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1.
In our previous studies, we demonstrated that the inner membrane of the nuclear envelope of pyramidal neurons of the СА1 hippocampal area possesses inositol trisphosphate receptors (ІР3Rs). In this study, we analyzed in more detail the kinetic properties of the channels of these receptors and examined the
dependence of the probability of their open state (Р
о) on the voltage inside the lumen of the nuclear envelope. At positive potentials, the activity of channels of the above type
was significantly more intense than at negative potentials. In the case where the potential was positive, the Р
о of channels of ІР3Rs increased at the expense of enhancement of both the frequency of their triggering and the duration of
the open state. We believe that the voltage dependence of the activity of ІР3Rs in the inner nuclear envelope is a significant factor influencing the regulation of calcium signals in the nucleus and
exerts a noticeable effect on the functioning of pyramidal hippocampal cells. 相似文献
2.
The genetic apparatus of an eukaryotic cell is surrounded by two membranes of the nuclear envelope that forms a half-permeable
barrier for the movement of molecules and ions. Using a patch-clamp technique in experiments on isolated nuclei of pyramidal
neurons from the hippocampal CA1 area, we describe the biophysical properties of spontaneously active ion channels in the nuclear membranes of these cells.
In the external nuclear membrane, we found anion channels with a unitary conductance of 156 pS and with very rapid kinetics
of fluctuation, while in the inner membrane we recorded cationic channels with a unitary conductance of 248 pS and very slow
kinetics. Channels of both types demonstrated clear voltage dependences. We hypothesize that the physiological importance
of these channels is related to the function of the intermembrane space of the nuclear envelope of these cells forming a considerable
calcium store. It seems possible that such channels in the nuclear membranes are necessary for the maintenance of the ion
balance between the cytoplasm and perinuclear space and between the latter and karyoplasm, and also for neutralization of
voltage shifts in the course of Ca2+ release.
Neirofiziologiya/Neurophysiology, Vol. 39, No. 1, pp. 3–8, January–February, 2007. 相似文献
3.
The membrane of the endoplasmic reticulum is, in fact, an extension of the nuclear envelope of eukaryotic cells; both these
compartments can fulfill the function of intracellular calcium stores. Using a patch-clamp technique, we studied the biophysical
properties of the channels expressed in the inner nuclear membrane of pyramidal neurons of the rat hippocampal CA1 area, in particular of large-conductance cationic channels and calcium channels of inositol trisphosphate receptors (the
main channels in membranes of this type). As the results of the measurements showed, the activity of channels of both types
demonstrates clearly pronounced voltage dependences. The probability of their open state (P
o) depends on the voltage inside the nuclear envelope lumen. At positive potentials, the activity of these channels is significantly
more intense than at negative potentials. Moreover, channels of both types are reversibly blocked at considerable negative
potentials. We believe that this property of ion channels in the nuclear envelope is an important factor responsible for the
control of calcium signals in the cell nucleus. We propose a hypothesis on the mechanism underlying termination of Ca2+ release from such intracellular stores, which is based on the specificity of the voltage dependence of ion channels of the
above-mentioned types. 相似文献
4.
