The effect of changing excitation frequency on parallel conductance in different sized hearts

OBJECTIVE: An important component of the ventricular volume measured using the conductance catheter technique is due to parallel conductance (Vc), which results from the extension of the electric field beyond the ventricular blood pool. Parallel conductance volume is normally estimated using the saline dilution method (Vc(saline dilution)), in which the conductivity of blood in the ventricle is transiently increased by injection of hypertonic saline. A simpler alternative has been reported by Gawne et al. [12]. Vc(dual frequency) is estimated from the difference in total conductance measured at two exciting frequencies and the method is based on the assumption that parallel conductance is mainly capacitive and hence is negligible at low frequency. The objective of this study was to determine whether the dual frequency technique could be used to substitute the saline dilution method to estimate Vc in different sized hearts. METHODS: The accuracy and linearity of a custom-built conductance catheter (CC) system was initially assessed in vitro. Subsequently, a CC and micromanometer were inserted into the left ventricle of seven 5 kg pigs (group 1) and six 50 kg pigs (group 2). Cardiac output was determined using thermodilution (group 1) and an ultrasonic flow probe (group 2) from which the slope coefficient (alpha) was determined. Steady state measurements and Vc estimated using saline dilution were performed at frequencies in the range of 5-40 kHz. All measurements were made at end-expiration. Finally, Vc was estimated from the change in end-systolic conductance between 5 kHz and 40 kHz using the dual frequency technique of Gawne et al. [12]. RESULTS: There was no change in measured volume of a simple insulated cylindrical model when the stimulating frequency was varied from 5-40 kHz. Vc(saline dilution) varied significantly with frequency in group 1 (8.63 +/- 2.74 ml at 5 kHz; 11.51 +/- 2.65 ml at 40 kHz) (p = 0.01). Similar results were obtained in group 2 (69.43 +/- 27.76 ml at 5 kHz; 101.24 +/- 15.21 ml at 40 kHz) (p < 0.001). However, the data indicate that the resistive component of the parallel conductance is substantial (Vc at 0 Hz estimated as 8.01 ml in group 1 and 62.3 ml in group 2). There was an increase in alpha with frequency in both groups but this did not reach significance. The correspondence between Vc(dual frequency) and Vc(saline dilution) methods was poor (group 1 R2 = 0.69; group 2 R2 = 0.22). CONCLUSION: At a lower excitation frequency of 5 kHz a smaller percentage of the electric current extends beyond the blood pool so parallel conductance is reduced. While parallel conductance is frequency dependent, it has a substantial resistive component. The dual frequency method is based on the assumption that parallel conductance is negligible at low frequencies and this is clearly not the case. The results of this study confirm that the dual frequency technique cannot be used to substitute the saline dilution technique.     

Suc-Phe-Leu-Phe-SBzl--a new substrate for functional study of Escherichia coli ATP-dependent Lon-proteinase and its modified forms

A new efficient substrate, Suc-Phe-Leu-Phe-SBzl, was proposed for studying the function of the Escherichia coli ATP-dependent Lon protease and its modified forms. The kinetic parameters of hydrolysis of the substrate were determined. The esterase activity of protease Lon was found to be nucleotide-regulated.     

A Golgi localization signal identified in the Menkes recombinant protein

Menkes disease arises from a genetic impairment in copper transport. The gene responsible for the phenotype has been identified as a copper transporting ATPase ( ATP7A ). Recently, the protein encoded by the ATP7A gene has been localized to the Golgi complex. In order to investigate the role of the Menkes disease protein in copper transport, recombinant constructs containing both the full-length open reading frame and an alternatively spliced form have been successfully expressed and localized in mammalian cells. Other studies of a patient with occipital horn syndrome, an allelic variant of Menkes disease, have demonstrated that only this alternatively spliced isoform and not the full-length form is expressed in this patient. The milder form of this patient's phenotype suggests that the alternatively spliced isoform has some functional role in copper transport. In the present study the full-length recombinant Menkes protein was shown by immunofluorescence to localize to the Golgi apparatus and the alternatively spliced form, lacking sequences for transmembrane domains 3 and 4 encoded by exon 10, was shown to localize to the endoplasmic reticulum. Using sequences from exon 10 fused to a non-Golgi reporter molecule, a 38 amino acid sequence containing transmembrane domain 3 of the Menkes protein was found to be sufficient for localization to the Golgi complex. Therefore, the protein sequence encoded by exon 10 may be responsible for this differential localization and both isoforms may be required for comprehensive transport of copper within the cell.     

