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1.
Transmembrane currents and changed [Ca2+]in produced by iontophoretic injection of cAMP were investigated in voltage clampedHelix pomatia neurons. The Fura-2 fluorescence probe technique was used to measure [Ca2+]in. Injection of cAMP was found to produce a protracted rise in the latter at a membrane potential range of –40 to –100 mV in conjunction with transmembrane inward current. Duration of the changes in [Ca2+]in largely dependent on neuronal size and varied between 50 and 500 sec (parameters for neurons with somata of around 100 and 40 µm respectively). In a medium with Ca2+ replaced by Mg2+ (as well as after addition of EDTA, a calcium chelator) both transmembrane current and the pattern of increase in [Ca2+]in remained unchanged. Inward current usually declined substantially but degree of change in [Ca2+]in remained the same when Na+ was eliminated from the solution by replacing its Tris+. Addition of 2 mM Cd2+ to the external medium hardly affected current level and increase in [Ca2+]in. Neither procaine, a local anesthetic, nor ryanodine (which inhibits release of calcium from the intracellular store) changed the cAMP effects observed. A concentration of 1 mM La3+ depressed both inward current and the [Ca2+]in increase. Findings would imply the occurrence of cAMP-dependent release of calcium from the intracellular store in the neurons tested.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 3, pp. 396–402, May–June, 1989.  相似文献   

2.
The effect of intracellular injection of cyclic AMP (cAMP) and extracellular application of theophylline on the inward calcium current was investigated in neurons RPa3 and LPa3 ofHelix pomatia. Iontophoretic injection of cyclic AMP (current 10–35 nA, duration about 1 min) led to a decrease in amplitude of the calcium current to a new stationary level, which depended on the injection current. After the end of injection the calcium current was restored to its initial level. Current-voltage characteristic curves of the calcium current were not shifted along the voltage axis by cAMP injection, indicating that the reduction in this current was connected with a change in maximal calcium conductance. An increase in the frequency of depolarizing shifts from 0.1 to 0.5 Hz caused a decrease in the calcium current but did not affect the time course of the decrease in calcium current in response to injection of cAMP or the time course of its recovery after the end of injection. Theophylline an inhibitor of cyclic nucleotide phosphodiesterase, in a concentration of 1 mM in the external solution, lowered the amplitude of the calcium current by 50–75% of its initial value. In 40% of neurons, abolition of the action of theophylline by rinsing was incomplete, but in the rest the effect of theophylline was irreversible. It is postulated on the basis of the results that cytoplasmic compounds take part in regulation of the calcium current of molluscan neurons. The possible physiological role of this process is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 14, No. 3, pp. 290–297, May–June, 1982.  相似文献   

3.
The effects of injecting cells with adenosine monophosphate (AMP) and cyclic adenosine monophosphate (cAMP) on calcium current were investigated during intracellular dialysis ofHelix pomatia neurons. Microiontophoretically injected AMP was found to lead to reinstatement of calcium current following dialysis-induced wash-out, as well as considerable stabilization of this current with the extracellular medium at normal pH. Current-voltage relationship of the current would then undergo a 10 mV shift towards depolarization values. Perfusing the cell with a solution containing 10 mM AMP then produced a qualitatively identical effect. Injecting the neuron iontophoretically with cAMP led to a decline in the amplitude of calcium current under the same conditions. Neither raising the pH of the intracellular solution to 8.1 nor adding 4-aminopyridine in order to depress the hydrogen ion current produced a qualitative alteration in the effects of injecting AMP and cAMP on calcium current.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 6, pp. 769–776, November–December, 1988.  相似文献   

4.
Using voltage clamping, changes in inward calcium current arising after the occurrence of postsynaptic currents were investigated in isolated neurons ofHelix lucorum. Inward calcium current was reversibly reduced during the formation of inhibitory or excitatory postsynaptic current, produced either by spontaneous activation of an unidentified interneuron or by stimulating the anal nerve. Application of serotonin to the neuronal cell body also reversibly suppressed calcium current. The possible cell mechanism of the changes under study and their putative physiological role are discussed.A. A. Bogomolete Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 1, pp. 77–85, January–February, 1986.  相似文献   

5.
The actions of intracellularly applied D890 on membrane currents of the identified neurons B1, B2 and B3 of Helix pomatia were investigated. The TTX-resistant component of the inward current, the inward currents in Na+-free sucrose solution and in Ca2+-free Ba2+ solution were reduced. In Ca2+-free Co2+ solution the inward current was not affected. The late outward currents were strongly reduced. In solutions containing 20 mmol/l NiCl2 the remaining parts of these currents were blocked only to a lesser extent. The early outward current remained unchanged. It is concluded that intracellularly applied D890 mainly exerts its effects on the calcium current.  相似文献   

