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1.
Summary Calcium markedly stimulates the respiration of the isolated chick chorioallantoic membrane. This stimulation of oxygen uptake appears to be closely associated with the membrane's active transcellular calcium transport mechanism. In the presence of 1mm Ca++ the rate of uptake increases from 9.3±0.15 to 13.0±0.2 liters O2/cm2/hr, an increase of about 40%. The calcium-stimulated respiration is specific for the ectodermal layer of cells, the known location of the calcium transport mechanism, and only occurs when the calcium transport mechanism is operative. Sr++ and Mn++ are transported by the tissue at a lower rate than Ca++ and cause a smaller stimulation of oxygen consumption. Mg++ and La3+ have no effect on tissue respiration. In the presence of Ca++, the organic mercurialp-chloromercuribenzene sulfonate (PCMBS) inhibits calcium transport and specifically decreases the oxygen uptake of the ectoderm to a rate identical to that obtained in a calcium-free medium. Stripping the inner shell membrane away from the chorioallantoic membrane mimics these effects. The specificity and locus of action of these two inhibitors suggest that a vital component of the active transcellular calcium transport mechanism resides on or near the outer surface of the plasma membrane of the ectodermal cells and that sulfhydryl groups are important to the normal function of this component. 相似文献
2.
Santiago LLovera Ramon Bonet Maria Dolores Simon-Pujol Francisco Congregado 《Applied microbiology and biotechnology》1993,39(3):424-426
The influence of some ions in pre-growth culture medium on chromate reduction by resting cells of Agrobacterium radiobacter strain EPS-916 was investigated. The reduction was dependent on the Fe2+ content of the culture medium: the higher the iron content, the lower the reduction rate. The cells showed maximum chromate reduction when pre-grown in the presence of 0.243 m Mg2+, 20 m Ca2+ and 3.6 m Mn2+. Chromate reduction was not affected by the addition of MgCl2, CdCl2, ZnCl2, MnCl2, Na2SO4 (1000 m), and Na2MoO4 (100 m) to the activity assays. However, activity was inhibited by the presence of Na2SO4 (10 mm), Na2MoO4 (200 m) and ferric citrate. 相似文献
3.
Mandal A Chakraborti T Choudhury R Ghosh B Ghosh AN Das S Chakraborti S 《Molecular and cellular biochemistry》2005,270(1-2):79-87
Treatment of microsomes (preferentially enriched with endoplasmic reticulum) isolated from bovine pulmonary artery smooth muscle tissue with H2O2 (1 mM) markedly stimulated matrix metalloproteinase activity and also inhibited Na+ dependent Ca2+ uptake. Electron micrograph revealed that H2O2 (1 mM) does not cause any damage to the microsomes. MMP-2 and TIMP-2 were determined to be the ambient protease and corresponding antiprotease of the microsomes. Pretreatment with vitamin E (1 mM) and TIMP-2 (50 g/ml) reversed the effect produced by H2O2 (1 mM) on Na+ dependent Ca2+ uptake in the microsomes. However, H2O2 (1 mM) caused changes in MMP-2 activity and Na+ dependent Ca2+ uptake were not reversed upon pretreatment of the microsomes with a low concentration of 5 g/ml of TIMP-2 which otherwise reversed MMP-2 (1 g/ml) mediated increase in 14C-gelatin degradation and inhibition of Na+ dependent Ca2+ uptake. Combined treatment of the microsomes with a low dose of MMP-2 (0.5 g/ml) and H2O2 (0.5 mM) inhibited Na+ dependent Ca2+ uptake in the microsomes compared to the respective low dose of either of them. Direct treatment of TIMP-2 (5 g/ml) with H2O2 (1 mM) abolished the inhibitory effect of the inhibitor on 14C-gelatinolytic activity elicited by 1 g/ml of MMP-2. Thus, one of the mechanisms by which H2O2 activates MMP-2 could be due to inactivation of TIMP-2 by the oxidant. The resulting activation of MMP-2 subsequently inhibits Na+ dependent Ca2+ uptake in the microsomes. (Mol Cell Biochem 270: 79–87, 2005) 相似文献
4.
