Effects of age and diabetes on blood flow rate and primary outcome of newly created hemodialysis arteriovenous fistulas

To study the feasibility of creating a radiocephalic hemodialysis fistula in elderly and diabetic patients, we prospectively studied 176 patients undergoing the first permanent vascular access creation and followed the outcome of fistula until primary failure or success was assessed. Color duplex ultrasonography was used to measure the blood flow rate. Fistula blood flow rate was significantly smaller in elderly patients, however, it was > 400 ml/min in over 78% of the elderly patients with successful fistulas. There was no difference in fistula blood flow rate between nondiabetics and diabetics. Dialysis adequacy (Kt/V) via fistula was the same between age groups and between diabetes mellitus status. Old age or diabetes per se did not significantly predispose a new fistula to primary failure, but concurrent old age and diabetes markedly increase the risk. In conclusion, a good primary outcome of newly created radiocephalic fistula and adequate dialysis via fistula were demonstrated for elderly and diabetic patients. However, the longevity of fistula in elderly and diabetic patients needs further study.

Assessment of the coronary artery disease and systolic dysfunction in hypertensive patients with the dobutamine-atropine stress echocardiography: effect of the left ventricular hypertrophy

This study was performed to evaluate whether left ventricular hypertrophy (LVH) can influence the diagnostic accuracy of coronary artery disease (CAD) using the dobutamine stress echocardiography (DSE) in hypertensive patients. In addition to the detection of CAD, the relationship between systolic dysfunction and the quantitation wall motion scoring system of DSE was studied also. DSE was performed in 101 patients. There were 45 (45%) patients with a history of acute myocardial infarction. Twenty-eight patients (28%) had electrocardiographic LVH and 59 patients (58%) had echocardiographic LVH. A total of 74 patients (73%) had angiographically documented CAD defined as > or = 50% diameter stenosis. For the 56 patients without history of myocardial infarction, the diagnostic sensitivity, specificity, and accuracy in detecting CAD were not influenced by LVH defined by either electrocardiography or echocardiography. For the total patients, the diagnostic sensitivity, specificity, and accuracy in detecting multivessel disease were also not influenced by LVH defined by either method. The resting global wall motion score was correlated well with the left ventricular ejection fraction in patients with and without LVH (r = -0.70, p < 0.001 vs. r = -0.70, p < 0.001). When using the resting wall motion score of 24 as a cutoff value, the diagnostic sensitivity, specificity, and accuracy of systolic dysfunction (defined by left ventricular ejection fraction <40%) were 79, 86 and 85%, respectively. In conclusion, the diagnostic accuracy of CAD using the DSE was not affected by LVH in hypertensive patients. In addition to detection of coronary artery disease, the resting wall motion score of DSE was able to detect systolic dysfunction in patients with and without LVH.

Surgical management of traumatic thoracic aortic rupture from falling

A 40-year-male was admitted to our hospital after falling from a four-story height. Thoracic aortic rupture was suspected based on chest roentgenography and helical computed tomography. The patient was in the operating room within 6 hours after admission to the hospital. A median sternotomy with a left thoracotomy in the fifth intercostal space was done after left femoral arterial cannulation. Profound hypothermic circulation arrest with retrograde cerebral perfusion was applied. The site of aortic rupture was the descending aorta, just distal to the origin of the left subclavian artery. There were two areas of rupture within 2 cm of each other. The ruptured aorta was grafted with a 20-mm woven double-velour Hemashield graft. The total circulatory arrest time was 80 minutes and the cardiopulmonary bypass time was 290 minutes. The postoperative course was complicated by prolonged mechanical ventilation support due to pulmonary contusion. The patient was discharged 30 days after surgery without neurologic deficit.

Adrenal myelolipoma--report of two cases

Adrenal myelolipoma, which is composed of hematopoietic and adipose elements, is a rare benign tumor. Most adrenal myelolipomas are asymptomatic and are found incidentally. We report two cases of adrenal myelolipoma. One was a middle-aged woman with right flank pain. Tumor size increased 8 years later. The other patient was a 63-year-old man presenting with right flank soreness. The right adrenal tumor was found by abdominal sonography. Both of them received adrenalectomy to relieve symptoms and the pathologic results showed adrenal myelolipoma. The clinical, radiologic and pathologic characteristics of these two cases are discussed together with a review of the literature.

