Kuba K, Nohmi M
Br J Pharmacol. 1987 Jul;91(3):671-81. doi: 10.1111/j.1476-5381.1987.tb11261.x.
The ionic mechanism of membrane hyperpolarization induced by adrenaline in rat diaphragm muscle fibres was studied. Removal of the extracellular K+ ([K+]o) from Krebs-Ringer solution initially increased the resting membrane potential and then caused an increase in the intracellular Na+ activity ([Na+]i) and a decrease in the intracellular K+ activity ([K+]i). All the changes were maintained for more than 3 h. Application of ouabain (0.1 mM) or lowering the temperature rapidly reduced the resting potential by about 10 mV in the K+-free solution. It then produced further progressive decreases in resting potential and in [K+]i and a progressive increase in [Na+]i. These observations indicate that an electrogenic Na-pump operates in the K+-free solution. Removal of most of the Cl- in the K+-free solution did not affect the resting potential or the magnitude of the initial decrease produced by ouabain, despite an increased input resistance; this result implies a passive distribution of Cl-. Adrenaline (30-60 microM) either added to the bathing solution or applied to the membrane by ionophoresis produced a hyperpolarization (3-10 mV: adrenaline hyperpolarization), the amplitude of which was decreased with a rise in [K+]o and increased with a reduction in [K+]o, but unaffected by the removal of Cl-. Adrenaline produced an increase in input resistance, the relative magnitude (17-18%) of which was constant whether external K+ or Cl- was removed. In contrast, a conditioning membrane hyperpolarization hardly affected the resistance. Ouabain (0.1 mM) or low temperature (8-10 degrees C) abolished both the hyperpolarization and the increased input resistance induced by adrenaline. The [K+]i, [Na+]i and the peak of the action potential remained unchanged after a 20 min exposure to adrenaline (30 microM). The hyperpolarization induced by the replacement of all Na+ with Tris (Tris-hyperpolarization) in the K+-free solution was depressed by 39% during the early period (4-31 min) of exposure to adrenaline (30 microM), while it was enhanced by 26% during the later period (80-130 min). The initial depression suggested a decrease in the ratio of the membrane permeability for Na+ (PNa) to that for K+ (PK). These results suggest that the adrenaline hyperpolarization is generated largely by a decrease in PNa/PK, which is associated with the activity of the Na-pump.
研究了肾上腺素诱导大鼠膈肌纤维膜超极化的离子机制。从 Krebs-Ringer 溶液中去除细胞外 K⁺（[K⁺]o）最初会增加静息膜电位，随后导致细胞内 Na⁺活性（[Na⁺]i）增加，细胞内 K⁺活性（[K⁺]i）降低。所有这些变化持续超过 3 小时。在无 K⁺溶液中应用哇巴因（0.1 mM）或降低温度会使静息电位迅速降低约 10 mV。然后它会使静息电位以及 [K⁺]i 进一步逐渐降低，[Na⁺]i 逐渐增加。这些观察结果表明，在无 K⁺溶液中存在电生性 Na⁺泵。在无 K⁺溶液中去除大部分 Cl⁻ 不会影响静息电位或哇巴因引起的初始降低幅度，尽管输入电阻增加；这一结果意味着 Cl⁻ 的被动分布。将肾上腺素（30 - 60 μM）添加到浴液中或通过离子载体施加到膜上会产生超极化（3 - 10 mV：肾上腺素超极化），其幅度随着 [K⁺]o 的升高而降低，随着 [K⁺]o 的降低而增加，但不受 Cl⁻ 去除的影响。肾上腺素会使输入电阻增加，无论去除外部 K⁺ 还是 Cl⁻，其相对幅度（17 - 18%）都是恒定的。相比之下，预处理的膜超极化几乎不影响电阻。哇巴因（0.1 mM）或低温（8 - 10℃）会消除肾上腺素诱导的超极化和增加的输入电阻。在暴露于肾上腺素（30 μM）20 分钟后，[K⁺]i、[Na⁺]i 和动作电位峰值保持不变。在无 K⁺溶液中用 Tris 替代所有 Na⁺ 诱导的超极化（Tris 超极化）在暴露于肾上腺素（30 μM）的早期（4 - 31 分钟）降低了 39%，而在后期（80 - 130 分钟）增加了 26%。最初的降低表明膜对 Na⁺（PNa）与对 K⁺（PK）的通透性比值降低。这些结果表明，肾上腺素超极化主要是由 PNa/PK 的降低产生的，这与 Na⁺泵的活性有关。