Synaptosomal acetylcholine synthesis was found to be dependent on the presence of Na+-dependent HC-3 sensitive choline transport at low (5.5 mM) and high (35 mM) K+ concentrations. However, at 5, 20, and 100 M choline, choline phosphorylation was proportional to total choline uptake, in the presence or absence of high affinity transport. Only in the presence of eserine (50 M) did acetylcholine synthesis increase as the choline concentration was elevated from 20 M to 100 M, and this effect was observed at low and high K+ concentrations. Our results suggest that: 1) the synthesis of non-surplus synaptosomal ACh is dependent on high affinity choline transport; and 2) choline is equally likely to be phosphorylated after being taken up by low or high affinity transport. 相似文献
5.
R. Salceda 《Neurochemical research》1980,5(5):561-572
A specific system for taurine transport is present at the early stages of development in both chick and rat retinas. The results obtained with taurine analogs indicate a high degree of specificity of taurine uptake. Two transport systems were detected for the adult rat retina: a high-affinity (K
m
21 M) and a low-affinity transport system (K
m
312 M). On the other hand, in the adult chick retina, only a low-affinity transport system (K
m
580 M) could be detected. Nevertheless, embryo chick retina accumulated [3H]taurine by two different kinetic mechanisms withK
m
s of 242 M and 21 M for the low- and high-affinity processes, respectively. Taurine uptake systems were absolutely Na+ dependent. The sodium-dependence curve for taurine uptake was sigmoid. These mechanisms appear not to be mediated by a Na+ cotransport system. In spite of the differences observed in taurine uptake in both species, in each of them it closely parallels the changes brought about by the morphological and functional maturation of the retina. 相似文献
6.
The chick blastoderm at the stage of late gastrula is a flat disc formed by three cell layers and exhibiting epithelial properties. Blastoderms were cultured in miniature chambers and their electrophysiological characteristics were determined under Ussing conditions.Under open-circuit condition and identical physiological solutions on both sides, spontaneous transblastodermal potential difference (V
oc) of –7.5±3.3 mV (ventral side positive) was measured. Under short-circuit condition (transblastodermal V = 0 mV), the blastoderm generated short-circuit current (I
sc) of 21±8 A/cm2, which was entirely dependent on extracellular sodium, sensitive to ouabain applied ventrally and independent of extracellular chloride. The net transblastodermal Na+ flux fully accounted for the measured I
sc, both under control conditions and with ouabain. The total transblastodermal resistance (R
tot) was 390±125 cm2.Frequently, the V
oc, I
sc and R
tot showed spontaneous oscillations with a period of 4–5 min. Removal of endoderm and mesoderm did not significantly affect the electrical properties, indicating that the electrogenic sodium transport is generated by the ectoderm.The V
oc and I
sc measured in the area pellucida (–1.3±0.8 mV, 9.3±4.4 A/cm2) and extraembryonic area opaca (–7.8±1.1 mV, 31.2±12.7 A/cm2) were significantly different. Such a heterogeneous distribution of electrical properties can explain the presence in the blastoderm of extracellular electrical currents found by using a vibrating probe.This work was supported by the Swiss National Research Foundation (grant. 3.418-0.86 to P.K.) and by Roche Research Foundation (grant. to U.K.). We thank Drs. E. Raddatz and Y. de Ribaupierre for helpful discussions. 相似文献
7.