Ultrasonic diagnosis of ureteral injury after laparoscopically-assisted vaginal hysterectomy

Ureteral injuries are uncommon but serious complications of laparoscopically-assisted vaginal hysterectomy. The ureter is particularly at risk for inadvertent injury when the cardinal-uterosacral ligament complex is coagulated and divided below the uterine vessels. We present two recent cases which describe the application of transabdominal ultrasound including color Doppler mapping in the diagnosis of ureteral injury after laparoscopically-assisted vaginal hysterectomy. Transabdominal ultrasound including color Doppler mapping has great diagnostic potential as a method for non-invasive evaluation of post-operative ureteral conditions. Ultrasonic triads (absence of a ureteric jet, ascites, and the presence or absence of hydronephrosis) are capable of differentiating diagnosis of complete, partial, or nonobstructive surgical ureteral injuries.

A novel St(a) glycophorin produced via gene conversion of pseudoexon III from glycophorin E to glycophorin A gene

Stone (St(a)) is a variant antigen carried on human erythrocyte MNSs glycophorins (GPSt(a)) that are genetically associated with splicing mutations in GPA genes or with hybrid formation between GPA and GPB genes. Here we identify the first and rare gene conversion event in which GPE, the third member of the family, recombined with GPA, giving rise to a GPA-E-A hybrid gene encoding the St(a) antigen. Western blot detected expression in the proband of both GPA and GPSt(a) on the plasma membrane. Southern blot showed a new restriction fragment from the GPSt(a) gene, indicating an altered exon III-intron 3 junction. Sequencing of RT-PCR products identified one full-length and two shortened glycophorin cDNAs. The shortened forms were derived from GPSt(a) lacking one (exon III) and two exons (exon III and IV), respectively. To define the molecular basis for exon skipping, the genomic region spanning exon III of the GPSt(a) gene was amplified and sequenced. This revealed transfer from GPE to GPA of a DNA segment containing the pseudoexon III and its silent donor splice site. Thus, the inactivation of GPA exon III by conversion of a silent GPE donor splice site portrays a new molecular mechanism for St(a) antigen expression in human erythrocytes.

Characterization of human RhCG and mouse Rhcg as novel nonerythroid Rh glycoprotein homologues predominantly expressed in kidney and testis

In mammals, the Rh family includes the variable Rh polypeptides and invariant RhAG glycoprotein. These polytopic proteins are confined to the erythroid lineage and are assembled into a multisubunit complex essential for Rh antigen expression and plasma membrane integrity. Here, we report the characterization of RhCG and Rhcg, a pair of novel Rh homologues present in human and mouse nonerythroid tissues. Despite sharing a notable similarity to the erythroid forms, including the 12-transmembrane topological fold, the RHCG/Rhcg pair is distinct in chromosome location, genomic organization, promoter structure, and tissue-specific expression. RHCG and Rhcg map at 15q25 of human chromosome 15 and the long arm of mouse chromosome 7, respectively, each having 11 exons and a CpG-rich promoter. Northern blots detected kidney and testis as the major organs of RHCG or Rhcg expression. In situ hybridization revealed strong expression of Rhcg in the kidney collecting tubules and testis seminiferous tubules. Confocal imaging of transiently expressed green fluorescence protein fusion proteins localized RhCG exclusively to the plasma membrane, a distribution confirmed by cellular fractionation and Western blot analysis. In vitro translation and ex vivo expression showed that RhCG carries a complex N-glycan, probably at the (48)NLS(50) sequon of exoloop 1. These results pinpoint RhCG and Rhcg as novel polytopic membrane glycoproteins that may function as epithelial transporters maintaining normal homeostatic conditions in kidney and testis.

