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11.
Jonathan A. Coles Gisela Schneider-Picard 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1989,165(1):109-118
Summary Photoreceptor cells of the drone,Apismellifera , have a voltage-gated Na+ membrane conductance that can be blocked by tetrodotoxin (TTX) and generates an action potential on abrupt depolarization: an action potential is triggered by the rising phase of a receptor potential evoked by an intense light flash (Autrum and von Zwehl 1964; Baumann 1968). We measured the intracellular voltage response to a small (9%), brief (30 ms) decrease in light intensity from a background, and found that its amplitude was decreased by 1M TTX. The response amplitude was maximal when the background intensity depolarized the cell to –38 mV. With intensities depolarizing the cell membrane to –45 to –33 mV the average response amplitude was decreased by TTX from 1.2mV to 0.5mV. TTX is also known to decrease the voltage noise during steady illumination (Ferraro et al. 1983) but, despite this, the ratio of peak-to-peak signal to noise was, on average, decreased by TTX. The results suggest that drone photoreceptors use voltage-gated Na+ channels for graded amplification of responses to small, rapid changes in light intensity.Abbreviations
TTX
tetrodotoxin
-
V
i
intracellular potential with respect to the bath
-
V
o
extracellular potential
-
V
m,V
i-V
o
approximate transmembrane potential
-
S
amplitude of the voltage response to an 8.9% decrease in light intensity
-
N
voltage noise, usually measured as root mean square voltage deviation as described in Methods 相似文献
12.
We have broadly defined the DNA regions regulating esterase6 activity in
several life stages and tissue types of D. melanogaster using P-
element-mediated transformation of constructs that contain the esterase6
coding region and deletions or substitutions in 5' or 3' flanking DNA.
Hemolymph is a conserved ancestral site of EST6 activity in Drosophila and
the primary sequences regulating its activity lie between -171 and -25 bp
relative to the translation initiation site: deletion of these sequences
decrease activity approximately 20-fold. Hemolymph activity is also
modulated by four other DNA regions, three of which lie 5' and one of which
lies 3' of the coding region. Of these, two have positive and two have
negative effects, each of approximately twofold. Esterase6 activity is
present also in two male reproductive tract tissues; the ejaculatory bulb,
which is another ancestral activity site, and the ejaculatory duct, which
is a recently acquired site within the melanogaster species subgroup.
Activities in these tissues are at least in part independently regulated:
activity in the ejaculatory bulb is conferred by sequences between -273 and
-172 bp (threefold decrease when deleted), while activity in the
ejaculatory duct is conferred by more distal sequences between -844 and
-614 bp (fourfold decrease when deleted). The reproductive tract activity
is further modulated by two additional DNA regions, one in 5' DNA (-613 to
-284 bp; threefold decrease when deleted) and the other in 3' DNA (+1860 to
+2731 bp; threefold decrease when deleted) that probably overlaps the
adjacent esteraseP gene. Collating these data with previous studies
suggests that expression of EST6 in the ancestral sites is mainly regulated
by conserved proximal sequences while more variable distal sequences
regulate expression in the acquired ejaculatory duct site.
相似文献
13.
Abstract: Changes in sympathetic nerve terminals of the heart after varying periods of exposure of rats to 4°C were investigated. Two indices were used for changes in the number of noradrenaline storage vesicles, i.e., vesicular dopamine β-hydroxylase (DBH) activity and noradrenaline storage capacity. The latter was obtained after uptake of [3 H]noradrenaline; endogenous content, uptake of exogenous noradrenaline, and degree of saturation of the vesicles were calculated using the specific activity of the [3 H]noradrenaline. As a measure of tyrosine hydroxylase activity, whole ventricular noradrenaline, dopamine, and dihydroxyphenylacetic acid content were used. After 4 h of cold exposure there was an increase in vesicular endogenous noradrenaline content, uptake, storage capacity, and DBH activity as well as a large increase in whole ventricular dopamine. After 6 h in the cold, vesicular endogenous noradrenaline content, storage capacity, and DBH activity were decreased. The results suggest that during cold exposure there is an initial increase followed by a decrease in the number of functional vesicles in the nerve terminal, which could explain the fluctuations in the rate of noradrenaline release. 相似文献
14.
Nucleotide variation at the hypervariable esterase 6 isozyme locus of Drosophila simulans 总被引:2,自引:0,他引:2
Esterase 6 (Est-6/EST6) is polymorphic in both Drosophila melanogaster and
D. simulans for two common allozyme forms, as well as for several other
less common variants. Parallel latitudinal clines in the frequencies of the
common EST6-F and EST6-S allozymes in these species have previously been
interpreted in terms of a shared amino acid polymorphism that distinguishes
the two variants and is subject to selection. Here we compare the sequences
of four D. simulans Est-6 isolates and show that overall estimates of
nucleotide heterozygosity in both coding and 5' flanking regions are more
than threefold higher than those obtained previously for this gene in D.
melanogaster. Nevertheless, the ratio of replacement to exon silent-site
polymorphism in D. simulans is less than the ratio of replacement to silent
divergence between D. simulans and D. melanogaster, which could be the
result of increased efficiency of selection against replacement
polymorphisms in D. simulans or to divergent selection between the two
species. We also find that the amino acid polymorphisms separating EST6- F
and EST6-S in D. simulans are not the same as those that separate these
allozymes in D. melanogaster, implying that the shared clines do not
reflect shared molecular targets for selection. All comparisons within and
between the two species reveal a remarkable paucity of variation in a
stretch of nearly 400 bp immediately 5' of the gene, indicative of strong
selective constraint to retain essential aspects of Est-6 promoter
function.