Summary Transepithelial Li+ influx was studied in the isolated epithelium from abdominal skin ofRana catesbeiana. With Na+-Ringer's as inside medium and Li+-Ringer's as outside medium, the Li+ influx across the epithelium was 15.6 A/cm2. This influx was considerably reduced by removal of either Na+ or K+ from the inside bath or by the addition of ouabain or amiloride. Epithelial K+ or Na+ concentration was respectively lower in epithelia bathed in K+-free Ringer's or Na+-free Ringer's. In conditions of negligible Na+ transport, a 20mm Li+ gradient (outin) produced across the short-circuited epithelium a Li+ influx of 11.8 A/cm2 and a mean short-circuit current of 10.2 A/cm2. The same Li+ gradient in the opposite direction produced a Li+ outflux of only 1.9 A/cm2. With equal Li+ concentration (10.3 and 20.6mm) on both sides of the epithelium, plus Na+ in the inside solution only, a stable Li+-dependent short-circuit current was observed. Net Li+ movement (outin) was also indirectly determined in the presence of an opposing Li+ gradient. Although Li+ does not substitute for Na+ as an activator of the (Na++K+)-ATPase from frog skin epithelium, Li+ influx appears to be related to Na+–K+ pump activity. It is proposed that the permeability of the outer barrier to Na+ and Li+ is regulated by the electrical gradient produced by electrogenic Na+–K+ pumps located in the membrane of the deeper epithelial cells. 相似文献
8.
Calcium entry in rabbit corneal epithelial cells: Evidence for a nonvoltage dependent pathway 总被引:1,自引:0,他引:1
We performed experiments to elucidate the calcium influx pathways in freshly dispersed rabbit corneal epithelial cells. Three possible pathways were considered: voltage-gated Ca++ channels, Na+/Ca++ exchange, and nonvoltage-dependent Ca++-permeable channels. Whole cell inward currents carrying either Ca++ or Ba++ were not detected using voltage clamp techniques. We also used imaging technology and the Ca++-sensitive ratiometric dye fura 2 to measure changes in intracellular Ca++ concentration ([Ca]i). Bath perfusion with NaCl Ringer's solution containing the calcium channel agonist Bay-K-8644 (1 m), or Ni++ (40 m), a blocker of many voltage-dependent calcium channels, did not affect [Ca++]i. Membrane depolarization with a KCl Ringer's bath solution resulted in a decrease in [Ca++]i. These results are inconsistent with the presence of voltage gated Ca++ channels. Nonvoltage gated Ca++ entry, on the other hand, would be reduced by membrane depolarization and enhanced by membrane hyperpolarization. Agents which hyperpolarize via stimulation of K+ current, such as flufenamic acid, resulted in an increase in ratio intensity. The cells were found to be permeable to Mn++ and bath perfusion with 5 mm Ni++ decreased [Ca++]i suggesting that the Ca++ conductance was blocked. These results are most consistent with a nonvoltage gated Ca++ influx pathway. Finally, replacing extracellular Na+ with Li+ resulted in an increase in [Ca++]i if the cells were first Na+-loaded using the Na+ ionophore monensin and ouabain, a Na+-K+-ATPase inhibitor. These results suggest that Na+/Ca++ exchange may also regulate [Ca++] in this cell type.The authors are grateful to Chris Bartling for expert technical assistance with the imaging experiments, Helen Hendrickson for cell preparation, and Jonathon Monck for helpful discussions regarding imaging technology. This work was supported by National Institutes of Health grants EYO3282, EYO6005, DK08677, and an unrestricted award from Research to Prevent Blindness. 相似文献
9.
George T. Byrd T. Loboda Clanton C. Black Jr. R. Harold Brown 《Photosynthesis research》1995,44(3):253-260
Onion (Allium cepa L.) plants were examined to determine the photosynthetic role of CO2 that accumulates within their leaf cavities. Leaf cavity CO2 concentrations ranged from 2250 L L–1 near the leaf base to below atmospheric (<350 L L–1) near the leaf tip at midday. There was a daily fluctuation in the leaf cavity CO2 concentrations with minimum values near midday and maximum values at night. Conductance to CO2 from the leaf cavity ranged from 24 to 202 mol m–2 s–1 and was even lower for membranes of bulb scales. The capacity for onion leaves to recycle leaf cavity CO2 was poor, only 0.2 to 2.2% of leaf photosynthesis based either on measured CO2 concentrations and conductance values or as measured directly by 14CO2 labeling experiments. The photosynthetic responses to CO2 and O2 were measured to determine whether onion leaves exhibited a typical C3-type response. A linear increase in CO2 uptake was observed in intact leaves up to 315 L L–1 of external CO2 and, at this external CO2 concentration, uptake was inhibited 35.4±0.9% by 210 mL L–1 O2 compared to 20 mL L–1 O2. Scanning electron micrographs of the leaf cavity wall revealed degenerated tissue covered by a membrane. Onion leaf cavity membranes apparently are highly impermeable to CO2 and greatly restrict the refixation of leaf cavity CO2 by photosynthetic tissue.Abbreviations Ca
external CO2 concentration
- Ci
intercellular CO2 concentration
-
CO2 compensation concentration
- PPFR
photosynthetic photon fluence rate 相似文献
10.
