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B Robertson

Publications and source records attributed to B Robertson.

At least 163 records · Page 9Linked to original sources
PubMed1994

On the mechanism of 4-aminopyridine action on the cloned mouse brain potassium channel mKv1.1.

1. This study used the whole-cell patch clamp technique to investigate the mechanism of action of the K+ channel blocker 4-aminopyridine (4-AP) on the cloned K+ channel mouse Kv1.1 (mKv1.1) expressed in Chinese hamster ovary cells. 2. Cells transfected with mKv1.1 expressed a non-inactivating, delayed rectifier-type K+ current. 4-AP induced a dose-, voltage- and use-dependent block of mKv1.1. 3. 4-AP blockade of mKv1.1 was similar whether 4-AP was administered extracellularly (IC50 = 147 microM) or intracellularly (IC50 = 117 microM). 4. Inclusion of the first twenty amino acids of the N-terminus sequence of the Shaker B K+ channel ('inactivation peptide') in the patch electrode transformed mKv1.1 into a rapidly inactivating current. The time constant of decay for the modified current was dependent on the concentration of inactivation peptide, and under these conditions extracellular 4-AP had a reduced potency (IC50 values of 471 and 537 microM for 0.5 and 2 mg ml-1 inactivation peptide, respectively). 5. A permanently charged analogue of 4-AP, 4-aminopyridine methiodide (4-APMI), was found to block mKv1.1 when applied inside the cell, but was without effect when administered externally. 6. Decreasing the intracellular pH (pHi) to 6.4 caused an increase in 4-AP potency (IC50 = 76 microM), whereas at pHi 9.0, the 4-AP potency fell (IC50 = 295 microM). Conversely, increasing extracellular pH (pHo) to 9.0 caused an increase in 4-AP potency (IC50 = 93 microM), whereas at pHo 6.4, 4-AP potency decreased (IC50 = 398 microM). 7. Taken together, these findings support the hypotheses that the uncharged form of 4-AP crosses the membrane, and that it is predominantly the cationic form which acts on mKv1.1 channels intracellularly, possibly at or near to the binding site for the inactivation peptide.

4-Aminopyridine↗
PubMed1994

Lack of effect of 2-chlorodeoxyadenosine therapy in patients with chronic lymphocytic leukemia refractory to fludarabine therapy.

BACKGROUND: Fludarabine and 2-chlorodeoxyadenosine are nucleoside analogues that have proved effective in patients with chronic lymphocytic leukemia (CLL). Although their mechanism of action is thought to be similar, a small number of patients who do not respond to fludarabine do respond to 2-chlorodeoxyadenosine. The extent to which 2-chlorodeoxyadenosine is effective in patients who do not respond to fludarabine is not known, however. METHODS: We treated 28 patients with CLL refractory to fludarabine therapy with a continuous infusion of 2-chlorodeoxyadenosine at a daily dose of 4 mg per square meter of body-surface area for seven days. The treatment could be repeated monthly. The number of treatments ranged from one to five; patients who responded continued to receive treatment until the maximal response was achieved. RESULTS: Two patients (7 percent) had partial remissions, but no patients had complete remissions. One other patient had a substantial response but had residual thrombocytopenia. The rate of response in most affected organs was 20 percent, but anemia or thrombocytopenia rarely improved. Myelosuppression was frequent, and 65 percent of the courses of 2-chlorodeoxyadenosine therapy were accompanied by febrile episodes or infections. Ten patients died within 60 days of starting therapy with 2-chlorodeoxyadenosine; eight deaths were related to infection. The median platelet count at the start of 2-chlorodeoxyadenosine therapy in these 10 patients was 24,000 per cubic millimeter, as compared with 109,000 per cubic millimeter in the other 18 patients. Five patients were alive after a median follow-up of 24 months. CONCLUSIONS: Patients with advanced CLL refractory to fludarabine therapy are unlikely to benefit from treatment with 2-chlorodeoxyadenosine. Although 20 percent of the patients have some response, thrombocytopenia and anemia are rarely corrected and may be made worse by 2-chlorodeoxyadenosine therapy.

