The effects of large reductions of [K+]o on membrane potential were studied in isolated rabbit ventricular myocytes using the whole-cell patch clamp technique. 2. Decreasing [K+]o from the normal level of 5.4 mM to 0.1 mM increased resting membrane potential (Vrest) from -75.6 +/- 0.3 to -140.3 +/- 1.9 mV (means +/- s.e.m; n = 127), induced irregular, transient depolarizations with mean maximal amplitudes of 19.5 +/- 1.5 mV and elicited action potentials in 56.7 % of trials. The action potentials exhibited overshoots of 37.9 +/- 1.5 mV (n = 72) and sustained plateaux. 3. Addition of 0.1 mM La3+ in the presence of 0.1 mM [K+]o significantly increased Vrest but decreased the amplitude of transient depolarizations and suppressed the firing of action potentials. 4. Replacement of external Na+ or Cl- with N-methyl-D-glucamine or aspartate, respectively, or internal dialysis with 10 mM EGTA or BAPTA had little effect on low [K+]o-induced membrane potential changes. 5. Hyperpolarizing voltage clamp pulses to potentials between -110 and -200 mV activated irregular inward currents that increased in amplitude and frequency with increasing hyperpolarization and were depressed by 0.1 mM La3+. 6. The generation of transient depolarizations by low [K+]o can be explained as being a consequence of decreasing the inward rectifier K+ current (IK1) and the appearance of inward currents reflecting electroporation resulting from strong electric fields across the membrane.
摘要
使用全细胞膜片钳技术，在分离的兔心室肌细胞中研究了细胞外液中[K⁺]大幅降低对膜电位的影响。2. 将细胞外液中[K⁺]从正常水平5.4 mM降至0.1 mM，静息膜电位（Vrest）从-75.6±0.3 mV增加至-140.3±1.9 mV（均值±标准误；n = 127），诱发不规则的瞬时去极化，平均最大幅度为19.5±1.5 mV，并在56.7%的实验中引发动作电位。这些动作电位的超射为37.9±1.5 mV（n = 72），并具有持续的平台期。3. 在存在0.1 mM [K⁺]o的情况下添加0.1 mM La³⁺显著增加了Vrest，但降低了瞬时去极化的幅度并抑制了动作电位的发放。4. 分别用N-甲基-D-葡糖胺或天冬氨酸替代细胞外的Na⁺或Cl⁻，或者用10 mM EGTA或BAPTA进行细胞内透析，对低[K⁺]o诱导的膜电位变化影响很小。5. 向-110至-200 mV之间的电位施加超极化电压钳脉冲，激活了不规则的内向电流，该电流的幅度和频率随着超极化程度的增加而增加，并被0.1 mM La³⁺抑制。6. 低[K⁺]o引起的瞬时去极化的产生可以解释为内向整流K⁺电流（IK1）减少以及由于跨膜强电场导致的反映电穿孔的内向电流出现的结果。
