A three-dimensional study of organelle interrelationships in regenerating rat liver. 7. Size, shape and dynamism of...

Digestion of macromolecules inside secondary lysosomes results in small molecules leaving the lysosome by permeation. This may cause a drop in osmotic pressure and a consequent shrinkage of the lysosome. A membrane invagination may be formed which becomes internalized and then digested. This digestion causes new shrinkage. Minimal-sized lysosomes may ensue. The later are again engaged in digestive events when fusing with larger lysosomes. Through consecutive shrinkage and fusion cycles of many lysosomes residues slowly accumulate. Shrinkage may be counteracted by adding digestible material without increasing the lysosomal membrane surface. Transfer tubules can do so. They deliver their content to multivesicular bodies. The other lysosome types, however, are subject to shrinkage since they fuse with organelles (phagosomes, primary lysosomes) which insert at least part of their membrane.