Gene expression profiling in the human hypothalamus-pituitary-adrenal axis and full-length cDNA cloning

The primary neuroendocrine interface, hypothalamus and pituitary, together with adrenals, constitute the major axis responsible for the maintenance of homeostasis and the response to the perturbations in the environment. The gene expression profiling in the human hypothalamus-pituitary-adrenal axis was catalogued by generating a large amount of expressed sequence tags (ESTs), followed by bioinformatics analysis (http://www.chgc.sh.cn/ database). Totally, 25,973 sequences of good quality were obtained from 31,130 clones (83.4%) from cDNA libraries of the hypothalamus, pituitary, and adrenal glands. After eliminating 5,347 sequences corresponding to repetitive elements and mtDNA, 20,626 ESTs could be assembled into 9, 175 clusters (3,979, 3,074, and 4,116 clusters in hypothalamus, pituitary, and adrenal glands, respectively) when overlapping ESTs were integrated. Of these clusters, 2,777 (30.3%) corresponded to known genes, 4,165 (44.8%) to dbESTs, and 2,233 (24.3%) to novel ESTs. The gene expression profiles reflected well the functional characteristics of the three levels in the hypothalamus-pituitary-adrenal axis, because most of the 20 genes with highest expression showed statistical difference in terms of tissue distribution, including a group of tissue-specific functional markers. Meanwhile, some findings were made with regard to the physiology of the axis, and 200 full-length cDNAs of novel genes were cloned and sequenced. All of these data may contribute to the understanding of the neuroendocrine regulation of human life.

The clinical implications of telomerase activity in upper tract urothelial cancer and washings

OBJECTIVE

To measure telomerase activity in upper tract urothelial carcinomas (as renal pelvic tumours comprise nearly half of all kidney tumours in Taiwan, a much higher percentage than in other countries) and to determine whether telomerase activity could be used as an additional diagnostic marker in exfoliated cancer cells present in upper tract urothelial washing fluids, thus providing earlier diagnosis and treatment. Materials and methods Telomerase activity was assessed using the telomeric repeat amplification protocol assay in tissue samples from 31 upper tract urothelial carcinomas (from 29 patients). The feasibility of identifying cancer using telomerase activity in exfoliated cancer cells in 17 upper tract urothelial washing samples was also investigated.

RESULTS

Telomerase activity was found in 30 (97%) of the 31 upper tract urothelial cancer tissue samples; telomerase activity was detectable in 95% of superficial cancers and in all 11 invasive tumours. The sensitivity of measuring telomerase activity was 100% for grade 1, 93% for grade 2 and 100% for grade 3 tumours. In contrast, telomerase activity was detected in only two (8%) of 26 normal adjacent tissue samples. When the telomerase activity of urothelial washing fluid was compared with that in the corresponding tumours, there was compatible telomerase activity in 15 of the 17 samples. Telomerase activity was more sensitive than voided urine cytology (15%) and washing fluid cytology (53%). In addition, the telomerase activity was high in metastatic lesions.

CONCLUSION

Telomerase activity is present in most upper tract urothelial cancer tissues and may be present at an early stage of carcinogenesis. Telomerase activity can be detected in exfoliated cells in urothelial washing fluids in a high proportion of patients with upper tract urothelial cancer. These results suggest that measuring telomerase activity in the exfoliated cancer cells obtained from urothelial washing could be a potentially useful addition to the conventional diagnostic tools used to identify patients with upper tract urothelial carcinoma.

Primary rhabdomyosarcoma of long bone. A case report

A case of rhabdomyosarcoma of the femur in a 45-year-old man is reported. The patient had a good response to intraarterial chemotherapy and was functionally well 4 years after limb salvage surgery.

Intravenous pretreatment with magnolol protects myocardium against stunning

Magnolol, an antioxidant, has been reported to possess various protective effects on the cardiovascular system. However, its effect on myocardial stunning has not been elucidated. The purpose of this study was to investigate the antistunning effect of magnolol by evaluating the recovery of regional myocardial function after 10-minute coronary artery occlusion in anesthetized, open-chest rabbits. There was no significant hemodynamic change after intravenous infusion of magnolol. Systolic wall thickening fraction (WThF) measured with an epicardial Doppler sensor in animals pretreated with normal saline and vehicle solution remained significantly depressed (60 +/- 7% and 77 +/- 4% of baseline WThF, respectively) 3 hours after coronary artery reperfusion (CAR). Pretreatment with magnolol (10(-7) and 10(-6) g/kg, intravenous infusion) significantly enhanced the recovery of systolic wall thickening fraction (98 +/- 1 and 99 +/- 1% of baseline WThF, respectively) 60 minutes after CAR. This study demonstrated that intravenous pretreatment with magnolol protected myocardium against stunning.

