Biomedical subjects

A Hills

Publications and source records attributed to A Hills.

16 recordsLinked to original sources

PubMed2001

Extracellular Ba2+ and voltage interact to gate Ca2+ channels at the plasma membrane of stomatal guard cells.

Ca2+ channels at the plasma membrane of stomatal guard cells contribute to increases in cytosolic free [Ca2+] ([Ca2+](i)) that regulate K+ and Cl- channels for stomatal closure in higher-plant leaves. Under voltage clamp, the initial rate of increase in [Ca2+](i) in guard cells is sensitive to the extracellular divalent concentration, suggesting a close interaction between the permeant ion and channel gating. To test this idea, we recorded single-channel currents across the Vicia guard cell plasma membrane using Ba2+ as a charge carrying ion. Unlike other Ca2+ channels characterised to date, these channels activate at hyperpolarising voltages. We found that the open probability (P(o)) increased strongly with external Ba2+ concentration, consistent with a 4-fold cooperative action of Ba2+ in which its binding promoted channel opening in the steady state. Dwell time analyses indicated the presence of a single open state and at least three closed states of the channel, and showed that both hyperpolarising voltage and external Ba2+ concentration prolonged channel residence in the open state. Remarkably, increasing Ba2+ concentration also enhanced the sensitivity of the open channel to membrane voltage. We propose that Ba2+ binds at external sites distinct from the permeation pathway and that divalent binding directly influences the voltage gate.

Barium↗

PubMed2001

Effects of aging on visuospatial attention: an ERP study.

The effects of aging on visuospatial attention were investigated with event-related brain potentials (ERPs). A central arrow pointed towards (75% valid cues) or away from (25% invalid cues) the location of upcoming visual targets to which subjects made two choice discriminations. Young and older adults responded faster following valid than invalid cues. The absolute magnitude of the cueing effect was larger for older than young subjects, but cueing effects were similar between groups when estimated proportionally to overall response time. Under the present conditions, the electrophysiological manifestations of visuospatial attention were similar for young and older adults. Early ERP components following the target stimulus (P1, N1, Nd1) were slower for older than young subjects, but amplitude was similarly affected by cueing in each group. The temporal correspondence between component latencies and the observed cueing effects are consistent with theories positing that attention amplifies the sensory gain of early perceptual processes. The observation that aging slowed latency of the ipsilateral but not the contralateral P1, is consistent with age differences in interhemispheric transfer times. A broadly distributed 200-400 ms validity effect on ERP amplitude was similar between groups in timing, spatial distribution, and magnitude. The 200-400 ms attention effect appeared to be a modulation of the P3 in younger subjects, as earlier observed. However, the present study dissociated the 200-400 ms attention effects from the P3 component because the P3 did not peak until 526 ms in older subjects.

Adolescent↗

PubMed2000

Ca2+ channels at the plasma membrane of stomatal guard cells are activated by hyperpolarization and abscisic acid.

In stomatal guard cells of higher-plant leaves, abscisic acid (ABA) evokes increases in cytosolic free Ca(2+) concentration ([Ca(2+)](i)) by means of Ca(2+) entry from outside and release from intracellular stores. The mechanism(s) for Ca(2+) flux across the plasma membrane is poorly understood. Because [Ca(2+)](i) increases are voltage-sensitive, we suspected a Ca(2+) channel at the guard cell plasma membrane that activates on hyperpolarization and is regulated by ABA. We recorded single-channel currents across the Vicia guard cell plasma membrane using Ba(2+) as a charge-carrying ion. Both cell-attached and excised-patch measurements uncovered single-channel events with a maximum conductance of 12.8 +/- 0.4 pS and a high selectivity for Ba(2+) (and Ca(2+)) over K(+) and Cl(-). Unlike other Ca(2+) channels characterized to date, these channels rectified strongly toward negative voltages with an open probability (P(o)) that increased with [Ba(2+)] outside and decreased roughly 10-fold when [Ca(2+)](i) was raised from 200 nM to 2 microM. Adding 20 microM ABA increased P(o), initially by 63- to 260-fold; in both cell-attached and excised patches, it shifted the voltage sensitivity for channel activation, and evoked damped oscillations in P(o) with periods near 50 s. A similar, but delayed response was observed in 0.1 microM ABA. These results identify a Ca(2+)-selective channel that can account for Ca(2+) influx and increases in [Ca(2+)](i) triggered by voltage and ABA, and they imply a close physical coupling at the plasma membrane between ABA perception and Ca(2+) channel control.

Abscisic Acid↗

PubMed2000

Interactions between hy1 and gun mutants of Arabidopsis, and their implications for plastid/nuclear signalling.

