The transient outward current exhibited by the histamine neurones of the tuberomammillary nucleus was studied using the single-electrode voltage clamp technique in an in vitro rat hypothalamic slice preparation. 2. The transient outward current exhibited steady-state inactivation at the resting potential. Inactivation was removed by priming hyperpolarization with a V1/2 of -85 +/- 1.2 mV, while the V1/2 for activation was -60.3 +/- 2.1 mV. 3. The decay of the transient outward current was best fitted by two exponentials with time constants of 104 +/- 36 and 568 +/- 128 ms. These two components were provisionally termed IA,f and IA,s for the fast and slowly decaying currents, respectively. 4. Removal of inactivation was time dependent; inactivation was fully removed by hyperpolarizing pulses to -110 mV of 200 ms or greater duration. Removal of inactivation of IA,f was rapid, becoming complete with hyperpolarizing pre-pulses of 50 ms or greater, while removal of inactivation of IA,s was not complete until hyperpolarizing pre-pulses were 200 ms in duration. 5. The fast decaying current IA,f was selectively blocked by 1 mM-4-aminopyridine. Tetraethylammonium chloride (10 mM) had no effect on either IA,f or IA,s. 6. The inactivation curves for IA,s, determined both by using the values obtained from the amplitude of the computed slower exponential function as well as that of the current remaining in 1 mM 4-aminopyridine, were negative to those of IA,f. Similarly derived activation curves for IA,s were positive to those of IA,f. 7. Superfusion with a nominal 0 Ca2+ medium containing 10 mM-Mg2+ did not reduce the maximal transient outward current. 8. The reversal potential of IA,s with 2.5 mM-K+ in the medium was -95 +/- 3 mV; the reversal potential of IA,f was at least 15 mV negative to that of IA,s. 9. It is concluded that histaminergic tuberomammillary neurones possess at least two transient outward currents which can be distinguished on the basis of their rates of decay, 4-aminopyridine sensitivity, voltage dependence and reversal potentials.
摘要
使用单电极电压钳技术，在体外大鼠下丘脑切片标本中研究了结节乳头体核组胺能神经元呈现的瞬时外向电流。2. 瞬时外向电流在静息电位时表现出稳态失活。通过以 -85±1.2 mV 的半激活电压（V1/2）进行预超极化可消除失活，而激活的半激活电压（V1/2）为 -60.3±2.1 mV。3. 瞬时外向电流的衰减最适合用两个指数函数拟合，时间常数分别为 104±36 和 568±128 ms。这两个成分分别暂时称为 IA,f 和 IA,s，代表快速衰减电流和缓慢衰减电流。4. 失活的消除具有时间依赖性；通过持续 200 ms 或更长时间的超极化脉冲至 -110 mV 可完全消除失活。IA,f 失活的消除很快，50 ms 或更长时间的超极化预脉冲即可使其完全消除，而 IA,s 失活的消除直到超极化预脉冲持续 200 ms 时才完成。5. 快速衰减电流 IA,f 被 1 mM 4-氨基吡啶选择性阻断。10 mM 氯化四乙铵对 IA,f 或 IA,s 均无影响。6. 通过使用从计算出的较慢指数函数的幅度以及在 1 mM 4-氨基吡啶中剩余电流的值获得的数值确定的 IA,s 的失活曲线与 IA,f 的失活曲线相反。类似地得出的 IA,s 的激活曲线与 IA,f 的激活曲线相反。7. 用含有 10 mM Mg2+ 的名义 0 Ca2+ 培养基灌注并未降低最大瞬时外向电流。8. 培养基中含有 2.5 mM K+ 时，IA,s 的反转电位为 -95±3 mV；IA,f 的反转电位比 IA,s 的至少负 15 mV。9. 得出结论，组胺能结节乳头体神经元至少具有两种瞬时外向电流，可根据它们的衰减速率、4-氨基吡啶敏感性、电压依赖性和反转电位加以区分。
