Bouyer Patrice G, Salameh Ahlam I, Zhou Yuehan, Kolba Tiffany N, Boron Walter F
Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT, United States.
Department of Biology, Valparaiso University, Valparaiso, IN, United States.
Front Physiol. 2024 Oct 9;15:1434359. doi: 10.3389/fphys.2024.1434359. eCollection 2024.
Metabolic acidosis (MAc)-an extracellular pH (pH) decrease caused by a [HCO ] decrease at constant [CO]-usually causes intracellular pH (pH) to fall. Here we determine the extent to which the pH decrease depends on the pH decrease vs the concomitant [HCO ] decrease. We use rapid-mixing to generate out-of-equilibrium CO/HCO solutions in which we stabilize [CO] and [HCO ] while decreasing pH (pure acidosis, pAc), or stabilize [CO] and pH while decreasing [HCO ] (pure metabolic/down, pMet↓). Using the fluorescent dye 2',7'-bis-2-carboxyethyl)-5(and-6)carboxyfluorescein (BCECF) to monitor pH in rat hippocampal neurons in primary culture, we find that-in naïve neurons-the pH decrease caused by MAc is virtually the sum of those caused by pAc (∼70%) + pMet↓ (∼30%). However, if we impose a first challenge (MAc, pAc, or pMet↓), allow the neurons to recover, and then impose a second challenge (MAc, pAc, or pMet↓), we find that pAc/pMet↓ additivity breaks down. In a twin-challenge protocol in which challenge #2 is MAc, the pH and [HCO ] decreases during challenge #1 must be coincident in order to mimic the effects of MAc on MAc. Conversely, if challenge #1 is MAc, then the pH and [HCO ] decreases during challenge #2 must be coincident in order for MAc to produce its physiological effects during the challenge #2 period. We conclude that the history of challenge #1 (MAc, pAc, or pMet↓)-presumably as detected by one or more acid-base sensors-has a major impact on the pH response during challenge #2 (MAc, pAc, or pMet↓).
代谢性酸中毒（MAc）——在[CO₂]恒定的情况下，由[HCO₃⁻]降低导致的细胞外pH值下降——通常会使细胞内pH值降低。在此，我们确定pH值下降在多大程度上取决于pH值的降低与伴随的[HCO₃⁻]降低。我们使用快速混合法生成非平衡的CO₂/HCO₃⁻溶液，在其中我们在降低pH值（单纯酸中毒，pAc）的同时稳定[CO₂]和[HCO₃⁻]，或者在降低[HCO₃⁻]（单纯代谢性/降低，pMet↓）的同时稳定[CO₂]和pH值。使用荧光染料2',7'-双（2-羧乙基）-5（和-6）-羧基荧光素（BCECF）监测原代培养的大鼠海马神经元中的pH值，我们发现——在未处理的神经元中——MAc导致的pH值下降实际上是由pAc（约70%）+ pMet↓（约30%）导致的pH值下降之和。然而，如果我们施加第一次刺激（MAc、pAc或pMet↓），让神经元恢复，然后施加第二次刺激（MAc、pAc或pMet↓），我们发现pAc/pMet↓的加和性消失。在第二次刺激为MAc的双刺激方案中，为了模拟MAc对MAc的影响，第一次刺激期间的pH值和[HCO₃⁻]下降必须同时发生。相反，如果第一次刺激是MAc，那么为了使MAc在第二次刺激期间产生其生理效应，第二次刺激期间的pH值和[HCO₃⁻]下降必须同时发生。我们得出结论，第一次刺激（MAc、pAc或pMet↓）的历史——大概是由一个或多个酸碱传感器检测到的——对第二次刺激（MAc、pAc或pMet↓）期间的pH值反应有重大影响。
