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11.
Manis PB Molitor SC Wu H 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2003,153(4):443-451
During intracellular recordings in rodent brainstem slice preparations, dorsal cochlear nucleus (DCN) pyramidal cells (PCs) exhibit characteristic discharge patterns to depolarizing current injection that depend on the membrane potential from which the responses are evoked. When depolarized from hyperpolarized potentials, PCs can respond with a short-latency action potential followed by a long silent interval (pauser) or a train of action potentials with a long latency (buildup). During the silent intervals in a pauser or a buildup response, the membrane potential slowly depolarizes towards spike threshold, often exhibiting distinct voltage oscillations of 1–2 mV before the first spike. The subthreshold voltage oscillations were investigated using whole cell recordings from DCN PCs in rat pup (P10–14) brainstem slices. The oscillations were unaffected by excitatory and inhibitory neurotransmitter antagonists, and were not temporally locked to the onset of the depolarization. The oscillations typically became larger as spike threshold was approached, and had a characteristic frequency between 40 and 100 Hz. In the presence of tetrodotoxin (TTX, 500 nM), the oscillations were significantly suppressed, and could not be evoked at any voltage below or above spike threshold. The oscillations were not blocked by phenytoin or Cd2+, but they were affected by prior activity in the neuron for approximately 1 s. We conclude that voltage-gated Na+ channels are required to generate membrane oscillations during the buildup phase. We suggest that the subthreshold oscillations play a role in controlling spike timing in PCs when the membrane potential slowly approaches, or hovers near, spike threshold. 相似文献
12.
The volume-activated chloride current in endothelial cells from bovine pulmonary artery is not modulated by phosphorylation 总被引:8,自引:0,他引:8
Géza Szücs Stephan Heinke Christine De Greef Luc Raeymaekers Jan Eggermont Guy Droogmans Bernd Nilius 《Pflügers Archiv : European journal of physiology》1996,431(4):540-548
We employed the patch-clamp technique to investigate the effects of various phosphorylation pathways on activation and modulation of volume-activated Cl- currents (I
Cl,vol) in cultured endothelial cells from bovine pulmonary arteries (CPAE cells). Half-maximal activation ofI
Cl,vol occurred at a hypotonicity of 27.5 ± 1.2%. Run-down of the current upon repetitive activation was less than 15% within 60 min. Stimulation of protein kinase C (PKC) by phorbol-12-myristate-13-acetate (PMA) or by (–)-indolactam did not affectI
Cl,vol. Down regulation of PKC activity by a 24-h preincubation of the cells with 0.2 mol/l PMA, or its inhibition by loading the cells with the specific inhibitory 19–31 pseudosubstrate peptide, did not influenceI
Cl,vol. Trifluoperazine and tamoxifen fully blockedI
cCl,vol with concentrations required for half-maximal inhibition of 3.0 and 2.4 mol/1 respectively. This inhibitory effect is probably not mediated by the calmodulin-antagonistic action of these compounds, because it occurs at free intracellular [Ca2+] of 50 nmol/l, which are below the threshold for calmodulin activation. The tyrosine kinase inhibitor herbimycin A (1 ol/1) and genistein (100 ol/1) did not affectI
Cl,vol Exposing CPAE cells to lysophosphatidic acid (1mol/1), an activator of p42 MAPkinase and the focal adhesion kinase p125FAK in endothelial cells, neither evoked a Cl– current nor affectedI
Cl,vol Neither wortmannin (10 mol/1), an inhibitor of MAP kinases and of PI-3 kinase, nor rapamycin (0.1 mmol/1), which interferes with the p70S6 kinase pathway, affectedI
Cl,vol Exposure of CPAE cells to heat or Na-arsenite, both activators of a recently discovered stress-activated tyrosine phosphorylation pathway, neither activated a current nor affected the hypotonic solution-induced Cl– current. We conclude that none of the studied phosphorylation pathways is essential for the activation of the Cl– current induced by hypotonicity. 相似文献
13.