6.
Summary 1. In molluscan neurons glutamate may, on different neurons, evoke either excitation or inhibition. We studied neurons ofHelix pomatia which have hyperpolarizing responses to glutamate and determined the effects of lead on these responses.2. In voltage clamp experiments, the reversal potentials of these glutamate responses indicate that they are due to a conductance increase to chloride ions. Further evidence for this conclusion was obtained by the demonstration that responses to glutamate remained unaffected in experiments with intracellular dialysis with K-free saline in the presence of Na- and K-free extracellular media. In these circumstances, there is effectively no other ion than chloride to carry the current. In isolated neurons the glutamate-evoked chloride current is concentration dependent between 25 and 2500 µM. The current rises over 200 msec and declines in the continued presence of glutamate over a period of about 3 sec.3. Lead (0.5–1.0 µM) potentiated the glutamate-evoked chloride current provided that the channels were not maximally activated. The potentiation was greater if lead was added 30–60 sec before glutamate application.4. These results suggest that potentiation of transmitter-evoked responses by lead must be considered as yet another possible site of action of lead on neurons, and thus this effect must be considered as a part of the mechanism responsible for the neurotoxicity of this heavy metal.  相似文献   

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8.
The effect of intracellular iontophoretic injection of cyclic AMP on electrical activity of neurons RPa1, RPa3, LPa2, LPa3, and LPl1 in the corresponding ganglia ofHelix pomatia was investigated. Injection of cyclic AMP into neuron LPl1 was found to cause the appearance of rhythmic activity (if the neuron was originally "silent"), an increase in the frequency of spike generation (if the neuron had rhythmic activity), and a decrease in amplitude of waves of membrane potential, in the duration of the interval between bursts, and in the number of action potentials in the burst (if the neuron demonstrated bursting activity). In the remaining "silent" neurons injection of cyclic AMP led to membrane depolarization. Injection of cyclic AMP into neurons whose membrane potential was clamped at the resting potential level evoked the development of an inward transmembrane current (cyclic AMP current), the rate of rise and duration of which increased proportionally to the size and duration of the injection. Theophylline in a concentration of 1 mM led to an increase in the amplitude and duration of the cyclic AMP current by about 50%. It is concluded that a change in the cyclic AMP concentration within the nerve cell may modify the ionic permeability of its membrane and, correspondingly, its electrical activity.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 5, pp. 517–525, September–October, 1980.  相似文献   

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11.
Summary 1. The effects of aluminium (Al) on calcium (Ca) currents were investigated by using the conventional two-electrode voltage clamp technique inHelix pomatia neurons. The peak amplitude, kinetics, and voltage dependence of activation and inactivation of the Ca currents were studied in the presence of 10–5–10–3 M AlCl3, at pH 6.2. Al prolonged the rising phase of the Ca currents and therefore increased the time to peak at each command voltage step used.3. There was no significant influence of Al on the peak amplitude of the Ca currents, but the voltage dependence of the time to peak, activation, and inactivation of the Ca currents shifted to more positive potentials as a consequence of Al treatment.4. The leak currents were not influenced by Al up to 1 mM, which was the maximal dose applied.5. The results support the suggestion that Al may modify the Ca homeostasis and that it exerts a neurotoxic effect, at least in part, by modulation of the Ca current of the neuronal membrane.  相似文献   

12.
The influence of the neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) on single Ca2+ channel activity was studied on unidentified neurons of the snailHelix pomatia. Only one type of Ca2+ channels with the unitary conductance of 5 pS was identified using 100 mM Ca2+ in the patch pippette under patch-clamp in a cell-attached configuration. The amplitude histogram showed only one peak with the mean value of 0.5 pA at the testing potential of –30 mV. The distribution of channel open times monotonically declined with the mean time constant of 0.2 msec. The distribution of channel closed times could be fitted by a double-exponential curve with time constants of 1 and 12 msec. The study of the effect of 5-HT on Ca2+ single channel activity showed that 5-HT influenced the channel molecule indirectly, as the transmitter could exert its effect by being added to the bath solution, which did not come into contact with the tested membrane fragment under the micropipette tip. 5-HT prolonged the mean channel open time (up to 0.3 msec) and proportionally decreased both channel closed time constants to 0.4 and 6.0 msec, respectively. A conclusion is made that enhancement of Ca2+ macrocurrent by 5-HT is determined by three factors: (i) changes in kinetics of aiready existing channels, (ii) an increase in the number of active channels of the same type, and (iii) an increase in probability of a channel being open. At the same time, the unitary channel conductance was not affected by the transmitter.Neirofiziologiya/Neurophysiology, Vol. 28, No. 2/3, pp. 132–140, March–June, 1996.  相似文献   

