in T or B cell proliferation correlated with enhanced IgE production. CsA also inhibited CD40 ligand expression and IL-2, IL-4, IL-5, IFN-gamma, and GM-CSF production by activated CD4+ T cell clones, whereas MPA and BQ were ineffective, indicating that these compounds do not inhibit early events in T cell activation. Collectively, our data indicate that BQ, MPA, and CsA block different stages of the IgG4 and IgE production process. In addition, we observed that CsA and MPA, in contrast to BQ, at lower concentrations can also have potentiating effects on the production of these Ig isotypes.

Plasma PTH and PTH-rP levels and clodronate therapy in cancer patients with hypercalcemia

To investigate the roles of parathyroid hormone (PTH) and parathyroid hormone-related peptide (PTH-rP) in hypercalcemic patients with various malignancies, we measured the plasma levels of intact PTH and intact PTH-rP in five hypercalcemic patients with hematologic malignancies and 29 hypercalcemic patients with solid cancers. Ten eucalcemic cancer patients with either hepatocellular carcinoma or squamous cancer of the lung served as controls. The results showed a suppressed PTH level in all of the 34 hypercalcemic cancer patients. The PTH-rP levels were within normal limits (< 2.5 pg/mL) for all of the eucalcemic cancer controls, all of the five hematologic cancer patients with hypercalcemia, and only two out of the 29 hypercalcemic patients with solid cancers. The PTH-rP level was elevated in nearly all (27/29) hypercalcemic patients with or without bony metastasis. There was a good correlation between the corrected total serum calcium level and the natural log of PTH-rP level in 39 patients (10 eucalcemic and 29 hypercalcemic) with solid cancers (r = 0.75, p < 0.001). These results suggest that PTH-rP plays an important role in the hypercalcemia of patients with solid cancers, but this was not the case in our patients with hematologic malignancies. True ectopic secretion of PTH is unlikely in most of these patients. The mean serum total calcium levels of 17 hypercalcemic patients (13 solid cancers, four hematologic malignancies) dropped significantly after the third day of treatment with a new-generation bisphosphonate-clodronate product. This treatment consisted of 300 mg daily intravenous infusion for seven days, followed by oral administration (800 mg, bid) for the following three weeks.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of functional involvement of tryptophan residues in phospholipase A2 from Naja naja atra (Taiwan cobra) snake venom

Phospholipase A2 (PLA2) from Naja naja atra snake venom was subjected to Trp modification with 2-nitrophenylsulfenyl chloride (NPS-Cl), and six derivatives were separated by HPLC. The results of amino-acid analysis and sequence determination revealed that Trp-18, Trp-19 and Trp-61 were modified by NPS-Cl. The order of accessibilities of the three Trp residues for NPS-Cl was Trp-18 > Trp-19 > Trp-61. Sulfenylation of Trp-18 caused a 92% drop in enzymatic activity. Modification of Trp-19 and Trp-61 resulted in a decrease in enzymatic activity of PLA2 by 45.5% and 51%, respectively. The enzyme modified on both Trp-18 and Trp-19 or on both Trp-18 and Trp-61 retained little PLA2 activity. It is evident that Trp-18 plays a more crucial function in PLA2 than Trp-19 and Trp-61. Sulfenylation did not significantly affect the secondary structure of the enzyme molecule as revealed by the CD spectra, and Ca2+ binding and antigenicity of sulfenylated PLA2 was unaffected. These observations, together with the fact that Trp-18 is involved in the substrate binding of PLA2, suggest that incorporation of a bulky NPS group on Trp-18 might give rise to a direct distortion of the interaction between substrate and the enzyme molecule. Alternatively, modification of Trp-19 and Trp-61 might indirectly affect the interfacial binding of PLA2 with its substrate.

