Analysis of training-induced changes in ethyl acetate odor maps using a new computational tool to map the glomerular layer of the olfactory bulb

Odor quality is thought to be encoded by the activation of partially overlapping subsets of glomeruli in the olfactory bulb (odor maps). Mouse genetic studies have demonstrated that olfactory sensory neurons (OSNs) expressing a particular olfactory receptor target their axons to a few individual glomeruli in the bulb. While the specific targeting of OSN axons provides a molecular underpinning for the odor maps, much remains to be understood about the relationship between the functional and molecular maps. In this article, we ask the question whether intensive training of mice in a go/no-go operant conditioning odor discrimination task affects odor maps measured by determining c-fos up-regulation in periglomerular cells. Data analysis is performed using a newly developed suite of computational tools designed to systematically map functional and molecular features of glomeruli in the adult mouse olfactory bulb. This suite provides the necessary tools to process high-resolution digital images, map labeled glomeruli, visualize odor maps, and facilitate statistical analysis of patterns of identified glomeruli in the olfactory bulb. The software generates odor maps (density plots) based on glomerular activity, density, or area. We find that training up-regulates the number of glomeruli that become c-fos positive after stimulation with ethyl acetate.

Severe acute exacerbations and mortality in patients with chronic obstructive pulmonary disease

BACKGROUND

Patients with chronic obstructive pulmonary disease (COPD) often present with severe acute exacerbations requiring hospital treatment. However, little is known about the prognostic consequences of these exacerbations. A study was undertaken to investigate whether severe acute exacerbations of COPD exert a direct effect on mortality.

METHODS

Multivariate techniques were used to analyse the prognostic influence of acute exacerbations of COPD treated in hospital (visits to the emergency service and admissions), patient age, smoking, body mass index, co-morbidity, long term oxygen therapy, forced spirometric parameters, and arterial blood gas tensions in a prospective cohort of 304 men with COPD followed up for 5 years. The mean (SD) age of the patients was 71 (9) years and forced expiratory volume in 1 second was 46 (17)%.

RESULTS

Only older age (hazard ratio (HR) 5.28, 95% CI 1.75 to 15.93), arterial carbon dioxide tension (HR 1.07, 95% CI 1.02 to 1.12), and acute exacerbations of COPD were found to be independent indicators of a poor prognosis. The patients with the greatest mortality risk were those with three or more acute COPD exacerbations (HR 4.13, 95% CI 1.80 to 9.41).

CONCLUSIONS

This study shows for the first time that severe acute exacerbations of COPD have an independent negative impact on patient prognosis. Mortality increases with the frequency of severe exacerbations, particularly if these require admission to hospital.

[Ischemic stroke and sleep apnea. Relationship between sleep breathing disorders and carotid stenosis]

OBJECTIVE

To investigate the possible relation between the number of sleep breathing disorders (SBD) and significant extracranial carotid stenosis (ECS) in patients suffering ischemic stroke or transient ischemic attack (TIA).

PATIENTS AND METHODS

Sixty-eight patients (72.2 years; 68 % males) surviving two months after ischemic stroke or TIA were studied, with the collection of general and anthropometric variables, the characteristics and repercussions of stroke, and the clinical manifestations related to sleep apnea-hypopnea syndrome (SAHS). Neurovascular status was evaluated by carotid continuous doppler flowmetry and transcraneal doppler, with cerebral MR-angio and/or arteriography when suspecting stenosis > 50 %, and respiratory polygraphy after the acute phase to assess the number and type of SBD.

RESULTS

Fifteen patients (22.1 %) presented ECS. Of these, 80 % had an apnea-hypopnea index (AHI) > 30. The patients with ECS presented increased drowsiness (p = 0.01), greater AHI (36.2 vs 21.9; p = 0.003), and increased nocturnal oxygen desaturation (p = 0.01). Arterial hypertension (AHT) was also significantly more prevalent in this group of patients (p = 0.003), as was diabetes mellitus (p = 0.01) and hypercholesterolemia (p = 0.02) though logistic regression analysis only showed AHT (odds ratio [OR]: 12,7) and AHI > 30 (OR: 13,6) to exhibit independent ECS predictive capacity.

CONCLUSIONS

The presence of numerous SBD is predictive of ECS, independently of the presence of AHT. Patients with ECS have more SAHS related clinical manifestations prior to stroke; as a result, SAHS could be anterior to the neurological event and act as a risk factor for the latter in this group of patients.