Adult↗
PubMed1994

Intracerebral haemorrhages in surfactant treated neonates with severe respiratory distress syndrome: age at diagnosis, severity and risk factors.

UNLABELLED: Within a randomized European multicentre trial the time of onset, severity and progression of intracerebral haemorrhages (ICH) were investigated prospectively by serial cranial ultrasonography in 343 ventilated infants with severe respiratory distress syndrome (RDS) following instillation of single or multiple doses of a natural porcine surfactant (Curosurf). In 148/343 infants (43%) ICH was diagnosed (grade I or II: 22%, grade III or IV: 21%). In 26 cases (8%) ICH was present on the ultrasound scan prior to surfactant instillation at a median age of 6 h. Incidence and severity of ICH was similar after single- or multiple-dose surfactant treatment. Using a logistic regression model the following risk factors predictive of ICH were defined: low birth weight, allocation to certain hospitals, vaginal delivery, Apgar score < or = 6, rectal temperature on admission < or = 36 degrees C, primary anaemia, acidosis prior to treatment, RDS grade IV in pre-treatment chest films and poor response to surfactant treatment. CONCLUSION: Our study provides supportive evidence that multiple doses of Curosurf do not increase the risk for ICH as compared to single-dose administration.

Biological Products↗
PubMed1994

Transganglionic transport and binding of the isolectin B4 from Griffonia simplicifolia I in rat primary sensory neurons.

The isolectin B4 from Griffonia simplicifolia I binds to a subpopulation of rat small-diameter dorsal root ganglion neurons, and to fibres and presumed terminals in laminae I-II of the spinal cord dorsal horn. In the present study we investigated B4 and B4 conjugated to horseradish peroxidase as potential transganglionic tracers of somatic primary afferent neurons after injection into a peripheral nerve. We also tried to identify the specific subpopulation of dorsal root ganglion neurons that bind and ganglion neurons that bind and transport B4. Following injection of B4 or B4-horseradish peroxidase into the sciatic nerve, labelled presumed terminals that reached peak labelling at two days were found exclusively in regions of the spinal cord gray matter known to receive unmyelinated primary afferent fibres. Almost all dorsal root ganglion cells that transported B4-horseradish peroxidase also bound B4. Cell counts showed that 51% of the dorsal root ganglion neurons were B4-positive and cell area measurements that these were all in the small size range. An extensive overlap was found between B4 and fluoride-resistant acid phosphatase (85%), and between B4 and calcitonin gene-related peptide (59%). Seventeen per cent of the B4-positive cells were substance P-immunoreactive and 9% were immunoreactive to somatostatin. Minimal overlap was seen between B4-positive cells and cells positive for RT97 (3%), a selective marker of primary afferent neurons with myelinated axons. All somatostatin-immunoreactive cells and almost all (95%) of the fluoride-resistant acid phosphatase-positive cells were contained within the B4-positive population. This comprised also 58% of the cells immunoreactive to calcitonin gene-related peptide and 42% of those immunoreactive to substance P. The results obtained show that B4 binds to a subpopulation of unmyelinated primary afferent neurons, and that B4 and B4-horseradish peroxidase can be used as selective transganglionic tracers of this specific cell subpopulation.

Animals↗
PubMed1994

Effect of different surfactants on pulmonary group B streptococcal infection in premature rabbits.

