Lung microvascular barrier strengthening by exogenous focal adhesion kinase

To determine effects of the focal adhesion kinase (FAK) on lung microvascular barrier function, we purified activated FAK (FAK p ). We determined relative solute permeability (Sp) by two‐photon microscopy in isolated blood‐perfused rat lungs at constant pulmonary artery, left atrial and alveolar pressures of 10, 3 and 5 cmH 2 O, respectively. Through a venous microcatheder, we infused the cytosolic dye, calcein red AM to load endothelial cells and fluorescently demarcate the vascular lumen. Then, viewing capillaries by two‐photon microscopy, we infused the fluorescent tracer, FITC‐dextran (20 kD, 0.5 mg/ml, 1 ml/h) for 3 min. We determined intravascular and interstitial fluorescence after 20‐min infusions of either buffer (BU), or FAK p (10 μg/ml) complexed with an intracellular protein‐delivery agent (Chariot). Intravascular fluorescence increased by 77±3 grey levels (mean±SE, n=3) for both groups. However, interstitial fluorescence increased 30±6 for BU, but markedly less at 7±3 for FAK p (P<0.05). We determined FI and FV as slopes of the linear regressions of fluorescence against time for interstitial and luminal fluorescence, respectively. Sp estimated as FI/FV, was 0.5±0.1 for BU, but markedly lower at 0.1±0.1 after FAK p infusion (P<0.05), indicating that FAK p decreased endothelial permeability. We conclude, that activated FAK strengthens the lung microvascular barrier. (Support: HL36024, HL78645)