Vacuolar ATPases: Insights into lung surfactant secretion

Abstract

Vacuolar ATPases (V‐ATPase) are multi‐subunit enzymes which utilize energy of ATP hydrolysis to transport protons across cell membranes. We investigated the role of V‐ATPases in lung surfactant secretion by alveolar type II cells. V‐ATpase subunits, a1 and B were highly enriched in lung lamellar bodies. The enzyme inhibition by Bafilomycin A1 (Baf A1) lead to the dissipation of lamellar body pH gradient as indicated by the loss of quinacrine staining. V‐ATPase inhibition increased surfactant secretion which was blocked by intracellular Ca2+‐chelator, indicating the mobilization of intracellular Ca2+ following enzyme inhibition. The Baf A1‐mediated increase was blocked by staurosporine, a inhibitors of protein kinase C. Further, quinacrine accumulation in the lamellar bodies gradually reduced upon the stimulation of type II cells. In summary, we conclude that V‐ATPase inhibition leads an increase in surfactant secretion via the mobilization of intracellular Ca2+ and the activation of protein kinase C. [NIH R01 HL‐052146; Student Seed Grant, CVHS (to NRC)].