OBJECTIVES: To evaluate the effects of different surfactants on pulmonary infection with group B streptococci in premature rabbits and to examine the effects of different surfactants on pulmonary alveolar macrophage function of newborn rabbits. MODEL: Preterm and term rabbit pups. METHODS: Rabbit pups were infected with GBS aerosols followed by intratracheal administration of either calf lung surfactant extract, minced porcine lung surfactant (Curosurf), synthetic surfactant (Exosurf Neonatal), minced bovine lung surfactant (Survanta), human amniotic fluid-derived surfactant, rabbit surfactant, saline vehicle, or no treatment. Intrapulmonary clearance of GBS was determined by comparing bacterial counts in left lungs cultured immediately after aerosol infection with similarly infected lungs analyzed 4 hours after surfactant therapy. Phagocytosis of streptococci was ascertained by microscopic examination of the right lungs fixed in situ at 4 hours. For comparison, an in vitro method was used to measure growth of GBS in the different surfactants. RESULTS: Preterm animals had a sixfold increase in pulmonary bacterial growth compared with a slight decrease in intrapulmonary GBS in term animals when all were delivered by cesarean section (p < 0.05). In premature rabbits, GBS proliferation was lowest in animals treated with Exosurf Neonatal and highest in animals receiving Curosurf and human amniotic fluid-derived surfactant (p < 0.05). None of the surfactants promoted accelerated growth of GBS in comparison with control animals. Similar growth of GBS was seen in in vitro cultures. Intrapulmonary phagocytosis of GBS in premature pups was not altered by any of the surfactants. In term rabbit pups, the following measures of macrophage population kinetics remained normal at 1 and 24 hours after surfactant administration: viability, cell numbers based on lung lavage, and in vivo incorporation of thymidine. CONCLUSIONS: Surfactants used in clinical practice do not accelerate the in vivo growth of group B streptococci in the lungs of preterm rabbits. Some surfactants inhibit streptococcal proliferation. The effects of different surfactants are not explained by changes in macrophage function.

Animals↗
PubMed1994

Sequenced alleles of the Caenorhabditis elegans sex-determining gene her-1 include a novel class of conditional promoter mutations.

In the control of Caenorhabditis elegans sex determination, the her-1 gene must normally be activated to allow male development of XO animals and deactivated to allow hermaphrodite development of XX animals. The gene is regulated at the transcriptional level and has two nested male-specific transcripts. The larger of these encodes a small, novel, cysteine-rich protein responsible for masculinizing activity. Of the 32 extant mutant alleles, 30 cause partial or complete loss of masculinizing function (lf), while 2 are gain-of-function (gf) alleles resulting in abnormal masculinization of XX animals. We have identified the DNA sequence changes in each of these 32 alleles. Most affect the protein coding functions of the gene, but six are in the promoter region, including the two gf mutations. These two mutations may define a binding site for negative regulators of her-1. Three of the four remaining promoter mutations are single base changes that cause, surprisingly, temperature-sensitive loss of her-1 function. Such conditional promoter mutations have previously not been found among either prokaryotic or eukaryotic mutants analyzed at the molecular level.

Alleles↗
PubMed1994

Comparison of surface properties and physiological effects of a synthetic and a natural surfactant in preterm rabbits.

AIMS: To compare the physical and physiological properties of a synthetic surfactant (Exosurf, Wellcome Foundation) and a natural surfactant (Curosurf, Chiesi Farmaceutici). METHODS: Surface properties of the surfactant suspensions (10 mg phospholipid/ml) were evaluated using the pulsating bubble surfactometer. Lung-thorax compliance was determined in 47 immature newborn rabbits with a gestational age of 27 days, treated with recommended clinical doses of either surfactant (Exosurf 67.5 mg/kg; Curosurf 200 mg/kg). The lungs were examined histologically. RESULTS: The mean (SD) contractile forces of the surface at maximum and minimum bubble size were significantly lower for Curosurf than for Exosurf: 31 (2) and 0 (0) mN/m v 53 (5) and 29 (4) mN/m, respectively. Mean (SD) lung-thorax compliance after one hour of ventilation was significantly higher in rabbits treated with Curosurf compared with animals receiving Exosurf or those serving as controls: 0.60 (0.15) ml/cm H2O.kg v 0.44 (0.03) and 0.34 (0.18) ml/cm H2O.kg, respectively. Both surfactants increased alveolar volume density compared with results for control animals, but only Curosurf significantly reduced the incidence of moderate or severe bronchiolar epithelial disruption. CONCLUSIONS: The natural surfactant, Curosurf, reduced the contractile force at an air-liquid interface to a greater extent than the synthetic surfactant, Exosurf, and led to a greater improvement in compliance and less airway epithelial damage when given in clinical treatment doses to immature rabbits.

