Calcium current and inactivation in identified neurons in Hermissenda crassicornis.
Calcium current and inactivation in identified neurons in Hermissenda crassicornis.
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Hermissenda crassicornis 中已识别神经元的钙电流和失活。
DOI：
10.1152/jn.1994.72.5.2196
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发表时间：
1994
影响因子：
2.5
通讯作者：
Sanchez-Andres,JV
中科院分区：
文献类型：
--
作者：
Yamoah,EN;Kuzirian,AM;Sanchez-Andres,JV
1. 在消除向内Na+电流（胆碱离子取代）和抑制向外K+电流（Cs+、四乙基铵和4-AP）的条件下，使用低电阻片电极（0.7 +/- 0.3 M ω; n = 101），在鉴定的Hermissenda crassicornis神经元中记录n型（ω - concontoxin敏感）钙电流（ICa）。从保持电位-60 mV到-30 mV以上的阶跃去极化引起ICa，其峰值约为20 mV，随着去极化的增加而下降。2. 存在低阈值电流的证据。在超极化电位（例如-90 mV）下，在-60 ~ -40 mV下，发现了一个小的肩（< 100 pA），对Co2+和Ni2+敏感。然而，在这里检查的条件下（保持电位为-60 mV），高压激活电流占主导地位。3. 钡（Ba2+）和锶（Sr2+）以相似的激活动力学渗透Ca2+通道（易于渗透；Ba2+ > Ca2+ > Sr2+）。Ca2+、Ba2+和Sr2+作为载流子时，渗透率随膜电位的稳态激活可以用玻尔兹曼方程拟合，ICa的半激活电压和斜率因子分别为2.9和7.7 mV， Ba2+电流（IBa）为-13.1 mV和7.8 mV， Sr2+电流（ISr）为-2.3 mV和7.8 mV。激活的时间过程单调，时间常数（tau）在2 ~ 8 ms之间。失活概况是复杂的。在负阶跃电位下（例如-20 mV），电流的失活很慢。相对正电压（如10 mV）下的去极化步骤比正电压（如40 mV）下的去极化步骤失活得更快。当细胞外Ca2+从5增加到10 mM时，观察到双相衰减（tau快25 +/- 4 ms； tau慢473 +/- 64 ms；平均+/- SD， n = 9）。这样的观察表明电流介导的失活。5. 当脉冲持续时间约为350 ms时，ISr表现为失活，而Ba2+几乎消除了衰变。然而，随着去极化时间的延长，IBa关闭了。6. 双脉冲方案用于评估失活的电压依赖性：观察到ICa， IBa和ISr的不完全u型失活曲线。可用于失活的通道在Ca2+离子的存在下增加。7. 进一步研究了Ca2+螯合剂乙二醇-双（β -氨基乙醚）-N，N，N‘，N’-四乙酸和双（邻氨基苯氧基）-N，N，N‘，N’-四乙酸（BAPTA）的失活作用。在移液管中加入10mm的BAPTA后，失活程度降低，但未消除。（摘要删节250字）
1. N-type (omega-conotoxin sensitive) calcium currents (ICa) were recorded in identified neurons in Hermissenda crassicornis using low-resistance patch electrodes (0.7 +/- 0.3 M omega; n = 101) under conditions that eliminated inward Na+ currents (choline ions substitution) and suppressed outward K+ currents (Cs+, tetraethylammonium, and 4-AP). Step depolarization from a holding potential of -60 mV to potentials above -30 mV elicited ICa, which peaked approximately 20 mV and declined with increasing depolarizations. 2. Evidence for a low-threshold current was present. Step depolarization from a more hyperpolarizing potentials (e.g., -90 mV) revealed a small shoulder (< 100 pA) at -60 to -40 mV that was sensitive to Co2+ and Ni2+. However, under the conditions examined here (holding potential of -60 mV), the high-voltage-activated current predominated. 3. Barium (Ba2+) and strontium (Sr2+) permeate the Ca2+ channel with similar activation kinetics (ease of permeation; Ba2+ > Ca2+ > Sr2+). Steady-state activation of permeability versus membrane potentials for Ca2+, Ba2+, and Sr2+ as charge carriers could be fitted with the Boltzmann equation, with half-activation voltage and slope factor of 2.9 and 7.7 mV for ICa, -13.1 mV and 7.8 for Ba2+ current (IBa) and -2.3 mV and 7.8 for Sr2+ current (ISr). The time course of activation was monotonic with time constant (tau) for ICa ranging from 2 to 8 ms. 4. The inactivation profile was complex. At negative step potentials (e.g., -20 mV), inactivation of the current was slow. Depolarization steps to relatively positive voltages (e.g., 10 mV) showed more rapid inactivation than those at more positive potentials (e.g., 40 mV). When extracellular Ca2+ was raised from 5 to 10 mM, a biphasic decay (tau fast of 25 +/- 4 ms; and tau slow of 473 +/- 64 ms; mean +/- SD, n = 9) was seen. Such an observation suggested a current-mediated inactivation. 5. With a pulse duration of approximately 350 ms, ISr showed inactivation whereas Ba2+ virtually removed the decay. However, IBa turned off with more prolonged depolarization. 6. A twin-pulse protocol was used to assess the voltage dependence of inactivation: an incomplete U-shaped inactivation curve was observed for ICa, IBa, and ISr. Channels available for inactivation were increased in the presence of Ca2+ ions. 7. Inactivation was further studied with the Ca2+ chelators, ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid and bis(o-aminophenoxy)-N,N,N',N'-tetraacetic acid (BAPTA). With 10 mM of BAPTA, in the pipette, inactivation was reduced but not removed.(ABSTRACT TRUNCATED AT 250 WORDS)