Role of coronary angiography in myxoma patients: a 14-year experience in one medical center

Cardiac myxoma is the most common form of primary heart tumor and often treated with surgical resection without a preoperative angiographic examination for fear of potential risk of sudden death. During the last 14 years, 24 of 38 patients with myxoma underwent coronary angiography. Coronary artery disease (CAD) and other abnormalities were found in 5. Our findings indicated that CAD is not uncommon among the myxoma patients, and coronary angiography should be performed preoperatively in all cases.

Effects of epidural fentanyl on labor pain during the early period of the first stage of induced labor in nulliparous women

BACKGROUND AND PURPOSE

It is generally accepted that epidural injection with local anesthetics and narcotics administered when the cervix has dilated to a diameter exceeding 4 cm can adequately control labor pain. However, many nulliparous women still suffer from labor pain for a few hours prior to the administration of epidural analgesia. This study examined the effectiveness of relief of labor pain obtained by injection of narcotics epidurally once the labor pain begins and the subject requests analgesia.

METHODS

Subjects scheduled for induced labour were divided into three groups: Group A (n = 60) received 5 x 10(-4)% fentanyl (10-20 mL) administered epidurally to relieve early first-stage labor pain. Group B (n = 60) received no analgesic in the early first stage of labor. For groups A and B, when cervical dilatation exceeded 4 cm, 10 to 15 mL of 5 x 10(-2)% bupivacaine and 2 x 10(-4)% fentanyl were injected epidurally and a continuous low dosage was maintained until full dilatation of the cervix resulted. Group C (n = 198) received no analgesic during the entire labor course.

RESULTS

There were no significant differences in the duration of the early period of the first stage of labor, the duration of the late period of the first stage, the duration of the second stage, the Apgar score, or the arterial blood gas of neonates among the three groups. However, group C had a significantly higher cesarean section rate (28.8%) than group A (16.7%) or group B (15%). Pain scores assessed with the Visual Analog Scale (VAS) throughout the entire labor course, were lower in group A than in group B; particularly during the early period of the first stage. The VAS scores in both groups A and B were significantly lower than those in group C during the late period of the first stage of labor.

CONCLUSIONS

The results indicate that once labor pain begins and the subject requests analgesia, epidural injection with fentanyl alone can relieve labor pain during the early period of the first stage. The analgesia does not cause adverse effects to the mothers or neonates. In addition, the labor course and the method of delivery are not affected.

Effect of magnolol on coronary vascular resistance in rabbits: measurement with pulsed Doppler velocimetry

BACKGROUND AND PURPOSE

Magnolol is an active component purified from Magnolia officinalis that has been reported to protect the myocardium against infarction and reperfusion injury. The purpose of this study was to investigate the effect of magnolol on the coronary circulation and to determine whether a change in coronary vascular resistance could be the mechanism underlying its myocardial protective effect.

METHODS

Male New Zealand white rabbits were anesthetized. A 3-mm suction-type pulsed Doppler velocimetry probe was applied to the proximal part of the left anterior descending coronary artery after median sternotomy. The 39 rabbits received intravenous injection of either vehicle (n = 5), magnolol (10(-6) g/kg, n = 6; 10(-5) g/kg, n = 5; 10(-4) g/kg, n = 5), or nitroglycerin (10(-5) g/kg, n = 6; 10(-4) g/kg, n = 6; 10(-3) g/kg, n = 6). The effects of magnolol and nitroglycerin on coronary vascular resistance were compared.

