Role of Ca2+ for protein turnover in isolated rat hepatocytes.
Experiments with bivalent-cation chelators (EGTA and EDTA), a Ca2+ ionophore (A23187) and a Ca2+-channel blocker (verapamil) indicate that Ca2+ is required for the lysosomal degradation of endogenous protein in hepatocytes. A distinction is made between lysosomal and non-lysosomal degradation by using the lysosomotropic agent methylamine. As Ca2+ does not appear to be required for the lysosomal degradation of endocytosed asialo-fetuin, the Ca2+-dependence for the degradation of endogenous protein is probably connected with the formation of autophagic vacuoles or the fusion of autophagic vacuoles with lysosomes. EGTA and EDTA had a slight inhibitory effect on the non-lysosomal degradation. This effect could be due to the activity of non-lysosomal Ca2+-dependent thiol proteinases. Together with previous experiments with thiol-proteinase inhibitors, the present experiments indicate that these proteinases have a very limited impact on the bulk protein degradation in the isolated hepatocytes.
D000818:Animals; D001212:Asialoglycoproteins; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D004492:Edetic Acid / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D060748:Fetuins; D066298:In Vitro Techniques; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism; D008297:Male; D008744:Methylamines / Q000494:pharmacology; D011506:Proteins / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D000509:alpha-Fetoproteins / Q000378:metabolism
D001212:Asialoglycoproteins; D060748:Fetuins; D008744:Methylamines; D011506:Proteins; D000509:alpha-Fetoproteins; C017029:asialofetuin; D000001:Calcimycin; D004533:Egtazic Acid; D004492:Edetic Acid; C027451:methylamine; D002118:Calcium