Topology of membrane exposure in the renal cortex slice. Studies of glutathione and maltose cleavage.
We measured glycine release from ([2-3H]glycine)-labelled GSH and glucose formation from maltose incubated with rat kidney whole cortex homogenate, thin cortex slices or collagenase-treated tubule fragments. Liberation of glycine was inhibited (74-83%) by serine borate (20 mM), indicating a gamma-glutamyltransferase-dependent hydrolysis of GSH. In whole cortex homogenate, the GSH cleavage activity was 17.4 +/- 0.6 nmol GSH degraded/mg protein per min (mean +/- S.D.); cleavage activity by intact slices was 3.5 +/- 0.7 (P less than 0.001 relative to whole cortex homogenate) and in tubule fragments 9.4 +/- 0.8 (P less than 0.001). Homogenizing the tissue preparation increased cleavage rate in slices about 4-fold (12.4 +/- 2.9; P less than 0.005 relative to intact slice) but did not change the rate in tubule fragments (9.8 +/- 0.5). Maltose cleavage activity in whole cortex homogenate was 512 +/- 22 nmol glucose formed/mg protein per min, in slices 162 +/- 12, and in tubules 884 +/- 48. These findings imply that substrate in the incubation medium has a limited access to the luminal membrane of cortex slices but not of tubule fragments. They further imply that basolateral membrane is preferentially exposed in the slice preparation.
D000818:Animals; D005978:Glutathione / Q000378:metabolism*; D005998:Glycine / Q000378:metabolism; D066298:In Vitro Techniques; D007672:Kidney Cortex / Q000378:metabolism*; D007684:Kidney Tubules / Q000378:metabolism; D007700:Kinetics; D008297:Male; D008320:Maltose / Q000378:metabolism*; D003012:Microbial Collagenase; D051381:Rats; D011919:Rats, Inbred Strains
D008320:Maltose; D003012:Microbial Collagenase; D005978:Glutathione; D005998:Glycine