RESULTS

Magnolol did not change blood pressure or coronary blood flow velocity. However, at a dose of 10(-4) g/kg, it decreased coronary vascular resistance significantly more than vehicle (88 +/- 1% vs 95 +/- 1% of baseline coronary vascular resistance, p < 0.001). Nitroglycerin increased coronary blood flow velocity and decreased coronary vascular resistance in a dose-dependent manner (p < 0.01).

CONCLUSIONS

Magnolol reduced coronary vascular resistance in anesthetized, open-chest rabbits only at a high concentration. Its effect was modest compared with that of nitroglycerin. Since magnolol protects the myocardium at relatively low doses, coronary vasodilatation is unlikely to be the underlying mechanism responsible for its myocardial protective effects.

A compound heterozygote in the NADH-cytochrome b5 reductase gene from a Chinese patient with hereditary methemoglobinemia type I

To elucidate the mutation in the nicotinamide adenine dinucleotide-cytochrome b5 reductase (b5R) gene from a Chinese patient with hereditary methemoglobinemia type I, we analyzed the coding sequences of b5R cDNA from the patient and from normal subjects by direct sequencing the reverse transcriptase-polymerase chain reaction (RT-PCR) products. The PCR-amplified genomic DNA fragments of the b5R gene from the patient, his mother, and normal controls were analyzed by restriction enzymes MspI and RsaI. A compound heterozygote Arg57Gln (CGG-->CAG)/Cys203Tyr (TGC-->TAC) was found in the b5R gene from the patient, and a CGG-->CAG mutant allele occurred in a chromosome inherited from his mother, while TGC-->TAC occurred in a chromosome inherited from his father. In this report, we discuss a compound heterozygote first observed in the b5R gene from a patient with hereditary methemoglobinemia type I.

Sequence, organization, and evolution of Rh50 glycoprotein genes in nonhuman primates

The human RHAG locus encodes Rh50 glycoprotein, a polytopic protein that modulates expression of Rh antigens carried by Rh30 polypeptides. Rh50 is almost invariant, whereas Rh30 shows high polymorphism. To assess the relative conservation and phylogenetic relationship of RHAG genes, we characterized their protein expression, transcript structure, genomic organization, and noncoding regions (promoter and introns) in seven nonhuman primate species. Western blot showed that only ape Rh50 glycoproteins are recognized by the antibody 2D10 specific for the human counterpart. Analysis of RHAG gene and its transcript showed a high degree of sequence identity and features of interspecific diversity. The nonhuman primate RHAG genes are highly similar in promoter region and identical in exon-intron organization. Genomic sequencing identified one retro-transposon-like element in intron 2 and three types of Alu elements in intron 4 and 9, with varying copies of minisatellites. Reconstruction of coding and noncoding sequence trees revealed concordances and discordances with regard to the branching of RHAG-like genes in higher primates. A joined tree of Rh50 glycoproteins and Rh30 polypeptides shows that the former evolved at a rate about two times slower than the latter. Statistical tests demonstrated that at least a portion of the RHAG gene was subjected to a positive selection during evolution of anthropoids.

Analysis of ultrahigh molecular weight polyethylene failure in artificial knee joints: thermal effect on long-term performance

The mechanism resulting in damage to and failure of ultrahigh molecular weight polyethylene (UHMWPE) tibial inserts was investigated on clinically retrieved components. The severity of the subsurface damage increased with the length of time that the component had been implanted. A theoretical analysis was developed to account for the generation of subsurface damage based on a heat transfer model. Friction generates surface heat during articulation of total knee systems. Due to the cooling effect of body fluid on the surface, the rise in temperature on the UHMWPE surface is lower than that below the surface. The peak temperature was estimated to occur on a plane positioned about 1 to 2 mm below the surface. This result was similar to the bulk temperature variation observed during in vivo and in vitro studies by other investigators. Although the difference in temperature on and below the surface is only a few degrees, the thermal effect becomes apparent after a long time and may be explained by the viscoelastic behavior of polymers: the temperature-time equivalence. It is therefore suggested that this thermal effect is another contributory factor to material damage, in addition to high stress and oxidative degradation (in appropriate cases). Therefore, any technological efforts aimed at improving the performance of artificial joint prostheses should minimize the thermal effects at the subsurface of the articular components.

