Hydrolysis of Phospholipid Esters localized in Lysosomes and Related Structures of Rat Muscle Cells in Culture

Abstract

THE fusion of normal myoblasts during differentiation of muscle leads to a multinucleated striated muscle fibril. The fusion reaction between cells is not well understood. Almost as soon as contact is made between two myoblasts, the plasma membranes of the two cells fuse to become one continuous plasma membrane surrounding the cytoplasm of both cells. It is not known whether such normal fusion reactions between muscle cells involve hydrolytic enzymes for digestion of carbohydrates, proteins and lipids constituting these membranes at their sites of fusion. The fusion reaction as well as the extensive cytoplasmic changes during differentiation prompted us to investigate digestive functions in our cultured cells using phosphate esters of a variety of compounds. This is the first report of histological localization for hydrolysis of phospholipid esters by cultured cells. Previous cytochemical studies on acid phosphatase in our cultured muscle cells showed an increase in lysosomal reaction product as myotubes formed and have been reported as ancillary observations to biochemical studies^1,2. Our in situ investigations for lipid phosphate hydrolysis were also prompted from reports by Tappel et al.^3,4 as well as Fowler and de Duve⁵ on digestion of lipids and organelle membranes with isolated rat liver lysosomal particles.