Doebler JA 《Neurochemical research》2000,25(7):941-948
The NG108-15 (neuroblastoma X glioma hybrid) cell line was used as an in vitro neuronal model to evaluate potential antagonists of the Na+-selective carboxylic ionophore monensin. Changes in membrane electrical characteristics induced by monensin with and without the simultaneous administration of antagonists were measured using intracellular microelectrode techniques. Bath application of monensin (3 M) produced a hyperpolarization of 35 mV. Monensin also altered the generation of action potentials in response to electrical stimulation in 14 of 24 (58%) exposed cells, as evident in a partial or complete loss of action potentials or in an alteration of action potential waveform. The antagonists used were Na+-K+ pump inhibitor ouabain (1–3 M), the Ca2+-dependent K+ channel blocker quinine (3–30 M) or drugs known to influence Ca2+ signaling in cells, i.e., trifluoperazine (3–10 M), verapamil (1–10 M) or chlorpromazine (3–30 M). On a molar basis, ouabain was the most and trifluoperazine the least effective of the antagonists. Quinine, verapamil and chlorpromazine all prevented the development of the hyperpolarization in an approximate concentration-dependent manner. However, none of these drugs was able to block the effects of monensin on action potentials. Indeed, high concentrations of the antagonists that were most effective in preventing the hyperpolarization accentuated impairments in action potential generation and also reduced input resistance in many cells. Thus, none of these antagonists appears suitable for transition to in vivo antidotal protection studies. 相似文献
11.
Summary The rate of fluid transport across rabbit corneal endothelium has been measured with an automatic volumetric method. The present resolution of the procedure is 1–3 nanoliters, and intervals of measurement can be made as small as seconds. In the presence of glucose, oxidized glutathione (GSSG), and adenosine, the maximal rates were 6.2±1.0 l/hr cm2, and 8.2±0.8 l/hr cm2 if a large portion of the stroma was dissected away. In the presence of glucose and GSSG only, the rates were lower, namely 3.7±0.5 l/hr cm2. The rates consistently increased or decreased when adenosine was added or deleted, respectively, during given experiments. The stimulation of fluid transport by adenosine was in the order of 40–50%. The results raise the possibility that this transport mechanism might be subject to metabolic control. 相似文献
12.
