AJP - Cell Physiology, Vol 245, Issue 1 61-C67, Copyright © 1983 by American Physiological Society
Metabolic alterations and distribution of rat liver lysosomes in colloidal silica
C. A. Surmacz, J. J. Wert Jr and G. E. Mortimore
Lysosome-enriched samples from normal fed rat livers have been shown to
separate into dense and buoyant bands when layered on self-generating
gradients of colloidal silica. The hypothesis that the buoyant peak is
comprised largely of autophagic vacuoles that are selectively restrained by
sedimenting mitochondria was tested in livers subjected to conditions known
to accelerate autophagy or suppress it. In all cases, a sharp peak of
beta-N-acetyl-D-glucosaminidase activity was evident when autophagy was
present but was undetectable when it was eliminated or virtually
eliminated. Moreover, the sensitivity to osmotic shock of buoyant peak
particles, but not those of the dense band, was increased after autophagic
stimulation. The total amount of enzyme that moved to buoyant fractions
with the induction of autophagy generally correlated with the degree of
autophagic acceleration. However, with maximal autophagy, the buoyant peak
was broad, and only 70% was capable of being dislodged and returned to the
dense peak by dispersing samples in the gradient medium and/or reducing the
sample size. On the other hand, at roughly half-maximal stimulation and
lower, the buoyant distribution was sharply defined and completely
reversible. These findings support the above hypothesis and suggest that
the buoyant peak could be used as a measure of autophagy in the
physiological range of regulation.