Molecular cloning and functional expression of human acyl-coenzyme A:cholesterol acyltransferase cDNA in mutant Chinese hamster ovary cells

Accumulation of cholesterol esters as cytoplasmic lipid droplets within macrophages and smooth muscle cells is a characteristic feature of early lesions of atherosclerotic plaque. Intracellularly, an essential element in forming cholesterol ester from cholesterol is the enzyme acyl-coenzyme A:cholesterol acyltransferase (ACAT). ACAT is a membrane protein located in the endoplasmic reticulum. The ACAT protein has never been purified to homogeneity, and no antibodies directed against ACAT have been reported. The gene(s) encoding this enzyme had not been isolated. This laboratory had previously reported the isolation of Chinese hamster ovary cells expressing human ACAT activity. From DNAs of these cells, we have cloned a 1.2-kb exonic human genomic DNA. This led to the eventual cloning of a 4-kb cDNA clone (K1) from a human macrophage cDNA library. Transfection of K1 in ACAT-deficient mutant Chinese hamster ovary cells complemented the mutant defect and resulted in the expression of human ACAT activity. K1 contained an open reading frame of 1650 bp encoding an integral membrane protein of 550 amino acids. Protein homology analysis showed that the predicted K1 protein shared homologous peptide sequences with other enzymes involved in the catalysis of acyl adenylate formation followed by acyl thioester formation and acyl transfer. These results indicate that K1 encodes a structural gene for ACAT. The cDNA reported here should facilitate future molecular studies on ACAT.

Pentoxifylline inhibits the proliferation and glycosaminoglycan synthesis of cultured fibroblasts derived from patients with Graves' ophthalmopathy and pretibial myxoedema

Excessive amounts of glycosaminoglycans accumulate in the extraocular muscles of patients with Graves' ophthalmopathy and in the affected skin of patients with pretibial myxoedema. It is widely accepted that fibroblasts are the sources of glycosaminoglycan synthesis. Pentoxifylline, an analogue of the methylxanthine theobromine, inhibits the proliferation and certain biosynthetic activities of fibroblasts derived from normal human skin and from skin of patients with some fibrotic disorders. Our objective was to determine whether pentoxifylline has similar effects on fibroblasts derived from patients with Graves' ophthalmopathy and pretibial myxoedema and could serve as a candidate for the treatment of these manifestations. Fibroblasts from the extraocular muscles of two patients with Graves' ophthalmopathy and normal extraocular muscles of two subjects with strabismus, as well as the affected skin of two patients with pretibial myxoedema were cultured in vitro in the presence and absence of pentoxifylline to assay its effect on the proliferation of fibroblasts and their production of glycosaminoglycans. In subconfluent fibroblast cultures, pentoxifylline treatment caused a dose-dependent inhibition of serum-driven fibroblast proliferation. In confluent fibroblast cultures both in the presence and absence of serum, exposure to pentoxifylline similarly resulted in a dose-dependent inhibition of glycosaminoglycan synthesis for all these different kinds of fibroblasts. These findings may form the rationale for a clinical trial using pentoxifylline for the treatment of Graves' ophthalmopathy and pretibial myxoedema.

A comparison between vecuronium and atracurium in myasthenia gravis

We evaluated the effect of vecuronium bromide and atracurium besylate on the train-of-four response in the management of muscle relaxation in 20 patients with myasthenia gravis (MG) who were undergoing thymectomy. We confirmed the safe use of these two non-depolarizing muscle relaxants in MG patients. Vecuronium (0.04 mg.kg-1) demonstrated a lesser clinical duration than did atracurium (0.2 mg.kg-1) (38 +/- 19 vs 50 +/- 21 min, mean +/- s.e.mean). The recovery time for vecuronium patients was shorter than that for atracurium patients (22 +/- 18 vs 38 +/- 18 min), but the time until onset of neuromuscular blockade was longer with vecuronium (246 +/- 105 vs 107 +/- 103 s). During spontaneous recovery from neuromuscular relaxation, at T1/C of 25% and 100%, the train-of-four fade with vecuronium was significantly greater than that with atracurium (0.04 +/- 0.02, 0.16 +/- 0.03 vs 0.17 +/- 0.01, 0.83 +/- 0.03), suggesting that vecuronium had a greater prejunctional effect than did atracurium.