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Biomedical subjects

J Robbins

Publications and source records attributed to J Robbins.

At least 235 records · Page 13Linked to original sources
PubMed1990

A transient outward current in NG108-15 neuroblastoma x glioma hybrid cells.

Outward currents were recorded from voltage-clamped NG108-15 mouse neuroblastoma X rat glioma hybrid cells, differentiated with prostaglandin E1. Depolarising voltage steps from -70 mV, evoked a transient outward current from a threshold of -30 mV. The outward current showed complete inactivation at potentials positive to -10 mV. Inactivation was removed by hyperpolarisation with half-inactivation at -53 mV. The time course of the inactivation could be best fitted by two exponentials with mean time constants of 280 ms and 1.6 s at +80 mV. Tail current measurements showed a shift in the reversal potential with changes in external K+ concentration, consistent with K+ as the current-carrying ion. The outward current amplitude was reversibly reduced by 4-aminopyridine, and the time course of inactivation modified. In the presence of other K+ channel blockers (tetraethylammonium, barium and tetrahydroaminoacridine) the amplitude of the outward current was also reversibly reduced, but with a negligible effect on its time course. The current was unaffected by dendrotoxin, d-tubocurarine, apamin, Cd2+ and Ni2+, and by replacing external Ca2+ with Co2+ or Mg2+. In current clamp, action potential duration was greatly increased by 4-aminopyridine. The findings show that the NG108-15 cell line displays a transient outward current that resembles IK(A) but with a higher than usual threshold and relatively slow inactivation, and that this current is likely to be important for action potential repolarisation.

4-Aminopyridine↗
PubMed1990

Test-retest variability in normal swallowing.

The test-retest variability of the modified barium swallow study using videofluoroscopy was analyzed. Sixteen normal subjects (8 men, 8 women) were organized into 2 age groups: middle-aged group (mean, 45 years) and old-age group (mean, 66 years). Nine durational measures of the swallow were evaluated. There were no statistically significant differences for any of the measures between the initial test and a retest conducted days later. The findings suggest that, on the whole, normal subjects perform similarly on test and a retest. However, the variability displayed by these normal subjects may be clinically significant, indicating that test-retest swallowing duration measures require careful interpretation.

Adult↗
PubMed1990

Immunogenicity and safety of a pertussis vaccine composed of pertussis toxin inactivated by hydrogen peroxide, in 18- to 23-month-old children.

A new pertussis vaccine, composed of purified pertussis toxin inactivated by hydrogen peroxide and adsorbed onto aluminum hydroxide (NICHD-Ptxd), was injected into 60 children aged 18 to 23 months without a history of pertussis or pertussis vaccination. Two doses of toxoid, 10 and 50 micrograms, were used. Two injections, given 8 to 12 weeks apart, elicited increases in serum levels of antitoxin and IgG antibodies in 56 children who had no detectable antitoxin (less than 5 units) before vaccination. Four children with detectable antitoxin (greater than or equal to 5 units) before the first vaccination had pronounced antibody increases after the first dose. After the second dose, the geometric mean antitoxin concentration was 29 units with the 50 micrograms dosage and 10 units with the 10 micrograms dosage (p less than 0.001). Serum antibody levels elicited by two injections of 50 micrograms were similar to those in patients convalescing from pertussis. A third injection given to seven children 9 to 10 months after the second injection gave a booster response, with high levels of antitoxin (160 to 1280 units) and of IgG antibodies. With few exceptions the antibody response was restricted to the IgG class. Transient local reactions greater than or equal to 2 cm in diameter occurred in 14% of the children after the first dose and in 44% after the second and third doses. Moderate fever was recorded after 6% of all injections. There were no changes in peripheral blood leukocyte counts or fasting blood glucose levels measured before and 24 hours after the first injection. We conclude that NICHD-Ptxd is immunogenic in children. No serious adverse effects were noted.

Antibodies, Bacterial↗
PubMed1990

Cloning and sequencing of a putative Escherichia coli [NiFe] hydrogenase-1 operon containing six open reading frames.

DNA encompassing the structural genes of an Escherichia coli [NiFe] hydrogenase has been cloned and sequenced. The genes were identified as those encoding the large and small subunits of hydrogenase isozyme 1 based on NH2-terminal sequences of purified subunits (kindly provided by K. Francis and K. T. Shanmugam). The structural genes formed part of a putative operon that contained four additional open reading frames. We have designated the operon hya and the six open reading frames hyaA through F. hyaA and hyaB encode the small and large structural subunits, respectively. The nucleotide-derived amino acid sequence of hyaC has a calculated molecular mass of 27.6 kilodaltons, contains 20% aromatic residues, and has four potential membrane-spanning regions. Open reading frames hyaD through F could encode polypeptides of 21.5, 14.9, and 31.5 kilodaltons, respectively. These putative peptides have no homology to other reported protein sequences, and their functions are unknown.

