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1.
Triethyl lead is the major metabolite of tetraethyl lead, which is used in industrial processes and as an antiknock additive to gasoline. We tested the hypothesis that low levels of triethyl lead (0.1 nmol/L to 5mol/L) interfere with the normal development of cultured E18 rat hippocampal neurons, possibly through increases in intracellular free calcium ion concentration, [Ca2+]in. The study assessed survival and differentiation using morphometric analysis of individual neurons. We also looked at short-term (up to 3.75-h) changes in intracellular calcium using the calcium-sensitive dye fura-2. Survival of neurons was significantly reduced at 5 mol/L, and overall production of neurites was reduced at 2 mol/L. The length of axons and the number of axons and dendrites were reduced at 1 mol/L. Neurite branching was inhibited at 10 nmol/L for dendrites and 100 nmol/L for axons. Increases in intracellular calcium were observed during a 3.75-h exposure of newly plated neurons to 5 mol/L triethyl lead. These increases were prevented by BAPTA-AM; which clamps [Ca2+]in at about 100 nmol/L. Culturing neurons with BAPTA-AM and 5 mol/L triethyl lead did not reverse the effects of triethyl lead, suggesting that elevation of [Ca2+]in is not responsible for decreases in survival and neurite production. Triethyl lead has been shown to disrupt cytoskeletal elements, particularly neurofilaments, at very low levels, suggesting a possible mechanism for its inhibition of neurite branching at nanomolar concentrations.Abbreviations BAPTA-AM
1,2-bis(2-aminophenoxy)ethane-N,N,N,N-tetraacetic acid acetoxymethyl ester
- [Ca2+]in
intracellular free calcium ion concentration
- DMSO
dimethyl sulfoxide
- E18
embryonic day 18
- FBS
fetal bovine serum
- fura-2AM
fura-2 acetoxymethyl ester
- HBSS
Hanks' Balanced Salt Solution
- MEM
Eagle's Minimum Essential Medium 相似文献
2.
J. N. Wu E. Tiffany-Castiglioni 《In vitro cellular & developmental biology. Plant》1987,23(11):765-774
Summary Time- and dose-dependent toxic effects of lead (Pb) acetate on astroglia, oligodendroglia, and meningeal fibroblasts cultured
from immature rat brain were measured. Cultures were exposed for 3 d to Pb (1,10, and 100 μM) and then examined immediately (Day 0) or 3 or 10 d after Pb treatment was discontinued. The percentages of astroglia and
fibroblasts excluding dye were unaffected by Pb, whereas the percentage of oligodendroglia excluding dye decrease significantly
(P<0.01) at all time points after exposure to 100 μM Pb. Lead (100 μM) also reduced the total cell numbers of astroglia, oligodendroglia, and meningeal fibroblasts. Amino acid incorporation into
protein by oligodendroglia was stimulated after exposure to 100 μM Pb at all time points and also by 1 and 10 μM on Day 3. Incorporation was stimulated in astroglia only on Day 0 by 10 and 100 μM. Hydrocortisone-stimulated glycerolphosphate dehydrogenase (GPDH) activity was assayed in oligodendroglia cultures. A significant
decrease in specific activity was seen after a 4-d exposure to lead. Because oligodendroglia are responsible for myelin synthesis
in the central nervous system, and GPDH may synthesize a precursor for myelin lipid synthesis, it was proposed that the hypomyelination
observed in lead-intoxicated neonatal rats may result partially from a primary toxic effect on oligodendroglia. GPDH activity
was not inhibited by Pb in mixed glial cultures containing both astroglia and oligodendroglia. This result suggests that astroglia
in culture have the ability to delay the lead-induced inhibition of oligodendroglial GPDH activity and supports the hypothesis
that astroglia in culture serve a protective function.
This work was supported by Environmental Protection Agency Grant R811500 and by U. S. Department of Agriculture Project M-6839
Animal Health Formula Funding Project 6652. This work was carried out by J.-N. Wu in partial fulfillment of the requirements
for a Master of Science degree in Veterinary Public Health at Texas A&M University. 相似文献
3.
