LYSOSOMAL DEGRADATION OF CELL ORGANELLES .3. UPTAKE AND DISAPPEARANCE IN KUPFFER CELLS OF INTRAVENOUSLY INJECTED ISOTOPE-LABELED MITOCHONDRIA AND MICROSOMES INVIVO AND INVITRO

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  • 1 January 1975
    • journal article
    • research article
    • Vol. 33  (3) , 262-272
Abstract
14C-leucine and 3H-glycerol-labeled microsomes and mitochondria were i.v. injected into a series of highly inbred rats. The uptake and disappearance of the organelles were followed in a crude liver lysosomal fraction and in serum. Approximately 1/2 of the injected dose was recovered in the liver, and only smaller amounts were found in lungs, kidneys, spleen and heart. The clearance in serum was more rapid for microsomes (t1/2, 5-15 min) than for mitochondria (t1/2, 30-60 min). Both organelles showed a biphasic type of disappearance curve consistent with the 2-phase theory of phagocytosis: attachment and engulfment. The estimated half-life for mitochondria in the liver was in the range of 3-4 h, whereas that of the microsomes was considerably longer, or 8 h. There was an increase of trichloroacetic acid-soluble material in the crude lysosomal fraction up to 2 h after injection of glycerol-labeled microsomes, whereas the peak was reached at 60 min after 14C-leucine labeling. In vitro hydrolysis of mitochondria was most extensive between pH 4.5-5.5. Rupture of the lysosomes decreased the rate of hydrolysis. Experiments with Kupffer cells previously labeled with Thorotrast and biochemical assay of hydrolysis indicated that there was a lag phase of approximately 10-20 min before the phagosomes gained acid hydrolases, presumably by fusion with lysosomes. Kupffer cell lysosomes apparently effectively degrade both mitochondria and microsomes, although at somewhat different rates. The remnants from lipid degradation, in comparison with protein degradation, seem to remain for a longer period within the lysosomal apparatus. These results are compatible with the concept that lysosomes represent an important, and at the present the only well defined locus for organelle turnover.

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