Amino Acid Sequence↗
PubMed1990

Neuropsychiatric manifestations of altered thyroid state.

The authors assessed the mood and cognitive effects of sequential T4, T3, and withdrawal of thyroid hormone replacement on 25 patients who had had thyroidectomies for thyroid cancer. The patients experienced increased sadness and anxiety when they were without medication, but not significant difference in mood was noted between T4 and T3. The patients who experienced increased affective symptoms when not taking medication were more likely to have histories of affective illness or mood lability.

Adult↗
PubMed1990

Enhancement of thyroxine entry into low density lipoprotein (LDL) receptor-competent fibroblasts by LDL: an additional mode of entry of thyroxine into cells.

Having demonstrated that plasma low density lipoproteins (LDL) bind T4 through a specific interaction with their sole apolipoprotein, apoB-100, we tested the hypothesis that cells could internalize the LDL-T4 complex via cell surface LDL receptors. These receptors are down-regulated by cholesterol loading and up-regulated by cholesterol deficiency. We, therefore, studied the uptake of [125I]T4 or [125I]T3 by human skin fibroblasts grown in 10% lipoprotein-deficient serum in the absence or presence of LDL. At concentrations of LDL (12.5 and 22 micrograms protein/ml) that gave significant binding of T4 but did not exceed LDL receptor capacity, both the initial rate of saturable T4 uptake and the uptake at equilibrium increased by 27-63%. No significant increase occurred at a LDL concentration of 1.6 micrograms protein/ml (less than 3% occupancy), whereas there was a 20 to 31% reduction at 125 micrograms/ml (approximately 5 times the saturation dose for the LDL receptor). These changes were confirmed with several different LDL preparations and were mimicked by isolated apoB-100 and apoE, the sole ligands for the LDL receptors (apoB/E receptors). T4 uptake did not increase in normal fibroblasts with down-regulated LDL receptors or in LDL receptor-deficient fibroblasts from a patient with familial hypercholesterolemia. In the latter cell line the uptake of T4 (and T3) in the absence of LDL was indistinguishable from that of normal fibroblasts. T3 uptake in normal fibroblasts was not enhanced by LDL. The specificity of the LDL effect was shown by the finding that T4-binding globulin, prealbumin, or serum albumin, at concentrations giving 10-90% T4 bound, failed to increase T4 uptake. Instead, each of these major thyroid hormone-binding plasma proteins caused a dose-dependent decrease in T4 entry. It is concluded that at least two modes of entry into fibroblasts are available for T4. The first is the cell surface thyroid hormone-binding sites, which recognize the free hormone and are present in both normal and LDL receptor-negative fibroblasts. The second, and additional, mode of entry is via the LDL receptors, which recognize the T4-LDL complex, are absent in LDL receptor-negative fibroblasts, are reduced in down-regulated fibroblasts, and are unavailable for T3, owing to the low affinity of T3 for LDL.

Cell Line↗
PubMed1990

The transport of thyroxine into mouse neuroblastoma cells, NB41A3: the effect of L-system amino acids.

Thyroid hormones must cross the plasma membrane to interact with nuclear or other intracellular receptors. In brain cells, most of the T3 in the nucleus is derived intracellularly from T4. While a saturable transport system has been demonstrated for T3 in a number of cell types, the evidence for such a system for T4 is less well established. In a mouse neuroblastoma cell line (NB41A3) the transport of T4 was found to be stereospecific, saturable, and energy dependent. When cells were incubated with radiolabeled hormone, the nuclear accumulation of L-T4 was 3.8-fold higher than that of D-T4, whereas isolated nuclei had a similar Ka for both enantiomers. Exposure of cells to antimycin and monodansylcadaverine decreased nuclear uptake of L-T4 (Ki of 197 and 55 microM, respectively), but had little effect on D-T4 uptake. Furthermore, L-system neutral amino acids, in particular L-phenylalanine at physiological concentrations, were shown to be competitive inhibitors of both T3 and T4 transport. In the presence of 0.1 mM L-phenylalanine the Km of the saturable plasma membrane transport of L-T3 increased 2.3-fold, and that of L-T4 increased 2.1-fold. In contrast, 1.0 mM L-serine or D-phenylalanine had little effect on L-T4 transport. This interaction of L-system amino acid and thyroid hormone transport may be of physiological importance.