Evans antigen: a new hybrid structure occurring on background of D.. and D-- Rh complexes

BACKGROUND AND OBJECTIVES

Previously, the Evans antigen (RH37) of the Rh blood group system was shown to be specified by a novel CE-D-CE hybrid gene. We studied further the heterogeneity of Evans and report here its new molecular type resulting from a novel intraexon fusion event on the background of D. and D-- complexes.

MATERIALS AND METHODS

A white family with 2 Evans+ and 2 Evans- members was analyzed by serological methods and molecular techniques.

RESULTS

The Evans+ proband (JD) typed D+C-c-E-e- and showed a partial loss of RHCE but an increased dose of RHD on DNA blots. On sequencing of Rh cDNAs, a normal D and 3 hybrid transcripts were detected. The D-CE hybrid is characterized by a single breakpoint located in exon 6. The CE-D hybrid derived its exon 1 (or 1 and 2) from RHCE and exons 2-10 (or 3-10) from RHD. The CE-D-CE hybrid had its internal exons 2-7 (or 3-7) from RHD. Family studies showed that the D-CE and CE-D hybrids were linked and cotransmitted from JD to his son, whereas RHD and CE-D-CE hybrid were transmitted from JD to his daughter.

CONCLUSION

In this family, Evans is specified by the novel D-CE intraexon fusion gene which occurs in cis to CE-D and trans to CE-D-CE interexon fusion genes. The observed large duplication of RHD reflects a convergent mosaicism underlying the enhancement of D and ablation of CcEe antigens.

Molecular biology and genetics of the Rh blood group system

The Rh (Rhesus) blood group system is the most complex of the known human blood group polymorphisms. The expression of its antigens is controlled by a two-component genetic system consisting of RH and RHAG loci, which encode Rh30 polypeptides and Rh50 glycoprotein, respectively. Over the past decade, there has been a rapid advance in knowledge of the biochemistry, molecular biology, and genetics of the Rh genes and proteins. The primary structures of D and CcEe antigens have become well understood and the molecular genetic basis of a vast array of phenotype polymorphisms has been delineated. The identification of various molecular defects associated with Rh deficiency syndrome clarifies the nature of the amorph, suppressor, and modifier genes. The observed mutation spectrum defines a basic set of components essential for Rh complex assembly in the erythrocyte membrane. The resulting molecular information, combined with new experimental tools, is helping to dissect the fine structure of Rh antigens in terms of epitope mapping. The discovery of novel Rh homologs in primitive organisms and in nonerythroid tissues opens new avenues of research beyond the scope of erythrocytes and Rh antigens. This review provides an update on the Rh family in antigen expression, phenotype diversity, and disease association.

Raman spectroscopic study of polycrystalline mono- and polyunsaturated 1-eicosanoyl-d(39)-2-eicosenoyl-sn-glycero-3-phosphocholines: bilayer lipid clustering and acyl chain order and disorder characteristics

Polycrystalline lipid samples of a series of mono- and polyunsaturated, double bond positional isomers of 1-eicosanoyl-d(39)-2-eicosenoyl-sn-glycero-3-phosphocholines [C(20-d(39)):C(20:1 Delta(j))PC, with j = 5, 8, 11, or 13; C(20-d(39)):C(20:2 Delta(11,14))PC; and C(20-d(39)):C(20:3 Delta(11, 14,17))PC] were investigated using vibrational Raman spectroscopy to assess the acyl chain packing order-disorder characteristics and putative bilayer cluster formation of the isotopically differentiated acyl chains. Perdeuteration of specifically the saturated sn-1 acyl chains for these bilayer systems enables each chain's intra- and intermolecular conformational and organizational properties to be evaluated separately. Various saturated chain methylene CD(2) and carbon-carbon (C&bond;C) stretching mode peak height intensity ratios and line width parameters for the polycrystalline samples demonstrate a high degree of sn-1 chain order that is unaffected by either the double bond placement or number of unsaturated bonds within the sn-2 chain. In contrast, the unsaturated sn-2 chain spectral signatures reflect increasing acyl chain conformational disorder as either the cis double bond is generally repositioned toward the chain terminus or the number of double bonds increases from one to three. The lipid bilayer chain packing differences observed between the sn-1 and sn-2 chains of this series of monounsaturated and polyunsaturated 20 carbon chain lipids suggest the existence of laterally distributed microdomains predicated on the formation of highly ordered, saturated sn-1 chain clusters.

