First detection of Ca2+ responses in alveolar macrophages in situ

Abstract

Alveolar macrophages (AMs) play a major role in ventilator‐induced lung injury (VILI). However, it is not clear whether AMs respond directly to lung expansion. Here we tested this hypothesis in intact alveoli of the mouse lung. To determine the time course of the AM response to lung expansion, we used the cre/lox recombinase system to specifically express Enhanced Yellow Fluorescent Protein (EYFP) in CD11c‐positive AMs (AMYFP). We isolated lungs from AMYFP–expressing mice and blood‐perfused them at constant pulmonary artery, left atrial and airway pressures of 10, 3 and 5 cmH2O, respectively. We viewed the lungs by means of confocal microscopy. To determine cytosolic Ca2+ in AMYFP, we microinfused alveoli with the Ca2+ fluorophore, fluo‐4. At baseline, AMYFP displayed slow Ca2+ oscillations at an amplitude of 11±2% of mean (n=5). Following a 15s inflation to 15 cmH2O, the oscillation amplitude increased by 60±10% (P<.05) within 5 min, and remained elevated for 20 min. The oscillation frequency was unchanged. We conclude, AMs respond rapidly to lung expansion by augmenting Ca2+ oscillations. In VILI, crosstalk signaling between the stretched alveolar epithelium and local AMs may initiate proinflammatory mechanisms leading to increased permeability of the alveolo‐capillary barrier (HL78645, HL64896).