Molecular basis for ultraviolet vision in invertebrates

Invertebrates are sensitive to a broad spectrum of light that ranges from UV to red. Color sensitivity in the UV plays an important role in foraging, navigation, and mate selection in both flying and terrestrial invertebrate animals. Here, we show that a single amino acid polymorphism is responsible for invertebrate UV vision. This residue (UV: lysine vs blue:asparagine or glutamate) corresponds to amino acid position glycine 90 (G90) in bovine rhodopsin, a site affected in autosomal dominant human congenital night blindness. Introduction of the positively charged lysine in invertebrates is likely to deprotonate the Schiff base chromophore and produce an UV visual pigment. This same position is responsible for regulating UV versus blue sensitivity in several bird species, suggesting that UV vision has arisen independently in invertebrate and vertebrate lineages by a similar molecular mechanism.

Heterologous expression of limulus rhodopsin

Invertebrates such as Drosophila or Limulus assemble their visual pigment into the specialized rhabdomeric membranes of photoreceptors where phototransduction occurs. We have investigated the biosynthesis of rhodopsin from the Limulus lateral eye with three cell culture expression systems: mammalian COS1 cells, insect Sf9 cells, and amphibian Xenopus oocytes. We extracted and affinity-purified epitope-tagged Limulus rhodopsin expressed from a cDNA or cRNA from these systems. We found that all three culture systems could efficiently synthesize the opsin polypeptide in quantities comparable with that found for bovine opsin. However, none of the systems expressed a protein that stably bound 11-cis-retinal. The protein expressed in COS1 and Sf9 cells appeared to be misfolded, improperly localized, and proteolytically degraded. Similarly, Xenopus oocytes injected with Limulus opsin cRNA did not evoke light-sensitive currents after incubation with 11-cis-retinal. However, injecting Xenopus oocytes with mRNA from Limulus lateral eyes yielded light-dependent conductance changes after incubation with 11-cis-retinal. Also, expressing Limulus opsin cDNA in the R1-R6 photoreceptors of transgenic Drosophila yielded a visual pigment that bound retinal, had normal spectral properties, and coupled to the endogenous phototransduction cascade. These results indicate that Limulus opsin may require one or more photoreceptor-specific proteins for correct folding and/or chromophore binding. This may be a general property of invertebrate opsins and may underlie some of the functional differences between invertebrate and vertebrate visual pigments.

A bifunctional dihydrofolate synthetase--folylpolyglutamate synthetase in Plasmodium falciparum identified by functional complementation in yeast and bacteria

Folate metabolism in the human malaria parasite Plasmodium falciparum is an essential activity for cell growth and replication, and the target of an important class of therapeutic agents in widespread use. However, resistance to antifolate drugs is a major health problem in the developing world. To date, only two activities in this complex pathway have been targeted by antimalarials. To more fully understand the mechanisms of antifolate resistance and to identify promising targets for new chemotherapies, we have cloned genes encoding as yet uncharacterised enzymes in this pathway. By means of complementation experiments using 1-carbon metabolism mutants of both Escherichia coli and Saccharomyces cerevisiae, we demonstrate here that one of these parasite genes encodes both dihydrofolate synthetase (DHFS) and folylpolyglutamate synthetase (FPGS) activities, which catalyse the synthesis and polyglutamation of folate derivatives, respectively. The malaria parasite is the first known example of a eukaryote encoding both DHFS and FPGS activities in a single gene. DNA sequencing of this gene in antifolate-resistant strains of P. falciparum, as well as drug-inhibition assays performed on yeast and bacteria expressing PfDHFS--FPGS, indicate that current antifolate regimes do not target this enzyme. As PfDHFS--FPGS harbours two activities critical to folate metabolism, one of which has no human counterpart, this gene product offers a novel chemotherapeutic target with the potential to deliver a powerful blockage to parasite growth.

