Loeh Benjamin, Baloglu Emel, Ke Alberto, Bärtsch Peter, Mairbäurl Heimo
Medical Clinic VII, Sports Medicine, University Hospital Heidelberg, Heidelberg, Germany.
Cell Physiol Biochem. 2010;25(1):123-34. doi: 10.1159/000272057. Epub 2009 Dec 22.
Hypoxia impairs alveolar fluid clearance by inhibition of Na(+) reabsorption, and also impairs beta(2) adrenergic signaling in alveolar epithelium. Since both are major rescue mechanisms preventing pulmonary edema, we studied whether acute and prolonged treatment with terbutaline would prevent hypoxic inhibition of ion transport. Short circuit currents (ISC) were measured on normoxic and hypoxic (1.5% O(2); 24h) primary rat alveolar type II (ATII) cells in absence and presence of terbutaline (1 to 100 microM, 24h). Control and pre-treated cells were stimulated acutely with terbutaline. Transepithelial transport was measured as short circuit current (ISC) in Ussing chambers. Terbutaline induced a rapid decrease ISC (-20%) followed by a slow raise. The transient change in ISC was not inhibited by amiloride but was prevented after Cl(-) depletion indicating a Cl(-) current. The slow increase after this transient was amiloride-sensitive indicating a Na(+) current. Total ISC, its amiloride-sensitive component, and the transient decrease upon terbutaline stimulation were decreased by hypoxia. 24h treatment with terbutaline stimulated these currents in normoxia and hypoxia, although stimulation was less in the latter. 24h treatment with terbutaline increased the capacity of Na(+)/K(+)-ATPase and ENaC as measured after permeabilization with amphotericin. These changes were not paralleled by altered mRNA expression. Acutely applied terbutaline induced a 4-fold increase in cAMP formation in normoxia; terbutaline-induced cAMP-formation was impaired by hypoxia (-20%). Pre-treatment with terbutaline for 24h decreased terbutaline-induced cAMP formation by 85%. Despite this desensitization, addition of terbutaline to terbutaline pre-treated cells caused a larger increase in Cl(-) and Na(+) transport both in normoxia and hypoxia than in non pre-treated cells. These results indicate that beta(2) adrenergic stimulation increased Na(+)- and Cl(-) transport in ATII cells even in hypoxia thus restoring normal reabsorption.
缺氧通过抑制钠离子重吸收损害肺泡液体清除，并且还损害肺泡上皮中的β₂肾上腺素能信号传导。由于这两者都是预防肺水肿的主要挽救机制，我们研究了用特布他林进行急性和长期治疗是否能预防缺氧对离子转运的抑制。在不存在和存在特布他林（1至100微摩尔，24小时）的情况下，在常氧和缺氧（1.5%氧气；24小时）的原代大鼠II型肺泡（ATII）细胞上测量短路电流（ISC）。对照细胞和预处理细胞用特布他林进行急性刺激。在尤斯灌流小室中，跨上皮转运以短路电流（ISC）来测量。特布他林导致ISC迅速下降（-20%），随后缓慢上升。ISC的瞬时变化不受氨氯吡咪抑制，但在氯离子耗竭后被阻止，表明存在氯离子电流。此瞬时变化后的缓慢增加对氨氯吡咪敏感，表明存在钠离子电流。缺氧降低了总ISC、其对氨氯吡咪敏感的成分以及特布他林刺激后的瞬时下降。在常氧和缺氧条件下，用特布他林处理24小时可刺激这些电流，尽管在后者中刺激作用较小。用特布他林处理24小时增加了用两性霉素通透后测量的钠钾ATP酶和上皮钠通道（ENaC）的活性。这些变化与mRNA表达的改变并不平行。急性应用特布他林在常氧条件下使环磷酸腺苷（cAMP）生成增加4倍；缺氧使特布他林诱导的cAMP生成受损（-20%）。用特布他林预处理24小时使特布他林诱导的cAMP生成减少85%。尽管存在这种脱敏现象，但在常氧和缺氧条件下，向用特布他林预处理的细胞中添加特布他林比未预处理的细胞引起更大的氯离子和钠离子转运增加。这些结果表明，即使在缺氧情况下，β₂肾上腺素能刺激也会增加ATII细胞中的钠离子和氯离子转运，从而恢复正常重吸收。