相似文献
15.
Stephen L. Coles 《Coral reefs (Online)》1984,3(3):123-130
The colonization and growth of reef corals settling on new substrata (concrete and basalt) and on a denuded coral reef were studied over a seven-year period. The study area is in the vicinity of an outfall discharging thermal effluent from a Hawaiian power station, and both numbers and coverage of settled corals were found to increase exponentially with proximity to the outfall's discharge. Recruitment rates adjacent to the outfall were at least ten times greater than values previously reported for open ocean areas in Hawaii, and the estimated time for recovery of the coral community near the outfall was comparable to the most rapid that has been reported worldwide. By contrast, coral recruitment and recovery more distant from the outfall compared well with slower rates reported for other areas in Hawaii. Entrainment of coral planulae in water discharged into the area by the outfall is proposed to be the principal mechanism promoting the high coral colonization. 相似文献
16.
17.
A proteolytic enzyme in the gut exudate of the common liver fluke has been purified. The enzyme is specific for globin with a pH optimum of 3.9–4.0 and breaks the protein down to peptides and a small percentage of free amino acids. Collagenase activity at pH 7.5 copurifies with the main globinolytic enzyme. The enzyme has a molecular weight of 12,000 and does not appear to be antigenic in fluke-infected animals. 相似文献
18.
Summary The effects have been analyzed of cytochalasin B and colchicine on the secretion of glycoconjugates by human bronchial expiants labeled in vitro with radioactive glucosamine. Both cytochalasin B and colchicine had no effect on baseline 14C-labeled glycoconjugate release but caused a dose-dependent (10–7–10–4 M) inhibition of 14C-glycoconjugate release and discharge of labeled macromolecules from mucous and serous cells induced by 5 · 10–5 M methacholine.Quantitative autoradiographic analyses showed that neither cytochalasin B nor colchicine inhibited 3H-threonine or 3H-glucosamine incorporation into mucous and serous cells of the submucosal glands or goblet cells of the airway epithelium. Colchicine (10–5 M) but not cytochalasin B significantly reduced the rate at which labeled macromolecules were transported through mucous, serous and goblet cells but this effect was not observed until 4 h after the addition of colchicine. Neither cytochalasin B nor colchicine affected the basal rate of labeled-macromolecule discharge from mucous, serous or goblet cells. At a concentration of 10–5 M, both agents completely inhibited the increase in labeled-macromolecule discharge induced in mucous and serous cells by methacholine.Our results suggest that in the submucosal gland of human airways microtubules and microfilaments may be important in secretagogue-induced but not in baseline cellular glycoconjugate discharge, implying that the mechanisms of the two processes differ significantly. Furthermore, a role for microtubules is suggested in the transport of secretory granules through mucous, serous and goblet cells.Supported by National Institutes of Health Research Grant 5R01HL22444. The authors gratefully acknowledge the technical assistance of Mr. Tudor Williams, Mr. Eduardo Quintanilla and Ms. Maureen Hayes 相似文献
19.
Results of semi-quantitative observations and quantitative sampling of seagrasses at coastal and offshore sites along the
western Arabian Gulf are presented. Overall seagrass cover (all species together) shows significant positive correlation with
latitude, but not with salinity, temperature or depth. The same pattern is shown by Halodule uninervis (Forsk.) Aschers., the dominant species. Mean seagrass biomass ranged from 53–235 g m-2 (dry weight). These values are comparable with biomass estimates from regions in which environmental conditions are generally
less extreme than in the Gulf. Seagrass biomass is significantly negatively correlated with depth and sediment grain size.
No significant correlation is apparent between seagrass biomass and factors such as season, salinity, or concentrations of
nutrients and heavy metals measured. It is pointed out that any correlations observed are not necessarily taken to imply causality. 相似文献
20.
Graeme D. Coles D. J. Abernethy Mary C. Christey A. J. Conner B. K. Sinclair 《Plant Molecular Biology Reporter》1991,9(1):13-20
Hairy roots, incited byAgrobacterium rhizogenes, form a useful system for analysing the expression and phenotypic effects of foreign genes in plant root tissue. Image analysis
offers a non-invasive method of describing their growth in culture. Images of pea (coarse) andBrassica (fine) hairy roots were captured, processed and analysed without difficulty using a commercially available image analysis
system. The value of this method in monitoring intermediate changes in growth pattern was illustrated by following the changes
in five putatively chlorsulfuron-resistantBrassicc hairy-root lines cultured with and without a selective level of chlorsulfuron. Areas of hairy-root research where this technique
will be particularly useful are discussed. 相似文献