The dependence of intracellular calcium dynamics on geometrical size relations between calcium-exchanging parts of the intracellular
space was studied in mathematical models corresponding to a thin fragment of the Purkinje neuron spiny dendrite. The plasma
membrane contained ion channels typical of this cell type, including channels that conduct an excitatory synaptic current,
and ion pumps. The model equations took into account calcium exchange between the cytosol, extracellular medium, intracellular
store (a cistern of the endoplasmic reticulum, ER), endogenous calcium buffers, and an exogenous buffer (fluorescent dye used
in the experiments). The ER membrane contained the calcium pump and channels of calcium-dependent and inositol-3-phosphate-dependent
calcium release, as well as leakage channels. With the compartment size fixed, the ER cistern diameter was varied so that
the proportion of the organelle in the total volume changed from 1 to 36%. Under these conditions, identical synaptic excitation
caused similar electrical reactions (calcium spikes) but different concentration responses. Equal increments in the ER diameter
led to unequal, more pronounced at thicker diameters, increments of the peak cytosolic concentrations of Са2+ ([Ca2+]
i
) and of a Са2+-fluorescent dye complex [CaD], as well as those of the Са2+ concentration in the dendrite ER (characterized by a shift from the basal level, Δ[Ca2+]ER). The changes in [Ca2+]
i
and [CaD] followed more adequately those in the volume of the organelle-free cytosol, while Δ[Ca2+]ER changes were more similar to those in the ER membrane area. Therefore, the relative occupancy of the intracellular volume
by organellar calcium stores and their sizes in a dendritic compartment are important structural factors that essentially
modulate the calcium dynamics, and this structural dependence can be adequately reflected in the experiments using fluorophores.
Neirofiziologiya/Neurophysiology, Vol. 41, No. 1, pp. 19–31, January–February, 2009. 相似文献
5.
In in vitro studies on superfused slices obtained from the rat hippocampus and cortex, we found that 50 μM N-methyl-D-aspartate (NMDA)
applied to the slices in the presence of 10 μM glycine for 15 min exerts a significant damaging action to neurons of these
structures. One hour after termination of the action of NMDA, this was manifested in more than a twofold decrease in the synaptic
reactivity of pyramidal neurons of the hippocampal СА1 area and layers II/III of the cerebral cortex. The excitotoxic effect of NMDA was prevented by application of competitive
(D-2-amino-5-phosphonovaleric acid, 50 μM) and noncompetitive (ketamine, 100 μM) blockers of NMDA receptors. A blocker of
glycine-binding sites of NMDA receptors (compound ТСВ 24.15, 10 μM) weakened NMDA-induced damage to the neurons. A competitive
blocker of glutamate АМРА receptors, 6,7-dinitroquinoxaline-2,3-dione (DNQX, 10 μM), and a local anesthetic, lidocaine hydrochloride
(50 μM), did not modify the excitotoxic effect of NMDA. A blocker of voltagedependent L-type calcium channels, verapamil (20
μM), demonstrated some trend to intensification of NMDA excitotoxic action. An inhibitor of tyrosine-protein phosphatases,
sodium vanadate, when i.p. injected into rats in a dose of 15 mg/kg 6 h prior to the electrophysiological experiment, decreased
the damaging action of NMDA. Two-hour-long treatment of cerebral slices with 1 μM genistein, an inhibitor of tyrosine kinases,
weakened the neuroprotective effect of sodium vanadate. Chronic injections (14 days in daily doses of 20 mg/kg) of antidepressants
belonging to different functional classes (imipramine, fluoxetine, and pyrazidol) into rats decreased (similarly to blockers
of NMDA receptors) the excitotoxic action of NMDA receptors. Neuroprotective effects of antidepressants were weakened upon
the action of genistein. We conclude that the neuroprotective activity of antidepressants under conditions of excitotoxic
action of NMDA is mainly determined by an increase in the activity of tyrosine kinases in the cytoplasm and/or neuronal nucleus. 相似文献
6.
We studied the role of Na+/Ca2+ exchanger (NCX) and Ca2+-ATPase of the plasma membrane (РМСА), known to be the most important intracellular systems controlling calcium exchange in
cerebellar neurons of a fish species tolerant to hypoxia, Carassius gibelio. In our experiments, we used the corresponding blockers of these transport systems, ions of lithium and lanthanum. The intracellular
Ca2+ concentration ([Ca2+]
і
) was measured using a calcium-sensitive dye, Fura-2AM, and a microfluorescence technique. We found that neurons of the Carassius cerebellum possess an effective system of cleaning of the cytoplasm from excessive Ca2+, which is provided by both NCX and РМСА functioning in the plasma membrane. Under conditions of the blockade of functioning
of РМСА using lanthanum, the basal Ca2+ level in the cells increased, on average, by 31.4% with respect to the control, independently of the duration of test depolarizations.