Sequential assignment of 1H, 15N, 13C resonances and secondary structure of human calmodulin-like protein determined by NMR spectroscopy

Human calmodulin-like protein (CLP) is closely related to vertebrate calmodulin, yet its unique cell specific expression pattern, overlapping but divergent biochemical properties, and specific target proteins suggest that it is not an isoform of calmodulin. To gain insight into the structural differences that may underlie the difference target specificities and biochemical properties of CLP when compared to calmodulin, we determined the sequential backbone assignment and associated secondary structure of 144 out of the 148 residues of Ca2+-CLP by using multinuclear multidimensional NMR spectroscopy. Despite a very high overall degree of structural similarity between CLP and calmodulin, a number of significant differences were found mainly in the length of alpha-helices and in the central nonhelical flexible region. Interestingly, the regions of greatest primary sequence divergence between CLP and calmodulin in helices III and VIII displayed only minor secondary structure differences. The data suggest that the distinct differences in target specificity and biochemical properties of CLP and calmodulin result from the sum of several minor structural and side-chain changes spread over multiple domains in these proteins.     

Toxic shock syndrome in 8 children

OBJECTIVE: Evaluation of patients with toxic shock syndrome (TSS) in a paediatric hospital. DESIGN: Retrospective analysis. SETTING: Paediatric Intensive Care Unit, University Hospital, Rotterdam, the Netherlands. METHOD: Analysis of the medical records on 155 patients admitted between January 1982 and January 1992 suffering from shock, 8 of whom had TSS. RESULTS: Five out of 8 TSS patients were under 5 years of age. All the patients needed mechanical ventilation. All patients survived. In 7 patients a probably causative focus of infection was found. The cultures of 6 patients showed growth of Staphylococcus aureus, those of 2 patients showed Lancefield group A beta-haemolytic streptococci (bacterial culture in one, increased antibody titer in the other). Systematic phage typing was not performed. CONCLUSION: Although TSS is a relatively rare disease in young children, it is a potentially lethal one, early recognition of which is very important.     

Inactivity of N229A thymidylate synthase due to water-mediated effects: isolating a late stage in methyl transfer

Mutation of thymidylate synthase N229(177) to alanine results in an essentially inactive enzyme, yet it leads to formation of a stable ternary complex. The kinetics of N229(177)A show that kcat for Escherichia coli is reduced by 200-fold while the Km for dUMP is increased 200-fold and the Km for folate increased by tenfold versus the wild-type enzyme. The crystal structures of N229(177)A in complex with dUMP and CB3717, and in complex with dUMP alone are determined at 2.4 A, and 2.5 A resolution. These structures identify the covalently bound ternary complex and show how N229(177)A traps an intermediate, and so becomes inactive in a later step of the reaction. Since the smaller alanine side-chain at N229(177)A does not directly sterically impair binding of ligands, the structures implicate, and place quantitative limits on the involvement of the structured water network in the active site of thymidylate synthase in both catalysis and in determining the binding affinity for dUMP (in contrast, the N229(177)V mutation in Lactobacillus casei has minimal effect on activity).     

Nutritional intervention and growth in children with chronic renal failure

During fifties there were at most few tens of persons in this country who believed in the future of computers and cybernetics. One group of such enthusiasts, headed by Antonín Svoboda, was working at a construction of the first Czech computer SAPO. The other group tried to analyse, anticipate, and prepare in advance various applications for the new systemic conceptions and for the information processing machines. Members of both groups met for discussions which opened prospects to the future and influenced many of other activities for a long time. At the early sixties, the Czechoslovak Cybernetic Society was established at the Czechoslovak Academy of Sciences and in 1962 the Main Problem Committee for the Medical Cybernetics was founded at the Department of Health. It coordinated majority of the research programmes in the medical cybernetics and informatics. In 1967-1969 the Committee prepared an extensive project of a medical information system (ZIS), but its accomplishment was finally blocked by the then authorities. However, interests for that topics kept growing and the new working places equipped with available computer technology were formed at the health and clinical centres. The first tentative lectures in medical cybernetics and biocybernetics at our faculty were introduced into the students curricula in the late sixties. Thematically, medical cybernetics subsequently differentiated into the medical informatics, simulations of biological and medical systems, and the biosignal analysis. The growing interest enabled to hold conferences since the middle of seventies, some of which were held periodically, sometimes with international participation. It is not possible in brevity to include the whole spectrum to those goal-directed activities nor to appraise adequately their future significance.     