Stanley D. Hillyard Willy Van Driessche 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1991,161(3):257-263
Summary The short-circuit current (SCC) across isolated skin from bullfrog larvae in developmental stage XXI was small and insensitive to amiloride. Overnight incubation of this tissue with 10-6
M aldosterone stimulated the SCC from 1.35±0.55 to 14.55±4.12 A·cm-2 with 11.18±4.46 A·cm-2 being blocked by 100 M amiloride. Histologic examination of aldosterone-treated skins revealed a separation of the apical cell layer from the underlying epidermis that was not seen in untreated preparations. The onset of amiloride-sensitive Na+ transport thus coincided with the exposure of the apical surface of newly differentiated epithelial cells. Similar results were obtained with skin from stage XXI larvae whose rate of metamorphosis had been stimulated by 10 g·l-1 thyroxine (T4) but not with skin from T4-treated larvae in stages XIX and XX. Fluctuation analysis of the amiloride-sensitive SCC of the above preparations failed to show a consistent Lorentzian component in the power-density spectrum. Fluctuation analysis was possible on skins from larvae whose development had been accelerated by 7–9 days treatment with 10 g·l-1 triiodothyronine (T3). Aldosterone treatment of these tissues resulted in a significant increase in Na+ channel density.Abbreviations
ASCC
component of the short-circuit current (A·cm-2) that is blocked by amiloride
-
fc
frequency (Hz) at which the magnitude of the Lorenzian component of the power spectra is reduced by half
-
i
current (pA) through individual amiloride-sensitive Na+ channels
-
I
Na+
amiloride-sensitive short-circuit current (A·cm-2) that remains after treatment with a given amiloride concentration
-
k
01
the rate constant (s-1·M-1) for the association of amiloride with Na+ channels
-
k
10
rate constant (s-1) for the dissociation of amiloride from Na+ channels
-
K
b
magnitude of the power spectrum (A2·s·cm-2) at a frequency of 1 Hz
-
KSCC
short-circuit (A·cm-2) current with K+ as the primary mucosal cation
-
M
density of amiloride-sensitive Na+ channels in the apical cell membrane
-
SCC
short-circuit current (A·cm-2)
-
S
(f)
magnitude of the power spectra (A2·s·cm-2) at a given frequency
-
S
0
the magnitude of the plateau region of the Lorentzian component of the power spectra (A2·s·cm-2)
-
T
3
Triiodothyronine
-
T
4
Thyroxine 相似文献
13.
A. H. Caswell 《The Journal of membrane biology》1969,1(1):53-78
Summary The addition of agents that uncouple electron transfer from energy conservation (uncouplers) to state 4 mitochondria causes the following ion movements: K+ is extruded from the mitochondria in association with phosphate and possibly other anions, but not H+. Endogenous Ca++ is extruded from the mitochondria, and H+ moves in to counter-balance the Ca++ movement; some phosphate movement may be associated with Ca++ extrusion. The rate and extent of K+ extrusion induced by uncoupler is dependent on the concentrations of external phosphate and divalent ions. Phosphate induces K+ extrusion, while Mg++ and Mn++ inhibit it. TheV
max of K+ transport is 300 moles K+/g protein per min. The K
m
for FCCP-induced potassium extrusion is 0.25 M at pH 7.4. The inhibitory effect of Mg++ is noncompetitive with respect to uncoupler concentration but competitive with respect to phosphate concentration. The experimental evidence does not support the existence of high H+ permeability in the presence of uncoupler. A correlation is observed between the rate of K+ extrusion and the energy reserves supplied from the high energy intermediate. The action of uncoupler in inducing K+ permeability is considered to arise through its action in depleting the energy reserves of mitochondria rather than through a specific activating effect of permeability by the uncoupler itself. The relationship of membrane potential to regulation of K+ permeability is discussed. 相似文献
14.
Microdissected Deiters' neuron plasma membranes have been used for studying the passage of GABA through the membrane both in the inward and outward direction. Working with 0.2 mM GABA in the compartment simulating the outside of the neurone and with 2.0 mM GABA in the one simulating the inside we found a net transport of GABA towards the inside. This mechanism does not require a Na+ ion gradient across the membrane. The nature of the transport process involved was studied by determining the rate of [3H]-GABA inward passage as a function of GABA concentration (1 nM–800 M) on the outward side of the membrane. The results have shown that until 50 M a diffusion process (v=D1×C, where D1=3.1×10–11 1/m2×sec) is the sole mechanism involved. Above 50 M a second diffusion process is activated v=D2×(C–50×10–6), where D2=2.8×10–11 1/m2×sec. Taking in account both inward and outward directed diffusion, one can calculate 16 M as the equilibrium concentration of GABA on the outward side of the membrane. From a kinetic point of view, these diffusion processes are able to reduce GABA concentration in a synaptic cleft from 3 mM to 20 M within 3 sec. These diffusion systems are discussed as extremely efficient in removing the excess of released GABA in the synaptic cleft. 相似文献
15.