Amino Acids↗
PubMed1990

Localization of the thyroxine binding sites in apolipoprotein B-100 of human low density lipoproteins.

By photoaffinity labeling human low density lipoproteins (LDL) with [125I]T4 we confirmed our previous observation that of the three T4 binding sites of apolipoprotein B-100 (apoB-100) one is in its 26% NH2-terminal portion [apoB-26, the 140 kDa fragment, residues 1-1297] and two in the remaining 74% COOH portion (apoB-74, 410 kDa, residues 1298-4536). We now show that of these two sites one is in the NH2 portion of apoB-74 (apoB-44, 240 kDa, residues 1298-3249) and the other in the nonoverlapping COOH portion (apoB-30, 170 kDa, residues 3250-4536). ApoB-100 contains 13 binding sites for heparin, a known inhibitor of T4 binding to the major T4 carrier plasma proteins; however, heparin failed to inhibit T4 binding to apoB-100 and fragments thereof. The same failure was seen with three monoclonal antibodies (MAbs), 4G3, 5E11, and 43 that block totally or partially LDL binding to the LDL receptor [respective epitopes at residues 2980-3084 (apoB-44), 3441-3569, and 4027-4081 (apoB-30)]. Of the other 3 MAbs, all without effect on LDL binding to the LDL receptor, [1D1, 2D8, and 16, respective epitopes at residues 474-539 (apoB-26), 1438-1481 (apoB-44), and 4154-4189 (apoB-30)], only two (MAbs 1D1 and 2D8) inhibited T4 binding (21 to 39%). We conclude that the three T4-binding sites of apoB-100 are outside the LDL receptor binding domain, distant from the heparin binding sites and, assuming no allosteric effects, in the vicinity of residues 474-539 (T4 site of apoB-26), 1438-1481 (T4 site of apoB-44), and in the C terminal quarter of apoB-30.

Antibodies, Monoclonal↗
PubMed1990

Sleep deprivation and cognitive testing in internal medicine house staff.

There is increased concern about the effects of sleep deprivation on physician performance. We administered four standard tests of cognitive function to 23 university hospital house staff. Each physician served as his or her own control, and the tests were administered at rest, after a night on call, and after a night of sleep for recovery. The study was designed so that normal learning would minimize any deterioration in the post-on-call test performance. Statistically significant deterioration occurred in 3 of the 4 tests after a night on call. Even physicians acclimated to sleep deprivation on a regular, every-third-or-fourth-night basis showed functional impairment. The results have implications for patient care under conditions where house staff are stressed by sleep deprivation and prolonged fatigue.

Clinical Competence↗
PubMed1989

A multipurpose vector for the study of transcriptional control.

To facilitate the insertion of transcriptional control regions next to a reporter gene, plasmid vectors containing multiple cloning sites next to the cat have been constructed. These vectors also contain features which make their use convenient for the construction of deletions in the inserted transcriptional control regions, as well as for the direct sequencing of the deletion series produced. The vectors have been constructed such that the control region cassette (and the deletions produced) may be easily removed with or without the reporter gene for placement into transgenic mice. The system's utility has been demonstrated by deletion analysis of a chicken myosin heavy chain-encoding gene promoter.

Animals↗
PubMed1989

Benzodiazepines and the mammalian retina. I. Autoradiographic localisation of receptor sites and the lack of effect on the electroretinogram.

The majority of specific benzodiazepine binding sites were found to be restricted to the innerplexiform layer of the rat retina, although there were minor amounts of binding in the inner nuclear and ganglion cell layers. Relatively high levels of non-specific benzodiazepine binding sites were, on the other hand, found in the pigment epithelium and ciliary body, as well as in the corneal epithelium. The specific binding was enhanced by the GABA-A agonist, muscimol. In both rats and cats, neither acute nor chronic administration of benzodiazepines or their antagonists altered the retinal functions, as determined by the electroretinogram. These results suggest that retinal benzodiazepine receptors do not influence visually induced preganglionic retinal activity.

Animals↗
PubMed1989

Benzodiazepines and the mammalian retina. II. Actions on retinal ganglion cells.

