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11.
Alain Coulombe Isabel Ann Lefèvre Isabelle Baro Edouard Coraboeuf 《The Journal of membrane biology》1989,111(1):57-67
Summary Ca2+- and Ba2+-permeable channel activity from adult rat ventricular myocytes, spontaneously appeared in the three single-channel recording configurations: cell-attached, and excised inside-out or outside-out membrane patches. Single-channel activity was recorded at steady-state applied membrane potentials including the entire range of physiologic values, and displayed no rundown in excised patches. This activity occurred in irregular bursts separated by quiescent periods of 5 to 20 min in cell-attached membrane patches, whereas in excised patch experiments, this period was reduced to 2 to 10 min. During activity, a variety of kinetic behaviors could be observed with more or less complex gating patterns. Three conductance levels: 22, 45 and 78 pS were routinely observed in the same excised membrane patch, sometimes combining to give a larger level. These channels were significantly permeable to divalent cations and showed little or no permeability to potassium or sodium ions. The inorganic blockers of voltage-gated Ca channels, cobalt (2mm), cadmium (0.5mm) or nickel (3mm), had no apparent effect on these spontaneous unitary currents carried by barium ions. Under 10–5
m bay K 8644 or nitrendipine, the activity was clearly increased in about half of the tested excised inside-out membrane patches. Both dihydropyridines enhanced openings of the larger conductance level, which was only very occasionally seen under control conditions. When the single-channel activity became sustained under 5×10–6
m Bay K 8644, it was possible to calculate the mean unitary current at different membrane potentials and show that the mean current value increased with membrane potential. 相似文献
12.
爪蟾卵母细胞经注射鲫鱼视网总RNA后,可表达大量电压依赖性钾离子通道。在此基础上,我们进一步发现,一个特定序列的寡核苷酸能专一地抑制该通道的表达。由于我们设计与合成的该片段与果蝇、小鼠中已克隆的钾通道中编码N端的一个多肽的mRNA完全互补,因此推测:鲫鱼视网膜中的K这个区域与其它物种的K通道有高度同源性,这为克隆该基因和研究它的功能提供了重要资料。 相似文献
13.
H. L. Sudan C. J. Kerry I. R. Mellor S. -K. Choi D. Huang K. Nakanishi P. N. R. Usherwood 《Invertebrate neuroscience : IN》1995,1(2):159-172
The effects of philanthotoxin-343 (PhTX-343; tyrosyl-butanoyl-spermine) and photolabile analogues of this synthetic toxin
on locust (Schistocerca gregaria) skeletal muscle have been investigated using whole muscle preparations (twitch contractions), single muscle fibres (excitatory
postsynaptic currents (EPSCs)) and muscle membrane patches containing single quisqualate-sensitive glutamate receptors (qGluR).
Analogues containing an azido group attached to either the butanoyl side-chain of PhTX-343 or as a substitute for the hydroxyl
moiety of the tyrosyl residue were about 6 fold more potent antagonists than PhTX-343; those with an azido group located at
the distal end of the toxin molecule were generally 2–3 fold less potent than PhTX-343. When these compounds were tested in
subdued light, they were reversible antagonists of the muscle twitch, EPSC and qGluR. When a muscle was irradiated with U.V.
during application of photolabile toxin combined with either neural stimulation of the muscle orl-glutamate application, antagonism of the twitch, EPSC and qGluR was complete and irreversible. 相似文献
14.
The effects of lead on Ca2+ homeostasis in nerve terminals was studied. Incubation with leadin vitro stimulated the activity of calmodulin and the maximum effect was observed at 30 M lead, higher concentrations had an inhibitory effect.In vivo exposure to lead increased the activity of calmodulin by 45%. Lead had an inhibitory effect on Ca2+ ATPase activity in both calmodulin-rich and calmodulin-depleted synaptic plasma membranes, the IC50 values for inhibition being 13.34 and 16.69 M respectively. Exogenous addition of calmodulin (5 g) and glutathione (1 mM) to calmodulin rich synaptic plasma membranes reversed the inhibition by IC50 concentration of lead.In vivo exposure of lead also significantly reduced the Ca2+ ATPase activity, resulting in an increase in intrasynaptosomal calcium. Concomitant with the increase in intrasynaptosomal calcium, lipid peroxidation values also increased significantly in lead-treated animals. In addition lead also had an inhibitory effect on depolarization induced Ca2+ uptake and the inhibition was found to be a competitive one. The results sugest that lead exerts its toxic effects by modifications of the intracellular calcium messenger system which would have serious consequences on neuronal functioning. 相似文献
15.