The structural determinants of mibefradil inhibition were analyzed using wild-type and inactivation-modified CaV1.2 (α1C) and CaV2.3 (α1E) channels. Mibefradil inhibition of peak Ba2+ currents was dose- and voltage-dependent. An increase of holding potentials from −80 to −100 mV significantly shifted dose-response
curves toward higher mibefradil concentrations, namely from a concentration of 108 ± 21 μm (n= 7) to 288 ± 17 μm (n= 3) for inhibition of half of the Cav1.2 currents (IC
50) and from IC
50= 8 ± 2 μm (n= 9) to 33 ± 7 μm (n= 4) for CaV2.3 currents. In the presence of mibefradil, CaV1.2 and CaV2.3 experienced significant use-dependent inhibition (0.1 to 1 Hz) and slower recovery from inactivation suggesting mibefradil
could promote transition(s) to an absorbing inactivated state. In order to investigate the relationship between inactivation
and drug sensitivity, mibefradil inhibition was studied in inactivation-altered CaV1.2 and CaV2.3 mutants. Mibefradil significantly delayed the onset of channel recovery from inactivation in CEEE (Repeat I + part of
the I–II linker from CaV1.2 in the CaV2.3 host channel), in EC(AID)EEE (part of the I–II linker from CaV1.2 in the CaV2.3 host channel) as well as in CaV1.2 E462R, and CaV2.3 R378E (point mutation in the β-subunit binding motif) channels. Mibefradil inhibited the faster inactivating chimera EC(IS1-6)EEE with an IC
50= 7 ± 1 μm (n= 3), whereas the slower inactivating chimeras EC(AID)EEE and CEEE were, respectively, inhibited with IC
50= 41 ± 5 μm (n= 4) and IC
50= 68 ± 9 μm (n= 5). Dose-response curves were superimposable for the faster EC(IS1-6)EEE and CaV2.3, whereas intermediate-inactivating channel kinetics (CEEE, CaV1.2 E462R, and CaV1.2 E462K) were inhibited by similar concentrations of mibefradil with IC
50≈ 55–75 μm. The slower CaV1.2 wild-type and CaV1.2 Q473K channels responded to higher doses of mibefradil with IC
50≈ 100–120 μm. Mibefradil was also found to significantly speed up the inactivation kinetics of slower channels (CaV1.2, CEEE) with little effect on the inactivation kinetics of faster-inactivating channels (CaV2.3). A open-channel block model for mibefradil interaction with high-voltage-activated Ca2+ channels is discussed and shown to qualitatively account for our observations. Hence, our data agree reasonably well with
a ``receptor guarded mechanism' where fast inactivation kinetics efficiently trap mibefradil into the channel.
Received: 14 March 2001/Revised: 25 June 2001 相似文献
4.
The Fusarium toxin deoxynivalenol (DON) often co-occurs along with the acetylated derivatives 3-acetyl-DON and 15-acetyl-DON in diets
for ruminants. De-epoxy-DON is formed by rumen micro-organisms, while the acetylated DON derivatives might also undergo ruminal
metabolism with de-epoxy-DON as an end product. However, despite the fact that de-epoxy-DON is the predominant substance finally
absorbed, a complete degradation of the mother compounds can not be assumed for all feeding and metabolic situations of the
cow, and thus raising the question of their possible post-absorptive effects. Hence, the aim of the study was to examine the
effects of all four compounds on the concanavalin A stimulated proliferation of bovine peripheral blood mononuclear cells
(PBMC) using MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide) as indicator in vitro and ex vivo. Among
the DON-related compounds, DON and 15-acetyl-DON resulted in a similar IC50 (i.e. the concentration where the proliferation was inhibited by 50%) of 0.5 μM, whereas 3-acetyl-DON was less toxic (IC50 = 2.6 μM), while actually no IC50 could be estimated for de-epoxy-DON which was characterized by a maximum inhibition of approximately 24% at the highest tested
in vitro concentration of 18.29 μM. For the in vivo experiment, 14 Holstein cows were used and fed either an uncontaminated control diet (CON) or a diet contaminated
with Fusarium toxins, with DON being the predominating toxin for 18 weeks when blood was collected for PBMC isolation and subsequent proliferation/viability
assay. The complete diets for the CON and FUS group contained 0.4 and 4.6 mg DON/kg DM, respectively, at that time. Exposure
of dairy cows to the FUS diet resulted in maximum serum de-epoxy-DON levels of 52 ng/ml (0.19 μM), while levels of the unmetabolized DON reached maximum levels of 9 ng/ml (0.03 μM). The PBMC of these cows were slightly less viable, by approximately 18% (p = 0.057), while stimulation capability was not decreased at the same time. Although de-epoxy-DON was characterized by the
lowest in vitro toxicity among the tested DON-related compounds, there appeared to be a lower viability of the PBMC isolated
from cows fed the FUS diet, which had nearly exclusively de-epoxy DON in serum beside slight traces of unmetabolized DON.