After switching off of the NCX functioning by the replacement of sodium ions in the extracellular solution by lithium ions,
the Ca2+ level in the cell increased by 36.6% with respect to the control (also independently of the duration of depolarization).
The obtained data indicate that the functioning of РМСА and NCX in Carassius cerebellar neurons significantly influences the intracellular calcium exchange providing the maintenance of an adequate basal
Ca2+ level in these neurons. 相似文献
7.
The objects of the study were single-compartment mathematical models corresponding to a fragment of the dendrite of a cerebellar
Purkinje neuron containing the mitochondria (model 1) or a cistern of the endoplasmic reticulum, ER, (model 2) as the calcium
stores. We investigated the dependence of the intracellular Ca2+ dynamics on geometrical sizes of calcium exchanging parts of the intracellular space and the difference between the kinetic
characteristics of storing in two types of stores occupying different portions of the compartment volume. The plasma membrane
of the compartment bore the ion channels, particularly those conducting excitatory synaptic current, and the calcium pump
typical of this neuron type. The model equations took into account Ca2+ exchange between the cytosol, extracellular medium, organelle stores, non-organelle endogenous buffers, and an exogenous
buffer (fluorescent dye), and also the diffusion of Са2+ into adjacent regions of the dendrite. In model 1, the mitochondria exchanged Са2+ with the cytosol via the uniporter and sodium/calcium exchanger; mitochondrial processes, such as the tricarboxylic acid
cycle and aerobic cellular respiration, were also taken into account. In model 2, the ER membrane contained the calcium pump,
channels of passive leak, and channels of calcium-induced and inositol-3-phosphate-dependent release of Са2+. Increases in the portion of the stores in the total volume of the compartment from 1 to 36% led to a proportional increase
in the peak values of the cytosolic calcium concentration ([Ca2+]
i
); the concentration of Са2+ in the mitochondria ([Ca2+]mit) or ER ([Ca2+]ER) increased correspondingly. During generation of bell-shaped cytosolic calcium signals of equal intensity and duration, the
ER (due to a greater rate of storing, as compared with that in the mitochondria) was able to uptake several times more Са2+ (four times at 36% filling of the volume by the organelles). It is suggested that the revealed different kinetic characteristics
of Са2+ storing by different organelles are determined by the rates of binding to transport molecules present in the store membrane
and, therefore, are defined by concentrations (surface densities) of these molecules and their saturation at certain levels
of [Ca2+]i. It has been shown that the occupancy of the intracellular volume by organelle stores of any type is a structural factor,
which is able to essentially modulate the values of Ca2+ concentration. 相似文献
8.
Yu. V. Kirichok Ya. A. Boychuk M. V. Kopanitsa T. Sh. Tsintsadze N. A. Lozovaya O. A. Krishtal 《Neurophysiology》2000,32(1):12-16
The effects of a novel anti-hypertensive drug, mibefradil, on voltage-dependent currents in isolated thalamic and hippocampal
neurons, as well as on synaptic transmission in the hippocampus have been studied. Mibefradil exerted a potent inhibitory
action on low-threshold calcium currents in thalamic neurons (IC50=160 nM). In higher concentrations (1–20 μM), this drug blocked not only low-threshold calcium current but also voltage-dependent
sodium and delayed potassium currents in pyramidal hippocampal neurons. The amplitude of population action potentials in hippocampal
slices decreased by 55% in the presence of 20μM mibefradil. All of the effects of mibefradil were almost completely reversible.
In our experiments, the sensitivity of low-threshold calcium channels in thalamic neurons to mibefradil was higher than that
observed on other objects. The ability of mibefradil to block not only calcium currents but also other types of voltage-dependent
ion conductances in hippocampal neurons may be considered an essential factor that determines the specificity of the pharmacological
profile of this drug. 相似文献
9.
