THE COMPOSITION AND FUNCTION OF SURFACE-ACTIVE LIPIDS IN THE GOLDFISHSWIM BLADDER

Goldfish (Carassius auratus: Cyprinidae) have a two-chambered su,im bl adder The anterior chamber is thick walled undergoes small volume chan ges does not empty itself of gas, and assists in hearing The posterior chamber is thin walled: undergoes extensive volume change that often results in bladder collapse, and controls animal buoyancy. Both chambe rs possess relatively thick inner lipid linings that differ in composi tion. The anterior-chamber lipids are rich in cholesterol and phosphol ipids, particularly in disaturated phospholipids. Posterior-chamber li pids are exceptionally rich in cholesterol but not in saturated phosph olipid. Lipids from both chambers lower surface tension below that of water but are not more surface active than a cell membrane preparation . This study demonstrates a new technique for determining the role of the lipids in bladder inflation and compliance. The pressure required to initiate the inflation of a collapsed bladder (termed ''opening pre ssure'') increased after lipids were removed from the posterior chambe r but nor after they were removed from the anterior chamber Posterior- chamber lipids act as an antiglue for collapsed bladders by preventing the folded inner surfaces from adhering Anterior-chamber lipids did n ot net as an antiglue, and their function remains unknown.