Thus, the factors responsible for these apparent discrepancies need to be clarified. 相似文献
5.
Mary Chebib Navnath Gavande Kit Yee Wong Anna Park Isabella Premoli Kenneth N. Mewett Robin D. Allan Rujee K. Duke Graham A. R. Johnston Jane R. Hanrahan 《Neurochemical research》2009,34(10):1704-1711
GABAC receptors play a role in myopia, memory-related disorders and circadian rhythms signifying a need to develop potent and selective
agents for this class of receptors. Guanidino analogs related to glycine, β-alanine and taurine were evaluated at human ρ1GABAC receptors expressed in Xenopus oocytes using 2-electrode voltage clamp methods. Of the 12 analogs tested, 8 analogs were active as antagonists and the remaining
were inactive. (S)-2-Guanidinopropionic acid (IC50 = 2.2 μM) and guanidinoacetic acid (IC50 = 5.4 μM; K
B = 7.75 μM [pK
B = 5.11 ± 0.06]) were the most potent being competitive antagonists at this receptor. In contrast, the β-alanine and GABA
guanidino analogs showed reduced activity, indicating the distance between the carboxyl carbon and terminal nitrogen of the
guanidino group is critical for activity. Substituting the C2-position of guanidinoacetic acid with various alkyl groups reduced
activity indicating that steric effects may impact on activity. The results of this study contribute to the structure–activity-relationship
profile required in developing novel therapeutic agents. 相似文献
6.
The effects of low concentrations of aluminium on the growth and uptake of nitrate-N by white clover 总被引:1,自引:0,他引:1
Summary The effects of aluminium (Al3+) at concentrations of 0, 25, 50 and 100 μM on the growth of white clover, dependent upon N supplied as NO
3
−
, were examined in flowing solution culture. Plants were established with a normal nutrient supply for 7 weeks and then grown
with carefully controlled pH (at 4.5) and P concentrations, and with 0, 25, 50 or 100 μM Al3+ for a further three weeks. There were rapid visual effects (i.e. symptoms of P deficiency and reduction in root extension) and the dry weights of shoots and roots were reduced at 50 and
100 μM. Less than 10% of Al absorbed from solution was transported to the shoots. The uptake of P, and its transport between roots
and shoots, were reduced in plants grown with Al. The uptake of NO
3
−
stopped immediately after the introduction of 50 or 100 μM Al, and was significantly reduced at 25 μM after three weeks.
During a second phase of the experiment, plants previously grown at 0, 25, 50 and 100 μM Al, were grown for a further 2 weeks either with NO
3
−
(with and without 50 μM Al3+) or without NO
3
−
but with inoculation by Rhizobia (and with or without 50 μM Al3+). The effects of the previous treatments with Al on N uptake were small during the second phase, but uptake by all plants
was restricted when Al was present. Inoculation did not result in nodulation in the second phase when Al3+ was present in the solution, but Al already in the plant from the first phase did not prevent nodulation in the absence of
Al during the second phase. 相似文献
7.
Identification of carotenoids with high antioxidant capacity produced by extremophile microorganisms
F Mandelli VS Miranda E Rodrigues AZ Mercadante 《World journal of microbiology & biotechnology》2012,28(4):1781-1790
In this study, the carotenoids produced by the extremophile microorganisms Halococcus morrhuae, Halobacterium salinarium and Thermus filiformis were separated and identified by high-performance liquid chromatography connected to a diode array detector and a tandem
mass spectrometer. The in vitro scavenging capacity of the carotenoid extracts against radical and non-radical species was
evaluated. In halophilic microorganisms, the following carotenoids were identified: bacterioruberin, bisanhydrobacterioruberin,
trisanhydrobacterioruberin and their derivatives. In the thermophilic bacterium, the carotenoids all-trans-zeaxanthin, zeaxanthin monoglucoside, thermozeaxanthins and thermobiszeaxanthins were identified. The antioxidant capacities
of the carotenoid extracts of H. morrhuae (trolox equivalent antioxidant capacity = 5.07 and IC50 = 0.85 μg mL−1) and H. salinarium (trolox equivalent antioxidant capacity = 5.28 and IC50 = 0.84 μg mL−1) were similar and higher than those of the bacterium T. filiformis (trolox equivalent antioxidant capacity = 2.87 and IC50 = 2.41 μg mL−1). This difference is related to the presence of acyclic carotenoids with both large numbers of conjugated double bounds and
of hydroxyl groups in the major carotenoid of the halophilic microorganisms. 相似文献
8.
