Vacuolar ATPase Regulates Surfactant Secretion in Rat Alveolar Type II Cells by Modulating Lamellar Body Calcium

Lung surfactant reduces surface tension and maintains the stability of alveoli. How surfactant is released from alveolar epithelial type II cells is not fully understood. Vacuolar ATPase (V-ATPase) is the enzyme responsible for pumping H+ into lamellar bodies and is required for the processing of surfactant proteins and the packaging of surfactant lipids. However, its role in lung surfactant secretion is unknown. Proteomic analysis revealed that vacuolar ATPase (V-ATPase) dominated the alveolar type II cell lipid raft proteome. Western blotting confirmed the association of V-ATPase a1 and B1/2 subunits with lipid rafts and their enrichment in lamellar bodies. The dissipation of lamellar body pH gradient by Bafilomycin A1 (Baf A1), an inhibitor of V-ATPase, increased surfactant secretion. Baf A1-stimulated secretion was blocked by the intracellular Ca2+ chelator, BAPTA-AM, the protein kinase C (PKC) inhibitor, staurosporine, and the Ca2+/calmodulin-dependent protein kinase II (CaMKII), KN-62. Baf A1 induced Ca2+ release from isolated lamellar bodies. Thapsigargin reduced the Baf A1-induced secretion, indicating cross-talk between lamellar body and endoplasmic reticulum Ca2+ pools. Stimulation of type II cells with surfactant secretagogues dissipated the pH gradient across lamellar bodies and disassembled the V-ATPase complex, indicating the physiological relevance of the V-ATPase-mediated surfactant secretion. Finally, silencing of V-ATPase a1 and B2 subunits decreased stimulated surfactant secretion, indicating that these subunits were crucial for surfactant secretion. We conclude that V-ATPase regulates surfactant secretion via an increased Ca2+ mobilization from lamellar bodies and endoplasmic reticulum, and the activation of PKC and CaMKII. Our finding revealed a previously unrealized role of V-ATPase in surfactant secretion

Top-Down Knowledge Hiding in Organizations: An Empirical Study of the Consequences of Supervisor Knowledge Hiding Among Local and Foreign Workers in the Middle East

[[abstract]]This study adds to the growing research exploring the consequences of knowledge hiding in organizations. Drawing from the social exchange theory and the norm of reciprocity, this paper examines the direct and indirect—via distrust in supervisor—relationships between supervisor knowledge hiding (SKH) and supervisee organizational citizenship behavior directed at the supervisor (OCB-S) in the context of the Middle East. Using a supervisor–supervisee dyadic design, two-source data were obtained from 317 employees (local and foreign) of 41 Saudi firms. The findings suggest that supervisees’ distrust in their supervisors mediates the significant and negative relationship between SKH and supervisees’ OCB-S. Furthermore, the significant and positive relationship between SKH and distrust in supervisor is more pronounced for foreign workers than for local workers. This study provides empirical support and a better understanding of the existence and consequences of SKH for local and foreign workers and also discusses the theoretical and practical implications of the findings.[[notice]]補正完