Synthesis and in vitro antimalarial activity of sulfone endoperoxides

A series of 4,8-dimethyl-4-phenylsulfonylmethyl-2,3-dioxabicyclo[3.3.1]+ ++nonanes, carrying a variety of substituents at position-8 (4) were prepared by a short and efficient method from R-(+)-limonene. Key reactions include thiol oxygen cooxidation, and alkylation and acylation of a sterically hindered tertiary alcohol compatible with the endoperoxy functionality. Some of compounds 4, which are structurally related to yingzhaosu A (2), were found to exhibit in vitro antimalarial activity comparable to that of artemisinin (1) and superior to that of arteflene (3).     

Bacterial phospholipase C upregulates matrix metalloproteinase expression by cultured epithelial cells

Phospholipase C (PLC) is a putative virulence factor of several pathogenic bacteria. We studied if exogenous PLC would perturb epithelial behavior in infected tissues. Gelatin and casein zymography of cell culture medium indicated that the broad-spectrum PLC of Bacillus cereus induced matrix metalloproteinase (MMP) production in epithelial cells of human skin (NHEK), human gingiva (HGE), and porcine periodontal ligament (PLE). In all three cell types, the strongest increase (ninefold) at 0.1 U/ml was seen in the MMP-9 (92-kDa gelatinase) activity, and the effect was dose dependent in the range of 0.1 to 1.0 U/ml. A relatively weaker increase (twofold) in MMP-2 (72-kDa gelatinase) was also observed in each cell type. PLC induction of MMP-3 (48-kDa stromelysin) was also seen in NHEK and HGE on gelatin and more sensitively for PLE by casein zymography (fivefold). Total gelatinolytic activity as measured by degradation of 14C-labeled denatured type I collagen increased by about 18-fold (NHEK), 12-fold (HGE), and 14-fold (PLE). Northern analysis showed a clear increase in the MMP-9, and a minor increase in MMP-3 mRNA levels but no significant increase in MMP-2 mRNA levels. Further studies with PLE revealed that MMP-9 induction by PLC progressively increased with the length of cell culture time in the absence of serum. PLC induction of MMPs was polar, with MMP-9 and MMP-3 secreted primarily in the apical direction and MMP-2 secreted mainly in the basal direction. The PLC effect was blocked by neomycin, an inhibitor of the phosphoinositol signal pathway. No significant effects were observed in MMP expression with the calcium ionophore A23187 or phospholipase A2. Morphologically, PLC treatment resulted in reduced contacts between the cultured cells and loss of the cell surface microvilli. These results suggest that PLC secreted by bacterial pathogens may disrupt epithelium of infected tissue and increase the subepithelial tissue destruction through induction of MMPs.     

The membrane-cytoplasm interface of integrin alpha subunits is critical for receptor latency

Localization of integrin receptors to focal contact sites occurs upon ligand binding. This activity is latent, since unoccupied integrin receptors do not localize to focal contacts. Deletion analysis has revealed that the alpha cytoplasmic domains is required for the maintenance of integrin receptor latency. Our current hypothesis for the mechanism of integrin post-ligand binding events is that there is a change in relationship of alpha and beta cytoplasmic domains, which overcomes receptor latency. One possible mechanism for such a change would involve the amino acid residues at the membrane-cytoplasm interface. To test this hypothesis, we have produced point mutations in the human integrin alpha 1 subunit. These mutations had no effect on the adhesion via alpha 1 beta 1 to its ligand, collagen IV. However, receptor latency is lost in one of these mutants, leading to constitutive focal contact localization. This effect did not occur in receptors with an exchange of intracellular domains, suggesting that the mechanism of loss of latency involves a relative motion of the integrin chains. These results suggest a model in which post-ligand binding events in integrin receptors are associated with changes in the position of the alpha and beta cytoplasmic domains.