Structural and physical changes in lysosomes from isolated rat hepatocytes treated with methylamine

Incubation of isolated rat hepatocytes with 10 mM methylamine resulted in an inhibition of endogenous protein degradation and a microscopically visible enlargement of the lysosomes. Lysosomes from methylamine-treated cells exhibited increased buoyancy in metrizamide gradients and increased fragility as measured by the release of acid phosphatase activity in vitro, despite the fact that no methylamine remained in the gradient-isolated organelles. When methylamine was extracted from intact cells, the inhibition of protein degradation was immediately relieved, whereas the lysosomal enlargement (and to a certain extent also the increased fragility) persisted for some time. The methylamine-induced osmotic swelling of the lysosomes would thus seem to involve not merely a passive stretching of the lysosomal membrane, but rather some structural change (e.g., an increased amount of membrane material) which is relatively slowly reversible, but without effect on lysosomal function.