M. J. Perry J. O’Connell C. Walker T. Crabbe D. Baldock A. Russell S. Lumb Z. Huang D. Howat R. Allen M. Merriman J. Walls T. Daniel B. Hughes F. Laliberte G. A. Higgs R. J. Owens 《Cell biochemistry and biophysics》1998,29(1-2):113-132
We present the in vitro characterization of a novel phosphodiesterase type 4 inhibitor, CDP840 (R-[+]-4-[2-{3-cyclopentyloxy-4-methoxyphenyl}-2-phenylethyl]pyridine), which has shown efficacy in a phase II allergen challenge
study in asthmatics without adverse effects. CDP840 potently inhibits PDE-4 isoenzymes (IC50 2–30 nM) without any effect on PDE-1, 2, 3, 5, and 7 (IC50>100 μM). It exhibited no significant selectivity in inhibiting human recombinant isoenzymes PDE-4A, B, C or D and was equally active
against the isoenzymes lacking UCR1 (PDE-4B2 and PDE-4D2). In contrast to rolipram, CDP840 acted as a simple competitive inhibitor
of all PDE-4 isoenzymes. Studies with rolipram indicated a heterogeneity within all the preparations of PDE-4 isoenzymes,
indicative of rolipram inhibiting the catalytic activity of PDE-4 with both a low or high affinity. These observations were
confirmed by the use of a PDE-4A variant, PDE-4A330–886, which rolipram inhibited with low affinity (IC50=1022 nM). CDP840 in contrast inhibited this PDE-4A variant with similar potency (IC50=3.9 nM), which was in good agreement with theK
d of 4.8 nM obtained from [3H]-CDP840 binding studies. Both CDP840 and rolipram inhibited the high-affinity binding of [3H]-rolipram binding to PDE-4A, B, C and D with similarK
d app (7–19 nM and 3–5 nM, respectively). Thus, the activity of CDP840 at the [3H]-rolipram binding site was in agreement with the inhibitor’s activity at the catalytic site. However, rolipram was ∼100-fold
more potent than CDP840 at inhibiting the binding of [3H]-rolipram to mouse brain in vivo. These data clearly demonstrate that CDP840 is a potent selective inhibitor of all PDE-4
isoenzymes. In contrast to rolipram, CDP840 was well-tolerated in humans. This difference, however, cannot at present be attributed
to either isoenzyme selectivity or lack of activity in vitro at the high-affinity rolipram binding site (Sr). 相似文献
9.
Violacein cytotoxicity and induction of apoptosis in V79 cells 总被引:8,自引:0,他引:8
Melo PS Maria SS Vidal BC Haun M Durán N 《In vitro cellular & developmental biology. Animal》2000,36(8):539-543
Summary Violacein, a pigment produced by Chromobacterium violaceum, is reported to be a potential drug for the treatment of Chagas' disease. Violacein is also effective against leukemia and
lymphoma cells in culture (IC50 10−8
M). Changes in the nuclear acid content, 3-(4,5-dimethylthiazole-2-yl)-2,5-biphenyl tetrazolium bromide reduction and neutral
red uptake in these cells were used to evaluate the cytotoxicity of violacein in V79 Chinese hamster (M-8) fibroblasts. Violacein
was highly cytotoxic to V79 fibroblasts (IC50 5–12 μM). Using the TUNEL method and the Feulgen reaction coupled to image analysis, violacein (5 and 10 μM) was found to trigger apoptosis but not necrosis in V79 cells. The morphological changes seen in the nuclei of these cells
included chromatin condensation and a decrease in deoxyribonucleic acid content. These results demonstrating that violacein
induces apoptosis in V79 cells strengthen its potential as a therapeutic agent. 相似文献
10.