Characterization of three genes encoding enzymes of the folate biosynthetic pathway in Plasmodium falciparum

Although the folate metabolic pathway in malaria parasites is a major chemotherapeutic target, resistance to currently available antifolate drugs is an increasing problem. This pathway, however, includes a number of enzymes that, to date, have not been characterized despite their potential for clinical exploitation. As a step towards evaluation of additional targets in this pathway, we report the isolation and characterization of 3 new genes that encode homologues of GTP cyclohydrolase I (GTP-CH), dihydrofolate synthase/folylpolyglutamate synthase (DHFS/FPGS) and serine hydroxymethyltransferase (SHMT). The genes encoding GTP-CH and SHMT are unambiguously assigned to chromosome 12, while that for DHFS/FPGS is tentatively assigned to chromosome 13. All 3 genes are expressed in blood-stage parasites, yielding transcripts of which only ca 60-70% is accounted for by coding sequence. All 3 of the proteins predicted to be encoded by these genes display sequence differences compared to the human host homologues that may be of functional significance. These data bring the complement of cloned genes that encode activities in the pathway to seven, leaving only the gene encoding dihydroneopterin aldolase (DHNA) to be identified in the route from GTP to folate synthesis and folate turnover in the thymidylate cycle.

Should the angiotensin II antagonists be discontinued before surgery?

Angiotensin II antagonists (AIIA) are part of a new rational treatment of hypertension. Because adverse circulatory effects during anesthesia can occur in patients chronically treated with angiotensin-converting enzyme inhibitors, some clinicians discontinue them at least 24 h before operation. No data are available concerning AIIA administration in patients scheduled for vascular surgery performed under general anesthesia. The aim of this prospective randomized study was to compare hemodynamics during induction of anesthesia in patients chronically treated with AIIA and those of patients not receiving this drug on the morning before operation. Thirty-seven patients chronically treated with AIIA for hypertension were randomly assigned to two groups: Group I: AIIA discontinued on the day before surgery (n = 18); Group II: AIIA given 1 h before anesthesia (n = 19). Patients received sufentanil 0.4 microg/kg, propofol 1.5 mg/kg, and atracurium 0.5 mg/kg. During the procedure, the anesthesiologist was required to maintain systolic blood pressure and heart rate within 30% of baseline values using intravascular fluid administration and vasoconstric- tors (e.g. , ephedrine, phenylephrine, or terlipressin). Hemodynamic variables were recorded each 1 min. Hemodynamic study ended at incision. The number and duration of hemodynamic events were collected, and total doses of vasoactive drugs were noted in each group. Systolic arterial pressure was significantly decreased in Group II at 5, 15 and 23 min after induction of anesthesia (*P < 0.05). In this group, the decrease in systolic arterial pressure was associated with more frequent episodes of hypotension (AIIA withdrawn: 1 +/- 1; AIIA given: 2 +/- 1; P < 0.01), with a larger number of patients developing at least 1 episode of hypotension (AIIA withdrawn: 12; AIIA given: 19; P < 0.01), and a longer duration of an episode of hypotension (AIIA withdrawn: 3 +/- 4 min; AIIA given: 8 +/- 7 min; P < 0.01), and an increased need for vasoactive drugs. In conclusion, blockade of the renin-angiotensin system increases the potential hypotensive effect of anesthetic induction. A severe hypotensive episode, requiring vasoconstrictor treatment, occurs after induction of general anesthesia in patients chronically treated with AIIA. Recommendations to discontinue AIIA drugs on the day before the surgery may be justified.

IMPLICATIONS

This prospective randomized study demonstrated that more severe hypotensive episodes, requiring vasoconstrictor treatment, occur after induction of general anesthesia in patients chronically treated with AIIA and receiving this drug on the morning before operation, in comparison with those in whom AIIA were discontinued on the day before operation. Recommendations to discontinue these drugs on the day before the surgery may be justified.