Animals↗
PubMed1994

Surface activity of lipid extract surfactant in relation to film area compression and collapse.

The physical properties of modified porcine surfactant (Curosurf), isolated from minced lungs by extraction with chloroform-methanol and further purified by liquid-gel chromatography, were investigated with the captive bubble technique. Bubble size, and thus the surface tension of an insoluble film at the bubble surface, is altered by changing the pressure within the closed bubble chamber. The film surface tension and area are determined from the shape (height and diameter) of the bubble. Adsorption of fresh Curosurf is characterized by stepwise decreases in surface tension, which can easily be observed by sudden quick movements of the bubble apex. These "adsorption clicks" imply a cooperative movement of large collective units of molecules, approximately 10(14) (corresponding to approximately 120 ng of phospholipid) or approximately 10(18) molecules/m2, into the interface during adsorption. Films formed in this manner are already highly enriched in dipalmitoyl phosphatidylcholine, as seen by the extremely low compressibility, close to that of dipalmitoyl phosphatidylcholine. Near-zero minimum tensions are obtained, even at phospholipid concentrations as low as 50 micrograms/ml. During dynamic cycling (20-50 cycles/min), low minimum surface tensions, good film stability, low compressibility, and maximum surface tensions between 30 and 40 mN/m are possible only if the films are not overcompressed near zero surface tension; i.e., the overall film area compression should not substantially exceed 30%.

Adsorption↗
PubMed1994

Exogenous surfactant improves lung compliance and oxygenation in adult rats with meconium aspiration.

We studied the effects of exogenous surfactant on lung function and morphology in an adult rat model of severe meconium aspiration syndrome. Animals ventilated with 100% oxygen received 4-6 ml of human meconium (25 mg/ml) intratracheally. After 30 min, lung-thorax compliance had decreased by > 30% and arterial PO2 was < 10 kPa. Animals were then treated with no material (MECO group), 0.9% NaCl (MECO-saline group), natural porcine surfactant (NPS group) at a dose of 100 mg/kg, or modified porcine surfactant at a dose of either 100 (MPS100 group) or 200 mg/kg (MPS200 group) and were ventilated for another 180 min. Immediate and sustained improvement of arterial PO2 and compliance was observed in the MPS200 group, whereas the MPS100 and NPS groups showed less pronounced effects. There was a significant improvement of quasi-static lung volumes at maximum insufflation pressure and during deflation in the MPS200, MPS100, and NPS groups. Recordings with Wilhelmy balance showed that minimum surface tension of bronchoalveolar lavage fluid from animals receiving either type or dose of surfactant was significantly lower than in the MECO and MECO-saline groups. Meconium aspiration induced diffuse and prominent atelectasis, intra-alveolar edema, and hyaline membranes. These morphological abnormalities were reversed by exogenous surfactant, especially by the high-dose regimen.

Animals↗
PubMed1994

Ethamsylate and lung permeability in ventilated immature newborn rabbits.

The leakage of proteins in the immature neonatal lung can reduce the effect of exogenous surfactant. The effect of ethamsylate, a more specific prostaglandin inhibitor than indomethacin and aspirin-like drugs, on alveolar albumin leak was studied in a group of 27 immature newborn rabbits (gestational age 27 days). A pilot study was carried out using 4 animals and low-dose ethamsylate (10 mg/kg). A second group of animals (n = 12) received at birth, by intravenous injection, ethamsylate (50 mg/kg) and 10% human albumin (7 ml/kg). Animals not receiving ethamsylate (n = 11) served as control group. After 30 min of artificial ventilation with standard tidal volume (10 ml/kg) the lungs were lavaged and the amount of human albumin in lung lavage fluid was determined by immunodiffusion. No statistically significant differences were found in lung-thorax compliance and vascular to alveolar albumin leak between ethamsylate-treated animals and controls (p > 0.5). However, there was a statistically significant negative correlation between protein leak and lung compliance (r = -0.41; p < 0.04). These results suggest no direct influence of early ethamsylate administration on neonatal lung permeability in the immature neonate confirming that lung permeability is inversely related to compliance.

