The macula densa tubular basement membrane: a unique plaque of basement membrane specialization.

The inner (luminal) surface of the macula densa (MD) basement membrane (BM) was exposed by solubilization of the overlying epithelium permitting examination of its structural features by scanning electron microscopy (SEM). Nineteen macula densa BM were identified in five autopsy kidneys and seven renal biopsies by this SEM technique. The MD BM consists of an oval plaque of specialized BM, restricted to the glomerular hilum and arteriolar aspect of the thick ascending limb of Henle. It contains haphazardly oriented shallow tunnels, slender pleats, and bridges of BM which do not resemble any other nephron BM examined by this technique. The MD BM, critically located between MD and lacis cells appears to firmly anchor the MD to the juxtaglomerular apparatus and may amplify the extent of interaction between lacis cell processes or lacis cell interstitial space and MD cell processes.