Terry L. Riss' David A. Sirbasku 《In vitro cellular & developmental biology. Plant》1989,25(2):136-142
Summary The effect of 17β-estradiol (E2) on growth of GH4C1 rat pituitary tumor cells was investigated under serum-free conditions and with medium containing charcoal-extracted serum.
Serum-free TRM-1 medium was a 1∶1 (vol/vol) mixture of F12-DME supplemented with 50 μg/ml gentamicin, 15 mM 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, 10 μg/ml insulin, 10 μg/ml transferrin, 10 ng/ml selenous acid, 10 nM 3,5,3′-triiodothyronine (T3), 50 μM ethanolamine, and 500 μg/ml bovine serum albumin. The cells grew continuously in TRM-1 but were E2 responsive only when growth was retarded by reducing the T3 concentration to 10 pM (TRM-MOD). Addition of 1 to 10 nM E2 to TRM-MOD increased growth by 0.3 to 0.9 cell population doublings over controls in 9 d. By using medium supplemented with
charcoal-extracted sera, basal growth became 1 to 1.5 cell population doublings in 9 d. Addition of 0.1 pM E2 to medium containing charcoal-extracted serum caused a significant increase in cell number whereas pM-nM concentrations stimulated 200 to 570% increases over controls. The effect of steroid hormone was the same in phenol-red-containing
and indicator-free medium. The data presented confirm that the major requirements for demonstration of estrogenic effects
in culture were optimum concentrations of thyroid hormones and the presence of yet-to-be-characterized serum factors.
This work was supported by National Cancer Institute (Bethesda, MD) grants CA-26617 and CA-38024, American Cancer Society
grant BC-255, and grant 2225 from The Council for Tobacco Research, U.S.A., Inc. 相似文献
11.
Solntseva EI Bukanova JV Marchenko EV Rossokhin AV Skrebitsky VG 《Cellular and molecular neurobiology》2009,29(2):219-224
Earlier, we have shown a strong inhibitory effect of donepezil on K+-current of molluscan neurons (Solntseva et al., Comp Biochem Physiol 144, 319–326, 2007). In the present work, a possible
interaction of donepezil with the external mouth of the channel was examined using, as a tool, tetraethylammonium (TEA), a
classical antagonist of potassium channels. Experiments were conducted in isolated neurons of snail Helix aspersa using the
two-microelectrode voltage-clamp technique. A high-threshold slow-inactivating K+-current involving Ca2+-dependent (I
C) and Ca2+-independent (I
K) components was recorded. The I
C was estimated at 30 mV, and I
K at 100 mV. The IC50 values for blocking effect of donepezil on I
C varied from 5.0 to 8.9 μM in different cells. Corresponding values for I
K varied from 4.9 to 9.9 μM. The IC50 values for blocking effect of TEA on I
C lied in the range of 200 to 910 μM, and on I
K lied in the range of 100 to 990 μM. The comparison of the effects of donepezil and TEA on the same cells revealed significant
correlation between IC50 values of these effects. The value of Spearman coefficient of correlation (r) was 0.77 for I
C (P < 0.05), and 0.82 for I
K (P < 0.05). In the presence of TEA, the effect of donepezil, both on I
C and I
K, appears significantly weaker than in control solution. Dose–response curves of donepezil effect both on I
C and I
K were shifted right along horizontal axis when donepezil was applied in combination with TEA. Results suggest that TEA interferes
with donepezil and precludes the occupation by donepezil of its own site. We suppose that the site for donepezil is situated
near the TEA site with possible overlap. 相似文献
12.