Characterization of the primary photointermediates of Drosophila rhodopsin

Invertebrate opsins are unique among the visual pigments because the light-activated conformation, metarhodopsin, is stable following exposure to light in vivo. Recovery of the light-activated pigment to the dark conformation (or resting state) occurs either thermally or photochemically. There is no evidence to suggest that the chromophore becomes detached from the protein during any stage in the formation or recovery processes. Biochemical and structural studies of invertebrate opsins have been limited by the inability to express and purify rhodopsins for structure-function studies. In this study, we used Drosophila to produce an epitope-tagged opsin, Rh1-1D4, in quantities suitable for spectroscopic and photochemical characterization. When expressed in Drosophila, Rh1-1D4 is localized to the rhabdomere membranes, has the same spectral properties in vivo as wild-type Rh1, and activates the phototransduction cascade in a normal manner. Purified Rh1-1D4 visual pigment has an absorption maximum of the dark-adapted state of 474 nm, while the metarhodopsin absorption maximum is 572 nm. However, the metarhodopsin state is not stable as purified in dodecyl maltoside but decays with kinetics that require a double-exponential fit having lifetimes of 280 and 2700 s. We investigated the primary properties of the pigment at low temperature. At 70 K, the pigment undergoes a temperature-induced red shift to 486 nm. Upon illumination with 435 nm light, a photostationary state mixture is formed consisting of bathorhodopsin (lambda(max) = 545 nm) and isorhodopsin (lambda(max) = 462 nm). We also compared the spectroscopic and photochemical properties of this pigment with other vertebrate pigments. We conclude that the binding site of Drosophila rhodopsin is similar to that of bovine rhodopsin and is characterized by a protonated Schiff base chromophore stabilized via a single negatively charged counterion.

Blue- and green-absorbing visual pigments of Drosophila: ectopic expression and physiological characterization of the R8 photoreceptor cell-specific Rh5 and Rh6 rhodopsins

Color discrimination requires the input of different photoreceptor cells that are sensitive to different wavelengths of light. The Drosophila visual system contains multiple classes of photoreceptor cells that differ in anatomical location, synaptic connections, and spectral sensitivity. The Rh5 and Rh6 opsins are expressed in nonoverlapping sets of R8 cells and are the only Drosophila visual pigments that remain uncharacterized. In this study, we ectopically expressed Rh5 and Rh6 in the major class of photoreceptor cells (R1-R6) and show them to be biologically active in their new environment. The expression of either Rh5 or Rh6 in "blind" ninaE(17) mutant flies, which lack the gene encoding the visual pigment of the R1-R6 cells, fully rescues the light response. Electrophysiological analysis showed that the maximal spectral sensitivity of the R1-R6 cells is shifted to 437 or 508 nm when Rh5 or Rh6, respectively, is expressed in these cells. These spectral sensitivities are in excellent agreement with intracellular recordings of the R8p and R8y cells measured in Calliphora and Musca. Spectrophotometric analyses of Rh5 and Rh6 in vivo by microspectrophotometry, and of detergent-extracted pigments in vitro, showed that Rh5 is reversibly photoconverted to a stable metarhodopsin (lambda(max) = 494 nm), whereas Rh6 appears to be photoconverted to a metarhodopsin (lambda(max) = 468 nm) that is less thermally stable. Phylogenetically, Rh5 belongs to a group of short-wavelength-absorbing invertebrate visual pigments, whereas Rh6 is related to a group of long-wavelength-absorbing pigments and is the first member of this class to be functionally characterized.

Histopathologic and immunohistochemical diagnosis of benign and malignant fibrous and fibrohistiocytic tumors of the skin

This article describes the histopathology and immunohistochemistry of benign and malignant fibrous and fibrohistiocytic tumors. Some of the benign fibrohistiocytic proliferation's have atypical variants which could be misinterpreted as malignant processes. Key points for the diagnosis of these entities based on routine histology and immunohistochemistry are presented.

[Hyponatremia in the postoperative period after a neurosurgical tumor condition]

A four-year-old girl suffered difficult-to-diagnose hyponatremia resistant to treatment following surgery for a suprasellar tumor. The final diagnosis was diabetes insipidus evolving in three stages. Hyponatremia is a common problem following surgery to remove brain tumors. Early diagnosis and treatment of this electrolytic imbalance are essential for preventing serious neurological symptoms or death. The conditions most closely related to hyponatremia are inappropriate antidiuretic hormone secretion syndrome (IADHSS) and cerebral salt wasting syndrome (CSWS). The latter has become more common in recent years among patients undergoing brain surgery. Whereas IADHSS is treated by restricting fluids, CSWS requires administration of salt and volume fluid volume. We believe that for differential diagnosis of postoperative hyponatremia, a fluid restriction test takes priority over of fluid loading following neurosurgery. The course of hyponatremia must be carefully monitored and a complete endocrinological workup must be performed to detect the possible presence of hypophyseal deficiencies, particularly hypothyroidism and suprarenal insufficiency.

