Heming T A, Bidani A
Division of Pulmonary, Critical Care and Sleep Medicine, Department of Internal Medicine, University of Texas Health Science Center, Houston, Texas 77030, USA.
Lung. 2003;181(3):121-35. doi: 10.1007/s00408-003-1013-2.
The acid-base status and functional responses of alveolar macrophages (mphi) are influenced by the activity of plasmalemmal V-type H+-pump (V-ATPase), an electrogenic H+ extruder that provides a possible link between intracellular pH (pHi) and plasma membrane potential (Em). This study examined the relationships among Em, pHi, and plasmalemmal V-ATPase activity in resident alveolar mphi from rabbits. Em and pHi were measured using fluorescent probes. Em was -46 mV and pHi was 7.14 at an extracellular pH (pHo) of 7.4. The pHi declined progressively at lower pHo values. Decrements in pHo, also caused depolarization of the plasma membrane, independent of V-ATPase activity. The pH effects on Em were sensitive to external K+, and hence, probably involved pH-sensitive K+ conductance. H+ were not distributed at equilibrium across the plasma membrane. V-ATPase activity was a major determinant of the transmembrane H+ disequilibrium. Pump inhibition with bafilomycin A1 caused cytosolic acidification, due most likely to the retention of metabolically generated H+. V-ATPase inhibition also caused depolarization of the plasma membrane, but the effects were mediated indirectly via the accompanying pHi changes. V-ATPase activity was sensitive to Em. Em hyperpolarization (valinomycin-clamp) reduced V-ATPase activity, causing an acidic shift in baseline pHi under steady-state conditions and slowing pHi recovery from NH4Cl prepulse acid-loads. The findings indicate that a complex relationship exists among Em, pHi, and pHo that was partially mediated by plasmalemmal V-ATPase activity. This relationship could have important consequences for the expression of pH- and/or voltage-sensitive functions in alveolar mphi.
肺泡巨噬细胞（mphi）的酸碱状态和功能反应受质膜V型H⁺泵（V - ATP酶）活性的影响，V - ATP酶是一种生电H⁺排出器，它可能在细胞内pH（pHi）和质膜电位（Em）之间建立联系。本研究检测了兔体内驻留肺泡mphi中Em、pHi和质膜V - ATP酶活性之间的关系。使用荧光探针测量Em和pHi。在细胞外pH（pHo）为7.4时，Em为 - 46 mV，pHi为7.14。在较低的pHo值下，pHi逐渐下降。pHo的降低也导致质膜去极化，这与V - ATP酶活性无关。pH对Em的影响对细胞外K⁺敏感，因此可能涉及pH敏感的K⁺电导。H⁺在质膜两侧并非处于平衡分布。V - ATP酶活性是跨膜H⁺不平衡的主要决定因素。用巴弗洛霉素A1抑制泵会导致胞质酸化，这很可能是由于代谢产生的H⁺滞留所致。V - ATP酶抑制也会导致质膜去极化，但其作用是通过伴随的pHi变化间接介导的。V - ATP酶活性对Em敏感。Em超极化（缬氨霉素钳制）会降低V - ATP酶活性，在稳态条件下导致基线pHi发生酸性偏移，并减缓pHi从NH₄Cl预脉冲酸负荷中的恢复。研究结果表明，Em、pHi和pHo之间存在复杂的关系，部分由质膜V - ATP酶活性介导。这种关系可能对肺泡mphi中pH和/或电压敏感功能的表达产生重要影响。
