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41.
I. M. Vinogradova I. I. Krivoi T. P. Sei 《Bulletin of experimental biology and medicine》1990,109(6):691-694
Leningrad State University, A. A. Ukhtomskii Leningrad Institute of Physiology. (Presented by Academician of the Academy of Medical Sciences of the USSR S. N. Golikov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 109, No. 6, pp. 523–525, June, 1990. 相似文献
42.
In order to examine temporal changes in enhancement of transmitter release during long-term potentiation (LTP), we examined amplitude fluctuation of excitatory postsynaptic potentials (EPSPs) for longer periods than 2 h after tetanic stimulation (up to 4 h in the longest observation). The relative magnitude of excitatory postsynaptic potentiation (EPSP) fluctuation (coefficient of variation, CV) reduced throughout the observation periods in association with an increase in EPSP amplitude after tetanic stimulation. The reciprocals of squared CVs (= mean2/variance) were almost in proportion to the magnitude of LTP, and the ratio of 1/CV2 and the LTP magnitude did not change significantly for up to 4 h. These findings suggest that a prolonged enhancement of transmitter release from presynaptic terminals underlies LTP, and the relative contribution of this presynaptic enhancement does not change significantly for 2 h (maybe up to 4 h, or longer) after tetanic stimulation. 相似文献
43.
Luke J. Janssen Stephen M. Sims 《Pflügers Archiv : European journal of physiology》1994,427(5-6):473-480
Spontaneous transient inward currents (STICs) were recorded in canine and guinea-pig tracheal myocytes held at negative membrane potentials. STICs were Cl– selective since their reversal potential was dependent on the Cl– gradient and they were blocked by the Cl– channel blocker niflumic acid. STICs were insensitive to Cs+, charybdotoxin, and nifedipine. Ca2+-activated K+ currents often preceded STICs, suggesting that the STICs are Ca2+ dependent. In support of this suggestion, we found the Cl– currents were: (1) abolished by depleting intracellular Ca2+ stores using caffeine, acetylcholine, histamine, or substance P; (2) enhanced by increasing external concentrations of Ca2+; (3) evoked by voltage-dependent Ca2+ influx. The channels responsible for this Cl– current are of small unitary conductance (<20 pS). Decay of the STICs was described by a single exponential with a time constant of 94±9 ms at –70 mV; the time constant increased considerably at more positive potentials. Using Ca2+-dependent Cl– currents and contractions as indices of internal levels of Ca2+, we found that isolated tracheal cells are capable of exhibiting rhythmic behaviour: bursts of currents and contractions with a periodicity of less than 0.1 Hz and which continued for more than 20 min. These rhythmic events were recorded at negative membrane potentials, suggesting that cyclical release of internally sequestered Ca2+ is responsible. We conclude that spontaneous release of Ca2+ from intracellular stores in tracheal muscle cells leads to transient currents in some cases accompanied by rhythmic contractions. Our studies provide evidence for a cellular mechanism that could underly myogenic oscillations of membrane potential in smooth muscle. 相似文献
44.
Excitatory synaptic potentials due to activation of neurons with short projections in the myenteric plexus 总被引:2,自引:0,他引:2
Intracellular microelectrodes have been used to examine the effects, on excitatory inputs to myenteric nerve cells, of lesions of intrinsic pathways in the myenteric plexus of the guinea-pig small intestine. The lesions consisted of circumferential cuts (myotomies) which severed the external musculature to the depth of the submucosa and thus interrupted pathways in the myenteric plexus. Sufficient time was allowed between creating the lesions and recording from the neurons for the endings of severed neurites to degenerate and this was confirmed histochemically by examining the distribution of varicose fibres with 5-hydroxytryptamine immunoreactivity in myenteric ganglia from which recordings were made. Two types of excitatory input, eliciting fast and slow excitatory post-synaptic potentials, respectively, were demonstrable in response to focal stimulation of nerves in the ganglia from which recordings were made. There were no differences in the proportions of neurons in which fast or slow excitatory synaptic potentials were evoked in unoperated preparations (controls), in islands 1.5-4 mm wide between myotomies, or within 1 mm on the oral or anal sides of myotomies. Possible differences in the amplitudes, durations at half amplitude, and threshold numbers of stimuli for initiation of slow excitatory synaptic potentials were analyzed. The only significant differences were found when data from control and oral areas were pooled and compared with combined data from island and anal areas (this assessed differences that could arise from severing nerve fibres running from oral to anal).(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
45.
Frequency-coded impulses are known to be converted into postsynaptic potentials (PSPs) at the synapse of a target neuron. This can be termed frequency-voltage (F-V) conversion. Studies on this problem in pyramidal tract neurons (PTNs) showed that not only the amplitude but also the duration of depolarizing PSPs was determined as a function of the input impulse frequency. Two opposite patterns of F-V conversion were observed following activation of two input systems to PTNs. Inhibitory postsynaptic potentials were found to play an important role in the regulation of the duration of PSPs by curtailing excitatory post-synaptic potentials. 相似文献
46.