R. Wondergem M. Cregan L. Strickler R. Miller J. Suttles 《The Journal of membrane biology》1998,161(3):257-262
These experiments were done to determine the effect of glibenclamide and diazoxide on the growth of human bladder carcinoma
(HTB-9) cells in vitro. Cell growth was assayed by cell counts, protein accumulation, and 3H-thymidine uptake. Glibenclamide added at 75 and 150 μm for 48 hr reduced cell proliferation. Dose-inhibition curves showed that glibenclamide added for 48 hr reduced cell growth
at concentrations as low as 1 μm (IC50= 73 μm) when growth was assayed in the absence of added serum. This μM-effect on cell growth was in agreement with the dose range
in which glibenclamide decreased open probability of membrane KATP channels. Addition of glibenclamide for 48 hr also altered the distribution of cells within stages of the cell cycle as determined
by flow cytometry using 10−5
m bromodeoxyuridine. Glibenclamide (100 μm) increased the percentage of cells in G0/G1 from 33.6% (vehicle control) to 38.3% (P < 0.05), and it reduced the percentage of cells in S phase from 38.3% to 30.6%. On the other hand, diazoxide, which opens
membrane KATP channels in HTB-9 cells, stimulated growth measured by protein accumulation, but it did not increase the cell number. We
conclude that the sulfonylurea receptor and the corresponding membrane KATP channel are involved in mechanisms controlling HTB-9 cell growth. However, KATP is not rate-limiting among the signaling mechanisms or molecular switches that regulate the cell cycle.
Received: 12 June 1997/Revised: 21 October 1997 相似文献
13.
Ging Kuo Wang Joanna Calderon Shiow-Jiin Jaw Sho-Ya Wang 《The Journal of membrane biology》2009,229(1):1-9
Articaine is widely used as a local anesthetic (LA) in dentistry, but little is known regarding its blocking actions on Na+ channels. We therefore examined the state-dependent block of articaine first in rat skeletal muscle rNav1.4 Na+ channels expressed in Hek293t cells. Articaine exhibited a weak block of resting rNav1.4 Na+ channels at −140 mV with a 50% inhibitory concentration (IC50) of 378 ± 26 μM (n = 5). The affinity was higher for inactivated Na+ channels measured at −70 mV with an IC50 value of 40.6 ± 2.7 μM (n = 5). The open-channel block by articaine was measured using inactivation-deficient rNav1.4 Na+ channels with an IC50 value of 15.8 ± 1.5 μM (n = 5). Receptor mapping demonstrated that articaine interacted strongly with a D4S6 phenylalanine residue, which is known
to form a part of the LA receptor. Thus the block of rNav1.4 Na+ channels by articaine is via the conserved LA receptor in a highly state-dependent manner, with a ranking order of open (23.9×) > inactivated
(9.3×) > resting (1×) state. Finally, the open-channel block by articaine was likewise measured in inactivation-deficient
hNav1.7 and rNav1.8 Na+ channels, with IC50 values of 8.8 ± 0.1 and 22.0 ± 0.5 μM, respectively (n = 5), indicating that the high-affinity open-channel block by articaine is indeed preserved in neuronal Na+ channel isoforms. 相似文献
14.
We compared the effects of four quaternary benzo[c]phenanthridine alkaloids – chelerythrine, chelilutine, sanguinarine, and sanguilutine – and two quaternary protoberberine
alkaloids – berberine and coptisine – on the human cell line HeLa (cervix carcinoma cells) and the yeastsSaccharomyces cerevisiae andSchizosaccharomyces japonicus var. versatilis. The ability of alkaloids to display primary fluorescence, allowed us to record their dynamics and localization in cells.
Cytotoxic, anti-microtubular, and anti-actin effects in living cells were studied. In the yeasts, neither microtubules nor
cell growth was seriously affected even at the alkaloid concentration of 100 μg/ml. The HeLa cells, however, responded to
the toxic effect of alkaloids at concentrations ranging from 1 to 50 μg/ml. IC50 values for individual alkaloids were: sanguinarine IC50 = 0.8 μg/ml, sanguilutine IC50 = 8.3 μg/ml, chelerythrine IC50 = 6.2 μg/ml, chelilutine IC50 = 5.2 μg/ml, coptisine IC50 = 2.6 μg/ml and berberine IC50 >10.0 μg/ml. In living cells, sanguinarine produced a decrease in microtubule numbers, particularly at the cell periphery,
at a concentration of 0.1 μg/ml. The other alkaloids showed a similar effect but at higher concentrations (5–50 μg/ml). The
strongest effects of sanguinarine were explained as a consequence of its easy penetration through the cell membrane owing
to nonpolar pseudobase formation and to a high degree of molecular planarity.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
Lotshaw DP 《The Journal of membrane biology》2006,210(1):51-70
Multiple genes of the TASK subfamily of two-pore domain K+ channels are reported to be expressed in rat glomerulosa cells. To determine which TASK isoforms contribute to native leak
