Undem Clark, Luke Trevor, Shimoda Larissa A
Division of Pulmonary and Critical Care Medicine, Department of Medicine, Johns Hopkins School of Medicine, Baltimore, Maryland, USA.
Pulm Circ. 2016 Mar;6(1):93-102. doi: 10.1086/685053.
In the lung, exposure to chronic hypoxia (CH) causes pulmonary hypertension, a debilitating disease. Development of this condition arises from increased muscularity and contraction of pulmonary vessels, associated with increases in pulmonary arterial smooth muscle cell (PASMC) intracellular pH (pHi) and Ca(2+) concentration ([Ca(2+)]i). In this study, we explored the interaction between pHi and [Ca(2+)]i in PASMCs from rats exposed to normoxia or CH (3 weeks, 10% O2). PASMC pHi and [Ca(2+)]i were measured with fluorescent microscopy and the dyes BCECF and Fura-2. Both pHi and [Ca(2+)]i levels were elevated in PASMCs from hypoxic rats. Exposure to KCl increased [Ca(2+)]i and pHi to a similar extent in normoxic and hypoxic PASMCs. Conversely, removal of extracellular Ca(2+) or blockade of Ca(2+) entry with NiCl2 or SKF 96365 decreased [Ca(2+)]i and pHi only in hypoxic cells. Neither increasing pHi with NH4Cl nor decreasing pHi by removal of bicarbonate impacted PASMC [Ca(2+)]i. We also examined the roles of Na(+)/Ca(2+) exchange (NCX) and Na(+)/H(+) exchange (NHE) in mediating the elevated basal [Ca(2+)]i and Ca(2+)-dependent changes in PASMC pHi. Bepridil, dichlorobenzamil, and KB-R7943, which are NCX inhibitors, decreased resting [Ca(2+)]i and pHi only in hypoxic PASMCs and blocked the changes in pHi induced by altering [Ca(2+)]i. Exposure to ethyl isopropyl amiloride, an NHE inhibitor, decreased resting pHi and prevented changes in pHi due to changing [Ca(2+)]i. Our findings indicate that, during CH, the elevation in basal [Ca(2+)]i may contribute to the alkaline shift in pHi in PASMCs, likely via mechanisms involving reverse-mode NCX and NHE.
在肺部，长期暴露于慢性低氧（CH）会导致肺动脉高压，这是一种使人衰弱的疾病。这种病症的发展源于肺血管肌肉增多和收缩，与肺动脉平滑肌细胞（PASMC）细胞内pH值（pHi）和钙离子浓度（[Ca(2+)]i）升高有关。在本研究中，我们探讨了常氧或慢性低氧（3周，10%氧气）暴露大鼠的PASMC中pHi与[Ca(2+)]i之间的相互作用。用荧光显微镜以及BCECF和Fura-2染料测量PASMC的pHi和[Ca(2+)]i。低氧大鼠的PASMC中pHi和[Ca(2+)]i水平均升高。在常氧和低氧PASMC中，暴露于氯化钾使[Ca(2+)]i和pHi升高程度相似。相反地，去除细胞外钙离子或用氯化镍或SKF 96365阻断钙离子内流仅使低氧细胞中的[Ca(2+)]i和pHi降低。用氯化铵升高pHi或去除碳酸氢盐降低pHi均不影响PASMC的[Ca(2+)]i。我们还研究了钠/钙交换（NCX）和钠/氢交换（NHE）在介导基础[Ca(2+)]i升高以及PASMC中pHi的钙依赖性变化方面的作用。NCX抑制剂苄普地尔、二氯苯甲酰胺和KB-R7943仅使低氧PASMC的静息[Ca(2+)]i和pHi降低，并阻断了因改变[Ca(2+)]i而诱导的pHi变化。暴露于NHE抑制剂乙基异丙基氨氯吡咪可降低静息pHi，并防止因[Ca(2+)]i变化导致的pHi改变。我们的研究结果表明，在慢性低氧期间，基础[Ca(2+)]i升高可能通过涉及反向模式NCX和NHE的机制导致PASMC中pHi发生碱化转变。