Animals↗
PubMed1994

Lung gas volumes and expiratory time constant in immature newborn rabbits treated with natural or synthetic surfactant or detergents.

Immature newborn rabbits delivered at a gestational age of 27 days were tracheotomized and treated, via the tracheal cannula, with clinically recommended doses of natural or synthetic surfactant (Curosurf and Exosurf, respectively). Littermates received 0.1% tyloxapol, 5% Tween 20, or saline. The dose volume of Curosurf was 2.5 ml/kg, that of the other materials 5 ml/kg. Animals were kept in a multiplethysmograph system and ventilated for 30 min with a standardized sequence of insufflation pressures. End-expiratory lung gas volume was calculated at the end of the experiment from measurements of lung weight and total lung volume. Tidal volumes were significantly improved in all groups of animals receiving surfactant or detergents. However, expiratory time constant (determined from the tidal volume tracing) was significantly longer, and end-expiratory gas volume significantly larger, in animals treated with Curosurf than in those receiving Exosurf or detergents. These differences were confirmed by semiquantitative evaluation of alveolar air expansion in histological sections. In addition, airway epithelial necrosis was reduced in animals receiving Curosurf, Exosurf, or Tween 20, but not in animals treated with tyloxapol. The discrepancy between improvements in tidal volume, expiratory time constant, and end-expiratory gas volume reflects failure of lung stabilization in animals treated with Exosurf or detergents, probably due to absence of specific hydrophobic proteins in the synthetic products.

Animals↗
PubMed1994

The proteins of the surfactant system.

The structural and functional integrity of pulmonary surfactant depends on several specific proteins. Two of these, SP-A and SP-D, are large and water-soluble, while SP-B and SP-C are small and very hydrophobic. SP-A is an 18-mer of 26 kDa polypeptide chains and contains N-linked oligosaccharides. Structurally, it can be characterized as a collagen/lectin hybrid. Together with SP-B, SP-A is required for conversion of secreted endogenous surfactant to tubular myelin in the alveolar lining. It also regulates surfactant secretion and reuptake of surfactant lipids by type II cells; these functions are probably receptor mediated. SP-D, a 12-mer of 39 kDa polypeptide chains, is a collagenous glycoprotein with structural similarities to C-type lectins. Both SP-A and SP-D stimulate alveolar macrophages. SP-B is a 79-residue polypeptide that contains three intrachain disulphide bridges. It exists mainly as a homodimer, which is strongly positively charged and may selectively remove anionic and unsaturated lipid species from the alveolar surface film, thereby increasing surface pressure. SP-C is a mainly alpha-helical, extraordinarily hydrophobic polypeptide containing 35 amino acid residues and covalently linked palmitoyl groups. Its alpha-helical portion is inserted into surfactant lipid bilayers. SP-C accelerates the adsorption of lipid bilayers to an interfacial monolayer. In babies with respiratory distress syndrome, the clinical response to treatment with surfactant containing SP-B and SP-C is much faster than in babies treated with protein-free synthetic surfactant. We speculate that, in the near future, surfactant preparations based on recombinant hydrophobic proteins will be available for clinical use.

Glycoproteins↗
PubMed1994

Experimental neonatal group B streptococcal pneumonia: effect of a modified porcine surfactant on bacterial proliferation in ventilated near-term rabbits.