Ca2+ (ICa) and K+ (IK) currents were recorded in single cultured cells from rat aorta using the whole cell clamp technique with patch electrodes. ICa was detected at–30 mV, and at 20 mV it reached a peak in about 10 ms and decayed with a t1/2=50 ms. The mean maximum slope conductance (GCa) was 30 S/cm2. IK was detected at–10 mV and at 20 mV reached its maximum with a t1/2=12 ms. For IK, GK=200 S/cm2. These channels can be activated during action potentials and play a role in the excitation and contraction of vascular smooth muscle cells.Doctoral training program UAM-1 相似文献
14.
Jean Valmier Michel Simonneau Sylvie Boisseau 《Pflügers Archiv : European journal of physiology》1989,414(3):360-368
The electrophysiological properties of a subset of dorsal root ganglion (DRG) neurons microdissected from 12-day-old (E12) mouse embryos and acutely isolated were analyzed as soon as 3 after their isolation. Two classes of neurons were defined according to their mean diameter. The larger diameter class was examined in this study. They display uniform cytoskeletal properties with co-expression of vimentin and neurofilament triplet proteins. Patch-clamp methods also revealed a homogeneous and limited repertoire of ionic channels that included (1) a TTX-sensitive Na+ current whose properties are similar to that reported in mature mammalian neurons, and (2) two types of K+ currents that can be compared with the delayed rectifier (I
k
) and the transient (I
a) potassium currents found in other mammalian preparations. It may be possible to use this in vitro model to examine the development of new types of currents, such as Ca2+ currents during neuronal growth and differentiation. 相似文献
15.
Voltage clamp experiments were carried out on sheep Purkinje fibers to determine the effect of Ach on the time-dependent currents.On the pacemaker current (i
K
2) Ach 10–6 mol·l–1 had the following effects: shift of the activation curve by a few mV in the depolarizing direction, without change in the rectifier ratio. The potential dependence of the time constants for activation and deactivation was influenced in a similar way as the activation curve.Ach had no effect on the positive dynamic current (i
qr
) or the late plateau outward current (i
x
).The slow inward current (i
si
) as well as the transient inward current (T.I.) were reduced in amplitude and slowed in time course by Ach.The changes in pacemaker current are important in explaining the increased rate of diastolic depolarization in the presence of Ach. The decrease of slow inward current by Ach cannot be made responsible for the plateau shift or the prolongation of the action potential.Supported by F.G.W.O. Belgium 3.0087.74 相似文献
16.
Using electrophysiological and radiotracer studies in parallel, we have investigated the characteristics of the endogenous Na+-dependent amino acid transporter (system B0,+) in Xenopus oocytes with regard to ion dependence, voltage dependence and transport stoichiometry. In voltage-clamped oocytes (–60 mV) superfusion with saturating concentrations of amino acids (1 mM) in 100 mM NaCl resulted in reversible, inward currents (mean±SEM): alanine, 1.83±0.09 nA (n=21); arginine, 2.54±0.18 nA (n=17); glutamine, 1.73±0.10 nA (n=19). Only arginine evoked a current in choline medium (0.50±0.13 nA, n=10), whereas Cl– replacement had no effect on evoked currents. The glutamine-evoked current was saturable (I
max=1.73 nA, glutamine K
m=0.12 mM) and linearly dependent upon voltage between –90 and –30 mV. Using direct and indirect (activation) methods, we found that transport can proceed with Na+/amino acid coupling stoichiometry of either 11 or 21, but coupling was the same for each amino acid tested (alanine, arginine and glutamine) within a batch of oocytes (i.e. from a single toad). Despite the net single positive charge on arginine, the magnitude of the net transmembrane charge movement during Na+-coupled arginine transport was identical to that for the zwitterionic neutral amino acids glutamine and alanine; this may be explained by a concomitant stimulation of K+ efflux during arginine transport with a putative coupling of 1 K+1 arginine. 相似文献
17.
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
18.
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
19.
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
20.
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