The effects of intravenously and iontophoretically applied benzodiazepines, midazolam and flurazepam and their receptor antagonist, flumazepil (RO 15 1788), on visually evoked and spontaneous activities of the mammalian retinal ganglion cells have been studied. Intravenously applied midazolam and flurazepam suppressed both light-evoked and spontaneous firing of rat optic tract fibres. They reduced both the sensitivity to light and the temporal resolution of the fibres. Flumazepil (RO-15-1788), on the other hand, enhanced both light-evoked and spontaneous firing of the optic tract fibres. It increased their light sensitivity but did not affect their temporal resolution. In the cat, iontophoretically applied benzodiazepines suppressed and flumazepil increased the receptive field centre and surround response as well as the spontaneous firing of ON-type retinal ganglion cells which mainly receive GABAergic inputs. However, these drugs did not affect the activities of the OFF-type cells which mainly receive glycinergic inputs. These results suggest not only that the action of benzodiazepines on the retinal ganglion cells is mediated by benzodiazepine receptors that are linked with GABA receptors, but also that the retinal benzodiazepine receptors receive an endogenous benzodiazepine receptor ligand.

Action Potentials↗
PubMed1989

Benzodiazepines and the mammalian retina. III. Postnatal development.

Iontophoretic effects of the benzodiazepine receptor agonist, flurazepam, and antagonist, flumazepil (RO-15-1788) on the retinal ganglion cells of kittens (7-9 weeks of age) have been compared with those of adult cats (18-22 weeks of age). In the adult retina, flurazepam decreased and flumazepil increased the visually evoked and spontaneous firing of ON-, but produced no effects on the response of OFF-retinal ganglion cells. However, in the kittens retina, in which ON-cells' selectivity to GABA is not fully developed, both the visually evoked and spontaneous activities of ON- and OFF-cells were inhibited by flurazepam and enhanced by flumazepil. This suggests that postnatal development of benzodiazepine action parallels that of GABA action at the retinal ganglion cells in the cat retina.

Action Potentials↗
PubMed1989

Binding of thyroxine to human plasma low density lipoprotein through specific interaction with apolipoprotein B (apoB-100).

Human plasma low density lipoprotein (LDL), which binds 0.2% of plasma T4, was shown to interact with the hormone through its protein moiety, apolipoprotein B-100. LDL and LDL2, the major subfraction of LDL, were found to have 3 equivalent binding sites for T4 with Ka = 2.5 x 10(6) M-1. Photoaffinity labeling of LDL with inner ring-labeled [125I]T4, followed by SDS-PAGE or agarose-SDS-PAGE of the labeled products, revealed that apoB-100 and its proteolytic cleavage products, apoB-74 and apoB-26, bound [125I]T4. In the presence of 1 or 10 microM T4, labeling was decreased in 7 separate experiments by 40-53% or 65-86%, respectively, consistent with a Ka of approximately 10(6) M-1. Binding of T4 to apoB-100 associated with VLDL was also demonstrated by photoaffinity labeling. The observed thyroid hormone binding property of lipid-complexed apoB-100 and the knowledge that receptors for the apolipoprotein exist in various tissues suggest a possible physiological role in thyroid hormone transport.

Apolipoproteins B↗
PubMed1989

Properties of excitatory amino acid receptors on sustained ganglion cells in the cat retina.

Iontophoretic effects of N-methyl-D-aspartate, quisqualate and kainate and a variety of excitatory amino acid receptor antagonists, on retinal ganglion cells, were studied in optically intact eyes of barbiturate anesthetized cats. All three agonists raised the spontaneous firing of both ON- and OFF-sustained retinal ganglion cells, with the potency order of kainate much greater than quisqualate greater than N-methyl-D-aspartate. However, the excitatory amino acid analogues readily saturated the receptors and reduced the visually driven firing of cells with high spontaneous firing, but mimicked an increase in endogenous excitatory amino acid release and raised the visually induced response in cells with low spontaneous firing. The quinoxaline compound, 6-cyano-2,3 dihydroxy-7-nitroquinoxaline and 6-7-dinitroquinoxaline-2,3-dione, blocked the visually driven firing and kainate- and quisqualate-induced excitation, whilst 3[+)-2-carboxypiperazin-4-yl)propyl-1-phosphonate, antagonized the N-methyl-D-aspartate-induced excitation, but failed to block visually driven firing of the retinal ganglion cells. The broadband excitatory amino acid receptor antagonists, such as kynurenate, were also effective in antagonizing the visually driven response and also blocked the N-methyl-D-aspartate- as well as kainate- and quisqualate-induced responses. These results suggest that the receptors at the bipolar/ganglion cell synapse are of the non-N-methyl-D-aspartate type, but that N-methyl-D-aspartate receptors are also present on ganglion cells although their physiological role is unclear.

Action Potentials↗