Summary The unidirectional influx of Na from the mucosal solution into the epithelium ofin vitro descending rabbit colon (J
me
Na
) determined under short-circuit conditions, is comprised of two components: one represents entry of Na into transporting epithelial cells and is abolished by amiloride which also abolishes Na absorption (J
net
Na
). The other represents diffusional Na entry into paracellular pathways traversing the epithelium. In all instances, exposure of the mucosal surface to amphotericin B increased tissue conductance andJ
me
Na
and elicited K secretion. Tissues showing a spontaneousI
sc of approximately 4 eq/cm2hr did not respond to amphotericin B with increasedI
sc andJ
net
Na
. However, in tissues characterized by a lowerI
sc under control conditions, amphotericin B increasedI
sc andJ
net
Na
to approximately 4eq/cm2hr. These findings suggest that amphotericin increasesJ
net
Na
and elicits K secretion by disrupting the normal permselectivity of the mucosal membrane. Under these conditions the extrusion of Na from cell-to-serosal solution becomes the rate limiting step in transepithelial Na transport. Finally, a close correlation betweenJ
me
Na
andJ
net
Na
was observed when the rate of Na absorption varied either spontaneously or experimentally with amiloride, suggesting that the backflux of Na from cell-to-mucosal solution is undetectably small. 相似文献
16.
Thomas H. Dietz S. Y. Graves 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1981,143(2):185-190
Summary Isolated gills of the freshwater mussel,Ligumia subrostrata, accumulate Na from a pondwater bathing medium. The rate of Na transport by the isolated gill is 13.2±1.1 mol (g dry gill·10 min)–1 which equals or exceeds the estimated Na transport rate of intact animals. Sodium influx is saturable with aV
max of 13.6±1.2 mol (g dry gill·10 min)–1 and an affinity (K
s) of 0.17 mM Na/l. The isolated gills survive prolonged exposure to pondwater with a constant
of 890 l O2 (g dry gill·h)–1 over a 4 h period. Sodium transport in the isolated gills is stimulated 80% above control values by 10–4 M serotonin, 60% by 0.5 mM cAMP and 60% by 12.5 g/ml nystatin. Sodium influx is inhibited by 0.5 mM amiloride and 1 mM lithium. 相似文献
17.
In potassium-limited chemostat cultures of Paracoccus denitrificans the maximum specific growth rate (µmax) was found to depend on the input potassium concentration: At 0.21mM µmax was 0.10–0.11 h-1; at 0.44 mM 0.15–0.16 h-1 and at 0.66 mM 0.20–0.21 h-1. The plots of the specific rates of oxygen-, succinate-and potassium consumption against gave straight lines. The intracellular potassium concentration was a linear function of and varied from 1% (0.13 M) at a value of 0.034 h-1 to 2.2% (0.29 M) at =0.26 h-1; the potassium concentration gradient and the potassium concentration in the culture fluid in the steady state were dependent on the input potassium concentration. The potassium concentration gradient varied from 8,900-1,200. At all values 20–25% of the total energy production was used for potassium transport. 350,100 and 30 ATP molecules were calculated to be required to maintain one potassium ion intracellular during 1 h at values of 0.034, 0.197 and 0.257 h-1 respectively. It is concluded that the amount of circulation of potassium is dependent on the potassium concentration gradient or on the potassium concentration in the culture in the steady state. The dependency of µmax on the input potassium concentration was explained by the assumption that at low input potassium concentrations the net uptake of potassium (influx-efflux) is not rapidly enough to maintain the high potassium gradient in the existing cells and to establish it in the newly formed cells. At high values and at high input potassium concentrations µmax is limited by the specific rate of oxygen consumption, which was found to be 11–12 mmol O2 g dry weight-1 h-1 at µmax for potassium-, succinate-and sulphate-limited chemostat cultures. 相似文献
18.