channels controlling resting membrane potential, patch-clamp studies were performed to identify biophysical and pharmacological
characteristics of macroscopic and unitary K+ currents diagnostic of recombinant TASK channel isoforms. Results indicate K+ conductance (gK+) is mediated almost exclusively by a weakly voltage-dependent (leak) K+ channel closely resembling TASK-3. Leak channels exhibited a unitary conductance approximating that expected for TASK-3 under
the recording conditions employed, brief mean open times and a voltage-dependent open probability. Extracellular H+ induced voltage-independent inhibition of gK+, exhibiting an IC50 of 56 nM (pH 7.25) and a Hill coefficient of 0.75. Protons inhibited leak channel open probability (Po) by promoting a long-lived closed state (τ > 500 ms). Extracellular Zn2+ mimicked the effects of H+; inhibition of gK+ exhibited an IC50 of 41 μM with a Hill coefficient of 1.26, inhibiting channel gating by promoting a long-lived closed state. Ruthenium red (5 μM) inhibited gK+ by 75.6% at 0 mV. Extracellular Mg2+ induced voltage-dependent block of gK+, inhibiting unitary current amplitude without affecting mean open time. Bupivacaine induced voltage-dependent block of gK+, exhibiting IC50 values of 116 μM at −100 mV and 28 μM at 40 mV with Hill coefficients of 1 at both potentials. Halothane induced a voltage-independent stimulation of gK+ primarily by decreasing the leak channel closed-state dwell time. 相似文献
16.
Scutellariae Radix is one of the well-known tocolytic Chinese herbs. Oroxylin A is isolated from the root of Scutellaria baicalensis. The main syndrome of preterm birth is caused by uterus contractions from excitatory factors. Administration of tocolytic
agents is a strategy to prevent the occurrence of preterm births. The aim of this study was to investigate the effects of
oroxylin A on contractions of uterine strips isolated from non-pregnant female Wistar rats (250~350 g). Contractions of the
uterus were induced with acetylcholine (Ach) (1 μM), PGF2α (0.1 μM), oxytocin (10-3 U/ml), KCl (56.3 mM), tetraethylammonium (TEA; 1 and 10 mM), 4-aminopyridine (4-AP; 5 mM), glipizide (30 μM), a nitric oxide
synthase (NOS) inhibitor (LNNA; 10-3M), a β-receptor blocker (propranolol; 10 μM), and a cyclooxygenase inhibitor (indomethacin; 60 μM). The inhibitory effects
of the amplitude and frequency of spontaneous contractions by oroxylin A were antagonized with Ach (IC50 22.85 μM), PGF2α (IC5027.28 μM), oxytocin (IC50 12.34 μM), TEA; 1 and 10 mM (IC50 52.73 and 76.43 μM), 4-AP (IC50 67.16 μM), and glipizide (IC5027.53 μM), but oroxylin A was not influenced by Ca2+-free medium, LNNA, propranolol, or indomethacin. Otherwise, oroxylin A-mediated relaxation of the rat uterus might occur
through opening of uterine calcium-dependent potassium channels or adenosine triphosphate potassium channel activation. This
suggests that oroxylin A is the tocolytic principle constituent of Scutellariae Radix, and oroxylin A may provide a lead compound for new tocolytic drug development in the future. 相似文献
17.
Summary A protocol has been developed for differentiation of shoot buds directly from leaf segments of white marigold (Tagetes erecta L.). Leaf segments were taken from in vitro-proliferated shoots of white marigold established in aseptic culture from shoot tips of field-grown plants. Gibberellic acid
(GA) played a significant role in the induction of shoot buds as well as in suppressing callus formation. Shoot buds were
induced directly in Murashige and Skoog's (MS) medium supplemented with 14.43 μM GA and 4.44 μM 6-benzyladenine in the absence of any auxin. In this medium two to five shoot buds differentiated from the margins as well
as leaf lamina of the lower petiolar segment within 4 wk of incubation. Differentiated shoots grew well and proliferated in
the MS medium having 1.1 μM BA and 29.41 μM AgNO3, as it had a beneficial effect on the growth and proliferation of shoots. Shoots were excised, rooted in 0.27 μm α-naphthaleneacetic acid (NAA) and transplanted under glasshouse conditions, where they grew and flowered. Data on different
morphological characters during flowering under field conditions were recorded for seed-grown control plants, tissue culture-raised
primary regenerants (R0) and first-generation (R1) plants. It was found that all the economically desired characters of plant height, number and size of flowers per plant,
number of viable seeds per flower, and days to full bloom, of the R1 generation plants were significantly better than the control, thus increasing the commercial value of the tissue culture-raised
plants in successive generations. 相似文献
18.