Honeybee blue- and ultraviolet-sensitive opsins: cloning, heterologous expression in Drosophila, and physiological characterization

The honeybee (Apis mellifera) visual system contains three classes of retinal photoreceptor cells that are maximally sensitive to light at 440 nm (blue), 350 nm (ultraviolet), and 540 nm (green). We performed a PCR-based screen to identify the genes encoding the Apis blue- and ultraviolet (UV)-sensitive opsins. We obtained cDNAs that encode proteins having a high degree of sequence and structural similarity to other invertebrate and vertebrate visual pigments. The Apis blue opsin cDNA encodes a protein of 377 amino acids that is most closely related to other invertebrate visual pigments that are thought to be blue-sensitive. The UV opsin cDNA encodes a protein of 371 amino acids that is most closely related to the UV-sensitive Drosophila Rh3 and Rh4 opsins. To test whether these novel Apis opsin genes encode functional visual pigments and to determine their spectral properties, we expressed them in the R1-6 photoreceptor cells of blind ninaE mutant Drosophila, which lack the major opsin of the fly compound eye. We found that the expression of either the Apis blue- or UV-sensitive opsin in transgenic flies rescued the visual defect of ninaE mutants, indicating that both genes encode functional visual pigments. Spectral sensitivity measurements of these flies demonstrated that the blue and UV visual pigments are maximally sensitive to light at 439 and 353 nm, respectively. These maxima are in excellent agreement with those determined previously by single-cell recordings from Apis photoreceptor cells and provide definitive evidence that the genes described here encode visual pigments having blue and UV sensitivity.

Left ventricular volume calculation with integrated backscatter from echocardiography

Integrated backscatter analysis (IB) is a new echocardiographic method for automatically differentiating tissue from blood on the basis of differences in the amplitude of reflected ultrasound. Left ventricular volume was estimated with IB by use of a modification of Pappus' theorem and a summated ellipsoid method. IB measurements correlated well with a standard biplane area-length method derived off-line from endocardial borders drawn by hand from the same echocardiographic data (y = 1.09 x - 35, r = 0.95). Integrated backscatter measurement of ventricular volume derived from six imaging planes with both the Pappus' rule and the summated ellipsoid methods correlated well with magnetic resonance imaging volume estimates (r = 0.91 and r = 0.90, respectively), whereas use of one imaging plane correlated less well (r = 0.75). Automated analysis of integrated backscatter differentiates tissue from blood sufficiently to allow accurate volume calculations compared with magnetic resonance imaging and to standard hand-drawn echo techniques. This method provides accurate measurement of left ventricular volumes that should be useful in clinical hemodynamic assessments.

Visualization of acute pulmonary emboli by transesophageal echocardiography

This report describes a patient who became hypoxic and hypotensive while awaiting cardiac surgery. An urgent transesophageal echocardiogram in the operating room showed a mass at the junction of the main and right pulmonary arteries consistent with thrombus. The thrombus was removed surgically, and the patient then had a successful aortic valve replacement. Transesophageal echocardiography is therefore useful in the evaluation of the critically ill patient.

Computer-assisted versus unassisted analysis of the exercise electrocardiogram in patients without myocardial infarction

Computer-assisted interpretation of the exercise electrocardiogram has been advocated to improve the accuracy of diagnosing coronary artery disease. Its accuracy was compared with a blinded visual interpretation of exercise-induced ST depression in 271 consecutive subjects without prior myocardial infarction who were referred for coronary angiography. The sensitivity of the visual and computer readings was 0.51 and 0.51, respectively, at a specificity of 0.87. Receiver operating characteristic curves were generated for the visual and computer ST depression in lead V5. Analysis of the areas under these curves showed no significant difference between them, indicating that computer-assisted analysis was not superior to unmodified visual analysis. A similar analysis was applied to two other computer indexes reported to be superior to visual assessments (treadmill exercise score and ST index). These computer indexes were not superior to a conventional visual analysis of leads I, II, V2, V4 and V5 in predicting severe disease (greater than 50% luminal narrowing). These results suggest that computer-assisted interpretation does not improve the accuracy of exercise electrocardiography in diagnosing coronary artery disease in subjects without prior myocardial infarction.