A mathematical model is proposed to describe the intracellularCa
2+ (Ca
i) transient and electrical activity of vascular endothelial cells (VEC) elicited by fluid shear stress (τ). The intracellularCa
2+ store of the model VEC is comprised of aCa
i-sensitive (sc) and an inositol (1,4,5)-trisphosphate (IP
3)-sensitive compartment (dc). The dc [Ca
2+] is refilled by the sc whose [Ca
2+] is the same as extracellular [Ca
2+].IP
3 produced by the τ-deformed mechanoreceptors discharges the dcCa
2+ into the cytosol. The increase of cytosolic[Ca
2+] inducesCa
2+ release (CICR) from the sc. The raisedCa
i activates aCa
i-activatedK
+ current (I
K, Ca) and inhibitsIP
3 production. The cell membrane potential is determined byI
K, Ca, voltage-dependentNa
+ andK
+ currents. Steady τ>0.1 dyne/cm2 elicits aCa
i varies sigmoidally withLog
10(τ) with a maximal peakCa
i of 150 nM at τ=4 dynes/cm2. Step increases of τ fail to elicit aCa
2+ response in cells previously stimulated by a lower shear. TheCa
2+ response gradually decreases with repetitive τ stimuli. Pulsatile shear elicits two to three times higherCa
i and hyperpolarizes the cell more than steady shear of the same magnitude. The simulatedCa
2+ responses to τ are quantitatively and qualitatively similar to those observed in cultured VEC. The model provides a possible
explanation of why the vasodilating stimulus is greater for pulsatile flow than for nonpulsatile flow. 相似文献
47.
Postsynaptic fibers reaching the dorsal column nuclei were investigated in rat by means of retrograde transport of wheat germ agglutinin-horseradish peroxidase conjugate. Each nucleus received only ipsilateral afferents with most of the labeled cells forming a band which covered the mediolateral extent of the dorsal horn in an area that resembled lamina IV in the cat. The labeling excluded the reticular extension of the neck of the dorsal horn. Lumbosacral afferents were restricted to the gracilis nucleus and cervicothoracic afferents to the cuneatus nucleus. Cervical and anterior lumbar levels showed additional projections coming from their most medial parts. The organization of this second-order pathway in rat is similar to that in cat and monkey. 相似文献
48.
Paul McIntosh Andrew P. Southan Sobia Akhtar Christina Sidera Yuri Ushkaryov J. Oliver Dolly B. Robertson 《Pflügers Archiv : European journal of physiology》1997,435(1):43-54
We have examined the effects of co-expression of Kvβ1.1 and Kvβ2.1 subunits on the gating of rat brain Kv1.4 channels, expressed
in Xenopus oocytes. Expression of Kv1.4 subunits alone produced a rapidly inactivating ”A” type current, which activated at potentials
beyond –60 mV in a solution containing high levels of rubidium. Current activation curves obtained from tail current measurements
were fitted with a Boltzmann function, with V
1/2 = –47 mV and k = 10 mV. Neither the Kvβ1.1 nor Kvβ2.1 subunits altered the voltage dependence of activation. Both subunits accelerated the
activation time constant of Kv1.4, without affecting its voltage dependence. Surprisingly, the Kvβ2.1 subunit, which lacks
an N-terminal inactivation domain, was almost as effective as the Kvβ1.1 subunit in speeding up Kv1.4. Steady-state inactivation
of Kv1.4 was unchanged upon co-expression with either Kvβ1.1 or Kvβ2.1 subunits. Kv1.4 recovered from inactivation with two
time constants; apart from an ≈ 50% lengthening of the slow time constant with a high Kvβ2.1 injection ratio, neither time
constant was altered by either the Kvβ1.1 or Kvβ2.1 subunits, suggesting little interaction with recovery from C-type inactivation.
Clearly, β subunits have the potential to modify the gating of Kv1.4 channels in the brain more subtly than has been suggested
previously.
Received: 17 March 1997 / Accepted: 30 June 1997 相似文献
49.
Vasoactive intestinal polypeptide nerve processes and cell bodies were identified by electron microscopic immunocytochemistry in the rat small intestine. Labeled nerve processes were numerous in the inner circular smooth muscle coat and mainly in the mucosa, but were absent in the longitudinal muscle layer. Submucosal blood vessels were often surrounded by immunoreactive vasoactive intestinal polypeptide positive nerves, in close associations (distance less than 40 mn) to blood vessel basement membranes and to smooth muscle cells. In the ganglia of the myenteric and submucous plexuses, labeled fibers surrounded unstained neural cell bodies. The synaptic vesicles of vasoactive intestinal polypeptide positive terminals were 35-40 nm in diameter and some dense core vesicles (80-120 nm in diameter) were also observed in the same profiles. These observations suggest that vasoactive intestinal polypeptide nerves may participate in regulating smooth muscle activity and local blood flow in the small intestine. 相似文献
50.
Changes in membrane potential and potassium concentration in the extracellular space ([K+]e) of rabbit vagus nerve were measured simultaneously during electrical activity and during the period of recovery using a
modified sucrose-gap method and potassium-sensitive microelectrodes. After stimulation for 15 s at 15 Hz the main activity-induced
increase in [K+]e reached 16.9 mM. This increase in [K+]e was paralleled by a depolarization of the preparation. The period of activity was followed by a post-tetanic hyperpolarization
(PTH) lasting tens of seconds, generated by the axonal electrogenic Na+-K+ pump and to a lesser extent by the pump of the surrounding Schwann cells. The amplitude of the PTH dramatically increased
in experiments in which inward currents were blocked by removal of Cl– or after application of Cs+ or Ba2+, indicating that under normal conditions the current generated by the Na+-K+ pump is strongly short-circuited. A pharmacological and kinetic study showed that these currents are: (1) the hyperpolarization-activated
current I
h, and (2) the inwardly rectifying I
KIR current. The results show that the latter originates from Schwann cells. Our data indicate that in non-myelinated nerves
there is a subtle association of inward ionic channels which (1) helps the cell to maintain an optimal membrane potential
after a period of activity, and (2) contributes to the removal of excess K+ from the extracellular space.
Received: 7 August 1997 / Received after revision 6 April 1998 / Accepted: 15 April 1998 相似文献