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目的:研究芋螺毒素SO3对培养大鼠海马神经元缺氧后胞内游离钙离子浓度的影响.方法:运用激光共聚焦显微镜(CLSM)测定缺氧后大鼠海马神经元胞内游离钙离子浓度的变化.结果与结论:芋螺毒素SO3可以明显抑制因缺氧所致原代培养大鼠海马神经元胞内游离钙离子浓度的上升.  相似文献   

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In neuronal growth cones, cycles of filopodial protrusion and retraction are important in growth cone translocation and steering. Alteration in intracellular calcium ion concentration has been shown by several indirect methods to be critically involved in the regulation of filopodial activity. Here, we investigate whether direct elevation of [Ca2+]i, which is restricted in time and space and is isolated from earlier steps in intracellular signaling pathways, can initiate filopodial protrusion. We raised [Ca2+]i level transiently in small areas of nascent axons near growth cones in situ by localized photolysis of caged Ca2+ compounds. After photolysis, [Ca2+]i increased from approximately 60 nM to approximately 1 microM within the illuminated zone, and then returned to resting level in approximately 10-15 s. New filopodia arose in this area within 1-5 min, and persisted for approximately 15 min. Elevation of calcium concentration within a single filopodium induced new branch filopodia. In neurons coinjected with rhodamine-phalloidin, F-actin was observed in dynamic cortical patches along nascent axons; after photolysis, new filopodia often emerged from these patches. These results indicate that local transient [Ca2+]i elevation is sufficient to induce new filopodia from nascent axons or from existing filopodia.  相似文献   

17.
1. The effect of external application of oxytocin on inward calcium current in dialyzed snail neurons has been investigated under clamp conditions. 2. External application of oxytocin in a dose-dependent manner (Kd 0.9 microM) inhibits inward calcium current in dialyzed neurons of the snail, Helix pomatia. 3. Inhibition of calcium current developed with the time constant of about 2 min. The degree of restoration of calcium current after oxytocin washout depends on duration of oxytocin action. 4. It has been suggested that inhibition of calcium current by oxytocin occurs in two stages, the initial one is more fast and reversible and the second one--more slow and irreversible. The participation of soluble second messengers in the inhibitory effect of oxytocin on calcium current is discussed.  相似文献   

18.
Recent studies have demonstrated that murine lymphocytes express specific cell-surface receptors for a range of sulfated polysaccharides. In order to determine whether polysaccharide binding induces transmembrane signaling, the effects of sulfated polysaccharides on the free intracellular calcium ion concentration [( Ca2+]i) of mouse thymocytes and spleen cells were determined. Cells were loaded with Indo-I, a fluorescent indicator of calcium ion concentration. The validity and limitations in the use of this indicator in the determination of [Ca2+]i are documented. Dextran sulfate (Mn = 500,000), iota-carrageenan, lambda-carrageenan and kappa-carrageenan all cause relatively large changes in the [Ca2+]i of thymocytes (change in [Ca2+]i greater than 50 nM). Of these, dextran sulfate (Mn = 500,000) always had the greatest effect on [Ca2+]i. Smaller responses were obtained with heparin and dextran sulfate (Mn = 5000), while no response was obtained with chondroitin 4-sulfate, chondroitin 6-sulfate, pentosan sulfate or fucoidin. This response pattern (with the exception of fucoidin and pentosan sulfate) corresponds with the expression of thymocyte receptors for these polysaccharides. The increase in [Ca2+]i caused by the sulfated polysaccharides requires extracellular Ca2+ ions however, it is unlikely that voltage-dependent ion channels are involved in these responses. In contrast to thymocytes, although spleen cells express receptors for sulfated polysaccharides, they were unresponsive to all of the sulfated polysaccharides tested, suggesting a basic difference between thymocytes and peripheral T and B lymphocytes in their response to the binding of sulfated polysaccharides.  相似文献   

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20.
The influence of cAMP on the electrical coupling of canine Purkinje fibers was investigated. It was found that the intracellular injection of the nucleotide enhances the cell-to-cell coupling appreciably. No change in the coupling coefficient (V2/V1) was found with the intracellular injection of 5-AMP. A slight decrease in input resistance (Vo/Io) was produced by cAMP injection and the time constant of the cell membrane (tau m) was also reduced. These findings indicate that the changes in intercellular coupling produced by cAMP were not related to an increase in resistance of the non-junctional membrane but to a decline in junctional resistance. The present results support the view that cAMP plays an important role in the modulation of junctional conductance in cardiac fibers.  相似文献   

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