Lhcb and other nuclear genes for chloroplastic proteins are regulated by several signals. Among them, light and retrograde signals from the plastid itself appear to act through closely related mechanisms. To investigate this interaction, we analysed an Arabidopsis mutant, hy1, deficient in plastidic heme oxygenase. hy1 is defective in phytochrome chromophore biosynthesis, which has other indirect effects on tetrapyrrole metabolism. We generated double mutants between hy1-6.2, genetically a null mutation, and three known gun (genome uncoupled) mutants, defective in retrograde plastid signalling. Recent molecular evidence shows GUN5 to be involved in tetrapyrrole metabolism (N. Mochizuki and J. Chory, manuscript in preparation). We observed hy1gun4 to be semi-albino plants, and hy1gun5 albino lethal, in a high-light-sensitive manner. Both double mutants showed defective greening and chloroplast development, and expressed Lhcb at reduced levels specifically in high light. Their degree of 'genome uncoupling' (Lhcb expression in the absence of functional chloroplasts) was similar to that observed in single mutants. These results can be interpreted as a metabolic (rather than genetic) interaction between HY1 and GUN4 or GUN5, and this in turn supports the involvement of tetrapyrroles as plastid signals. The tetrapyrrole precursor 5-aminolevulinic acid (ALA) inhibited Lhcb expression in hy1. Surprisingly, ALA also rescued photomorphogenesis of hy1. We speculate that either one tetrapyrrole intermediate, which can accumulate anomalously in hy1, or an altered ratio between two intermediates, plays a role as a repressor of Lhcb expression. gun1 did not exacerbate the plastid or Lhcb expression phenotype of hy1. This can be interpreted as a role for gun1 strictly on the same pathway as hy1 or, more likely, as evidence for the existence of at least one separate, non-tetrapyrrole related plastid signal.

Aminolevulinic Acid↗

PubMed1999

Specificity and function of immunogenic peptides from the 35-kilodalton protein of Mycobacterium leprae.

We identified a T-cell determinant of the 35-kDa antigen of Mycobacterium leprae which is discriminatory against cross-sensitization by its closely related homologue in Mycobacterium avium. From synthetic peptides covering the entire sequence, those with the highest affinity and permissive binding to purified HLA-DR molecules were evaluated for the stimulation of proliferation of peripheral blood mononuclear cells (PBMCs) from leprosy patients and healthy sensitized controls. Responses to the peptide pair 206-224, differing by four residues between M. leprae and M. avium, involved both species-specific and cross-reactive T cells. Lymph node cell proliferation in HLA-DRB1*01 transgenic mice was reciprocally species specific, but only the response to the M. leprae peptide in the context of DR1 was immunodominant. Of the cytokines in human PBMC cultures, gamma interferon production was negligible, while interleukin 10 (IL-10) responses in both patients and controls were more pronounced. IL-10 was most frequently induced by the shared 241-255 peptide, indicating that environmental cross-sensitization may skew the response toward a potentially pathogenic cytokine phenotype.

Animals↗

PubMed1998

Purification of a multipotent antideath activity from bovine liver and its identification as arginase: nitric oxide-independent inhibition of neuronal apoptosis.

Catalase is an antioxidant enzyme that has been shown to inhibit apoptotic or necrotic neuronal death induced by hydrogen peroxide. We report the purification of a contaminating antiapoptotic activity from a commercial bovine liver catalase preparation by following its ability to inhibit apoptosis when applied extracellularly in multiple death paradigms. The antiapoptotic activity was identified by protein microsequencing as arginase, a urea cycle and nitric oxide synthase-regulating enzyme, and confirmed by demonstrating the presence of antiapoptotic activity in a >97% pure preparation of recombinant arginase. The pluripotency of recombinant arginase was demonstrated by its ability to inhibit apoptosis in multiple paradigms including rat cortical neurons induced to die by glutathione depletion and oxidative stress, by 100 nM staurosporine treatment, or by Sindbis virus infection. The protective effects of arginase in these apoptotic paradigms, in contrast to previous studies on excitotoxic neuronal necrosis, are independent of nitric oxide synthase inhibition. Rather, arginase-induced depletion of arginine leads to inhibition of protein synthesis, resulting in cell survival. Because inhibitors of nitric oxide synthesis and of protein synthesis have been shown to decrease necrotic and apoptotic death, respectively, in animal models of stroke and spinal cord injury, arginine-depleting enzymes, capable of simultaneously inhibiting protein synthesis and nitric oxide generation, may be propitious therapeutic agents for acute neurological diseases. Furthermore, our results suggest caution in attributing the cytoprotective effects of some catalase preparations to catalase.

Amino Acid Sequence↗

PubMed1998

Predominant recognition of species-specific determinants of the GroES homologues from Mycobacterium leprae and M. tuberculosis.

The Mycobacterium leprae and M. tuberculosis 10,000 MW heat-shock protein homologues of GroES have previously been identified as major immunogens for human T cells. We used synthetic peptides to characterize the determinants recognized by murine T cells. The findings suggest that, despite 90% sequence identity between these two proteins, T cells recognize prominently the species-specific determinants localized within amino acid residues 21-40 and 49-72. Analysis of the molecular determinants of species-specificity for the M. leprae GroES sequence 25-40, using T-cell hybridomas and major histocompatibility complex (MHC)-binding assays, led to the identification of epitope cores and critical residues. Interestingly, closely overlapping epitope cores were found to be restricted by either H-2Ad (24-34) or H-2Ed (28-34). Furthermore, the site recognized by the M. leprae-specific monoclonal antibodies ML06 and ML10 was also localized in the overlapping sequences 25-31 and 25-29. In conclusion, we demonstrated that immunodominant species-specific T- and B-cell epitopes can be found in a mycobacterial heat-shock protein despite its highly conserved amino acid sequence. This finding suggests the feasibility of identifying a sufficient number of M. leprae-specific determinants for a composite T-cell immunodiagnostic reagent for tuberculoid leprosy.

