Membrane currents were recorded in cells freshly dispersed from the rabbit portal vein with patch pipette techniques in the whole-cell configuration of recording. In potassium-containing solutions at a holding potential of -50 mV noradrenaline usually evoked an inward current and enhanced greatly the outward current evoked by depolarizing voltage steps. 2. The ionic mechanism of the inward current was investigated in potassium-free solutions in which the inward current elicited by noradrenaline was produced by an increase in membrane conductance. 3. In the first series of experiments NaCl was the main salt in the patch pipette solution (representing the intracellular milieu) and the ionic composition of the bathing solution was altered. In these conditions the reversal potential of the noradrenaline-induced current was close to the chloride equilibrium potential (ECl). 4. When sodium glutamate was the major salt in the pipette solution the reversal potential of the noradrenaline-evoked current was influenced by the cation rather than the anion gradient. 5. With 89 mM-BaCl2 in the external solution (and sodium glutamate in the pipette) noradrenaline produced a membrane current with a reversal potential which was much more positive than ECl or ENa. These results indicate that noradrenaline opens a chloride-selective channel and a cation channel which is permeable to monovalent and divalent cations. 6. Bath application of 10 mM-caffeine evoked a membrane current with a reversal potential close to ECl with either NaCl or sodium glutamate in the pipette. This is interpreted to mean that the increase in membrane chloride conductance can occur as a consequence of a rise in intracellular calcium concentration. It is less evident that the cation channel is calcium activated.
摘要
采用膜片钳技术的全细胞记录模式，在新鲜分离的兔门静脉细胞中记录膜电流。在含钾溶液中，保持电位为 -50 mV 时，去甲肾上腺素通常会诱发内向电流，并极大增强去极化电压阶跃诱发的外向电流。2. 在无钾溶液中研究内向电流的离子机制，其中去甲肾上腺素诱发的内向电流是由膜电导增加产生的。3. 在第一系列实验中，氯化钠是膜片钳微电极溶液中的主要盐（代表细胞内环境），并改变浴液的离子组成。在这些条件下，去甲肾上腺素诱导电流的反转电位接近氯离子平衡电位（ECl）。4. 当谷氨酸钠是微电极溶液中的主要盐时，去甲肾上腺素诱发电流的反转电位受阳离子而非阴离子梯度的影响。5. 外部溶液中含有 89 mM - 氯化钡（微电极中含有谷氨酸钠）时，去甲肾上腺素产生的膜电流的反转电位比 ECl 或 ENa 正得多。这些结果表明，去甲肾上腺素打开了一个氯离子选择性通道和一个对单价和二价阳离子都通透的阳离子通道。6. 浴液中加入 10 mM - 咖啡因会诱发膜电流，其反转电位接近 ECl，微电极中无论是含有氯化钠还是谷氨酸钠。这被解释为意味着膜氯离子电导的增加可能是细胞内钙浓度升高的结果。阳离子通道是否由钙激活则不太明显。