Fabrication and Characterization of a New Self-Assembled Monolayer of Fullerene Dicarboxylic Acid Derivative and Its Photoelectric Conversion Property

A new fullerene self-assembled monolayer (SAM) which has the property of photoelectric conversion is reported here. The SAM was fabricated on hydrophilic substrates by an esterification reaction. The SAM is characterized by contact angle, AFM, UV spectrum, and cyclic voltammetry. A cathodic photocurrent of 226 nA/cm(2) was obtained. Copyright 2000 Academic Press.

Characterization of the functional role of Asp141, Asp194, and Asp464 residues in the Mn2+-L-malate binding of pigeon liver malic enzyme

Pigeon liver malic enzyme was inactivated and cleaved at Asp141, Asp194, and Asp464 by the Cu2+-ascorbate system in acidic environment. Site-specific mutagenesis was performed at these putative metal-binding sites. Three point mutants, D141N, D194N, and D464N; three double mutants, D(141,194)N, D(194,464)N, and D(141,464)N; and a triple mutant, D(141,194,464)N; as well as the wild-type malic enzyme (WT) were successfully cloned and expressed in Escherichia coli cells. All recombinant enzymes, except the triple mutant, were purified to apparent homogeneity by successive Q-Sepharose and adenosine-2',5'-bisphosphate-agarose columns. The mutants showed similar apparent Km,NADP values to that of the WT. The Km,Mal value was increased in the D141N and D194N mutants. The Km,Mn value, on the other hand, was increased only in the D141N mutant by 14-fold, corresponding to approximately 1.6 kcal/mol for the Asp141-Mn2+ binding energy. Substrate inhibition by L-malate was only observed in WT, D464N, and D(141,464)N. Initial velocity experiments were performed to derive the various kinetic parameters. The possible interactions between Asp141, Asp194, and Asp464 were analyzed by the double-mutation cycles and triple-mutation box. There are synergistic weakening interactions between Asp141 and Asp194 in the metal binding that impel the D(141,194)N double mutant to an overall specificity constant [k(cat)/(Kd,Mn Km,Mal Km,NADP)] at least four orders of magnitude smaller than the WT value. This difference corresponds to an increase of 6.38 kcal/mol energy barrier for the catalytic efficiency. Mutation at Asp464, on the other hand, has partial additivity on the mutations at Asp141 and Asp194. The overall specificity constants for the double mutants D(194,464)N and D(141,464)N or the triple mutant D(141,194,464)N were decreased by only 10- to 100-fold compared to the WT. These results strongly suggest the involvement of Asp141 in the Mn2+-L-malate binding for the pigeon liver malic enzyme. The Asp194 and Asp464, which may be oxidized by nonspecific binding of Cu2+, are involved in the Mn2+-L-malate binding or catalysis indirectly by modulating the binding affinity of Asp141 with the Mn2+.

Sinus node dysfunction in a patient with lithium intoxication

Lithium can suppress sinus node function, especially when it is used concomitantly with carbamazepine. We describe a 42-year-old woman who took lithium and carbamazepine for manic-depressive psychosis and seizure disorders, and developed marked sinus node dysfunction. Drug screening showed a toxic serum lithium level of 3.38 mmol/L and a normal serum carbamazepine level of 22.1 mumol/L. An electrophysiologic study showed prolongation of the corrected sinus node recovery time (CSNRT) of up to 9,708 msec. After three sessions of hemodialysis, normal sinus rhythm was resumed. The serum lithium level was 0.1 mmol/L 2 weeks later, and the CSNRT shortened to 309 msec. Because the combination of lithium and carbamazepine in psychiatric patients is not uncommon, recognition of the potential complication of severe bradyarrhythmia is essential in the emergency care of such patients.