Ionized COOH groups are present in molecular structures involved in the process of formation of mitochondrial permeability
transition pores (MPTPs), in particular, in the ADP/ATP antiporter and/or voltage-dependent anion channels. In experiments
on preparations of isolated mitochondria obtained from rat hepatocytes, we found that, in the case of induction of nonspecific
permeability through mitochondrial membranes under the action of Cа2+ in a relatively low concentration (15 μM), modulation of the activity of COOH groups with the use of 2-ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline
(1 mM) led to unidirectional effects, namely to acceleration of the processes of formation of MPTPs and transport of incubation
solution and Са2+ through these megachannels, prolongation of the open state of the latter, as well as to increases in the final volume (swelling)
of the mitochondria and to a rise in the amount of Са2+ released from these organelles. In contrast, when calcium was used in a high concentration (100 μM), the directions of the
above processes were dissimilar. Slowing down of the flow of incubation solution through MPTPs and the process of their formation
was observed; at the same time, Са2+ release from the mitochondria was accelerated. However, the final volume of the mitochondria and the amount of Са2+ released from these cellular structures increased. Differences between the effects of the used modulator of the activity
of COOH groups on the nonspecific permeability of the mitochondria induced by calcium applied in low and high concentrations
are perhaps determined by the following. The process of swelling of the mitochondria is saturable, while Са2+ release from these organelles shows an unlimited pattern. The latter process (Са2+ release) probably undergoes calcium-initiated inactivation. The mechanisms of induction of nonspecific permeability of the
mitochondrial membranes under the action of low and high calcium concentrations differ from each other. The calcium uniporter
in the mitochondria is sensitive to the modulator of the activity of COOH groups. Diffusion of water through the inner mitochondrial
membrane and/or other systems provides some contribution to the studied processes; this can lead to changes in the transport
of liquids in these organelles. 相似文献
10.
The actions of the neonicotinoid imidacloprid on cholinergic neurons of Drosophila melanogaster 总被引:2,自引:0,他引:2
The neonicotinoid insecticide imidacloprid is an agonist on insect nicotinic acetylcholine receptors (nAChRs). We utilised
fura-2-based calcium imaging to investigate the actions of imidacloprid on cultured GFP-tagged cholinergic neurons from the
third instar larvae of the genetic model organism Drosophila melanogaster. We demonstrate dose-dependent increases in intracellular calcium ([Ca2+]i) in cholinergic neurons upon application of imidacloprid (10 nM–100 μM) that are blocked by nAChR antagonists mecamylamine
(10 μM) and α-bungarotoxin (α-BTX, 1 μM). When compared to other (untagged) neurons, cholinergic neurons respond to lower
concentrations of imidacloprid (10–100 nM) and exhibit larger amplitude responses to higher (1–100 μM) concentrations of imidacloprid.
Although imidacloprid acts via nAChRs, increases in [Ca2+]i also involve voltage-gated calcium channels (VGCCs) in both groups of neurons. Thus, we demonstrate that cholinergic neurons
express nAChRs that are highly sensitive to imidacloprid, and demonstrate a role for VGCCs in amplifying imidacloprid-induced
increases in [Ca2+]i. 相似文献
11.
Calcium currents through the somatic membrane of cultivated (a low-density culture) hippocampal neurons of rats were studied
with the use of a patch-clamp technique in the whole-cell configuration. Low- and high-threshold components of calcium currents
were found in the somata of all studied cells. Low-threshold currents were activated at a membrane potential of about−75 mV
and reached the maximum amplitude at −45±4 mV, while the maximum amplitude of high-threshold currents was observed at 17±6
mV. Low-threshold calcium currents differed from high-threshold current in weak suppression by low Cd2+ concentration (10–20 μM), while Ni2+ inhibited both types of calcium currents to an equal extent. Experiments with organic channel blockers showed that in most
neurons at least four channel types were expressed: these were L, N, P, and channels insensitive to the used blockers (presumably,
R-type). A blocker of L-type calcium channels, nifedipine (10 μM), blocked, on the average, 22.7±5.2%; a blocker of N-type
channels, ω-CTx-GVIA (1.0 μM), blocked 30.0±5.0% and a blocker of P/Q channels, ω-Aga-IVA (200 nM), blocked 37.2±13.3% of
the integral high-threshold current. A resistive component equalled 15.7±5.1% of the latter current. It is concluded that
hippocampal neurons cultivated with a low density express a pharmacologically heterogeneous population of calcium channels,
and the relative proportions of different type channels are close to the earlier described channel type composition in rat
hippocampal slices. Our study shows that the low-density culture can be used as an adequate model for studying calcium channels
in the somatic membrane of hippocampal neurons. 相似文献
12.
