Inhibitors of myosin light chain kinase and phosphodiesterase reduce ventilator-induced lung injury

Alveolar overdistension due to high peak inflation pressures (PIP) is assoc iated with an increased capillary filtration coefficient (K-fc). To determi ne which signal pathways contribute to this injury, we perfused isolated ra t lungs with 5% bovine albumin in Krebs solution and measured K-fc after su ccessive 30-min periods of ventilation with peak inflation pressures (PIP) of 7, 20, 30, and 35 cmH(2)O. In a high-PIP control group, K-fc increased s ignificantly after ventilation with 30 and 35 cmH(2)O PIP, but significant increases were prevented by treatment with 100 muM trifluoperazine, an inhi bitor of Ca2+/ calmodulin, 500 nM ML-7, an inhibitor of myosin light chain kinase (MLCK), a combination of isoproterenol (20 muM) and rolipram (10 muM ) to enhance intracellular cAMP levels, and a dose of KT-5720 (2 muM), whic h inhibits MLCK and protein kinase C. These studies suggest that the Ca2+/c almodulin-MLCK pathway augments capillary fluid leak after a modest high-PI P injury and that this is attenuated by kinase inhibition and increased int racellular cAMP.