16.
Single Ca2+ channel records were obtained from plasma membrane-enriched fractions of wheat roots incorporated into artificial planar lipid bilayers. The channel had a unitary conductance of 15 pS for a 10 to 95 mM CaCl2 gradient (cytoplasm: outside of the cell). The voltage dependence displayed by the channel agreed with that expected for Ca2+ channels in the plasma membrane. The channel gating was strongly modified by addition of 20 M extracellular verapamil (a Ca2+ channel antagonist). Extracellular AlCl3 (70 M, pH 4.9) almost completely blocked the channel. 相似文献
17.
I. I. Pottosin P. R. Andjus D. Vučelić G. N. Berestovsky 《The Journal of membrane biology》1993,136(2):113-124
We studied the effects of H2O/D2O substitution on the permeation and gating of the large conductance Ca2+-activated K+ channels inChara gymnophylla droplet membrane using the patchclamp technique. The selectivity sequence of the channel was: K+>Rb+≫Li+, Na+, Cs+ and Cl−. The conductance of this channel in symmetric 100mm KCl was found to be 130 pS. The single channel conductance was decreased by 15% in D2O as compared to H2O. The blockade of channel conductance by cytosolic Ca2+ weakened in D2O as a result of a decrease in zero voltage Ca2+ binding affinity by a factor of 1.4. Voltage-dependent channel gating was affected by D2O primarily due to the change in Ca2+ binding to the channel during the activation step. The Hill coefficient for Ca2+ binding was 3 in D2O and around 1 in H2O. The values of the Ca2+ binding constant in the open channel conformation were 0.6 and 6 μm in H2O and D2O, respectively, while the binding in the closed conformation was much less affected by D2O. The H2O/D2O substitution did not produce a significant change in the slope of channel voltage dependence but caused a shift as large
as 60 mV with 1mm internal Ca2+. 相似文献
18.
19.
Tachykinins Potentiate N-Methyl-D-Aspartate Responses in Acutely Isolated Neurons from the Dorsal Horn 总被引:6,自引:0,他引:6
K. I. Rusin D. Bleakman P. S. Chard M. Randic R. J. Miller 《Journal of neurochemistry》1993,60(3):952-960
Abstract: Substance P and neurokinin A both potentiated N -methyl- d -aspartate (NMDA)-induced currents recorded in acutely isolated neurons from the dorsal horn of the rat. To elucidate the mechanism underlying this phenomenon, we measured the effects of tachykinins and glutamate receptor agonists on [Ca2+ ]i in these cells. Substance P, but not neurokinin A, increased [Ca2+ ]i in a subpopulation of neurons. The increase in [Ca2+ ]i was found to be due to Ca2+ influx through voltage-sensitive Ca2+ channels. Substance P and neurokinin A also potentiated the increase in [Ca2+ ]i produced by NMDA, but not by α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, kainate, or 50 m M K+ . Phorbol esters enhanced the effects of NMDA and staurosporine inhibited the potentiation of NMDA effects by tachykinins. It is concluded that activation of protein kinase C may mediate the enhancement of NMDA effects by tachykinins in these cells. However, the effects of tachykinins on [Ca2+ ]i can be dissociated from their effects on NMDA receptors. 相似文献
20.
新生大鼠脊髓切片运动神经元的电生理参数测定 总被引:1,自引:0,他引:1
汪萌芽 《中国应用生理学杂志》1993,9(2):164-167
用微电极技术对新生大鼠脊髓横切薄片运动神经元(MN)进行细胞内记录,测得静息电位为-62±4mV(n=26),膜电阻为67±31MΩ,时间常数3.8±1.6ms,动作电位幅度68±7mV(n=26),阈电位-50±8mV,超射值6±4mV。灌流谷氨酸(1~30mmol/L)诱导伴膜电阻降低的缓慢去极化反应,5-羟色胺(50μmol/L)介导伴膜电导降低的电压依赖性内向电流。结果表明新生大鼠脊髓切片MN的细胞内生物电记录是一种稳定可靠的电生理学和药理学研究方法。 相似文献