Johansen J, Kleinhaus A L
J Neurophysiol. 1986 Sep;56(3):812-22. doi: 10.1152/jn.1986.56.3.812.
The properties of a quickly inactivating transient K current (IA) and a slowly inactivating delayed K current (IK) were investigated with two-electrode voltage-clamp techniques in the isolated soma of the Retzius cell of the leech, Macrobdella decora. The two currents could be pharmacologically separated according to their different sensitivities to tetraethylammonium ions (TEA) and 4-aminopyridine (4-AP). IA was totally blocked by 3 mM 4-AP but not affected by 25 mM TEA. IK was suppressed almost completely by 25 mM TEA, whereas its peak amplitude only decreased by 10-15% in 3 mM 4-AP. IA was activated at membrane potentials more positive than -35 to -30 mV, whereas the threshold for IK was at more positive potentials of approximately -20 to -15 mV. The activation of IA was rapid with a voltage-dependent time constant [tau m(A)] that varied from 6 to 2 ms for command potentials between -20 and 10 mV (at 22-24 degrees C). The inactivation, which was independent of voltage, was somewhat slower with a time constant (tau A) of approximately 90-110 ms. The time constants for activation [tau m(K)] and the early inactivation phase (tau K) of IK were both voltage dependent. In the range of potential steps from 0 to 30 mV, tau m(K) varied from 12 to 4.5 ms and tau K from 1,500 to 700 ms. The steady-state inactivation of IA varied with holding potential and was complete at potentials more positive than -30 mV. IA was fully available from potentials more negative than -70 mV. IK did not show steady-state inactivation below its threshold of activation. The time course of IA during a maintained depolarization could be reasonably described by the expression IA(t) = IA(infinity) [1-exp(-t/tau m(A))]2 exp(-t/tau A). The time course of activation of IK without allowance for inactivation was approximated by the expression IK(t) = IK(infinity) [1-exp(-t/tau m(K))]2. The reversal potentials and magnitude of both IA and IK were dependent on extra-cellular K concentration, which suggest that a substantial part of the two currents was carried by K ions.
采用双电极电压钳技术，在美洲水蛭（Macrobdella decora）Retzius细胞的分离胞体中，研究了快速失活的瞬时钾电流（IA）和缓慢失活的延迟钾电流（IK）的特性。根据这两种电流对四乙铵离子（TEA）和4-氨基吡啶（4-AP）的不同敏感性，可对它们进行药理学分离。IA可被3 mM 4-AP完全阻断，但不受25 mM TEA的影响。IK几乎被25 mM TEA完全抑制，而在3 mM 4-AP中其峰值幅度仅降低10 - 15%。IA在膜电位高于 - 35至 - 30 mV时被激活，而IK的阈值在约 - 20至 - 15 mV的更正电位处。IA的激活迅速，其电压依赖性时间常数[τm(A)]在 - 20至10 mV的指令电位下（在22 - 24℃）从6变化到2 ms。失活过程与电压无关，但稍慢一些，时间常数（τA）约为90 - 110 ms。IK的激活时间常数[τm(K)]和早期失活阶段（τK）均与电压有关。在0至30 mV的电位阶跃范围内，τm(K)从12变化到4.5 ms，τK从1500变化到700 ms。IA的稳态失活随钳制电位而变化，在高于 - 30 mV的电位时完全失活。在低于 - 70 mV的电位时，IA完全可用。IK在其激活阈值以下未表现出稳态失活。在持续去极化期间，IA的时间进程可用表达式IA(t) = IA(∞) [1 - exp(-t/τm(A))]2 exp(-t/τA)合理描述。不考虑失活时，IK激活的时间进程可用表达式IK(t) = IK(∞) [1 - exp(-t/τm(K))]2近似表示。IA和IK的反转电位和幅度均取决于细胞外钾浓度，这表明这两种电流的很大一部分是由钾离子携带的。
