Time delay to thrombolytic therapy--a Sri Lankan perspective

Reducing the time delay in initiating thrombolytic therapy in acute myocardial infarction is critical in maximising the functional and survival benefit. We analysed 120 consecutive admissions for thrombolytic therapy to the Coronary Care Unit. The total delay was divided into prehospital, in-hospital and Coronary Care Unit stages, and the median delays were found to be 130, 70, and 15 minutes, respectively. The delay was significantly longer in patients who sought prehospital medical advice, and when the diagnosis was not made at the emergency treatment unit. Educating at-risk groups and modifying the admission system may help to minimise these delays, while the establishment of an emergency ambulance service with well-trained crew would also improve the prognosis after acute myocardial infarction in Sri Lanka.     

Somatostatin increases a voltage-insensitive K+ conductance in rat CA1 hippocampal neurons

Somatostatin (SST) is a neuropeptide involved in several central processes. In hippocampus, SST hyperpolarizes CA1 pyramidal neurons and augments the K+ M current (IM). However, the limited involvement of IM at resting potential in these cells suggests that the peptide also may modulate another channel to hyperpolarize hippocampal pyramidal neurons (HPNs). We studied the effect of SST on noninactivating conductances of rat CA1 HPNs in a slice preparation. Using MK886, a specific inhibitor of the enzymatic pathway that leads to the augmentation of IM by SST, we have uncovered and characterized a second conductance activated by the peptide. SST did not affect IM when applied with MK886 or the amplitudes of the slow Ca2+-dependent K+ afterhyperpolarization-current and the cationic Q current but still caused an outward current, indicating that SST acts upon another conductance. In the presence of MK886, SST elicited an outward current that reversed around -100 mV and that displayed a linear current-voltage relationship. Reversal potentials obtained in different external K+ concentrations are consistent with a conductance carried solely by K+ ions. The slope of the current-voltage relationship increased proportionately with the extracellular K+ concentration and remained linear. This suggests that SST opens a voltage-insensitive leak current (IK(L)) in HPNs not an inwardly rectifying K+ current as reported in other neuron types. A low concentration of extracellular Ba2+ (150 M) only slightly decreased the SST-induced effect in a voltage-independent manner, whereas a high concentration of Ba2+ (2 mM) completely blocked it. Extracellular Cs+ (2 mM) did not affect the outward SST current but inhibited the inward component. We conclude that SST inhibits HPNs by activating two different K+ conductances: the voltage-insensitive IK(L) and the voltage-dependent IM. The hyperpolarizing effect of SST at resting membrane potential appears to be mainly carried by IK(L), whereas IM dominates at slightly depolarized potentials.     

Multiple functions for actin during filamentous growth of Saccharomyces cerevisiae

Saccharomyces cerevisiae is dimorphic and switches from a yeast form to a pseudohyphal (PH) form when starved for nitrogen. PH cells are elongated, bud in a unipolar manner, and invade the agar substrate. We assessed the requirements for actin in mediating the dramatic morphogenetic events that accompany the transition to PH growth. Twelve "alanine scan" alleles of the single yeast actin gene (ACT1) were tested for effects on filamentation, unipolar budding, agar invasion, and cell elongation. Some act1 mutations affect all phenotypes, whereas others affect only one or two aspects of PH growth. Tests of intragenic complementation among specific act1 mutations support the phenotypic evidence for multiple actin functions in filamentous growth. We present evidence that interaction between actin and the actin-binding protein fimbrin is important for PH growth and suggest that association of different actin-binding proteins with actin mediates the multiple functions of actin in filamentous growth. Furthermore, characterization of cytoskeletal structure in wild type and act1/act1 mutants indicates that PH cell morphogenesis requires the maintenance of a highly polarized actin cytoskeleton. Collectively, this work demonstrates that actin plays a central role in fungal dimorphism.     

Different phenotypic classes of Sinorhizobium meliloti mutants defective in synthesis of K antigen

For Sinorhizobium meliloti (also known as Rhizobium meliloti) AK631 to establish effective symbiosis with alfalfa, it must be able to synthesize a symbiotically active form of its K antigen, a capsular polysaccharide containing a Kdo (3-deoxy-D-manno-octulosonic acid) derivative. Previously isolated mutants defective in the synthesis of K antigen are resistant to bacteriophage phi16-3. By screening ca. 100,000 Tn5-mutagenized R. meliloti bacteria for resistance to bacteriophage phi16-3, we isolated 119 mutants, 31 of which could not be complemented by genes previously identified as being required for K-antigen synthesis. Of these 31 new mutants, 13 were symbiotically defective and lacked the K antigen. Through genetic and phenotypic analyses, we have grouped these mutants into four distinct classes. Although all of these mutants lack the K antigen, many also have altered lipopolysaccharides (LPS), suggesting that the biochemical pathways for the synthesis of K antigen and LPS have common enzymatic steps. In addition, we have found that these and other classes of K-antigen-defective mutants of S. meliloti AK631 exhibit unique patterns of sensitivities to phage strains to which the parental strain was resistant. Our studies have identified new classes of genes required for both the synthesis of K antigen and the symbiotic proficiency of S. meliloti AK631. Some of these classes of genes also play a role in LPS synthesis.     