N. A. Lozovaya T. Sh. Tsintsdaze M. V. Kopanitsa Ya. A. Boichuk O. A. Kryshtal' 《Neurophysiology》1997,29(1):4-9
Effect of hypoxia/aglycemia episodes on excitatory postsynaptic currents (EPSC) evoked in pyramidal neurons of the rat hippocampalCA1 area by electrical stimulation of Schaffer collaterals was studied using voltage-clamp and intracellular perfusion techniques.
By 60–80 min after a 10-min-long hypoxia/aglycemia episode, the EPSC amplitude increased and the EPSC decay was considerably
slowed down, if compared with control. In contrast to control conditions, under which EPSC decay kinetics did not depend on
the stimulus strength, hypoxia/aglycemia was followed by slowing down of the EPSC decay when stimulus intensity increased.
The stimulus-dependent posthypoxic “slow” EPSC component was depressed both by D-(−)-2-amino-5-phosphonovaleric acid, an NMDA
receptor blocker, and by 6-cyano-7-nitroquinoline-2,3-dion, a non-NMDA receptor blocker, which suggested possible polysynaptic
origin of the above EPSC component. We suggest that short-term hypoxia/aglycemia transforms into an active state the NMDA
receptors in the synapses of excitatory reccurrent collaterals of theCA1 hippocampal area, which had not functioned before. An increase in the intracellular calcium concentration from 1.5 to 5.0
mM resulted in the effect similar to that produced by hypoxia/aglycemia, which suggests that calcium channels play an important
role in the mechanisms responsible for hypoxia-related activation of “silent” NMDA receptors. 相似文献
13.
M. V. Storozhuk S. M. Fredman S. Yu. Ivanova P. M. Balaban P. G. Kostyuk 《Neurophysiology》2007,39(4-5):353-354
Our experiments and studies of a few other authors demonstrated that L-type calcium channels and mitochondria are involved
in the induction of post-tetanic potentiation (PTP) in a number of preparations (Aplysia central nervous system, hippocampal cell cultures, crayfish neuromuscular junctions, etc.). We extend this conclusion on
cortical synapses by the demonstration that inhibitors of mitochondrial Ca2+ uptake and release suppress PTP in rat neocortical cell cultures.
Neirofiziologiya/Neurophysiology, Vol. 39, Nos. 4/5, pp. 403–404, July–October, 2007. 相似文献
14.
