Pharmacological properties of T-type Ca2+ current in adult rat sensory neurons:: Effects of anticonvulsant and anesthetic agents
Pharmacological properties of T-type Ca2+ current in adult rat sensory neurons:: Effects of anticonvulsant and anesthetic agents
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DOI：
10.1152/jn.1998.79.1.240
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发表时间：
1998-01-01
影响因子：
2.5
通讯作者：
Lingle, CJ
中科院分区：
文献类型：
--
作者：
Todorovic, SM;Lingle, CJ
本实验采用全细胞膜片钳技术研究了成年大鼠背根神经节新鲜分离神经元低电压激活（LVA）钙电流的药理学特性。从-90 mV的负保持电位到-25 mV的测试电位诱发向内钡电流[在存在内部氟化物以减少L型高压激活（HVA）和外部1 μ M ω-芋螺毒素GVIA以阻断N型HVA电流的情况下]，并在200 ms测试脉冲期间显示完全失活。阿米洛利阻断类似于90%的电流，半最大阻断（EC 50）为75 μ M，希尔系数（n）为0.99。LVA电流：可被无机钙通道阻断剂完全阻断：镧（EC_（50）= 0.53 μ M）>锌（EC_（50）= 11.3 μ M）>镉（EC_（50）= 20 μ M）>镍（EC_（50）= 51 μ M）。抗癫痫药乙琥胺（EC 50 = 23.7 mM，n = 1.4），苯妥英（EC 50 = 7.3 μ M，n = 1.3），α-甲基-α-苯基琥珀酰亚胺（EC 50 = 170 μ M，n = 2.1），丙戊酸（EC 50 = 330 μ M，n = 1.9）最大程度地阻断T电流，分别为100%、60%、26%和17%。另一种抗癫痫药卡马西平（小于或等于100 μ M）和惊厥药如戊四唑（1 mM）和叔丁基双环[2.2.2]硫代磷酸酯（50 μ M）对T电流没有影响。巴比妥类药物完全阻断T电流：硫喷妥钠（EC 50 = 153 μ M，n = 1.2）>戊巴比妥（EC 50 = 334 μ M，n = 1.2）>美索比妥（EC 50 = 502 μ M，n = 1.3）>苯巴比妥（EC 50 = 1.7 mM，n = 1.2）。硫喷妥钠和戊巴比妥的阻断作用没有表现出电压或使用依赖性。全身麻醉药完全可逆地阻断T电流：异丙酚（EC 50 = 12.9 μ M，n = 1.3）>辛醇（EC 50 = 122 μ M，n = 1.2）>依托咪酯（EC 50 = 205 μ M，n = 1.3）>异氟烷（EC 50 = 303 μ M，n = 2.3）>氟烷（EC 50 = 655 μ M，n = 2.0）>氯胺酮（EC 50 = 2.5 mM，n = 1.1）。米贝拉地尔是一种新型的钙通道阻滞剂，以电压和使用依赖的方式阻断背根神经节T电流，EC 50为3 μ M（n = 1.3）。当与其他T电流的结果相比，这些数据表明，不同的T电流的药理学敏感性方面存在显着差异。此外，外周神经元、中枢神经系统和神经内分泌细胞之间T电流的药理学敏感性差异可能导致特定镇痛药、抗惊厥药和麻醉药的效应谱。
We have used the whole cell patch-clamp method to study pharmacological properties of low-voltage-activated (LVA) Ca2+ current in freshly dissociated neurons from dorsal root ganglia of adult rats. Inward barium current [in the presence of internal fluoride to reduce L-type high-voltage-activated (HVA) and external 1 mu M omega-conotoxin GVIA to block N-type HVA current] was evoked from negative holding potentials of -90 mV to lest potentials of -25 mV and showed complete inactivation during 200-ms test pulses. Amiloride blocked similar to 90% of current with half-maximal block (EC50) of 75 mu M and a Hill coefficient (n) of 0.99. LVA current: was blocked completely by inorganic Ca2+ channel blockers: lanthanum (EC50 = 0.53 mu M) > zinc (EC50 = 11.3 mu M) > cadmium (EC50 = 20 mu M) > nickel (EC50 = 51 mu M). The antiepileptics, ethosuximide (EC50 = 23.7 mM, n = 1.4), phenytoin (EC50 = 7.3 mu M, n = 1.3), alpha-methyl-alpha-phenylsuccinimide (EC50 = 170 mu M, n = 2.1), and valproic acid (EC50 = 330 mu M, n = 1.9) maximally blocked similar to 100, 60, 26, and 17% of T current, respectively. Another antiepileptic, carbamazepine (less than or equal to 100 mu M), and convulsants such as pentylenetetrazole (1 mM) and tert-butyl-bicyclo [2.2.2] phosphorothionate (50 mu M) had no effect on T current. Barbiturates completely blocked T current: thiopental (EC50 = 153 mu M, n = 1.2) > pentobarbital (EC50 = 334 mu M, n = 1.2) > methohexital (EC50 = 502 mu M, n = 1.3) > phenobarbital (EC50 = 1.7 mM, n = 1.2). Blockade by thiopental and pentobarbital did not show voltage or use dependence. General anesthetics blocked T current completely and reversibly: propofol (EC50 = 12.9 mu M, n = 1.3) > octanol (EC50 = 122 mu M, n = 1.2) > etomidate (EC50 = 205 mu M, n = 1.3) > isoflurane (EC50 = 303 mu M, n = 2.3) > halothane (EC50 = 655 mu M, n = 2.0) > ketamine (EC50 = 2.5 mM, n = 1.1). Mibefradil, a novel Ca2+ channel blocker, blocked dorsal root ganglion T current in a voltage- and use-dependent fashion with an EC50 of similar to 3 mu M (n = 1.3). When compared with results on other T currents, these data indicate that significant differences exist among different T currents in terms of pharmacological sensitivities. Furthermore, differences in pharmacological sensitivity of T currents among peripheral neurons, CNS, and neuroendocrine cells may contribute to the spectrum of effects of particular analgesic, anticonvulsant, and anesthetic drugs.