Xu Z, Rozanski G J
Department of Physiology, University of Nebraska Medical Center, Omaha 68198-4575, USA.
J Mol Cell Cardiol. 1997 Feb;29(2):481-90. doi: 10.1006/jmcc.1996.0292.
Acidosis elicited during myocardial ischemia is a significant pathophysiological condition markedly affecting the electrical and contractile properties of heart muscle. We examined the effects of protons on K channel activity in rat ventricular myocytes by recording transient outward (Ito) and inward rectifier (IKl) K+ currents using the whole cell, voltage clamp technique. Proton concentration was controlled by independently varying the pH of HEPES-buffered external (pHo) or pipette (pHp) solutions. Mean Ito density in myocytes preconditioned in acidic external solution (pHo 6.0) for 15-20 min was significantly less than control cells equilibrated at physiological pHo. In contrast, IKl was not changed during this period of acidosis. External acidification did not decrease Ito when initiated after intracellular dialysis with standard pHp 7.2. However, when myocytes were dialyzed with acidic pHp, Ito density was significantly less than control, while alkaline pHp had little effect. Despite marked reduction in current density produced by low pHp solutions, steady-state activation and inactivation parameters of Ito were not significantly altered. In addition, the reversal potential of this current, kinetics of inactivation, and recovery from inactivation were not significantly affected by acidic or alkaline pHp solutions. Acidic pHp alone did not change IKl density compared with control, but when combined with Na+/H+ exchange blockade with 5-(N,N-dimethyl)-amiloride or Na(+)-free external solution, IKl density was significantly reduced. Our data suggest that protons inhibit Ito predominantly from the intracellular side of the channel, possibly by altering its conductance or gating properties. Moreover, intracellular protons differentially affect Ito and IKl channels, with the former exhibiting greater sensitivity for a given level of acidosis.
心肌缺血期间引发的酸中毒是一种显著的病理生理状况，会明显影响心肌的电特性和收缩特性。我们通过使用全细胞电压钳技术记录瞬时外向（Ito）和内向整流（IKl）钾电流，研究了质子对大鼠心室肌细胞钾通道活性的影响。通过独立改变HEPES缓冲的细胞外（pHo）或移液管（pHp）溶液的pH值来控制质子浓度。在酸性细胞外溶液（pHo 6.0）中预处理15 - 20分钟的心肌细胞中的平均Ito密度显著低于在生理pHo下平衡的对照细胞。相比之下，在这段酸中毒期间IKl没有变化。在用标准pHp 7.2进行细胞内透析后开始的细胞外酸化并没有降低Ito。然而，当用酸性pHp透析心肌细胞时，Ito密度显著低于对照，而碱性pHp影响很小。尽管低pHp溶液使电流密度显著降低，但Ito的稳态激活和失活参数没有明显改变。此外，该电流的反转电位、失活动力学以及从失活中恢复均未受到酸性或碱性pHp溶液的显著影响。与对照相比，单独的酸性pHp并没有改变IKl密度，但当与用5 -（N，N - 二甲基）- 氨氯吡脒进行的Na⁺/H⁺交换阻断或无Na⁺细胞外溶液联合使用时，IKl密度显著降低。我们的数据表明，质子主要从通道的细胞内侧抑制Ito，可能是通过改变其电导或门控特性。此外，细胞内质子对Ito和IKl通道有不同的影响，对于给定程度的酸中毒，前者表现出更高的敏感性。