O. V. Vlasenko A. V. Dovgan’ A. I. Pilyavskii V. A. Maisky A. V. Maznichenko 《Neurophysiology》2009,41(2):148-156
The expression of early c-fos gene (marker of neuronal activation) and NADPH-diaphorase reactivity (NADPH-dr) was studied in various hypothalamic structures
of rats in the norm, in the state of starvation, and after realization of long-lasting (repeated 4 to 12 times per minute
for 30 min) motivated stereotyped food-procuring forelimb movements. In rats in the starving state, as compared with the control,
the densities (number of units within a 200 × 200 μm2 test area of a 40-μm-thick slice) of Fos-immunoreactive (Fos-ir) neurons in the parvicellular part of the paraventricular
nucleus (Ра), supraoptic (SO), and medial preoptic (МРО) nuclei, anterior hypothalamic region (АН), and lateral hypothalamic nucleus (LH) were significantly greater (Р < 0.05) than in the control. In the dorsomedial (DMD) and ventromedial (VMHD) hypothalamic nuclei, this index did not differ from control values. After the performance of intense unilateral operant
movements, higher densities of labeled neurons (as compared with that in control and starving animals) were observed in the
PаAP, SO, МРО, and DMD, while smaller densities were observed in the LH and VMH. NADPH-dr neurons (i.e., NO synthase-containing cells) were observed in many hypothalamic nuclei; the maximum density of
such NO-generating neurons was found in the Pa, SO, MPO, and DMD. The overwhelming majority of Fos-ir and NADPH-dr neurons in neurons was observed after realization of stereotyped food-procuring
movements in the Ра and SO. This specificity of changes in the number of Fos-irand NADPH-dr neurons in the hypothalamic nuclei reflects, perhaps, the
involvement of these structures in the control of autonomic functions in the course of realization of operant reflexes and
adaptation of the function of the cardiovascular system to the corresponding intense physical and emotional loading. 相似文献
15.
The genetic apparatus of the nucleus of eukaryotic cells is surrounded by the nuclear envelope containing ion channels with
different biophysical properties. The channels responsible for calcium release from the nuclear envelope into the intranuclear
space have attracted special attention. As we found, a great number of large-conductance ion channels selective with respect
to monovalent cations and impermeable for bivalent cations are present in all membranes where inositol trisphosphate receptors
are expressed. We showed that channels of this type are insensitive to blockers of potassium channels and, according to their
properties, cannot be attributed to one well-known type of ion channels or another. In addition, since their blockers remain
unknown, these channels at present cannot be isolated and cloned. Channels of this type deserve further investigation; we
hypothesize that large-conductance cationic channels can be involved in the control of the duration of Ca2+ release from the calcium store. 相似文献
16.
In neurons of the rat dorsal root ganglia (DRG), using a patch-clamp technique in the whole-cell configuration, we studied
the characteristics of calcium channels activated by depletion of the ryanodine-sensitive calcium stores of the endoplasmic
reticulum. Current-voltage (I-V) relationships of these store-operated calcium channels were obtained by subtraction of the
integral I-V characteristics after application of caffeine from the integral I-V characteristics of calcium channels in the
control. Currents through store-operated calcium channels could be induced by application of a series of hyperpolarization
current pulses to the cell under conditions of replacement of a calcium-free solution containing caffeine by a caffeine-free
solution containing 2 mM Ca2+. In this case, the following two main conditions were abserved: Voltage-operated calcium channels were inactivated, while
a gradient of the electrochemical potential for calcium ions was increased, which made easier passing of these currents through
store-operated calcium channels. Therefore, we found that in DRG neurons, despite the presence of great numbers of both voltage-operated
and receptor-dependent calcium channels, one more mechanism underlying the entry of calcium through store-operated channels
does exist.
Neirofiziologiya/Neurophysiology, Vol. 39, No. 3, pp. 195–200, May–June, 2007. 相似文献
17.
18.
We examined the actions of 5- or 7.5-min-long episodes of oxygen/glucose deprivation, OGD (temperature, 37°C), on pyramidal
neurons of the CA1 hippocampal area and granular neurons of the gyrus dentatus. The respective damage to these neurons was manifested as an irreversible decrease in the amplitude of field EPSPs developing
in such neuronal populations. Antagonists of NMDA receptors, D-2-amino-5 phosphonovaleric acid (50 μM), ketamine (50 μM),
and compound TSB 24.15 (10 μM), demonstrated neuroprotective activities under these conditions, but only in the case of the
5-min-long exposure to OGD. A blocker of AMPAreceptors, DNQX (10 μM), combined with a local anesthetic, lidocaine hydrochloride
(50 μM), induced comparable effects at the 7.5-min-long exposure. A blocker of calcium channels, verapamil (20 μM), exerted
no effect on the level of injury of the neurons induced by the OGD influence. An inhibitor of tyrosine phosphoprotein phosphatases,
sodium orthovanadate (15 mg/ml), demonstrated protective activities at both exposures, 5 and 7.5 min long. Chronic (during
two weeks) preliminary injections of imipramine, fluoxetine, and pyridazol (everyday doses 20 mg/kg) into experimental animals
resulted in noticeable weakening of the OGD-induced impairments of hippocapmal slices in the case of both exposures used,
5 and 7.5 min. The neuroprotective effects of chronically introduced antidepressants were augmented under the action of sodium
orthovanadate. It is supposed that neuroprotective actions of preliminarily chronically introduced antidepressants with respect
to the anoxic damage to hippocampal neurons is determined (at least to a considerable extent) by intensification of expression
of neurotrophins. Under the influence of the latter, the functional activity of NMDA receptors decreases, and consequences
of OGD-induced increase in the intracellular Ca2+ concentration are weakened. 相似文献
19.
