Apical trypsin increases ion transport and resistance by a phospholipase C-dependent rise of Ca

Swystun, Veronica, Lan Chen, Phillip Factor, Brian Siroky, P. Darwin Bell, and Sadis Matalon. Apical trypsin increases ion transport and resistance by a phospholipase C-dependent rise of Ca . Am J Physiol Lung Cell Mol Physiol 288: L820–L830, 2005. First published December 30, 2004; doi:10.1152/ajplung.00396.2004.— We investigated the mechanisms by which serine proteases alter lung fluid clearance in rat lungs and vectorial ion transport in airway and alveolar epithelial cells. Inhibition of endogenous protease activity by intratracheal instillation of soybean trypsin inhibitor (SBTI) or 1antitrypsin decreased amiloride-sensitive lung fluid clearance across rat fluid-filled lungs; instillation of trypsin partially restored this effect. Gelatin zymography demonstrated SBTI-inhibitable trypsinlike activity in rat lung lavage fluid. Apical trypsin and human neutrophil elastase, but not agonists of protease activated receptors, increased Na and Cl short-circuit currents (Isc) and transepithelial resistance (RTE) across human bronchial and nasal epithelial cells and rat alveolar type II cells, mounted in Ussing chambers, for at least 2 h. The increase in Isc was fully reversed by amiloride and glibenclamide. The increase in RTE was not prevented by ouabain, suggesting that trypsin decreased paracellular conductance. Apical trypsin also induced a transient increase in intracellular Ca in human airway cells; treatment of these cells with BAPTA-AM mitigated the trypsininduced increases of intracellular Ca and of Isc and RTE. Increasing intracellular Ca in airway cells with either ionomycin or thapsigargin reproduced the increase in Isc, whereas inhibitors of phospholipase C (PLC) prevented the increases in both Ca and Isc. These data indicate trypsin-like proteases and elastase, either present in lung cells or released by inflammatory cells into the alveolar space, play an important role in the clearance of alveolar fluid by increasing ion transport and paracellular resistance via a PLC-initiated rise of intracellular Ca .