KINETIC AND PHARMACOLOGICAL PROPERTIES OF LOW VOLTAGE-ACTIVATED CA-2+ CURRENT IN RAT CLONAL (GH3) PITUITARY-CELLS
KINETIC AND PHARMACOLOGICAL PROPERTIES OF LOW VOLTAGE-ACTIVATED CA-2+ CURRENT IN RAT CLONAL (GH3) PITUITARY-CELLS
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DOI：
10.1152/jn.1992.68.1.213
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发表时间：
1992-07-01
影响因子：
2.5
通讯作者：
LINGLE, CJ
中科院分区：
文献类型：
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作者：
HERRINGTON, J;LINGLE, CJ
1. 用全细胞记录技术研究了克隆性垂体细胞（GH 3）的低电压激活（LVA）钙电流。 使用内氟促进高电压激活（HVA）的钙电流的下降，使得在虚拟隔离中研究LVA电流成为可能. 在10 mM [Ca 2 +]o中，可检测的LVA电流在约-50 mV时开始出现，半最大激活发生在-33 mV。 激活的时间过程由n = 3的Hodgkin-Huxley表达式最好地描述，这表明在通道打开之前必须穿过至少三个闭合状态。 发现失活随膜电位在-60和-160 mV之间呈指数变化，表明通道关闭受单个电压依赖性转变的速率限制。 在-40 mV和-130 mV之间失活的开始和消除最好用两个指数之和来描述。 在-80 mV和-130 mV之间，灭活去除的两个组分显示出很小的电压依赖性，时间常数约为200-300 ms和1-2 s。 在膜电位高于-40 mV时，检测到失活起始的单一组分。 该分量在-20 mV和+20 mV（tau = 22 ms）之间与电压无关。 因此，LVA电流的失活最好用多个电压依赖性过程来描述。 在-65 mV下发生LVA电流的显著失活，未检测到宏观电流。 这表明失活并不严格耦合到通道开放。 峰值LVA电流随着[Ca 2 +]o的增加而增加，饱和度约为50 mM。峰值LVA电流的Ca 2+依赖性通过单位点结合等温线合理地描述，半最大LVA电流约为7 mM。 GH 3细胞的LVA电流对Ni ~（2+）的阻断有很大的抵抗力。 无机阳离子阻断GH 3 LVA电流的相对效力为（产生50%阻断的浓度）：La 3+（2.4 μ M）> Cd 2+（188 μ M）> Ni 2+（777 μ M）。 测试了几种有机药物，包括推定的LVA阻断剂、HVA电流阻断剂和各种麻醉剂阻断LVA电流的能力。 产生50%阻滞的浓度如下：硝苯地平（约50 μ M）、D 600（51 μ M）、地尔硫卓（131 μ M）、辛醇（244 μ M）、戊巴比妥（985 μ M）、甲氧氟烷（1.41 mM）和阿米洛利（1.55 mM）。 苯妥英和乙琥胺在100 μ M和2.5mM时分别产生36%和10%的阻断。 这些结果表明，在GH 3细胞的LVA钙电流是，在许多方面，动力学和在其他组织中类似的电流不同。
1. Low voltage-activated (LVA) Ca2+ current in clonal (GH3) pituitary cells was studied with the use of the whole-cell recording technique. The use of internal fluoride to facilitate the rundown of high voltage-activated (HVA) Ca2+ current allowed the study of LVA current in virtual isolation.2. In 10 mM [Ca2+]o, detectable LVA current begins to appear at about -50 mV, with half-maximal activation occurring at -33 mV. The time course of activation was best described by a Hodgkin-Huxley expression with n = 3, suggesting that at least three closed states must be traversed before channel opening.3. Deactivation was found to vary exponentially with membrane potential between -60 and -160 mV, indicating that channel closing is rate-limited by a single, voltage-dependent transition.4. Onset and removal of inactivation between -40 and -130 mV were best described by the sum of two exponentials. Between -80 and -130 mV, both components of removal of inactivation showed little voltage dependence, with time constants of approximately 200-300 ms and 1-2 s. At membrane potentials above -40 mV, a single component of inactivation onset was detected. This component was voltage independent between -20 and +20 mV (tau = 22 ms). Thus inactivation of LVA current is best described by multiple, voltage-in-dependent processes.5. Significant inactivation of LVA current occurred at -65 mV without detectable macroscopic current. This suggests that inactivation is not strictly coupled to channel opening.6. Peak LVA current increased with increasing [Ca2+]o, with saturation approximately 50 mM. The Ca2+ -dependence of peak LVA current was reasonably well described by a single-site binding isotherm with half-maximal LVA current at approximately 7 mM.7. LVA current in GH3 cells was largely resistant to blockade by Ni2+. The relative potency of inorganic cations in blocking GH3 LVA current was (concentrations which produced 50% block): La3+ (2.4-mu-M) > Cd2+ (188-mu-M) > Ni2+ (777-mu-M).8. Several organic agents, including putative LVA blockers, HVA current blockers and various anesthetic agents, were tested for their ability to block LVA current. The concentrations that produced 50% block are as follows: nifedipine (approximately 50-mu-M), D600 (51-mu-M), diltiazem (131-mu-M), octanol (244-mu-M), pentobarbitol (985-mu-M), methoxyflurane (1.41 mM), and amiloride (1.55 mM). Phenytoin and ethosuximide produced 36 and 10% block at 100-mu-M and 2.5 mM, respectively.9. These results suggest that LVA Ca2+ current in GH3 cells is, in many respects, both kinetically and pharmacologically different than similar currents in other tissues.