EXOCYTOTIC EXCRETION OF DEXTRAN SULFATES FROM LIVER TO BILE

Abstract

When dextran 35S-sulfates (DS), anticoagulants and antilipemic agents, were given i.v. to rats, the specific radioactivity was 5-20 times higher in the lysosomal than in the other subcellular fractions of liver, but the counts in this fraction were only 10% of total radioactivity distributed to the liver. The biliary excretion of 32S-DS with a similar S content of 18% and 3 different average molecular weights (AMW) of 3000, 20,000 and 200,000 were studied. The excretion rate was .apprx. 2% of the radioactivity given, per hour, after i.v. administration of 35S-DS with AMW of 20,000, 10 mg/kg. At this time, acid phosphatase activity and Ca content of bile increased, and well correlated with the amount of the radioactivity excreted to bile. The amount of the radioactivity distributed to the lysosomal fraction is correlated with the enhanced activities of Na+-K+-dependent and Ca2+-activated ATPase in this fraction, indexes of endocytotic and exocytotic transports. DS significantly enhanced 45Ca levels of the lysosomal, but not the cytosol fraction when 45CaCl2 was given alone or simultaneously with DS. According to previous reports that DS are transferred to the lysosomal fraction of liver and intestinal mucosa by endocytosis, the present results suggest that DS, especially with high AMW and which are distributed to liver lysosomes, are rapidly excreted into bile by exocytosis and accompanied by Ca and lysosomal enzymes.