Abstract
The presence of lipids in the basement membrane of the mouse kidney tubules was examined by histochemical staining with malachite green. Pieces of mouse kidney cortex were immersed in a fixative containing 3% glutaraldehyde and 0.1% malachite green in 0.067 M sodium cacodylate buffer, pH 6.8, for 18 hr at 4 degrees C. Control tissue was fixed in the same way except that no malachite green was added to the fixative. The tissue pieces were cryoprotected, frozen in Freon 22, and subjected to freeze-substitution in dry acetone containing 1% OsO4. Thin sections of Epon-embedded specimens were observed by electron microscopy at first without uranyl-lead counterstaining. The basement membrane of mouse kidney tubules was positively stained in a pattern composed of an irregular assembly of 5-8-nm wide strands. The nature of these malachite green-positive strands was further examined by counterstaining thin sections with uranyl-lead, and they were identified as 4.5-5-nm wide ribbon-like "double tracks" previously characterized as the form taken by heparan sulfate proteoglycan in basement membranes. It is concluded that lipids are present in the basement membrane of mouse kidney tubules in association with heparan sulfate proteoglycan.