In vivo biosynthesis and turnover of 35S-labeled glomerular basement membrane

Renal glomerular basement membrane was labeled in vivo by the injection of tracer amounts of radioactive sulfate into normal adult rats. The biosynthesis and turnover of [35S]glycosaminoglycans in purified basement membrane was determined from the specific activity of 35S in pronase digests of basement membranes isolated 1-7 days after injection. Peak radioactive labeling occurred 24 h after injection following which the specific activity of basement membrane sulfate, expressed as cpm/microgram uronic acid, progressively declined over the ensuing period of study. The biologic half-life of radioactive sulfate in basement membrane was estimated at about 7 days, which is within the range previously reported for [35S]glycosaminoglycans in whole renal cortex. The findings indicate that 35S-labeled components of glomerular basement membrane have a relatively rapid turnover.