Sialylated N-glycans in adult rat brain tissue--a widespread distribution of disialylated antennae in complex and hybrid structures

This paper extends our earlier work on the analysis of neutral N-glycans from adult rat brain to glycans carrying NeuAc residues as their sole charged groups. These structures comprised at least 40% of the total (acidic and neutral) N-glycan pool. Compounds were identified by a combination of endoglycosidase and exoglycosidase digestions, anion-exchange chromatography, normal and reverse-phase high-performance liquid chromatography, matrix-assisted laser desorption/ionisation-mass spectrometry and combined gas chromatography/mass spectrometry. Mono-, di- and trisialylated components, together with components substituted with four (or more) NeuAc residues, showed abundances of approximately 12, 10, 7 and 7%, respectively, relative to the total N-glycan pool. In addition, neuraminidase digestion resulted in the neutralisation of a fraction of highly charged species, possibly indicating the presence of N-glycans substituted with short chains of polysialic acid. Sialylated bi-, tri- [mainly the (2,4)-branched isomer], tetraantennary complex, polylactosamine and hybrid structures were detected. Typically, for 'brain-type' N-glycosylation, these sialylated structures were variously modified by the presence of core alpha1-6-linked and outer-arm alpha1-3-linked fucose residues and by a bisecting GlcNAc. Structural groups such as sialyl Lewis(x) and NeuAc alpha2-3 substituted Galbeta1-4GlcNAc antennae were common. In contrast to the neutral glycans, however, a widespread distribution of terminal beta1-3-linked galactose residues was observed. The presence of beta1-3-linked galactose allowed for a high degree of sialylation as afforded by the presence of the NeuAc alpha2-3Galbeta1-3(NeuAc alpha2-6)GlcNAc structural group. This revealed a number of novel structures including the presence of tetraantennary N-glycans with more than one beta1-3galactose residue and (2,4)-branched triantennary oligosaccharides containing three such residues. Disialylated hybrid glycans containing beta1-3-linked galactose and 'polylactosamine' N-glycans with one to three terminal beta1-3galactose residues were additional novel features. The N-glycans modified by polysialylation lacked outer-arm fucose and bisecting GlcNAc residues but all contained one or more terminal beta1-3-linked galactose residues. These may be representative, therefore, of the polysialylated N-glycans expressed mainly on neural cell-adhesion molecules and known to be present in adult rat brain. The diversity of presentation of terminal sialylated groups in rat brain implies potential specificity for possible charge or lectin-mediated interactions. The distinguishing sets of sialylated structures described here are indicative of differences in the natural glycosylation processing pathways in different cell types within the central nervous system, a specificity that may be further magnified on the individual glycoproteins.     

Use of emergency departments by elder patients: a five-year follow-up study

OBJECTIVE: To compare the use of emergency medical care by elders in the United States in 1995 with that previously described for 1990. METHODS: A computerized billing database of 88 EDs in 21 states was retrospectively reviewed for 1995, comparing elder and nonelder patients, estimating national use of emergency medical services by elders, and comparing the 1995 data with previously published results for 1990. RESULTS: From 1990 to 1995, the number of ED visits in the United States increased from 92 million to 100 million. The number of visits made by patients aged 65 years or older increased from 13,639,400 (15%) to 15,666,300 (15.7%), but this increase did not reach statistical significance (p = 0.17). The admission rate for elder ED patients increased from 32% to 46% over the five-year interval (p<0.01). This represents more than 7 million hospital admissions for elder patients in 1995. The rate of intensive care unit (ICU) admission for elders decreased from 7% to 6% over the five-year interval (p = 0.56), compared with 1.3% for nonelder patients for both years. Thirty percent of elder ED patients arrived by ambulance in 1990, compared with 33% in 1995 (p = 0.02). Based on 1995 data, elders comprised 39% of patients arriving by ambulance [odds ratio (OR) 4.75, 95% confidence interval (CI) = 4.71 to 4.79], 43% of all admissions (OR 6.59, 95% CI = 6.54 to 6.64), and 47% of ICU admissions (OR 5.00, 95% CI = 4.91 to 5.09). The comparable ORs in 1990 were 4.4, 5.6, and 5.5, respectively. CONCLUSIONS: From 1990 to 1995, the overall number of ED visits increased. The rate of increase was somewhat greater for elder patients. The use of ambulance services also disproportionately grew among elder patients, as did the rate of hospital admission. The overall rate of ICU admission was stable, but actually fell modestly for elder patients. Of these changes, only the increase in the rate of hospital admission for elders reached statistical significance.     

Evaluation of setting properties and retention characteristics of mineral trioxide aggregate when used as a furcation perforation repair material

Furcation perforations were created in 32 extracted maxillary and mandibular molars. The perforations were prepared in the center of the pulp chamber floor parallel to the long axis of each tooth and a saline-moistened Gelfoam matrix was placed below the perforation to simulate a clinical condition. The teeth were randomly divided into four groups, and the perforations were all repaired with mineral trioxide aggregate (MTA) and then covered with either a wet or dry cotton pellet for 24 or 72 h. Instron testing was used to measure the force required to displace the material from the perforation. The force measurements showed that MTA resisted displacement at 72 h to a significantly greater level than at 24 h (p < 0.05). When slight displacement occurred at 24 h the material demonstrated the ability to re-establish resistance to dislodgement from the dentin wall. The presence of some moisture in the perforation during placement was advantageous in aiding adaptation of MTA to the walls of the perforation, but there was no significant difference in MTA retention when a wet or dry cotton pellet was placed in the pulp chamber during the setting time (p > 0.05).