Exercise electrocardiographic variables: a critical appraisal

To compare four recently proposed methods of analyzing the exercise electrocardiogram with the conventional analysis of ST segment depression, 303 consecutive patients without myocardial infarction who had been referred for coronary arteriography underwent stress electrocardiography and stress thallium imaging. The specificity for the prediction of a greater than 50% coronary obstruction of 0.5, 1.0, 1.5 and 2.0 mm ST segment depression measured in the conventional way was 0.59, 0.73, 0.88 and 0.94, respectively. The specificity of a thallium perfusion defect was 0.79. Sensitivities of the conventional ST depressions, thallium defect, the change in the sum of the R amplitudes and the slope adjusted for heart rate increase were calculated and compared at the cited levels of specificity. R wave changes had a significantly lower sensitivity than did the conventionally analyzed ST depression at each level of specificity. Slope-adjusted ST depression had a slightly higher sensitivity than that of conventional ST depression only at a specificity of 0.73 (0.68 versus 0.65, p = 0.07). R wave-adjusted ST depression was significantly more sensitive than conventional ST depression only at a specificity of 0.94 (0.45 versus 0.36, p = 0.01). Heart rate-adjusted ST depression was more sensitive than conventional ST depression at all of the specificities except 0.59. This pattern of superior accuracy of heart rate-adjusted ST depressions was preserved for the prediction of multivessel coronary disease. Heart rate adjustment is a simpler and more accurate modification of the conventional electrocardiographic analysis than are the other three methods studied.

Amaurosis fugax in a patient with a left ventricular endocardial pacemaker

A transvenous left ventricular endocardial pacemaker catheter is a potential source of systemic arterial embolization. The case of a woman who presented with left-eye amaurosis fugax is reported. The patient had a history of contralateral carotid atherosclerosis; however, the digital subtraction angiography of the carotid arteries was not sufficiently abnormal to account for her present symptoms. The patient had a history of two myocardial infarctions and the tachycardia-bradycardia syndrome for which she was treated with a demand ventricular pacemaker. The chest x-ray and electrocardiogram suggested pacemaker catheter malposition. By M-mode and two-dimensional echocardiography, the catheter was shown to cross the atrial septum and the mitral valve to implant in the left ventricular endocardium. The approach to diagnosis and therapy that led to surgical removal of the pacing catheter is presented. The causes of the electrocardiographic right bundle branch block pattern in cardiac pacing and the usefulness of echocardiography in evaluating pacing catheters are discussed.

Cardiac function in adolescents and young adults with anorexia nervosa

Twelve patients with anorexia nervosa (mean age 17.6 years) underwent noninvasive cardiac evaluation. All patients had normal sinus rhythm at rest, during exercise, and following 24-hr electrocardiographic monitoring. The chest roentgenograms demonstrated a small heart secondary to a loss of left ventricular mass. Three of four patients studied had left ventricular mass measurements less than 100 g (normal is 90-360 g). Most patients had an elevated heart rate response to exercise with a slightly blunted systolic and a normal diastolic blood pressure response. Eleven of the 12 patients had reduced overall maximal working capacity. All but one had normal left ventricular ejection fraction at rest. There was no evidence of arrhythmias at rest, during exercise, or with continuous electrocardiographic recording. Young patients with anorexia nervosa appeared to have essentially normal cardiac function with a reduction in left ventricular muscle mass.

Acute effects of hemodialysis on echographic-determined cardiac performance: improved contractility resulting from serum increased calcium with reduced potassium despite hypovolemic-reduced cardiac output

The hemodialysis session leads to reduction in circulating blood volume (TBV) and arterial pressure (BP) plus correction of electrolyte imbalance. The effect of these alterations on cardiac performance was evaluated in 18 patients with end-stage renal disease. Hemodialysis for 5 hours led to significant reduction (p less than 0.001) in weight TBV, and BP. Neither ejection fraction nor percentage fiber shortening was altered, whereas mean velocity of circumferential fiber shortening (mean VCF) and mean systolic ejection rate (MSER) were both significantly increased (1.17 +/- 0.20 to 1.38 +/- 0.28 circ/sec and 2.38 +/- 0.27 to 2.80 +/- 0.40 EDV/sec, respectively; p less than 0.001 for each). Since both venous return and systolic BP were decreased, increase in velocity of ventricular contraction implies enhancement of cardiac performance beyond what would be expected from alterations in ventricular filling and resistance to ejection. This enhancement is possibly related to concomitant reduction in serum potassium (p less than 0.001) and increase in serum calcium (p less than 0.005) achieved by hemodialysis.