We studied the Са2+- and Cd2+-induced development of the nonspecific permeability of the mitochondrial inner membrane in preparations obtained from rat
liver tissue, which is accompanied by swelling of these organelles and intensification of light dispersion of their suspension.
Addition of 5 to 100 μM Са2+ or 1 to 50 μM Сd2+ to the medium caused swelling of the mitochondria. With increase in concentrations of Са2+ and Cd2+, the latency of the effect decreased, and the rate of swelling of these organelles increased. Upon isolated action of Са2+, the intensity of the process (amplitude of changes) did not depend significantly on the concentration of the above ions,
while upon isolated action of Cd2+, it was the maximum at the concentration of 1 mM and noticeably decreased with increase in the concentration. The dependence
of the rate of Са2+- and Cd2+-induced swelling of the mitochondria on the concentration of these ions was described by power and sigmoid functions, respectively.
The calculated maximum rate and the constant of 50% saturation of these processes were equal to 0.609 and 1.084 extinction
units/min⋅mg protein and 19.85 and 7.28 μM for Са2+- and Cd2+-induced swelling of the mitochondria, respectively. Cyclosporine A (10 μM) suppressed completely the Са2+-induced swelling of the mitochondria and decreased only partly the Cd2+-induced swelling. Dithiothreitol (1 mM) inhibited completely the latter effect but did not influence significantly the Са2+-stimulated process. Therefore, the distinctions between the kinetics of Са2+- and Cd2+-induced swelling of the mitochondria, as well as the different sensitivity of these processes to cyclosporine A and dithiothreitol,
prove that the mechanisms underlying interactions between the cations of the above metals and the inner mitochondrial membrane
in the course of the development of nonspecific permeability of these organelles are dissimilar.
*Deceased 相似文献
20.
A method for detecting and characterizing possible ligands of neuronal GABA(A) receptors has been developed, which is based
on measuring the calcium response to GABA by the fluorescence of a two-wavelength Ca-sensitive probe Fura-2. In a young (2–4
days) rat hippocampal cell culture, GABA induced depolarization and a transient increase in Ca2+ concentration in the cytosol of neurons due to activation of voltage-dependent calcium channels. A brief application of GABA
could attenuate the calcium response to a subsequent addition of depolarizing agents (GABA or KCl). However, at modest amplitudes
of calcium response to GABA, the reduction of the subsequent effect of KCl was insignificant, and the amplitudes of responses
to KCl and to GABA proved to be linearly correlated, with a slope of ∼3.4. Therefore, the GABA calcium signals could be normalized
in order to compare experiments performed on different days and different cultures. With such normalization, we estimated
the EC50 for GABA in neurons at ∼2.23 μM and the Hill coefficient at ∼1.9. A blocker of voltage-dependent calcium channels nifedipine
suppressed the calcium responses both to KCl and to GABA, so that the linear relationship between their amplitudes was retained.
To further validate the method, the IC50 and the type of inhibition were verified for known noncompetitive and competitive
antagonists of GABA(A) receptors. 相似文献