The effect of divalent metal ions on the activity of Mg++ depleted ribulose-1,5-bisphosphate oxygenase 总被引:1,自引:0,他引:1
Ribulose-1,5-bisphosphate carboxylase-oxygenase is deactivated by removal of Mg++. The enzyme activities can be restored to a different extent by the addition of various divalent ions in the presence of CO2. Incubation with Mg++ and CO2 restores both enzyme activities, whereas, the treatment of the enzyme with the transition metal ions (Mn++, Co++, and Ni++) and CO2 fully reactivates the oxygenase: however, the carboxylase activity remains low. In experiments where CO2-free conditions were conscientiously maintained, no reactivation of RuBP oxygenase was observed, although Mn++ ions were present. Other divalent cations such as Ca++ and Zn++, restore neither the carboxylase nor the oxygenase reaction. Furthermore, the addition of Mn++ to the Mg++ and CO2 preactivated enzyme significantly inhibited carboxylase reactions, but increased the oxygenase reaction.Abbreviation RuBP
ribulose-1,5-bisphosphate. The enyme unit for RuBP carboxylase is defined as mol CO2 fixed·min-1 and for the RuBP oxygenase as mol O2 consumed · min-1 相似文献
19.
Lidocaine, a local anaesthetic, has been shown to reduce ventricular arrhythmias associated with myocardial infarction and ischemic myocardial injury and its protective effects has been attributed to its membrane stabilizing properties. Since oxygen radicals are known to be produced during ischemia induced tissue damage, we have investigated the possible antioxidant properties of lidocaine and found that lidocaine does not scavenge 02
–· radicals at 1 to 20 mM concentrations. However, lidocaine was found to be a potent scavenger of hydroxyl radicals and singlet oxygen. Hydroxyl radicals were produced in a Fenton type reaction and detected as DMPO-OH adducts by electron paramagnetic resonance spectroscopic techniques. Lidocaine inhibited DMPO-OH adduct formation in a dose dependent manner. The amount of lidocaine needed to cause 50% inhibition of that rate was found to be approximately 80 M and at 300 M concentration it virtually eliminated the DMPO-OH adduct formation. The production of OH-dependent TBA reactive products of deoxyribose was also inhibited by lidocaine in a dose dependent manner. Lidocaine was also found to inhibit the 1O2-dependent 2,2,6,6-tetramethylpiperidine N-oxyl (TEMPO) formation in a dose dependent manner. 1O2 was produced in a photosensitizing system using Rose Bengal or Methylene Blue as photosensitizers and was detected as TEMP-1O2 adduct by EPR spectroscopy. The amount of lidocaine required to cause 50% inhibition of TEMP-1O2 adduct formation was found to be 500 M. These results suggest that the protective effect of lidocaine on myocardial injury may, in part, be due to its reactive oxygen scavenging properties. These results may also explain the membrane stabilizing actions of lidocaine by scavenging OH · and 1O2 that are implicated in membrane lipid peroxidation. 相似文献
20.
Gary Hoel Dr. Mary L. Michaelis William J. Freed J. E. Kleinman 《Neurochemical research》1990,15(9):881-887
Procedures were developed for measurement of Na+/Ca2+ exchange in resealed plasma membrane vesicles from postmortem human brain. The vesicle preparation method permits use of stored frozen tissue with minimal processing required prior to freezing. Vesicles prepared in this manner transport Ca2+ in the presence of a Na+ gradient. The kinetic characteristics of the Na+/Ca2+ exchange process were determined in membrane vesicles isolated from hippocampus and cortex. The Kact for Ca2+ was estimated to be 32 M for hippocampal and 17 M for cortical tissue. The maximal rate of Ca2+ uptake (Vmax) was 3.5 nmol/mg protein/15 sec and 3.3 nmol/mg protein/15 sec for hippocampal and cortical tissue, respectively. Exchange activity was dependent on the Na+ gradient, and was optimal in the high pH range. Therefore, membranes in which Na+-dependent o Ca2+ transport activity is preserved can be isolated from postmortem human brain and could be used to determine the influence of pathological conditions on this transport system. 相似文献