Amino Acid Sequence↗

PubMed1997

Butch, femme, or straight acting? Partner preferences of gay men and lesbians.

On average, gay men are somewhat feminine and lesbians somewhat masculine, but there is variation within each group. The authors examined the consequences of this variation for gay men's and lesbians' desirability as romantic partners. In 2 studies the authors analyzed personal advertisements. Homosexual people were more likely than heterosexual people to mention traits related to sex typicality and more likely to request sex-typical than sex-atypical partners. In 2 studies the authors assessed partner preferences directly. On average, gay men preferred men who described themselves as masculine rather than feminine, but this preference was weaker among men who rated themselves as relatively feminine. Lesbians preferred women who described themselves as feminine looking but did not discriminate against women calling themselves masculine acting. The authors discuss implications of the results for theories of sexual orientation and the adjustment of sex-atypical homosexual people.

Adult↗

PubMed1996

T cell responses to a mixture of Mycobacterium tuberculosis peptides with complementary HLA-DR binding profiles.

The T cell response to a mixture of eight peptides derived from sequences of the Mycobacterium tuberculosis 16-, 19- and 38-kD antigens (MTBmix-8) has been studied. The peptides were selected on the basis of complementary binding to nine HLA-DR molecules (HLA-DR1 to DR9). MTBmix-8 at 6.25 and 50 micrograms/ml gave rise to significant stimulation (P < 0.05) of peripheral blood mononuclear cells (PBMC) from healthy tuberculin-positive and both untreated and treated diseased subjects, but not in any of a control group of healthy tuberculin-negative subjects. MTB-mix-8 stimulated proliferation of PBMC from healthy tuberculin-positive individuals at lower concentrations than the individual component peptides. However, the maximal stimulation achieved was only slightly higher than that achieved with individual peptides. MTBmix-8 also stimulated the production of interferon-gamma (IFN-gamma) in vitro. Using the mean +/- 2 s.d. of the values for IFN-gamma production in the tuberculin-negative population as a cut-off, MTBmix-8 at 6.25 micrograms/ml was able to detect infection with a sensitivity of 100% in untreated patients, 87% in treated patients, and 82% in tuberculin-positive controls. The corresponding figures for the most potent single peptide (16p91-110) were: 66% in untreated patients, 71% in treated patients and only 42% in controls. Thus, using the IFN-gamma-based assay, which has the additional advantages of speed and does not require radioactivity, the mixture of peptides is more sensitive than single peptides in diagnosing infection.

Adult↗

PubMed1996

Distinct conformations of a peptide bound to HLA-DR1 or DRB5*0101 suggested by molecular modelling.

The conformation of peptides when bound to different HLA class II molecules is of interest in the study of specificity and function of responding T cells. Here, we report the investigation of the HLA-DR binding profiles of an immunodominant and HLA-promiscuous mycobacterial peptide, p38G. Its binding affinities were found to be high for DR1, moderate for DR2, DR7 and DR8, low for DR4, DR5, DR6 and DR9, and below detection for DR3. The minimum peptide length required for binding was, in the majority of cases, nine residues and 11 in two instances (DR2 and DR4). Peptide binding to DR2 was attributed to the DRB5*0101 and not to the DRB1*1501 gene product. Substitution analysis of the amino acid residues involved in binding to DR1 and DRB5*0101 identified F-354 as the common primary contact residue (P1), while allele-specific differences were found in positions P4, P6 and in the C-terminal anchor residue (valine at P9 for DR1 or lysine at P10 for DRB5*0101). Computer-assisted evaluation of these empirical data produced a molecular model, suggesting that the peptide binds to DR1 in an elongated conformation, similar to that of other peptide MHC class II complexes. In contrast, the DRB5*0101 bound peptide is likely to be kinked, which so far was considered characteristic only for peptides within MHC class I complexes. The different conformations imposed on the same peptide by distinct HLA alleles may represent an important mechanism for the control of T cell responses.

Alleles↗

PubMed1988

Replication of nonvocal system for teaching nonreaders to read in an adult training centre.

An attempt was made to replicate a study to evaluate a system used by Kuntz, et al. in 1978 to teach children with mental handicaps to read. The original study was done in a children's hospital training centre with children who had considerable communication difficulties, whereas the present study was undertaken with adults with mental handicaps in an adult training centre. In the UK, adult training centres are currently at the centre of service provision by Social Services for the instruction of adults with mental handicaps, providing both a sheltered workshop and a practical educational situation. Nine out of 33 nonreaders completed the programme so the success rate was well short of that of the original study.

Adult↗

PubMed1988