Actin and secretion of surfactant

Type II cells were examined in situ in order to study the role played by actin filaments in secretion of surfactant. Following β-adrenergic stimulation, the number of lamellar bodies per cell profile decreased substantially, an indication that exocytosis had occurred. In isoproterenol-stimulated cells decoration of actin by S₁ revealed greater numbers of filaments associated with lamellar bodies, free in the cytoplasm, and associated with the cellular apex than in control cells. If cells were treated prior to β-agonist stimulation with cytochalasin D, a drug which disrupts filamentous actin, the secretory response to the agonist was abolished. Together these two observations suggest that actin filaments participate in the intracellular movement and/or extrusion of lamellar bodies from the cells.