Department of Anesthesiology, Chang Gung Memorial Hospital, Chiayi, Taiwan; Chang Gung University of Science and Technology, Chiayi, Taiwan.
Department of Physiology, China Medical University, Taichung 40402, Taiwan.
Life Sci. 2022 Nov 1;308:120913. doi: 10.1016/j.lfs.2022.120913. Epub 2022 Aug 26.
Lung type 2 alveolar cells, by secreting surfactant to lower surface tension, contribute to enhance lung compliance. Stretching, as a result of lung expansion, triggers type 1 alveolar cell to release ATP, which in turn stimulates Ca-dependent surfactant secretion by neighboring type 2 cells. In this report, we studied ATP-triggered Ca signaling in human alveolar type 2 A549 cells.
Ca signaling was examined using microfluorimetric measurement with fura-2 as fluorescent dye.
Ca oscillations triggered by ATP relied on inositol 1,4,5-trisphosphate-induced Ca release and store-operated Ca entry. Pathological conditions such as influenza virus infection and diabetes reportedly inhibit sarcoplasmic/endoplasmic reticulum Ca ATPase (SERCA). We found that a very mild inhibition of SERCA by cyclopiazonic acid (CPA) sufficed to decrease Ca oscillation frequency and the percentage of cells exhibiting Ca oscillations. Ochratoxin A (OTA), an activator of SERCA, could prevent the suppressive effects by CPA. Inhibition of SERCA by hydrogen peroxide also suppressed Ca oscillations. Interestingly, hydrogen peroxide-induced inhibition was prevented by OTA but aggravated by CDN1163, an allosteric activator of SERCA. CDN1163 also had an untoward effect of releasing intracellular Ca.
Different modes of activation of SERCA may determine the outcome of rescue of Ca oscillations in case of SERCA inhibition in alveolar type 2 cells.
Ⅱ型肺泡细胞通过分泌表面活性物质来降低表面张力，从而有助于增加肺顺应性。由于肺扩张，伸展会触发Ⅰ型肺泡细胞释放 ATP，进而刺激邻近的Ⅱ型细胞中 Ca 依赖性表面活性物质的分泌。在本报告中，我们研究了人肺泡Ⅱ型 A549 细胞中 ATP 触发的 Ca 信号。
使用荧光染料 fura-2 的微荧光测量法检查 Ca 信号。
ATP 触发的 Ca 振荡依赖于肌醇 1,4,5-三磷酸诱导的 Ca 释放和储存操纵的 Ca 内流。据报道，流感病毒感染和糖尿病等病理条件会抑制肌浆/内质网 Ca-ATP 酶（SERCA）。我们发现，用环匹阿尼酸（CPA）轻度抑制 SERCA 足以降低 Ca 振荡频率和表现出 Ca 振荡的细胞百分比。桔青霉素 A（OTA）是 SERCA 的激活剂，可以预防 CPA 的抑制作用。过氧化氢抑制 SERCA 也会抑制 Ca 振荡。有趣的是，过氧化氢诱导的抑制作用可被 OTA 预防，但可被 SERCA 的别构激活剂 CDN1163 加重。CDN1163 还具有释放细胞内 Ca 的不良作用。
在肺泡Ⅱ型细胞中 SERCA 抑制的情况下，不同的 SERCA 激活方式可能决定对 Ca 振荡的挽救结果。
