Surfactant in the gas mantle of the snail Helix aspersa

Surfactant occurs in cyclically inflating and deflating, gas-holding struct ures of vertebrates to reduce the surface tension of the inner fluid lining , thereby preventing collapse and decreasing the work of inflation. Here we determined the presence of surfactant in material lavaged from the airspac e in the gas mantle of the pulmonate snail Helix aspersa. Surfactant is cha racterized by the presence of disaturated phospholipid (DSP), especially di saturated phosphatidylcholine (PC), lavaged from the airspace, by the prese nce of lamellated osmiophilic bodies (LBs) in the airspaces and epithelial tissue, and by the ability of the lavage to reduce surface tension of fluid in a surface balance. Lavage had a DSP/phospholipid (PL) ratio of 0.085, c ompared to 0.011 in membranes, with the major PL being PC (45.3%). Choleste rol, the primary fluidizer for pulmonary surfactant, was similar in lavage and in lipids extracted from cell homogenates (cholesterol/PL: 0.04 and 0.0 3, respectively). LB were found in the tissues and airspaces. The surface a ctivity of the lavage material is defined as the ability to reduce surface tension under compression to values much lower than that of water. In addit ion, surface-active lipids will vary surface tension, increasing it upon in spiration as the surface area expands. By these criteria, the surface activ ity of lavaged material was poor and most similar to that shown by pulmonar y lavage of fish and toads. Snail surfactant displays structures, a biochem ical PL profile, and biophysical properties similar to surfactant obtained from primitive fish, teleost swim bladders, the lung of the Dipnoan Neocera todus forsteri, and the amphibian Bufo marinus. However, the cholesterol/PL and cholesterol/DSP ratios are more similar to the amphibian B. marinus th an to the fish, and this similarity may indicate a crucial physicochemical relationship for these lipids.