We studied bacterial proliferation in relation to surfactant treatment in a model of neonatal group B streptococcal (GBS) pneumonia. Surfactant (Curosurf) was isolated from pig lungs with a method preserving only polar lipids and hydrophobic proteins. Near-term rabbit fetuses were ventilated in a body plethysmograph system. At 15 min, a suspension of GBS strain 090 Ia LD (5 mL/kg, concentration approximately 10(9)/mL) was instilled intratracheally. At 30 min, surfactant (n = 12) or sterile saline (n = 13) was administered via the airways (2.5 mL/kg). A control group (n = 12) received the same volumes of saline. After 5 h the animals were killed, and samples for blood cultures and blood gases were taken from the heart. The left lung was aseptically removed, weighed, homogenized, serially diluted, and cultured on blood agar plates. The results were expressed as mean log10 colony forming units/g lung +/- SD. Compared with animals (n = 12) killed immediately after GBS instillation (8.13 +/- 0.54), there was a significant increase in bacterial numbers in both groups ventilated for 5 h, but values for surfactant-treated animals (8.96 +/- 0.38) were lower than those for animals receiving saline (9.46 +/- 0.50; p < 0.05). After 5 h, 96% of GBS-infected animals had positive blood cultures. Light microscopic examination of the right lung of GBS-infected animals revealed inflammatory changes that tended to be less prominent in surfactant-treated rabbits. We conclude that intratracheal inoculation of near-term rabbits with GBS resulted in a significant bacterial proliferation during 5 h of ventilation and that bacterial growth was mitigated by treatment with surfactant.

Animals↗
PubMed1994

Ontogeny of a human polychlorinated biphenyl-binding protein. Level of expression in tracheal aspirates in bronchopulmonary dysplasia.

A human lung polychlorinated biphenyl binding protein (PCB-BP,M(r) 13 kd) has recently been purified from lavage fluid. Polyclonal monospecific antibodies against PCB-BP were produced and used for immunohistochemical staining in sections of human lung tissue. PCB-BP was found to localize preferentially to the nonciliated (Clara) cells of the lung, whereas the alveolar cells and ciliated cells of the larger airways were devoid of staining. Tracheal aspirates from infants receiving mechanical ventilation were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis separation and Western immunoblotting. The antibodies to human PCB-BP detected a single band of the expected molecular weight, and a quantitative analysis of the ontogeny of PCB-BP in tracheal aspirates was performed by construction of Western immunoblot standard curves. A significant increase in the levels of PCB-BP in late gestation (gestational weeks 39 to 41) was demonstrated. In similar experiments, levels of PCB-BP in tracheal aspirates obtained from infants with bronchopulmonary dysplasia (BPD) at the postconceptional age of less than 38 weeks were found to be significantly elevated as compared with a normal study group of similar gestational age (21.8 +/- 4.8 vs 3.1 +/- 0.8 ng of PCB-BP per microgram of total protein, p < 0.005). It is suggested that the high levels of PCB-BP at the postconceptional age of less than 38 weeks observed in infants with BPD may reflect inflammatory injury and regeneration of airway epithelium, associated with proliferation of Clara cells.

Blotting, Western↗
PubMed1994

Acute effects of a single dose of porcine surfactant on patients with the adult respiratory distress syndrome.

In an attempt to restore functional surfactant to the lungs of patients with the adult respiratory distress syndrome (ARDS), we have treated six patients within the first 2 days of the onset of ARDS with a single dose of hydrophobic components of porcine surfactant. Surfactant (4 g in 50 ml) delivered via a bronchoscope in aliquots to each of the lobar bronchi was well tolerated and caused a modest transient improvement in gas exchange. No significant changes in chest radiograph or lung compliance were detected. Analysis of bronchoalveolar lavage (BAL) fluid showed no change in albumin, alpha-1-proteinase inhibitor specific activity, or cell count. Bronchoalveolar lavage phospholipid concentrations were elevated 3 h after surfactant administration relative to preadministration levels and fell by 24 h. In addition, in two patients we found reduced inhibition of surfactant function in BAL after surfactant replacement. These observations suggest a role for surfactant replacement in the treatment of patients with ARDS and support the need for continuing investigation.

Adult↗
PubMed1994

The good old days.

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