Sister chromatid exchange (SCE) frequency and high-frequency cells (HFCs) were analyzed in 50 storage battery plant workers
with mean blood lead level (BLL) of 40.14±9.99 μg/dL. The mean BLL in the control group (n=30) was 9.77±1.67 μg/dL. This difference in mean BLLs between control and exposed group was statistically significant (p<0.05) and reflects clearly the lead exposure in the workers. Urinary aminolevulinic acid (U-ALA) was also determined in both
control (3.37±0.89 mg ALA/g creatinine) and exposed groups (12.39±6.18 mg ALA/g creatinine) and U-ALA excretion was statistically
higher (p<0.05) in lead-exposed workers. The relationship between biomarkers of lead exposure/effect and HFC percentage was higher
than the relationship between biomarkers of lead exposure/effect and SCE frequency. Accordingly, HFC analysis seemed to be
more sensitive than the SCE analysis as a cytogenetic biomarker for lead exposure. Additionally, the statistically significant
correlation (r
2=0.880, p<0.01) between U-ALA excretion and HFC percentage in lead-exposed workers supported the probability of ALA mediated indirect
mechanism for lead genotoxicity. 相似文献
19.
R. Rodríguez M. Rey L. Cuozzo G. Ancora 《In vitro cellular & developmental biology. Plant》1990,26(5):531-536
Summary A twenty fold multiplication per twenty days of caper was achieved by culturing nodal shoot segments in the presence of BAP
(4 μM) plus IAA (0.3 μM) and GA3 (0.3 μM). The use of a modified MS medium facilitated this response. Plantlet regeneration was induced on single shoots taken from
proliferating clusters subcultured for 20 days on a reduced BAP (2 μM) without auxin and gibberellin Higher rooting responses (70%) were obtained after a 20-day incubation period in darkness
on solid half-strength MS1 medium plus IAA (30 μM), followed by a subsequent 20 day culture period on half-strength MSI basal medium. Proliferation was mainly due to axillary
shoot-bud development as revealed by histological studies. The extensive meristematic activities observed indicated the enormous
morphological potential of this species. 相似文献
20.
P. Light Y. Shimoni S. Harbison W. Giles R.J. French 《The Journal of membrane biology》1998,162(3):217-223
The effects of thyroid status on the properties of ATP-sensitive potassium channels were investigated. Single-channel recordings
were made using excised inside-out membrane patches from enzymatically dissociated ventricular myocytes from hearts of control
and thyroidectomized rats and each group was studied with and without administration of thyroid hormone.
In patches excised from hypothyroid myocytes the IC50 for ATP inhibition of KATP channels was 110 μm. This value was 3-fold higher than the IC50 in control myocytes (43 μm). Treatment of hypothyroid rats to restore physiological levels of thyroid hormone (tri-iodothyronine, T3), resulted in a return to normal ATP-sensitivity (IC50= 46 μm). In patches from animals rendered hyperthyroid, the IC50 for ATP was 50 μm and this value was not significantly different from the control. There was no difference in the cooperativity of ATP-binding
(Hill coefficient, nH) among control (nH= 2.2), hypothyroid (nH= 2.1), T3-treated (nH= 2.0) and hyperthyroid groups (nH= 2.4). The unitary conductance was unchanged and there was no apparent change in intraburst kinetics between examples of
single KATP channels from control and hypothyroid rats. Action potentials recorded in myocytes from hypothyroid rats were significantly
shortened by 50 μm levcromakalim, a KATP channel opener (P < 0.001) but unchanged in control myocytes.
We conclude that hypothyroidism significantly decreased the ATP-sensitivity of KATP channels, whereas the induction of hyperthyroid conditions did not alter the ATP-sensitivity of these channels. Thus, hypothyroidism
is likely to have important physiological consequences under circumstances in which KATP channels are activated, such as during ischemia.
Received: 1 July 1997/Revised: 24 December 1997 相似文献