Glycoprotein reutilization in regenerating microvilli after renal ischemia in rats

Renal ischemia causes a reversible loss of microvillar membrane (MVM) of the proximal tubule cell and of MVM enzyme specific activities (S.A.). We sought to determine if recovery of the MVM glycoprotein was accomplished through de novo synthesis or recycling. Renal ischemia (25 min) was induced in rats by occlusion of the left renal artery, followed by 15 min or 4 hrs of reflow of blood. Radiolabelled fucose was injected into rats before or after ischemia and was used as a marker for new glycoprotein synthesis or recycling of prelabelled glycoprotein. Ischemia, followed by 15 min of reflow, caused a 49% reduction in protein associated with the isolated MVM fraction of the ischemic kidney. There was also a decrease in newly fucosylated glycoprotein in both homogenate and MVM fraction measured as S.A. or total amount of labeled glycoprotein. Pre-labelled glycoproteins had no change in S.A. in homogenates or MVM fractions of ischemic or contralateral kidneys. However, the total amount of labeled glycoprotein in the ischemic MVM fraction was reduced. At 4 hrs of reflow, protein content of the MVM fraction was back to normal. Pre-labelled glycoproteins of the ischemic homogenate and MVM fraction were also back to normal with no significant dilution of glycoprotein S.A. by newly synthesized protein, indicating that glycoprotein recycling occurs to a large extent in the ischemic kidney.