A regional study of some osmotic, ionic and age factors affecting the stability of cerebral lysosomes.

Abstract-An examination was made of the effect of changes in the osmolarity and the ionic composition of the homogenizing medium on the partition of lysosomal arylsulphatase and N-acetylglucosaminidase of cerebral cortex, hypothalamus and thalamus of the rat. Sulphatase appeared to be more sensitive to hypotonicity than glucosaminidase, since a higher proportion of the sulphatase was released from the lysosomes into the soluble fraction of the cells from all three neuroanatomical areas examined. In the presence of 250 mM-sucrose, supplementation with 10 mM-Mg led to clumping of the lysosomes and their translocation into the heavy-particulate fraction; no such effect of 10 mM-Mg was noted in the absence of 250 mM-sucrose. The intracellular distribution of bound N-acetylneuraminic acid (bound-NANA) was also examined. The shifts observed in its intracellular localization as a result of changes in the ionic composition of the homogenizing medium rule out bound-NANA as a structural component of the membrane of the cortical lysosome. However regional differences in the response of bound-NANA to ionic factors were observed. Lysosomes from cerebral cortex of adult and 12-day-old rats were also Compared. Differences in the pattern of distribution of lysosomes in linear sucrose gradients and in response to ionic factors were uncovered. The results support the previously enunciated concept (SELLINGER and H I A ~ , 1968) of a regional microheterogeneity of lysosomes and add a new, age-related dimension to it.